Geochronology Methods and Case Studies

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Geochronology Methods and Case Studies Edited by Edited by Nils-Axel Morner

Geochronology: Methods and Case Studies

D3pZ4i & bhgvld, Dennixxx & rosea (for softarchive)

Edited by Nils-Axel Morner

Stole src from http://avaxho.me/blogs/exLib/ Published by AvE4EvA Copyright © 2014 All chapters are Open Access distributed under the Creative Commons Attribution 3.0 license, which allows users to download, copy and build upon published articles even for commercial purposes, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. After this work has been published, authors have the right to republish it, in whole or part, in any publication of which they are the author, and to make other personal use of the work. Any republication, referencing or personal use of the work must explicitly identify the original source. As for readers, this license allows users to download, copy and build upon published chapters even for commercial purposes, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. Notice Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher. No responsibility is accepted for the accuracy of information contained in the published chapters. The publisher assumes no responsibility for any damage or injury to persons or property arising out of the use of any materials, instructions, methods or ideas contained in the book. Publishing Process Manager Technical Editor AvE4EvA MuViMix Records Cover Designer

Published: 25 July, 2014 ISBN-10 953-51-1643-6 ISBN-13 978-953-51-1643-1

Contents

Preface Chapter 1 Quaternary Geochronology Using Accelerator Mass Spectrometry (AMS) – Current Status of the AMS System at the TONO Geoscience Center by Akihiro Matsubara, Yoko Saito-Kokubu, Akimitsu Nishizawa, Masayasu Miyake, Tsuneari Ishimaru and Koji Umeda Chapter 2 Luminescence Chronology by Ken Munyikwa Chapter 3 Varve Chronology by Nils-Axel Mÿrner Chapter 4 Geochronology From The Castelo Branco Pluton (Portugal) — Isotopic Methodologies by Antunes Imhr Chapter 5 In situ U-Pb Dating Combined with SEM Imaging on Zircon — An Analytical Bond for Effective Geological Recontructions by Annamaria Fornelli, Giuseppe Piccarreta and Francesca Micheletti Chapter 6 Layered Pge Paleoproterozoic (LIP) Intrusions in the N-E Part of the Fennoscandian Shield — Isotope Nd-Sr and 3He/4He Data, Summarizing U-Pb Ages (on Baddeleyite and Zircon), Sm-Nd Data (on Rock-Forming and Sulphide Minerals), Duration and Mineralization by T. Bayanova, F. Mitrofanov, P. Serov, L. Nerovich, N. Yekimova, E. Nitkina and I. Kamensky

Preface

Chronology is the backbone of history, and there is a wise saying stating there is no history without a chronology. Earths evolutionary history is built up by geochronology, i.e. time benchmarks upon which the geological history is built up step by step over its total time period of about 4.5 billion years. The first marker in this history is the Jack Hills zircon from Australia dated at about 4.4 GA. The most detailed records come from seasonal changes within annual varves. Stratigraphy provides the basic chronological ordering of layers by layers, units by units, fossil assemblage by assemblage, varves by varves, growth zone by growth zone, etc. The radiometric techniques implied the introduction of absolute age determinations. This book includes a combination of methodological presentations and related case studies, from where we learn about practical problems and achievements. Therefore, the book should be of basic interest both for scientists in their practical in field and laboratory, as well as for general educational purpose.

Chapter 1

Quaternary Geochronology Using Accelerator Mass Spectrometry (AMS) Current Status of the AMS System at the TONO Geoscience Center Akihiro Ma“s”bara, Yoko Sai“o-Kok”b”, Akimi“s” Nishizawa, Masayas” Miyake, Ts”neari Ishimar” and Koji Umeda Addi“ional informa“ion is available a“ “he end of “he chap“er h““p://dx.doi.org/10.5772/58549

. Introduction . . Background The Tono Geoscience Center TGC oλ the Japan “tomic Enerμy “μency J“E“ has been conductinμ research into the lonμ term several million years stability oλ underμround environments, in order to provide the scientiλic knowledμe needed to ensure saλety and reliability λor the μeoloμical disposal oλ hiμh-level radioactive waste [ – ]. The time scale λor occurrence oλ the relevant μeoscientiλic activities, as shown in Fiμure , i.e., earthquake/λault and volcanic activities, behavior oλ μroundwater λlow, upliλt/subsidence and erosion oλ the μround surλace, and so on, corresponds well to the duration oλ the Quaternary Period μeoloμy. Geochronoloμy oλ the Quaternary Period has been stronμly enhanced by measurement oλ terrestrial in situ cosmoμenic radionuclides, such as ”e, C, “l, and Cl, produced by secondary cosmic rays e.μ., neutron, muon which are μenerated by interaction between the atmosphere oλ earth and primary cosmic rays that oriμinate λrom the sun and μalactic systems. “pplications oλ accelerator mass spectrometry “MS usinμ those rare radionuclides λor μeoloμical studies have been summarized by various authors [ – ]. It is a well-known λact that C has been widely utilized in several disciplines, includinμ μeoloμy, environmental science, archaeoloμy, and biomedicine. With reμard to research into underμround μeoloμical disposal oλ waste, radiocarbon datinμ oλ orμanic samples e.μ., bulk orμanic, humic acid, and humin λractions taken λrom λaults provide an historical archive oλ typical conventional applications

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Geochronology - Me“hods and Case S“”dies

to the investiμation oλ seismic activity [ , ]. The dates obtained, combined with other scientiλic and historical inλormation, help to determine whether or not the λault is a so called active λault , and to estimate cyclicity oλ seismic events and probability λor serious larμe λault movements durinμ the post-closure duration oλ μeoloμical disposal.

Figure 1. Long-“erm geological ac“ivi“ies relevan“ “o “he geological disposal of high-level radioac“ive was“e.

Lonμ-lived cosmoμenic radionuclides, such as ”e, “l, and Cl enable us to apply to the exposure datinμ methods on boulder and bedrock surλaces λor exposure aμes up to years [ – ]. These methods can provide inλormation relevant to μeoloμical disposal with respect to μeomorpholoμical evolution, i.e., erosion rates oλ rock surλaces, burial histories oλ rock surλaces and sediments, λault slip rates, and so on. One oλ the typical radionuclides λor surλace exposure datinμ is ”e, or both ”e and “l. The halλ-lives oλ ”e and “l are lonμ enouμh . Myr and . Myr, respectively to span the entire Quaternary timescale. They can be produced simultaneously in a sinμle sample oλ quartz where “l and ”e are mainly produced throuμh nuclear spallation λrom Si and O, respectively. Concentration oλ each depends on balance between in situ production and surλace erosion and μenerally, there are two unknown variables. The simultaneous measurement oλ “l and ”e concentration has the advantaμe oλ solvinμ λor the two variables exposure aμe and erosion rate. On the other hand, Cl is produced throuμh multi-channel reactions spallation on Ca and K with neutron and muon, and the thermal neutron capture on Cl. This λeature provides an advantaμe to the Cl exposure datinμ that is not restricted to speciλic rock types or minerals such as carbonates or silicates under a number oλ conditions. Furthermore, decomposition oλ contribution λor Cl production into spalloμenic, muμenic, and thermal neutron can increase the amount oλ inλormation λor one sample, with the potential λor μreater erosion-exposure history accuracy. The measurement oλ C and Cl is also applicable to hydroμeoloμic investiμations studies oλ μroundwater aμe, oriμin and mixinμ. Most oλ these nuclides are produced throuμh interaction

Q”a“ernary Geochronology Using Accelera“or Mass Spec“rome“ry (AMS) – C”rren“ S“a“”s of “he AMS Sys“em… h““p://dx.doi.org/10.5772/58549

with alpha-particle/neutron emitted λrom radioactive elements such as Th and U within the sediment or rock dozens oλ meters or more underμround, where there is no cosmoμenic radionuclide production [ ]. . . Purpose and contents of this article Our onμoinμ eλλorts, thereλore, have been dedicated to development oλ a multi-nuclide “MS λor measurement oλ the rare radionuclides ”e, C, “l, and Cl. In this article, the current status oλ the “MS system at the J“E“-“MS-TONO and our activities leadinμ to development oλ a multi-nuclide “MS are presented. The next section shows the history and present-day status oλ our “MS system. The detail oλ the “MS system and its conλiμuration are described in Section . The current status λor C, ”e and “l measurements is presented in Sections , , and , respectively. Section provides the research and development related to improvement oλ the isobar discrimination λor the ionization chamber. Finally, Section presents a summary.

Figure 2. Timeline of “he JAEA-AMS-TONO developmen“.

. Operation status The history oλ the J“E“ “MS system is depicted in Fiμure . The “MS system was installed at TGC in , and routine measurement oλ C started in [ ]. The preliminary development oλ the ”e-“MS started around [ ], intensive development was implemented λrom to [ , ], and proμress oλ which will be described in Section . “λter that, the routine measurement oλ ”e started at the beμinninμ oλ λiscal year . “t present, we have initiated the development oλ the “l-“MS described in Section [ , ]. Furthermore, as a part oλ preparatory activity λor the development oλ the Cl-“MS, we have started to investiμate the nature oλ the pulse trace that is disturbed by interλerinμ particles in the heavy ion detector, in order to improve the discrimination perλormance λor the detector system presented in Section [ ].

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The evolutions oλ the measurement time and the number oλ sample cathode tarμet are shown in Fiμure . Total, cumulative, measurement time the blue line has increased more or less continuously λor years, and reached , hours this λiscal year. “round , routine measurements ceased λor a while due to system maintenance by the lab-staλλ. “s shown on the bar chart, the averaμe number oλ samples measured annually is between and , and the total number oλ samples will exceed , within the next λew months. “λter the devel‐ opment oλ the ”e measurement has been intensive since the start, the proportion oλ ”e samples to the total sample number has increased rapidly. In λiscal year , the proportion oλ C, ”e and “l sample cathodes are %, %, and %, respectively.

Figure 3. Evol”“ion of “he meas”remen“ “ime and sample n”mber.

In Fiμure , the pie chart on the leλt shows the proportion oλ C-“MS samples measured λor the various study λields in λiscal year . Geoscience accounted λor about %, while environmental studies accounted λor most oλ the balance. The proportion labeled as “nalysis stands λor the cathode number used in our technical development. The pie chart on the riμht in Fiμure illustrates the relative proportion oλ measured samples requested by users in J“E“ to other users. “lmost all oλ the samples were requested by J“E“ users. The measurement oλ the other samples were perλormed under J“E“’s common-use λacility proμram λor non-J“E“ users [ ]. This proμram started in , in order to enlarμe and expand the public use oλ J“E“’s λacilities. The study λields usinμ the proμram were mostly in environmental science and archaeoloμy.

Q”a“ernary Geochronology Using Accelera“or Mass Spec“rome“ry (AMS) – C”rren“ S“a“”s of “he AMS Sys“em… h““p://dx.doi.org/10.5772/58549

Figure 4. Propor“ion of 14C-AMS samples meas”red in “he vario”s inves“iga“ion fields (lef“) and, on “he righ“, “hose req”es“ed by JAEA ”sers “o by o“hers in fiscal year 2012.

. AMS system . . Overall features The “MS system is a versatile system based on the PelletronTM tandem accelerator Model SDH- , MV terminal voltaμe [ ]. The same type MV Pelletron oλ the “MS system has been used in other λacilities, λor example, at the Micro “nalysis Laboratory, Tandem accelerator M“LT at the University oλ Tokyo, Japan [ ], the “MS system at the National Institute λor Environmental Studies NIES oλ Japan [ ], at the Scottish Universities Environmental Research Center SUERC in the United Kinμdom [ , ], and at the Uppsala MV Pelletron tandem accelerator developed in the Uppsala University, Sweden [ , ]. This “MS system is desiμned λor the “MS analysis with most radio-isotopes includinμ ”e, C, “l, Cl, and I. “lthouμh technoloμical advances in recent years have enabled practical use oλ compact “MS systems below MV allowinμ the measurement oλ ”e, C, and “l [ – ], the relatively wide ranμe oλ hiμh terminal voltaμe μreater than several meμavolts has, even now, been μenerally recoμnized to be beneλicial to eλλicient suppression oλ siμnal backμround, resultinμ in λurther potential λor expandability λor a multi-nuclides measurement. . . System description [

]

Fiμure is a schematic oλ the “MS system layout. The system can be divided into λive major subsystems the ion sources, the sequential injection system, the tandem Pelletron accelerator, the post-accelerator beamline with the hiμh-enerμy mass spectrometer components, and the heavy ion detection system by means oλ the ionization chamber. There are eiμht vacuum turbomolecular pumpinμ systems attached alonμ the beamline, where, several beam steerers

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Geochronology - Me“hods and Case S“”dies

and maμnetic or electrostatic lenses are located, and the total lenμth oλ the system is around metres. Summary oλ the system conλiμuration λor rare isotopes are presented individually in Table .

Figure 5. AMS sys“em a“ JAEA-AMS-TONO.

Nuclide

C

14

Terminal vol“.

4.5 MV

(To“. Energy) Targe“ C”rren“ Injec“ion

(Co”n“ ra“e) Backgro”nd Ioniza“ion chamber

26

Al

4.3 MV

(22.5 MeV)

(16.3 MeV)

(17.2 MeV)

Graphi“e wi“h Fe

BeO wi“h Nb

Al2O3 wi“h Ag

powder

powder

powder

20 μA (C-)

2 μA (BeO-)

0.1 μA (Al-)

C: 0.9 ms, 14C: 98.6 ms) 58% (12C) C / C , C / C

14

Be

4.8 MV

Seq”en“ial (12C: 0.3 ms , 13

Transmi“. Meas. ra“io

10

4+ 12

4+ 13

4+ 12

Sim”l“aneo”s

Seq”en“ial

(10Be16O, 9Be17O)

(26Al: 98 ms, 27Al: 1 ms)

21% (9Be) 4+

Be / O

10

3+ 17

5+

39% (27Al) Al3+/ 27Al3+

26

(60 cps@ HOxII)

(70 cps @S5-1)

(15 cps @S4-1)

< 7x10-16 (< 0.06 pMC) @WAKO

< 7 x 10-15

< 3 x 10-14

Powder

@MITSUWA powder

@Blank†

ΔE1-ERes

ΔE1-ERes (wi“h gas cell)

ΔE1-ETo“

† Sample of BLK was made from a q”an“ified s“andard sample for a“omic absorp“ion spec“rome“ry s”pplied from Wa‐ ko P”re Chemical Ind”s“ries, L“d. Table 1. S”mmary of c”rren“ AMS specifica“ions for “he JAEA-AMS-TONO.

Q”a“ernary Geochronology Using Accelera“or Mass Spec“rome“ry (AMS) – C”rren“ S“a“”s of “he AMS Sys“em… h““p://dx.doi.org/10.5772/58549

The ion sources, the Multi-Cathode, Source oλ Neμative Ions by Cesium Sputterinμ MCSNICS λor solid samples cathodes and the Multiple Gas Feed, SNICS MGF-SNICS λor CO -μas samples cathodes are connected to the main beamline throuμh the ° electrostatic spherical analyzer ES“ . The sources consist oλ a cesium oven μeneratinμ Cs vapour, a heated ionizer electrode producinμ a λocused Cs+ beam at the sample cathode, and extraction and λocus electrodes. Particles sputtered λrom the sample cathode by Cs+ bombardments pick up electrons as they pass throuμh the cesium layer condensed on the sample thus, neμative ions are produced. To stabilize the cesium vapour λeed to the source, we added a simple autocontrollable electrical heatinμ subsystem to the cesium oven and its λeeder pipe the standard deviation oλ the temperature monitored durinμ the routine measurement has been kept within a ranμe oλ ± . C° [ ]. This type oλ simple technical addition or modiλication is commonly used λor the same purpose [ ]. The acceleration voltaμe oλ the ion source is usually set to kV. ”y usinμ the beam-slit located at the imaμe point oλ the ES“ beλore the injection maμnet , the tail oλ the beam proλile can be trimmed, where the tail is due to an enerμy spread in the sputterinμ process. This trimminμ assures open-aperture optical properties oλten called λlat top transmission on the downstream side oλ that slit. The combination oλ the ES“ and the injection maμnet ME / q , where M is the mass number oλ the ion, E is the ion enerμy in MeV and q is the charμe number, and the nominal radius is . m limits the speciλic charμeto-mass ratio, M / q, λor the transmittance oλ neμative ions in the pre-accelerator reμion to remove unwanted particles λrom the ion beam. The mass resolution M /ΔM reaches λor the electrostatic and maμnetic λilters combination. The same concept is applied λor the hiμhenerμy post-accelerator reμion containinμ the analyzinμ maμnet and electrostatic cylindrical analyzer EC“ listed below. The “MS system employs the sequential injection method λor the precise measurement oλ the ratio oλ rare to abundant isotopes reμardless oλ λluctuations oλ source conditions. This method, or the rapid switchinμ oλ the masses isotopes to be injected toward the accelerator, so called sequence bounced or jumpinμ beams is accomplished by applyinμ an appropriate bias potential to the electrically insulated bent chamber inside the injection maμnet. Most oλ the duration ~ % in the sequential injection is allocated λor the measurement oλ the rare isotope details in Table . In the tandem Pelletron accelerator -SDH , there are two parallel chains charμinμ the hiμhvoltaμe terminal with current up to “. The consequent maximum terminal potential oλ MV leads to the suitable stripped ionization state oλ + λor carbon by usinμ a μas stripper the ion beam enerμy is up to MeV . For the chlorine, the charμe state is desiμned to be + or + by usinμ a λoil stripper and its enerμy would be lie in the ranμe oλ - MeV. The pressure oλ the stripper μas is typically Torr, Torr, and Torr λor C-, ”e-, and “l-measurement, respectively. The hiμh-enerμy mass spectrometer in the post-accelerator reμion is composed oλ maμnetic and electrostatic λilters and detector systems. The analyzinμ maμnet produced by Danλysik “/S is a double λocusinμ ° sector maμnet with a nominal radius oλ . m, havinμ param‐ eters oλ ME /q and M /ΔM= . “λter the oλλ-axis, multi-Faraday cup detector λor the abundant isotopes, the ° EC“ with a nominal radius oλ . m is used to remove abundant

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isotopes havinμ the same mass enerμy product as the rare isotopes. The resolution attained by the EC“ is M /ΔM= . The λinal detector λor countinμ the rare isotopes, the heavy ion detector , is the μas ionization detector that contains multiple ΔE electrodes λive arranμed alonμ the axis oλ the beamline λor details see Section . . “ nearly equivalent type oλ detector is used at the SUERC λacility in the UK [ ]. The ΔE electrodes determine the speciλic oλ enerμy loss arisinμ in their respective reμions. In the case λor the ion enerμy over MeV/u, the rate oλ the enerμy loss or stoppinμ power increases with increasinμ atomic number. Thus, the spectrum on the plane μiven by enerμy-loss D-coordinates λor various combinations oλ ΔE electrodes shows its characteristic position on that plane, which makes it possible to distinμuish the spectrum oλ desired nuclide λrom other spectra oλ interλerinμ particles. Typical particles interλerinμ with the rare isotopes oλ ”e, C, and Cl are respectively ”, Li, and S their M / q ratios can be equivalent to those oλ the rare isotop es, thus allowinμ their entry into the detector. The problem with respect to the ” and S is known as an isobar problem diλλerent elements but same atomic weiμht . The M / q ratio oλ C + coincides with that oλ Li + althouμh the prime number oλ charμe state + λor C in this case is preλerable to avoid the coincidence oλ the M / q ratio, we λocus on the hiμher strippinμ yield λor + % at . MV [ ] rather than + % at . MV [ ] . Since the relative diλλerence between atomic numbers λor the case oλ ”e and ” or Cl and S is much smaller than the diλλerence λor C and Li, distinμuishinμ them in the λormer case is harder than in the latter case. Thereλore, discrimination techniques are crucial λor measurements oλ ”e and Cl. “ μas absorber technique has been employed in the ”e-“MS operation, which is described in Section . . In addition, investiμation oλ a pulse trace λluctuation caused by interλerinμ particles in a preparation λor the Cl measurement is presented in Section .

. C measurement . . Stability and reliability In the C-“MS operation, the stability and reliability oλ the routine measurements have been checked continuously aμainst measurinμ standards. The typical standards are, I“E“C , -C , and -C [ ], and the oxalic acid HOxII SRMC that is produced by the National Institute oλ Standards and Technoloμy, NIST in the US“. Such checks have been perλormed simultaneously with routine measurements. In our “MS analysis, usually only the HOxII is used λor obtaininμ the normalization constant that is μiven by the C corrected activity divided by the fraction modern λor the HOxII . . Here, the term fraction modern is a quantity deλined as the ratio oλ a sample C activity ASN to a normalized sample C activity AON, where AON is equal to the C-decay corrected absolute international standard specific activity Aabs that is intended to correspond to the hypothetical speciλic activity oλ atmospheric carbon oλ year in detail see Reλ.[ , ] . With respect to data quality oλ the HOxII standard, thereλore, only the relative precision or relative standard deviation, rsd aλλects the normalization constant in other words, the accuracy itselλ has no mean‐ inμ. The value oλ rsd λor the HOxII is around . % in every routine-measurement. The

Q”a“ernary Geochronology Using Accelera“or Mass Spec“rome“ry (AMS) – C”rren“ S“a“”s of “he AMS Sys“em… h““p://dx.doi.org/10.5772/58549

procedure oλ data analysis, as well as ”e and “l analyses has λollowed an alμorithm in the soλtware code abc available λrom the NEC Corporation [ ]. It is noted that to obtain the net activity the C/ C ratio λor all samples except C is normally subtracted by the I“E“-C value as the chemical backμround due to the sample preparation, where C is made λrom marble, and its nominal value in the percent Modern Carbon pMC that is equivalent to the %× fraction modern described above is . ± . [ ]. The leλt column oλ rectanμles on Fiμure shows the evolution oλ pMC λor I“E“-C , -C , and -C in the year . In some periods no C measurements were perλormed. The period λrom May to June was allotted λor ”e measurements. Intensive system maintenance was carried out normally annually in “uμust, and then ”e measurements were perλormed until the end oλ September. “lmost all measured pMC-values λor both C and C are in aμreement with the nominal values within σ oλ each point σ is basically the statistical uncertainty that is inversely proportional to the square root oλ C counts . “ λew irreμular points in C could be due to surλace rouμhness oλ the μraphite sample. The rouμhness is reλlected by unsuccessλul μraphite compression with an “rbor press hammerinμ with a press-pin . We continue to check the surλace condition and data related to such irreμular results.

Figure 6. Meas”remen“ q”ali“y in a 12-mon“h period for 14C-AMS s“andards: C6 (a), C5 (b), and C1 (c). The lef“ col”mn shows evol”“ions of “he meas”red val”e in percen“ Modern Carbon for “he year 2013. The gray line and ha“ch for bo“h lef“ and righ“ col”mns depic“s respec“ively “he nominal val”e and i“s range of ”ncer“ain“y. The righ“ col”mn shows corresponding his“ograms for “he lef“ col”mn meas”remen“ poin“s. The dashed and do““ed lines presen“ respec“ively “he ari“hme“ic mean m and i“s s“andard devia“ion σH on “he his“ogram. The symbol c.n. s“ands for “he n”mber of sam‐ ple ca“hodes ”sed in cons“r”c“ing “he his“ogram, and σHrsd is “he rela“ive s“andard devia“ion given by σH/m× 100%.

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The λrames in the riμht-hand side oλ Fiμure show histoμrams correspondinμ to temporal evolution λor each standard in the leλt λrames. It can be seen that the arithmetic mean oλ the histoμram λor C labelled as m is siμniλicantly lower than the ranμe oλ its nominal value in other words, a diλλerence between them oλ . % is quite a bit larμer than the standard deviation oλ m” oλ . % μiven by σH/ c.n. . where c.n. is the cathode number used in constructinμ the histoμram. This λact, however, is very similar to results obtained in other λacilities [ , ], suμμestinμ to us to reconsider use oλ the nominal value λor the purpose oλ comparisons with measured data. On the other hand, the arithmetic mean λor C is consistent with its nominal value the diλλerence between them is within the standard deviation oλ m oλ . %. The ± σH . % oλ the histoμram λor C is equivalent to ± years in its C aμe oλ , years, which can be a measure oλ the conλidence interval λor one-year. This perλormance is comparable with the other λacilities, e.μ., a well-known carbon datinμ lab in Japan, the Paleo Labo Co.,Ltd [ , ]. For C , althouμh the arithmetic mean is . pMC, sometimes values are below . pMC. This scatter implies possibility oλ contamination durinμ the sample prepara‐ tion, which is supported by another λact described as λollows. In contrast with C in the estimation oλ backμround, a hiμh-purity synthetic μraphite powder No. Wako Pure Chemical Industries, Ltd, Osaka, Japan is used as a machine backμround samples. This powder is made λrom coke C-λree , and is directly poured into the cathode hole without any chemical preparations thus, C counts detected with the powder are due to machine back‐ μround. We have continuously observed around . pMC λor the μraphite powder, which shows potential λor improvement λor lowerinμ the backμround due to chemical process. . . Inter-laboratory comparison testing Comparison oλ the results obtained in diλλerent laboratories on the same samples is λunda‐ mental to objectively assessinμ accuracy and system perλormance. Comparison tests were carried out twice, in and , with another “MS λacility, the J“E“-“MS-MUTSU, oλ the “omori Research and Development Center, J“E“ [ , ]. This λacility has provided hiμhquality I-and C-“MSs λor environmental science studies, especially λor marine transport properties oλ radio-isotopes, as well as λor radiocarbon datinμ. The typical properties oλ the “MS system are as λollows a MV Tandetron Cockcroλt–Walton accelerator manuλactured by Hiμh Voltaμe Enμineerinμ Europa, and the simultaneous injection system with the sepa‐ rator-combiner. In the comparison test perλormed in , the samples oλ the HOxII, C , and C were prepared in the MUTSU, distributed to the TONO, and measured in both λacilities. The measurement condition such as the duration time or the beam current was taken as the normal condition in each λacility. Fiμure shows results obtained in . For the data analysis, the alμorithm used in the TONO was employed. It can be seen λor the C , that there was no siμniλicant diλλerence between data obtained in both λacilities. The results oλ the C analyzed in the TONO are much lower than that λor the MUTSU. This is mostly due to the λact that durinμ C countinμ, C ions λor the simultaneous injection also entered the accelerator continuously, thus the countinμ rate or its possibility oλ C cominμ into the ionization detector is much hiμher λor the simultaneous injection than λor the sequential injection, in spite oλ λilterinμ by the combination oλ maμnetic

Q”a“ernary Geochronology Using Accelera“or Mass Spec“rome“ry (AMS) – C”rren“ S“a“”s of “he AMS Sys“em… h““p://dx.doi.org/10.5772/58549

and electrostatic analyzers. Consequently, the measurement oλ quite low concentration samples is suitable relative to use by the TONO. The detailed results and discussion λor the series oλ comparison tests will be summarised in a J“E“ report in the λuture.

Figure 7. Res”l“s of comparison “es“ be“ween JAEA-AMS-TONO (shaded circles) and JAEA-AMS-MUTSU (emp“y sq”ares). This “es“ was carried o”“ in 2012. The samples were prepared in “he MUTSU, dis“rib”“ed “o “he TONO, and meas”red in bo“h facili“ies. The algori“hm for “he da“a analysis followed “he sof“ware code ”sed in “he TONO.

. Be measurement . . System configuration and method The conλiμuration λor our ”e-“MS operation is λundamentally standard, and is based on that used in the M“LT [ , , ]. Samples are made λrom the solid oxide oλ beryllium, ”eO, λor its positive electron aλλinity to produce neμative ions. Since the amount oλ the rare isotope ”e is distributed accordinμ to the abundance oλ oxyμen isotope ratios, i.e., O O O= . . . , respectively, the ”e O is selected λor injection into the accelera‐ tor to ensure hiμh extraction eλλiciency oλ ”e λrom the sample. The terminal voltaμe, usually set at . or . MV, is made preλerably as hiμh as possible within the ranμe oλ around MV so as to increase the strippinμ eλλiciency λrom neμative ions to + in our “MS system, the terminal voltaμe is limited to the speciλication oλ MV . In addition, the hiμher ion enerμy is also preλerred λor ensurinμ the μood perλormance oλ the discrimination between ”e and ” λor the heavy ion detector as described below details in Section . . One oλ the most siμniλicant λeatures oλ ”e measurement is the simultaneous injection oλ ”e O with mass the same as ”e O λor countinμ the abundance oλ ”e isotopes. For this purpose the current oλ O + is measured to avoid uncertainty in the amount oλ beryllium hydrox‐ ide ”e OH contamination in the sample [ ]. The abundance isotope is detected with a Faraday cup behind the analyzinμ maμnet as shown in Fiμure . The mathematical λormula used λor obtaininμ the measured isotope ratio Rm= ”e/ ”e is

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Geochronology - Me“hods and Case S“”dies

Rm =

a a

Be Be

T T

O Be

+

cps

+

cps

Be O

+ +

,

where a is the correction λactor λor the abundance ratio oλ the oxyμen isotopes, T is transmittance λor yieldinμ positive ions λrom the neμative ions, and cps is counts per second. The transmittance values λor O + and ”e + are substituted by the values λor O + = % and ”e + = % , respectively. The absolute isotope ratio, R“, is obtained by correctinμ the measured ratio, as R“=Rm/Const, where Const is the normalization constant that is μiven by the measured ratio oλ a standard divided by its nominal ratio. For the ”e standard, usually so-called ICN standard - hereinaλter simply S - is used. The series oλ ICN standards has been prepared and distributed by Nishiizumi oλ U oλ C, ”erkeley to worldwide “MS laboratories [ ]. The boron ions ” + has the same charμe-to-mass ratios as the ”e +, thus it remains on the beamline reμardless oλ the maμnetic and electrostatic λilters, and results in the entry into the ionization chamber, with respect to the isobar problem as mentioned in Section . Usually a μas or solid absorber technique has been used to discriminate between them. Thereλore, optimization oλ the absorber is λundamental in the ”e measurement. . . Optimization of the rare isotope detector For the development oλ the ”e-“MS, discrimination between the ”e and ” isotopes was accomplished by optimization oλ μas pressures in the ionization chamber and the absorber μas cell hereinaλter simply the μas-cell attached in λront oλ μas ionization chamber. Fiμure shows the conλiμuration oλ the rare isotope detector λor the ”e-“MS in our system. Ionization chamber consists oλ the cathode electrode plate , μrid, and anodes that are multiple λive ΔE electrodes arranμed alonμ the axis oλ the beamline. The μrid so called Frisch grid is to remove the dependence oλ the pulse amplitude on position oλ ion pair μeneration by ionization due to an incident particles. “s mentioned in Section . , the ΔE electrode provides the pulse siμnal equivalent to the enerμy loss arisinμ in the area correspondinμ to the electrode. For incident ion enerμy over a million electron volts, the rate oλ enerμy loss depends larμely on the atomic number. Thus, the spectrum peak on the plane μiven by, e.μ., both the coordinates ΔE and ERes where Res means residual, see Fiμure takes a characteristic position on that plane. This individuality oλ the peak position helps to discriminate the ”. However, the amount oλ ” enterinμ into the ionization chamber is enormous over times larμer than that oλ the ”e [ ] , so that the ”e siμnal is disturbed iλ there is no additional absorber λor it. The μas-cell method is an absorbance technique λor ” based on the λact that the enerμy loss rate λor the boron is expected to be larμer than that λor beryllium λor the dependence oλ enerμy-loss rate on the atomic number. In our system, the μas-cell is prepared with -inch diameter pipe covered by the Havar and Mylar λoils at both ends. The nitroμen μas pressure in the absorber siμniλicantly aλλects the shape oλ the ”e spectrum, as described below.

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Figure 8. Config”ra“ion of “he rare iso“ope de“ec“or (heavy ion de“ec“or) for 10Be-AMS. The absorber gas-cell is a““ach‐ ed in fron“ of ioniza“ion chamber. The anode elec“rode is separa“ed in“o m”l“iple (five) ΔE elec“rodes. ΔE1 and ERes (“ha“ means Resid”al energy) indica“e “he energy loss arising in “he region corresponding “o “he anode pla“e 1 and pla“es 2-4, respec“ively.

We investiμated experimentally the discrimination λunction oλ the detector system throuμh observation oλ the variation oλ the ΔE -ERes spectrum by varyinμ the μas pressure oλ the μas cell. Fiμure shows the eλλect oλ μas pressure on the ΔE -ERes spectrum. It can be seen that the horizontal width ΔE component is reduced siμniλicantly with increasinμ PC. It should be noted that the μas pressure oλ the ionization chamber PI is decreased with increasinμ PC, so as to balance between pulse heiμhts λor ΔE and ERes, because the peak position on the ”raμμ curve that provides the distribution oλ enerμy-loss rate as a λunction oλ the distance alonμ the beam axis shiλts toward the μas-cell, as Pc is increased. There is a lower limit oλ . V in ERes λor data points. This is because the both pulse heiμhts correspondinμ to ΔE , ERes coordinates oλ data points is acquired iλ the electrical voltaμe oλ the ERes-trace exceeds . V to discriminate between siμnal and noise. The middle and bottom λrames in Fiμure show the peak proλiles in the ΔE component λor ”e and ”, respectively. These peak proλiles are well λitted with the Gaussian curve characterized by the standard deviation oλ σ ”e and σ ”. The width oλ the ”e peak deλined by σ ”e is approximately / smaller at PC= Torr than that at Torr. “s a measure oλ the discrimination λunction, the dimensionless normalized distance between ”e and ” peaks μiven by

s

Be , H

+s

D Be ,V

+s

B,H

+s

B ,V

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Geochronology - Me“hods and Case S“”dies

where, Δ is the distance between ”e and ” peaks, and subscripts H and V mean horizontal and vertical, respectively. Fiμure shows the experimentally obtained normalized distance with equation as a λunction oλ PC. In the calculation oλ Equation the value oλ σ ”e,H is substituted in σ ”,H λor the λollowinμ two reasons. i The precision oλ σ ”,H is inadequate λor hiμher PC, because the peak oλ boron becomes so small that the main portion oλ the peak hides under the lower limit oλ ERes . V as shown in Fiμure . ii It has been experimentally observed that the relation σ ”e,H ≈ σ ”,H holds independent oλ PC within the ranμe where σ ”e,H and σ ”,H vary siμniλicantly in the same way with PC. It is λound that the values oλ normalized distance peak at PC= Torr. This is due to the λact that as PC increases over Torr, the reduction oλ peak widths becomes saturated, while the distance Δ μoinμ into decline because oλ the enhancement in the enerμy loss in the μas-cell. It can be said that the optimum PC is around Torr providinμ the best discrimination. The nature oλ the PC-dependence on the peak-width is attributed to the baseline λluctuation oλ the pulse trace detected in the ionization chamber, which is brieλly discussed in Section .

Figure 9. The varia“ion of ΔE1-ERes spec“r”m for “wo gas press”res of “he gas-cell, PC (”pper frames). Corresponding peak profiles of 10Be and 10B are also depic“ed for “he ΔE1 componen“ in “he middle and bo““om frames, respec“ively. The peak is fi““ed by a Ga”ssian dis“rib”“ion charac“erized wi“h a s“andard devia“ion of σ. The gas press”re for “he ioniza“ion chamber for lef“ and righ“ cases are 114 Torr and 56 Torr, respec“ively.

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Figure 10. Varia“ion of “he normalized dis“ance be“ween 10Be and 10B spec“r”m peaks as a f”nc“ion of “he PC. The range of PC indica“ed by “he shaded region is an op“imized range, and is ”s”ally employed.

. . Test measurements, Long-term reliability We completed the development oλ the ”e measurement technique last λiscal year , conλirminμ hiμh stability and reliability oλ the ”e/”e ratios in numerous test measurements. Even aλter we started to perλorm requested ”e measurements in , data quality has been continuously checked λor every routine measurement usinμ standards. Three typical standards are the ICN standards mention in the Section . , S - , S - , S - , and a blank sample. The blank sample hereaλter ”LK is made λrom a quantiλied standard λor atomic absorption spectrometry No. produced by Wako Pure Chemical Industries λor which a ”e/”e ratio oλ ~ × - is expected [ ]. “s shown in Section . , S - is used to obtain the normali‐ zation constant μiven by the measured ratio oλ S - divided by its nominal ratio. With respect to the data quality oλ the S - standard, the relative precision, in terms oλ the relative standard deviation rsd is important, since only the rsd aλλects the normalization constant, where the role oλ the S - standard is similar to that oλ HOxII standard in the C measurement, as described in Section . . The value oλ rsd is around . % λor each routine measurement. Fiμure shows the quality oλ measurements λrom October to December . The leλt column shows the evolution oλ the ”e/”e ratios usinμ the S - , S - , and ”LK standards. The ”e measurements have been conducted at intervals ranμinμ λrom around a λew months to halλ a year. “ll ”e/”e ratios λor both S - and S - aμree with the nominal values within σ oλ each point, where the σ is the combined uncertainty oλ the countinμ and the nominal ratio oλ the S - standard. On the other hand, althouμh the ratio oλ ”LKs lies around its expected ranμe, it seems to vary systematically up and down. This variation can be related to at least two λactors one is beam slit condition, and the other is the problem oλ the sample preparation. “s shown in Fiμure , the time when the ”LK ratio is low, in December , coincides with the time when we beμan to narrow the beam slit behind the EC“ to improve the EC“ resolu‐

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tion. The rise in the ratio aλter December implies that there could still remain a somewhat unidentiλied route λor contamination in the sample preparation. This interpretation is sup‐ ported by the observation that the ratio λor the commercial, hiμh-purity chemical reaμent ”eO powder produced by the Mitsuwa Chemical Co., Ltd. stabilized below - aλter Dec. .

Figure 11. Meas”remen“ q”ali“y from Oc“ober 2011 “o December 2013 ”sing 10Be-AMS s“andards: S5-2 (a), S6-2 (b), and blank BLK (c). The lef“ col”mn shows evol”“ion of “he meas”remen“ res”l“s. The gray line and ha“ching in bo“h “he lef“ and righ“ col”mns depic“s respec“ively “he nominal val”es and “heir ”ncer“ain“y. The ”ncer“ain“y range is based on a nominal ”ncer“ain“y of 1.1% (1σ) [39]. The righ“ col”mn depic“s “he corresponding his“ograms based on “he lef“ col‐ ”mn meas”remen“ poin“s. The dashed and do““ed lines represen“ respec“ively “he mean val”es (m) and “heir ”ncer‐ “ain“y (1σH). The symbol c.n. s“ands for “he n”mber of sampling ca“hodes ”sed in b”ilding “he his“ograms, and σHrsd is “he rela“ive s“andard devia“ion of “he σH.

The λrames on the riμht-hand side oλ Fiμure are histoμrams correspondinμ to the leλt-hand λrames. It can be seen that the value oλ m the arithmetic mean oλ the histoμram λor the S and S - standards are λairly consistent with correspondinμ nominal values each diλλerence between measured and nominal value is within the standard deviation oλ m, μiven by σH/ c.n. . , i.e., . × - λor S - , and . × - λor S - . . . Comparison test We perλormed a comparison test with the “MS system in the M“LT usinμ beryllium samples made λrom an ice core. The samples measured in our system were oriμinally prepared as spares

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λor the ”e measurements that had already been perλormed in the M“LT accelerator in . In this test, thereλore, the samples measured at both λacilities are produced by the same process λor the comparison. Fiμure and Table show the results oλ the comparison test. “lmost all oλ the measured ”e/ ”e ratios are consistent with the values obtained by the M“LT “MS system. There is a siμniλicant diλλerence between samples ” and H indicated by the arrow takinμ into consid‐ eration their uncertainties, which could be due to unknown systematic errors. For the results oλ the ”e/”e ratio measured in the M“LT “MS system, two data sets are depicted λor diλλerent data processinμ methods one method is used at Hirosaki Univ. Japan, and the other is our method. The alμorithms used λor drawinμ the ”e/”e ratios λor both methods are almost the same , but the uncertainty has diλλerent interpretations, dependinμ on which method is chosen. The uncertainty in the Hirosaki Univ., unc , represents the standard deviation obtained by repeated measurements, whereas in our method, the uncertainty, unc , is drawn basically by combininμ both the countinμ uncertainty oλ ”e and the uncertainty in the nominal value oλ S . % λor σ [ ] . The uncertainty in the nominal value aλλects that in the normalized constant, but is μenerally not always considered. This is because a lot number oλ standards does not chanμe until the sample bottle is renewed, and thus the true value oλ the normalization constant rarely shiλts. However, even when one assesses the data quality over a lonμ time λrame or perλorms an inter-laboratory comparison test, one should consider the diλλerence in the lot number in order to accurately compare the isotope ratio values. Despite this λact, as shown in Table , there seems to be no systematic diλλerence between unc and unc , as expected. It is noted that the countinμ uncertainty itselλ is around % oλ unc .

Sample A B C D E F G H I J

TONO Ratio unc x10-12 x10-14 3.278 4.4 6.252 8.0 4.067 5.8 4.406 5.6 2.869 4.1 3.846 5.0 4.501 6.0 4.414 5.6 4.148 5.5 3.618 4.8

Ratio1 x10-12 3.273 6.637 4.095 4.379 2.970 3.967 4.585 4.643 4.266 3.688

MALT* unc1 Ratio2 x10-14 x10-12 6.4 3.253 14.4 6.617 7.1 4.077 9.3 4.362 9.2 2.951 4.8 3.945 10.0 4.561 5.6 4.620 4.7 4.244 5.7 3.666

unc2 x10-14 6.1 9.9 7.4 7.2 5.6 6.1 7.0 7.1 6.8 6.2

*Ra“io1:HIROSAKI Univ., Ra“io2: TONO. Table 2. Res”l“s of “he comparison “es“ corresponding “o “he poin“s in Fig”re 12. In the calculation in the normalized constant, S - and/or S - were used atHirosaki Univ., but only S - was used in the TONO.

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Figure 12. Comparison “es“ ”sing ”nknown samples.

On the other hand, the averaμe uncertainty λor the TONO unc is approximately % oλ that λor the M“LT unc . This is due to the λact that the total counts oλ the ”e siμnal λor the TONO were three times larμer than that λor the M“LT because oλ lonμer measurement time at the TONO. It should be mentioned that the averaμe count rate is cps at the TONO but is cps at the M“LT “MS system, a reλlection oλ the diλλerent speciλications oλ their respective ion sources. “ctually, the ion current λor the M“LT “MS system can provide a λew times larμer current than λor the TONO.

. Al measurement . . Development and test measurements Tuninμ up oλ the system and the test measurements λor the routine “l-“MS operation started in March oλ , aλter the development oλ routine ”e measurements was λinished. We plan to complete the development oλ the routine “l-“MS operation in the middle oλ λiscal year , conλirminμ the lonμ term stability and reliability oλ the operation throuμh statistical analysis oλ accumulated data. For the “l measurements, “l O powder is chosen as the sample material mixed with silver powder , and λundamentally no isobar problems occur because Mμ does not λorm neμative ions. Thereλore, the development oλ the “l-“MS procedure is more straiμhtλorward than the ”e-“MS procedure. The conλiμuration λor “l-“MS is listed in Table . Fiμure shows the observed “l + peak in the ETot-ΔE spectrum. “s described above, there is no other peak. The data points outside the countinμ μate the μreen square can be attributed to some incident ions reachinμ the electrode without complete volumetric enerμy-loss due to larμe-anμle scatterinμ at the window oλ the ionization chamber.

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Figure 13. Example of “he observed 26Al3+ peak in “he ETo“-ΔE1 spec“r”m.

We have perλormed test measurements usinμ “l standards, in order to investiμate measure‐ ment stability. For the test measurements, the series oλ standards prepared and distributed by Nishiizumi have been used [ ], as well as the ”e measurement mentioned in Section . . Typical standards, - - and - - S - and S - , respectively , especially the λormer have been employed to compute the normalization constant that is μiven by the measured ratio oλ a standard S - divided by its nominal ratio. The blank sample ”LK was made λrom a quantiλied standard λor atomic absorption spectrometry No. supplied by Wako Pure Chemical Industries. The leλt column on Fiμure shows the results oλ the two test measurements carried out between routine C- and ”e-“MS operations. Concerninμ the isotope ratio λor the S standard, only the precision is meaninμλul in other words, the accuracy has little meaninμ , since the arithmetic mean oλ the points obtained in the same batch or on same date is already normalized to the nominal value. “ lonμ-term precision can be drawn λrom the statistical dispersion oλ the data points displayed on the same λiμure, which will be mentioned in the below description related to the histoμram. “ll data points λor the S - standard are consistent with the nominal value within σ, where σ indicated as error bars is combined uncertainty λrom the statistical uncertainty and the uncertainty normalized constant oriμinated λrom the uncertainty oλ the nominal ratio oλ the S - standard . On the other hand, the result oλ the ”LK implies a decrease in the isotope ratio. This can be due to improvement oλ the enerμy resolution oλ the EC“ accomplished by narrowinμ the beam slit located behind the EC“. It is believed that the contamination to the beamline oriμinates in the ion source or in the hiμh enerμy beamline where unwanted ions can exist because oλ the dissociation oλ molecular ions [ ]. “lthouμh the expected isotope ratio λor the ”LK is not yet known, the observed ranμe miμht be acceptable considerinμ the ranμe oλ the ”LK ratio λor ”e [see Section . ].

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Figure 14. Da“a q”ali“y in “es“ meas”remen“s implemen“ed from March 2013 for 26Al s“andards: S4-1 (a), S5-1 (b), and BLK (c). The lef“ col”mn shows “ime series plo“s. The gray line and ha“ching in (b) for lef“ and righ“ frames indica“e “he nominal val”e and “he range of i“s ”ncer“ain“y, respec“ively. This range is based on “he ”ncer“ain“y of “he absol”“e val”e of “he nominal val”e (0.37% for 1σ [42]). The righ“ side shows corresponding his“ograms represen“ing “he lef“ meas”remen“s. The dashed and do““ed lines s“and for ari“hme“ical mean (m) and ”ncer“ain“y (σH), respec“ively, for “he his“ogram. The symbol c.n. deno“es “he n”mber of ca“hodes ”sed for b”ilding “he his“ogram, and σHrsd is “he rela“ive s“andard devia“ion of σH.

The histoμrams in the riμht-side λrames in Fiμure

present the data distributions shown as

data points in the leλt-side λrames. The lonμ-term precision oλ the S - standard can be indicated by the statistical dispersion oλ their points in Fiμure oλ σH, or σHrsd = .

a labelled as σH. The relative uncertainty

% is less than . %. This maμnitude relation, or σHrsd < . %, provides a

necessary condition that the precision oλ the S - standard would be less than % where the value itselλ is comparable to the precision in the “l measurements in the M“LT “MS system [

]. Here we assume that the ”e counts are simply proportional to the nominal ratio, and

the S - standard is reμarded as representative oλ “l standards except the S - standard. “ctually, the nominal “l/“l ratio oλ the S - standard is nearest to a loμ-averaμe or a μeometric mean λor all the

“l-“MS standards. “s shown in the histoμram oλ the S -

standard, the precision is, indeed, less than %. Furthermore, the diλλerence between m and the nominal value is less than the standard deviation oλ the mean μiven by σH/ c.n.

.

, indicatinμ

there is consistency between them. For all the results shown in this λiμure, data points are inadequate λor a statistical discussion thus we will need to acquire additional data λor evaluation oλ the measurement stability, in order to develop “l routine measurements.

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. Research and development: Baseline fluctuation of the Be pulse trace “s described in Section . , we saw that discrimination between ”e and ” in the ”e-“MS is stronμly dependent on the μas pressure oλ the μas-cell PC located in λront oλ μas ionization chamber. The ΔE component oλ the ”e peak on the ΔE -ERes spectrum shrinks siμniλicantly with decreased PC value. This shrinkinμ, it should be emphasized, accompanies the reduction oλ the ΔE component oλ the ” see Fiμure , implyinμ the shape oλ the ”e peak is closely related to the occurrence oλ incident ”, an interλerinμ particle, is brieλly discussed. The peak width is a reλlection oλ the statistical dispersion oλ the pulse heiμht oλ siμnal traces detected λrom the ionization chamber. Fiμure shows pulse traces observed by the ΔE electrode λor the two PC values correspondinμ to Fiμure . One can see that the λluctuation oλ the baseline oλ the ”e siμnal is μreater λor the lower PC. It is noted that there was no remarkable λluctuation in the pulse trace observed by the ERes-electrode this indicates the dependence oλ the λluctuation on the distance λrom the inlet oλ ionization chamber. In addition, the λluctuation contains λrequency components oλ around a λew tenths oλ a kilohertz. It was observed that the λrequency oλ the major component seems to decrease as PC increases. Fiμure shows both the variation oλ the standard deviation oλ the λluctuation σ in Fiμure and the enerμy loss oλ ” in the area oλ ΔE , ΔE ” evaluated usinμ SRIM [ ] as a λunction oλ PC. The values oλ σ and ΔE ” decrease in a similar way with increasinμ PC, indicatinμ that the λluctuation can be closely related to the incident enerμy oλ the ”.

Figure 15. P”lse “races de“ec“ed by “he ΔE1-elec“rode in “he ioniza“ion chamber for “wo val”es of PC corresponding “o “hose shown in Fig”re 9. The “rigger for acq”iring “he p”lse “race is “aken from “he p”lse de“ec“ed sim”l“aneo”sly by “he Eres-elec“rode a“ “=0.5 ms. The dashed line shows “he s“andard devia“ion of “he fl”c“”a“ion.

In μeneral, iλ the incident λrequency can no lonμer be iμnored comparinμ the reciprocal oλ the time scale λor the pulse width, a hiμh countinμ rate induces pulse pile-up, and deteriorates the time resolution oλ the ionization chamber. Our investiμation, by measurinμ the ” current shows that the averaμe λrequency oλ the ” incident is on the order oλ a meμahertz, which is comparable to the reciprocal oλ the pulse width. In λact, the amount oλ ” enterinμ toward the ionization chamber is expected to be over times larμer than that oλ ”e [ ]. The mechanism λor the baseline λluctuation, however, is independent oλ the siμnal pile-up, but can be due to

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Figure 16. PC-dependence on “he s“andard devia“ion of “he fl”c“”a“ion σ. The energy loss of 10B in “he ΔE1 region, ΔE110B, ded”ced by ”sing “he SRIM is also shown. The shaded h”“ch depic“s “he PC-range normally ”sed.

the eλλect oλ the charμe accumulation in the ionization chamber, as qualitatively described below. In ordinary cases, electrons neμative charμes and ions positive charμes produced by the ionization caused by the incident ion collidinμ with atoms in the ionization chamber driλt toward the anode and cathode, respectively, in the applied electric λield, and λinally lose their charμe at the electrodes. In the present case, it should be noted that the time interval oλ the ” incident is much shorter than the time scale λor the ions-loss on the order oλ milliseconds λor the ordinary condition as mentioned above. This can lead to the charμe accumulation in the space the positive charμe reaches a certain level so as to provide a balance between production rate and loss rate. The substantial positive charμe lowers the anode potential throuμh the ineλλiciency oλ the Frisch-μrid playinμ a role in shieldinμ the charμes [ , ]. Iλ some instability exists inherently in the relationship between the enhancement oλ the charμe and the ion loss system, the anode potential, thereλore, can λluctuate around its equilibrium value. Volumetric ion-electron recombination would be a candidate system λor causinμ an instability so as to enhance the λluctuation oλ positive charμe. This kind oλ deμradation oλ the perλormance oλ the ionization chamber caused by the residual positive charμe is not just related to the ”e measurement, but to more μeneral measurements oλ rare isotopes accompanied by the isobar problem. Indeed, an eλλect oλ remaininμ charμe was mentioned in a paper λor improvinμ the discrimination oλ S in Cl-“MS [ ]. Thereλore, it can be said that the investiμation oλ the nature oλ pulse trace presented here has been conducted as a preparatory activity in the development oλ the Cl-“MS operation.

. Summary The “MS system operatinμ at the Tono Geoscience Center TGC has not only continued to contribute reliable routine “MS measurements, but also made steady proμress in developinμ

Q”a“ernary Geochronology Using Accelera“or Mass Spec“rome“ry (AMS) – C”rren“ S“a“”s of “he AMS Sys“em… h““p://dx.doi.org/10.5772/58549

multi-nuclide “MS in order to provide μeochronoloμical datinμ methods applicable to the entire Quaternary timescale. Our versatile “MS system, based on the MV PelletronTM tandem accelerator, is desiμned λor “MS analysis oλ most radio-isotopes includinμ ”e, C, “l, Cl, and I. The “MS system is in μood condition aλter λiλteen years oλ operation, ensured by reμularly scheduled maintenance. Total measurement time has been increasinμ λor the last years, and reached , hours this year. The averaμe annual number oλ samples measured is , and the μrand total number oλ samples will exceed , within a λew months. In the C-“MS operation, the lonμ-term reliability oλ routine measurements has been contin‐ uously veriλied by measurinμ standard samples such as C , C , and so on, produced by the I“E“, and HOxII produced by the NIST and by comparative testinμ with other “MS λacilities. “lmost all the relative standard deviations oλ the isotope ratios oλ HOxII in percent modern carbon are less than . % λor each measurement, and the averaμe isotope ratio oλ C lies around . pMC. The comparison tests were carried out twice, in and in , with the “MS λacility at the J“E“-“MS-MUTSU. The results showed that there was no siμniλicant diλλerence in the data obtained λrom the λacilities. With respect to the ”e-“MS operation, we completed the development oλ ”e measurement capability last year, conλirminμ both hiμh stability and reliability oλ the ”e/”e ratios obtained λrom numerous test measurements. Then, routine measurements started since the beμinninμ oλ λiscal year . The detection limit oλ the isotope ratio can be less than × - , estimated by usinμ samples made oλ commercial hiμh-purity ”eO powders. For the development oλ ”e“MS, discrimination oλ ”e λrom ” was accomplished by optimization oλ μas pressure in the μas cell located in λront oλ μas ionization chamber. We also perλormed a comparison test with the “MS system at the M“LT in the University oλ Tokyo usinμ beryllium samples taken λrom an ice core. Measured ”e/”e ratios were consistent with the values obtained by the M“LT μroup, conλirminμ the reliability oλ our measurements. We have now entered into the development oλ “l-“MS. This development and the test measurement have proμressed and have shown satisλactory results. We have perλormed system tuninμ and test measurements usinμ “l standard samples. “lmost all measured ratios oλ “l/“l are consistent with nominal values, within the ranμe oλ their uncertainty and routine measurements oλ “l will start in the near λuture. We have also conducted investiμations λor improvinμ the heavy ion detection system based on the ΔE-ERes type-μas ionization chamber with multi-anodes. It has been observed that the hiμh incident ion rate oλ the stable isobars into the μas ionization chamber disturbs the baseline oλ the pulse trace λor the measured rare nuclide. This can be related to the λact that the remaininμ positive charμe produced by isobars makes the anode siμnal λluctuate, which will be one oλ key λactors that should be resolved λor achievinμ the Cl-“MS with μood discrimi‐ nation oλ S, a stable isobar. The development λor the Cl-“MS analysis will be one λocus λor development work in the next λew years.

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Acknowledgements We would like to express our μratitude to Proλ. Matsuzaki oλ the University oλ Tokyo λor his continuous academic and practical advice. We would like to oλλer our special thanks also to Dr. Horiuchi oλ Hirosaki University λor providinμ unknown beryllium samples and measure‐ ment data. Special thanks to Mr. Hanaki oλ the λacility administrator λor his manaμement support and constant encouraμement. We also thank the staλλ members oλ the “MS laboratory λor their help and support.

Author details “kihiro Matsubara *, Yoko Saito-Kokubu , “kimitsu Nishizawa , Masayasu Miyake , Tsuneari Ishimaru and Koji Umeda *“ddress all correspondence to matsubara.akihiro@jaea.μo.jp Tono Geoscience Center, Japan “tomic Enerμy “μency, Jorinji, Izumi, Toki, Japan Pesco Corp., Ltd., Tokiμuchiminami, Toki, Japan

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and Methods in Physics Research Section ” ”eam Interactions with Materials and “toms – . [

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] Travertine M, Wood C, Sucrose W. Reλerence Sheet λor Quality Control Materials. “vailable http //nucleus.iaea.orμ/rpst/Documents/rs_I“E“-C _to_I“E“-C .pdλ.

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] Sato M, Itoh S, “HN S, Hirota M, Yamaμata H, et al. Current status oλ the Compact “MS system at Paleo Labo Co., Ltd. . Proceedinμs oλ the th Japaneses Sym‐ posium on “ccelerator Mass Spectrometry. Naμoya. pp. – .

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] “ramaki T, Mizushima T, Mizutani Y, Yamamoto T, Toμawa O, et al. The “MS λacili‐ ty at the Japan “tomic Enerμy Research Institute J“ERI . Nuclear Instruments and Methods in Physics Research Section ” ”eam Interactions with Materials and “toms – .

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] Kabuto S, Kinoshita N, Tanaka T, Yamamoto N. Operational Status oλ the J“E“MUTSU Tandetron “MS . Prosceedinμs oλ the Second J“E“ Tandetron “MS Utilization Workshop November - , , Mutsu-shi, Japan. J“E“. pp. – .

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] Imamura M, Hashimoto Y, Yoshida K, Yamane I, Yamashita H, et al. Tandem “ccel‐ erator Mass Spectrometery oλ ”e/ ”e with Internal ”eam Monitor Method. Nuclear Instruments and Methods in Physics Research ” – .

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] Grajcar M. New concepts oλ ”e “ccelerator Mass Spectrometry at low enerμies. Swiss Federal Institute oλ Technoloμy .

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[

] Martschini M, “ndersson P, Forstner O, Golser R, Hanstorp D, et al. “MS oλ Cl with the VER“ MV tandem accelerator. Nuclear Instruments and Methods in Phys‐ ics Research Section ” ”eam Interactions with Materials and “toms – .

Chapter 2

Luminescence Chronology Ken M”nyikwa Addi“ional informa“ion is available a“ “he end of “he chap“er h““p://dx.doi.org/10.5772/58554

. Introduction Luminescence datinμ is a collective term λor datinμ methods that encompass thermolumines‐ cence TL and optically stimulated luminescence OSL datinμ techniques. OSL is also less commonly reλerred to as optical datinμ [ ], photon stimulated luminescence datinμ or photoluminescence datinμ [ ]. Luminescence datinμ methods are based on the ability oλ some mineral μrains to absorb and store enerμy λrom environmental ionizinμ radiation emanatinμ λrom the immediate surroundinμs oλ the mineral μrains as well as λrom cosmic radiation. When stimulated these minerals, μenerally reλerred to as dosimeters [ ], will release the stored enerμy in the λorm oλ visible liμht hence the term luminescence. Measurinμ the enerμy and deter‐ mininμ the rate at which the enerμy accumulated allows an aμe representinμ the time that has elapsed since the enerμy beμan accumulatinμ to be determined. Stimulation oλ enerμy release usinμ heat is termed TL while stimulation usinμ liμht is reλerred to as OSL. The aμe ranμe oλ luminescence methods μenerally spans λrom a λew decades to about , years, thouμh aμes exceedinμ several hundred thousand years have been reported in some studies [λor example, , ]. In addition, there are datinμ protocols that are currently under investiμation that, iλ successλul, could extend the ranμe even λurther [ ]. Thus, the method is useλul λor datinμ Late Quaternary events and, not only does it provide chronoloμy beyond the ranμe that can be attained usinμ radiocarbon methods, but it oλλers an alternative chronometer in settinμs where no carbon bearinμ material can be λound. This chapter aims to acquaint readers who are not λamiliar with luminescence datinμ methods with the basics oλ the techniques. It is not intended to be used as a manual but rather as an introductory primer that brinμs awareness about the principles behind the datinμ methods, their practical aspects, as well as their applications. “ccordinμly, the chapter comprises nine sections. Followinμ the introduction in the λirst section which brieλly lays out the historical development oλ luminescence datinμ, the second section examines the principles oλ the datinμ methods. This is λollowed by a discussion oλ sample stimulation mechanisms and basic

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measurement equipment used in luminescence datinμ in the third section. Luminescence properties oλ diλλerent minerals are examined in the λourth section. In the λiλth section, methods used to determine the enerμy stored within mineral μrains paleodose as well as the rate at which the enerμy accumulates dose rate are explored. In the sixth section, practical aspects pertaininμ to sample collection and laboratory preparation λor analysis are discussed aλter which the types oλ materials that can be dated usinμ luminescence materials are examined in the seventh section. To illustrate the multiλaceted character oλ some luminescence datinμ studies, the eiμhth section presents a case study that uses the chronoloμy oλ postμlacial eolian dune deposition in western Canada to constrain the timinμ oλ Late Pleistocene deμlaciation in the reμion. The chapter concludes in the ninth section with a look at current and potential λuture developments in luminescence datinμ. . . The historical development of luminescence dating The history oλ the development oλ luminescence datinμ spans the last six decades and it beμan with experimental applications oλ the phenomenon oλ thermoluminescence, which is the emission oλ liμht when materials are heated to temperatures below those oλ incandescence. One oλ the earliest documented suμμestions oλ the possibility oλ usinμ thermoluminescence to measure time in archaeoloμy was by Daniels et al. [ ] who in proposed usinμ thermolu‐ minescence observed λrom ancient pottery artiλacts that had previously been λired as a measure oλ their aμe [ ]. “ λew years later, the application oλ thermoluminescence to date pottery was discussed by Kennedy and Knopλλ [ ] and technical aspects oλ measurements that would be employed λor datinμ were described by Gröμler et al. [ ]. Notably the application oλ thermo‐ luminescence in μeoloμy to study aμes oλ carbonates [ ] and lava λlows [ ] was already beinμ discussed. “n early study that tested the application oλ thermoluminescence datinμ on pottery was reported by “itken et al. [ ] when in they applied the method on pottery sherds ranμinμ in aμe λrom around , – , years and collected λrom sites spread over a larμe area. Results indicated that the luminescence aμes were linearly proportional to radiocarbon chronoloμy λrom contemporaneous materials. Subsequently, developments throuμhout the rest oλ the s and the s saw improvements in datinμ procedures that used thermolu‐ minescence in archaeoloμical applications [ ]. Incidentally, parallel developments in the λormer Soviet Union durinμ the late s and early s beμan seeinμ the tentative application oλ thermoluminescence datinμ on unburnt Quaternary sediments [ , ] when it was noted that older sediments returned hiμher TL siμnals than younμer ones. Datinμ oλ unburnt sediments was based on the recoμnition that stored enerμy in sediment μrains could also be depleted by exposure to sunliμht as opposed to heatinμ that occurs in λired artiλacts. In the West, attempts to apply thermoluminescence on unburnt sediments appear to have beμun around the end oλ the s [ ] includinμ attempts by Wintle and Huntley [ , ] to apply the technique on deep sea sediments. “ccurate sediment aμes λrom TL datinμ, however, remained elusive since the optimal conditions λor solar resettinμ were not yet λully understood [ ]. Huntley [ ] conducted some oλ the earliest studies investiμatinμ the most appropriate conditions λor solar bleachinμ. In a related devel‐ opment, sediment datinμ usinμ luminescence methods proμressed rapidly when it was noted

L”minescence Chronology h““p://dx.doi.org/10.5772/58554

[ ] that liμht could also be used to stimulate enerμy release λrom sediments durinμ measure‐ ment as opposed to heatinμ. This led to the birth oλ OSL datinμ and throuμhout the rest oλ the s [ , ], the s [ - ] and the early part oλ the λollowinμ decade, improved protocols were introduced [ , ] and OSL datinμ equipment reλined. “ll these developments saw luminescence datinμ emerμe as a robust method λor datinμ clastic Quaternary sediments, especially eolian deposits. “ comprehensive historical account oλ the λirst yrs oλ lumines‐ cence datinμ is provided by Wintle [ ].

. Principles of luminescence dating . . Luminescent materials Some dielectric materials insulators that include many minerals such as quartz, λeldspar, zircon and calcite have the ability to store enerμy in their crystal lattices that emanates λrom ionizinμ radiation. In natural μeoloμical settinμs, such ionizinμ radiation λor example, alpha, beta, and μamma radiation occurs naturally within the immediate surroundinμs oλ the μeoloμical materials while a small component is also contributed by cosmic radiation. When stimulated, the minerals will exhibit luminescence which essentially represents a release oλ the stored enerμy. Luminescence datinμ employs this phenomenon by measurinμ the enerμy stored in the mineral, called the paleodose, and dividinμ it by the rate at which the enerμy was received by the mineral in question. Hence, the basic aμe equation λor luminescence datinμ is Luminescence Age =

Paleodose Dose rate

. . Electron trapping mechanisms The exact mechanisms throuμh which luminescence enerμy accumulates in the minerals are complex. However, it is thouμht that the enerμy is stored when electrons in the mineral crystal lattices are displaced λrom the valence band oλ their parent nuclei. Once detached, the electrons diλλuse into the surroundinμs oλ lattice deλects that act as electron traps. Such deλects include a missinμ atom in the crystal lattice oλ the mineral, an atom out oλ its riμhtλul place or the occurrence oλ impurity atoms in the lattice [ ]. Importantly λor datinμ purposes, the number oλ trapped electrons increases with the duration oλ exposure oλ the mineral to the ionisinμ radiation. Fiμ. is a depiction oλ an enerμy level diaμram that is commonly used to visualise the trappinμ mechanism involved in luminescence. The depth oλ the trap T below the conduction band, indicated by E’ [Fiμ. ], is an indication oλ the eλλicacy oλ a μiven trap. Stable traps are those that can withstand perturbations such as lattice vibrations that could dislodμe the electrons λrom their traps. Stimulation oλ the crystal lattice structure by heatinμ to an appropriate temperature or by optical means usinμ a suitable wavelenμth will excite the electrons out oλ the traps. Once expelled λrom the traps, the electrons diλλuse within the crystal lattice until they come across another site that is attractive to electrons and these are reλerred to as recombination centres [ ]. When electrons reach some recombination centres, enerμy is

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emitted in the λorm oλ liμht and these are described as luminescence centres. Thermal stimu‐ lation would yield TL whereas optical stimulation would produce OSL. Importantly, the diλλusion process is very rapid such that the time between stimulation and recombination can be treated as instantaneous. For a recombination centre to be eλλective, an electron must be missinμ λrom the site in the lattice, creatinμ what is termed a hole. Holes are created in materials by ionisinμ radiation. The intensity oλ the luminescence μiven out λollowinμ stimulation is proportional to the number oλ trapped electrons and this is assumed to be proportional to the enerμy absorbed λrom the nuclear radiation [ ]. Siμniλicant λor datinμ applications, however, thouμh the enerμy storaμe mechanisms miμht be the same λor a μiven mineral, the sensitivity to radiation will vary between samples a consideration that has huμe implications λor methodoloμical approaches as will be shown later.

Figure 1. Energy Level diagram ill”s“ra“ing “he crea“ion of l”minescence cen“res in crys“al la““ices “hro”gh expos”re “o ionising radia“ion (redrawn from [29]). (a) Irradia“ion leads “o elec“rons being expelled from “heir original si“e and dif‐ f”se wi“hin “he la““ice. (b) Elec“rons become “rapped while holes of missing elec“rons become localised a“ par“ic”lar cen“res. (c) S“im”la“ion (by hea“ or ligh“) res”l“s in elec“rons being evic“ed from “he “raps and diff”sing ”n“il “hey mee“ a recombina“ion cen“re. Ligh“ (l”minescence) is emi““ed when l”minescence cen“res are enco”n“ered by “he elec“rons “o give TL or OSL.

It is pertinent to note that the number oλ traps within the lattice oλ any dosimeter is not inλinite and, hence, they will be exhausted λollowinμ extended exposure to radiation, beyond which enerμy will not be stored eλλiciently. This is reλerred to as saturation. For datinμ purposes this is what deλines the upper limit on the aμe beyond which samples cannot be dated usinμ luminescence methods [ ]. The exact aμe representinμ this upper limit will ultimately depend on the dose rate, with samples experiencinμ hiμh dose rates havinμ lower aμe limits. . . Natural sources of ionizing radiation For purposes oλ luminescence datinμ, natural sources oλ ionisinμ radiation that contribute to the trapped enerμy in mineral μrains are isotopes oλ uranium U and U and thorium Th decay chains, potassium K and rubidium Rb . These elements occur in natural materials in very low levels around - parts per million λor uranium and thorium and μenerally less

L”minescence Chronology h““p://dx.doi.org/10.5772/58554

than % λor potassium, where K is one part in , . However, collectively, their radioactive isotopes emit enouμh radiation to cause detectable luminescence λor datinμ purposes. The radiation emitted includes alpha and beta particles as well as μamma radiation. “lpha particles have penetration ranμes oλ . mm while beta and μamma rays have ranμes oλ around . cm and cm respectively [ ]. The shorter distance travelled by alpha particles is because they are heavier and much more ionizinμ, which results in more rapid loss oλ enerμy as they knock atoms oλ materials throuμh which they are travelinμ out oλ the way. ”eta particles and μamma rays, on the other hand, tend to μet scattered. ”esides the radiation λrom radioactive isotopes, an additional, albeit smaller, component to the enerμy received by the mineral μrains is contributed by cosmic rays λrom outer space. The cosmic radiation comprises a soλt and a hard component and once it reaches the earth’s surλace, the soλt component is absorbed by the upper cm oλ the near-surλace substrate. Only the hard component can penetrate deeper and is oλ interest to luminescence datinμ. This hard component comprises muons mostly and at sea level it varies sliμhtly with latitude, increasinμ in intensity by about % λrom the equator to latitude °. “bove ° latitude however, it remains constant up to the poles [ ]. “t altitudes hiμher than km, the contribution λrom the hard component also increases siμniλicantly with both latitude and altitude. For datinμ purposes, special λormulae have been developed λor evaluatinμ cosmic ray contribution to the dose rate [ ].

. Basic luminescence measurement equipment and sample stimulation mechanisms The primary objective oλ TL or OSL measurements in datinμ studies is to ascertain the amount oλ enerμy that has accumulated in the mineral μrains since the start oλ the event beinμ dated. This enerμy is determined by stimulatinμ the mineral μrains usinμ an appropriate mechanism and measurinμ the amount oλ liμht released. “s already outlined, trapped electrons in luminescence datinμ can be evicted λrom their traps by heatinμ, as is done in TL, or usinμ liμht, in OSL methods. Fiμ. illustrates the basic layout oλ equipment used to measure the lumines‐ cence. Typically, samples are placed on discs about cm in diameter and then introduced into the machine in multiples on an appropriate sample holder. “ servo-control mechanism moves the sample to the appropriate position λor stimulation and measurement. Most modern luminescence measurement systems possess both thermal and optical stimulation capabilities. The luminescence siμnal λrom the sample is captured by the photomultiplier tube aλter μoinμ throuμh optical λilters. For TL measurements, the λilters help exclude inλrared siμnals λrom the heatinμ while allowinμ blue or violet siμnals. For OSL measurements, the λilters reject wavelenμths used λor stimula‐ tion while usually allowinμ violet and near-ultraviolet wavelenμths. The end oλ the photo‐ multiplier tube closest to the sample is λitted with a photocathode that emits electrons when struck by liμht photons as a result oλ the photoelectric eλλect. Potential diλλerences allow emitted electrons to be attracted by the λirst dynode in the photomultiplier. For each electron arrivinμ

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at the dynode, several are emitted and the process is repeated throuμh the photomultiplier many times such that several millions oλ electrons reach the anode at the other end oλ the photomultiplier λor each electron leavinμ the photocathode. These electrons μive an easily detectable current pulse at the anode that is commensurate with the arrival oλ photons at the photocathode. The current pulses are then ampliλied and the output is presented as photon counts, representinμ the luminescence siμnal. “s will be shown below, TL output is distinctly diλλerent λrom OSL output.

Figure 2. Basic fea“”res of a TL/OSL reader “ha“ can be ”sed “o meas”re l”minescence signals ”sing ei“her hea“ or op“ical s“im”la“ion (modified af“er [31]).

. . Stimulation by heat TL When stimulatinμ usinμ heat, a sample is heated rapidly at rates in the ranμe oλ °C /s. Once a temperature commensurate with E’ in Fiμ. and characteristic oλ a particular trap type is reached, electrons are rapidly evicted λrom the traps [ ]. The temperature is represented by a peak in emission on a plot oλ the luminescence versus temperature reλerred to as the TL μlowcurve. Continued heatinμ will empty the traps and the luminescence μiven out will be proportional to the number oλ electrons trapped in the mineral μrains since the beμinninμ oλ the event beinμ dated. Fiμ. shows a μlow-curve oλ a sample observed aλter the λirst heatinμ. Iλ a sample is heated λor a second time immediately aλter the λirst heatinμ, a diλλerent curve is observed. This second curve is the red-hot μlow that is the incandescence μiven out by any

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material when heated to a temperature hiμh enouμh. “bsent λrom this second heatinμ will be the luminescence emanatinμ λrom ionizinμ radiation that accrued since the last event that emptied the electrons λrom the traps.

Figure 3. Examples of TL glow-c”rves showing (a) na“”ral signal ob“ained from a mineral sample (q”ar“z) d”ring “he firs“ hea“ing and (b) red-ho“ glow-c”rve ob“ained from a second hea“ing (incandescence). No“e “ha“ in c”rve (a), in‐ candescence is also ob“ained d”ring “he firs“ hea“ing when “he sample is hea“ed above 400° C (redrawn from [31].

. . Optical Stimulation OSL Optical stimulation oλ luminescence uses liμht oλ a particular wavelenμth λor example, blue, μreen, or near-inλrared to expel electrons λrom their traps. Notably, the rate at which these electrons are evicted directly depends on the rate at which the stimulatinμ photons are received. The sensitivity oλ a μiven trap-type to photostimulation is also an important λactor inλluencinμ the rate at which electrons leave their traps. In essence, the curve that depicts the emission λollows an exponential decay oλten reλerred to as a shine-down curve , with hiμh emission rates in the beμinninμ that μradually λall with continued stimulation Fiμ. . Iλ the process is continued, at a certain point, all electron traps that are sensitive to optical stimulation become exhausted. Inteμratinμ the number oλ photons released over the period oλ stimulation quantiλies the luminescence oλ the sample and this should be commensurate with the sample’s aμe [ ]. Factors that inλluence the sensitivity oλ a trap type to electron eviction by liμht include characteristics oλ the trap as well as the wavelenμth oλ the stimulatinμ liμht. Generally, shorter wavelenμths are associated with λaster eviction rates. Stable traps may require more enerμy than that available λrom some optical stimulation wavelenμths and in such cases, thermal assistance can be used to bridμe the μap. This enables lonμer wavelenμths to be used λor stimulation in cases where they would not be able to unassisted [ ]. When selectinμ a stimulation wavelenμth λor OSL measurements, it is important to select a wavelenμth that eλλectively allows separation to be made between the wavelenμth oλ the stimulatinμ source and that oλ the emitted siμnal. “s described earlier, λilters are used to assist this process. Quartz and λeldspar λor instance, have stronμ emissions in the near-ultraviolet nm and violet nm respectively and λilters used in either case are selected because

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they have windows in the respective wavelenμth ranμe. Wavelenμths used λor stimulation, thereλore, should be excluded by the λilters [ ].

Figure 4. OSL shine-down c”rve for a hypo“he“ical mineral s“im”la“ed ”sing ligh“ for abo”“ 100 s (modified from [29]).

. . Advantages of OSL over TL “s will be shown later, advantaμes oλ OSL datinμ versus TL datinμ mainly apply to datinμ oλ sediments that have been zeroed by solar bleachinμ. Studies have demonstrated that solar bleachinμ oλ natural TL occurs much more slowly than OSL [ ].

Figure 5. Comparison of bleaching ra“es of na“”ral TL and OSL (green ligh“) signals of q”ar“z (q) and feldspar (f) con‐ d”c“ed by Godfrey-Smi“h e“ al. [19] (redrawn from [29]). The slower bleaching c”rves are from “he TL signals.

L”minescence Chronology h““p://dx.doi.org/10.5772/58554

In a study examininμ the bleachinμ rates oλ quartz and λeldspar Fiμ. , it was shown [ ] that aλter hrs oλ exposure to sunliμht, samples oλ both minerals had less than . % oλ their oriμinal OSL siμnal remaininμ Fiμ. . Conversely, similar samples had TL siμnals that were at least times hiμher remaininμ aλter an equal time under solar radiation. This means that the optical siμnal is zeroed much more rapidly by the sun and the hard to bleach TL traps μenerally result in a much hiμher residual siμnal λollowinμ solar bleachinμ compared to the OSL siμnal. Consequently, it is oλten diλλicult to date very younμ samples usinμ TL [ , ] , with OSL beinμ preλerred λor datinμ sediments in μeneral. However, datinμ oλ λired artiλacts and baked sediments usinμ TL remains an appropriate methodoloμy since the zeroinμ mechanism in nature will be similar to the stimulation mechanism at measurement.

. Luminescence properties of some common minerals The discovery oλ luminescence in minerals is not a recent event. “itken [ , , ] has oλten cited the case oλ Robert ”oyle who in reported holdinμ a diamond close to his body and notinμ that it shined in the dark’. This is because many minerals are capable oλ luminescinμ in the dark when appropriately irradiated and stimulated. For datinμ purposes usinμ lumi‐ nescence methods, however, quartz and λeldspar are the dosimeters that have received the most λocus. “ttempts have also been made to use zircon and calcite but these are not commonly used λor datinμ because oλ a number oλ drawbacks. In this section, the luminescence properties oλ these minerals are brieλly examined. . . Quartz Quartz is a widely used mineral in luminescence datinμ because oλ the advantaμes it oλλers compared to the alternatives. It is one oλ the most abundant minerals on the earth’s surλace, makinμ it ubiquitous in most depositional environments, a λeature arisinμ λrom its hiμh stability at the earth’s surλace and resistance to abrasion. It also has very stable luminescence properties. ”ecause oλ its chemistry, quartz itselλ has no internal source oλ radiation that is a major element oλ its composition. “s a result, the radiation quartz μrains receive in nature usually oriμinates λrom outside the μrain. In some settinμs, however, quartz may contain some trace amounts oλ uranium [ ]. . . . Quartz TL properties For TL analysis, natural quartz siμnals normally display two peaks above °C [ ]. One peak is at °C and another at °C and it is the latter that is usually used λor datinμ. Laboratory irradiated quartz also shows a peak at °C. In terms oλ emissions, when heated above °C, quartz has a TL emission band in the ranμe nm blue and another in the ranμe nm oranμe [ ]. ”elow °C, quartz has an emission in the ranμe nm near UV to violet when irradiated with a laboratory dose. The °C peak is thouμht to be λrom “lO impurities in the quartz lattice servinμ as holes [ ].The peak has a hiμh thermal

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stability but it tends to saturate at low doses such that it is oλ limited use beyond unless very low dose rates are involved [ ].

-

ka

The °C TL peak bleaches more rapidly than that at °C [ ] and its emission peaks at about nm [ ]. Hence, by usinμ appropriate λilters, the emission can be separated λrom that oλ the °C peak. Studies suμμest that, because oλ its relative stability, the °C peak could in theory be used λor datinμ up to million years, which is much older than aμes that can be measured usinμ the °C peak [ ]. . . . Quartz OSL properties Irradiated quartz has been shown to emit OSL when stimulated by liμht λrom any part oλ the visible spectrum. For datinμ purposes usinμ current methods, however, blue liμht is preλerred in most applications because, as indicated earlier, OSL yield is proportional to the wavelenμth used λor stimulation, with hiμher enerμies yieldinμ hiμher OSL intensities [ ]. The OSL siμnal λrom sedimentary quartz has been demonstrated to comprise at least three or λour components and these are reλerred to as λast medium and slow components with respect to the rates at which they decay [ ]. Others have reported up to seven components [ ]. These components can only be separated when stimulation uses a constantly increasinμ stimulatinμ power, reλerred to as linearly modulated OSL LM-OSL [ ]. “ stimulation source with a constant power continuous wave , as is used in most reμular datinμ, cannot resolve the components. However by usinμ heat treatments to eliminate unstable siμnals or stimulatinμ λor controlled times to exclude dominant slow components the appropriate siμnal can be λocused on when usinμ continuous wave stimulation. . . Feldspar Feldspar has been used extensively in OSL datinμ. Like quartz, it is a mineral that is widely available at the earth’s surλace, thouμh it weathers more rapidly. The chemistry oλ λeldspars has important implications with respect to how they are used in luminescence datinμ. They are aluminosilicates that have potassium K , calcium Ca or sodium Na as end members. The presence oλ potassium in some oλ the λeldspars is critical in that K isotopes that λorm part oλ the potassium constitute an internal source oλ radiation, in addition to any external radiation the μrains may receive. Feldspars that do not have hiμh potassium as part oλ their chemistry λor example, Ca and Na-λeldspars , however, would not have this additional internal dose. Hence, λor datinμ purposes, as will be discussed later, K-λeldspars are normally separated λrom other λeldspars prior to conductinμ analysis. For datinμ applications, λeldspar has a number oλ attractive characteristics. One is that, in terms oλ emissions, λeldspars have a hiμher briμhtness compared to quartz which means that it μives stronμ siμnals, allowinμ smaller doses to be measured. Secondly, the internal dose in λeldspars that have a hiμh potassium content constitutes a reliable radiation source that is immune λrom environmental chanμes that would aλλect external sources λor example, interstitial water . “s a result, dose rates can be determined more accurately. The third advantaμe oλ λeldspar, which will be discussed below, is that it can be stimulated usinμ inλrared stimulation. “ major

L”minescence Chronology h““p://dx.doi.org/10.5772/58554

drawback λor λeldspar, however, which delayed its application in routine datinμ, is that it is aλλlicted by a phenomenon called anomalous λadinμ [ ]. In anomalous λadinμ, the measured luminescence intensity decays with increasinμ time λrom the time oλ irradiation because some electrons have much shorter residence times in their traps than predicted by physical models [ , ]. The ultimate result is that most λeldspar μrains will return equivalent doses sliμhtly lower than they would iλ the dose were stable over time. To address this phenomenon in λeldspar datinμ, correction methods λor the λadinμ have been devised [ , ]. . . . Feldspar TL properties Many K-λeldspars oλ sedimentary oriμin have been shown to display natural siμnals with TL peaks at °C and °C [ ]. With reμards to emissions, some studies [λor example, ] have reported emissions λrom K-rich λeldspars in the nm ranμe violet to blue while plaμioclase λeldspar emissions have been reported in the nm ranμe blue-μreen . However, results λrom other studies [ ] suμμest a more complex pattern. . . . Feldspar OSL properties Luminescence λrom λeldspars has been investiμated usinμ visible liμht stimulation. Earlier investiμations used lasers λor example, . nm μreen λrom arμon and nm red λrom krypton and observed the emissions at shorter wavelenμths [ , ]. For plaμioclase λeldspars, results showed that the spectra observed were similar to those λrom TL. “nother study [ ] that used a stimulation wavelenμth oλ nm also showed that the emission was centred at nm. OSL applications λor datinμ usinμ μreen liμht stimulation have been very limited and this has larμely been because inλrared stimulation IRSL , as discussed below, was λound to be a much better alternative. However, a study [ ] that compared μreen liμht stimulation luminescence GLSL and IRSL data λrom λeldspars λrom alluvial sediment showed results that suμμested the siμnals had diλλerent thermal stabilities, with GLSL siμnals beinμ more stable than IRSL siμnals at °C. Stimulation oλ λeldspars usinμ a wide ranμe oλ wavelenμths in the ranμe nm, apart λrom μreen and red, has also been demonstrated by [ ]. . . . Feldspar IRSL properties Feldspars can also be stimulated usinμ the near inλrared part oλ the electromaμnetic spectrum around nm . Since the discovery oλ this stimulation peak [ ], most datinμ research that uses optical stimulation oλ λeldspars λor sediment datinμ has been λocussed on IRSL. “ major advantaμe oλ this, as stated earlier, is that it leaves the rest oλ the visible part oλ the spectrum open λor use in emission detection. Other investiμations usinμ IRSL include studies on λineμrained sedimentary samples containinμ both plaμioclase and K-λeldspar that have also shown a major stimulation peak at nm . eV and another weaker one at nm . eV at room temperature [ ]. Overall, these characteristics allow λeldspars to be stimulated by liμht emittinμ diodes that have emission peaks at around ± nm and these are widely available and cheap. Emission spectra oλ the K-λeldspars stimulated usinμ IRSL were reported by Huntley et al. [ ] to show a dominant peak at nm and another minor peak between and nm. Plaμioclase λeldspars, on the other hand, showed an emission peak at nm.

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Krbetschek et al., [ ] reported additional natural emission peaks λor K-λeldspar at well as at and nm.

nm as

Feldspar samples irradiated with a laboratory dose have been shown to display an additional emission peak at nm. For λeldspar samples with a natural siμnal however, this nm peak is absent. In datinμ studies, the nm peak can be eliminated by preheatinμ [ ]. . . Calcite The mineral calcite has been demonstrated to have a TL siμnal with an emission at nm [ ] and attempts have been made to use the mineral λor datinμ. However, calcite which oλten occurs in carbonate cave deposits has a limited environmental occurrence, which constrains its applicability. The luminescence λrom calcite is also complicated by the tendency oλ calcite to preλerentially concentrate uranium. Thus, evaluation oλ the dose rate has to account λor the disequilibrium oλ the decay chain oλ uranium. Notably, calcite datinμ usinμ the uranium disequilibrium can be used to establish better chronoloμies than would be attainable usinμ luminescence methods [ ]. Hence, overall, the incentive to use calcite in luminescence studies has been low. Published attempts to use OSL emissions λrom calcite λor datinμ include studies by Uμumori and Ikeya [ ]. Nonetheless, as with the TL eλλorts, these have not translated into widespread applications. . . Zircon Zircon also has luminescence properties. Its properties as a dosimeter are particularly inter‐ estinμ because zircons naturally have a hiμh concentration oλ uranium such that the internal dose that they receive is usually λar μreater than any radiation oriμinatinμ λrom the μrain’s exterior. “s a result, the dose rate is very constant because it is not susceptible to variations that may be induced by chanμes in interstitial water content or burial depth [ ]. “ major methodoloμical drawback, however, is that the uranium content is variable between μrains and, as a result, measurements have to be made on individual μrains. Zircon studies usinμ TL include investiμations by Huntley at al. [ ] and Templer and Smith [ ]. OSL analyses on zircons include studies by Smith [ ]. In addition to variations in the uranium content between individual μrains, zircon μrains also have inhomoμeneities in their crystal structures that develop durinμ λormation. Hence, λor datinμ purposes, the luminescence λrom the internal dose is not easily comparable to the siμnal λrom the artiλicial dose administered in the laboratory as would be done with quartz or λeldspar. To circumvent this problem, zircon datinμ oλten employs the autoreμeneration method whereby the natural siμnal oλ the zircon is measured aλter which the μrains are stored λor several months [ , ]. “t the end oλ this storaμe period, the μrains are measured aμain to determine the siμnal that has accrued λrom the internal dose since the initial measurement. This storaμe siμnal is then used to calibrate the natural siμnal λrom antiquity to determine an aμe [ ].

L”minescence Chronology h““p://dx.doi.org/10.5772/58554

. Paleodose and dose rate determination “s outlined earlier, in order to calculate an aμe, the basic luminescence aμe equation divides the dose that has accumulated since the beμinninμ oλ the event beinμ dated paleodose by the rate at which the enerμy was accumulated dose rate Equation . Hence, the two basic parameters that have to be determined are the paleodose and the dose rate. In this section methods used to determine these variables are discussed. . . Paleodose determination Paleodose determination aims to ascertain the amount oλ enerμy that has accumulated in a dosimeter since the event beinμ dated occurred. In luminescence datinμ this is μenerally the period that coincides with the time when the mineral μrains were emptied oλ any previously accumulated enerμy or zeroed . The dose is μenerally deλined as the enerμy absorbed per kiloμram oλ material and the unit used to measure it is the μray Gy where Gy= joule per kμ. For λired or heated materials, the period correspondinμ to zeroinμ would be the time when the samples were last heated to the appropriate temperature whereas, λor unheated sediments, it would commonly be the time when they were last adequately exposed to the bleachinμ eλλects oλ the sun. The luminescence siμnal obtained λrom a sample λrom the λield is reλerred to as the natural siμnal. In principle, in order to determine the natural siμnal in a μiven sample in Gy, artiλicial irradiation that is well calibrated is used to induce luminescence in the sample in a laboratory settinμ aλter which the natural siμnal is compared to the siμnals λrom the artiλicial irradiation. This allows the maμnitude oλ the laboratory dose that induces a siμnal equivalent to that produced by the natural dose to be ascertained. That laboratory dose is reλerred to as the equivalent dose De . “s depicted in Fiμ. , there are two main methods that have been developed λor determininμ De and these are the additive dose and the reμenerative dose or reμeneration methods [ , ]. Other methods that have been used in the past include the partial bleach method [λor example, ]. However, these are no lonμer widely used. . . . Additive dose method “s initially developed, to determine the equivalent dose usinμ the additive dose method, samples λrom the λield are typically separated into multiple aliquots. One set oλ aliquots would have the natural siμnal measured aλter which the other aliquots are irradiated with well calibrated incremental doses and then measured, with multiple aliquots beinμ used λor each dose level. The acquired siμnals are then plotted to μive a dose-response curve that shows the luminescence siμnal aμainst the laboratory irradiation Fiμ. a . This is reλerred to as a μrowth curve and it is essentially a simulation oλ the evolution oλ the total dose had the sample experienced similar dose levels in its natural settinμ over time. Since the method employs multiple aliquots, siμnal normalisation is perλormed to correct λor inter-aliquot variations by μivinμ the aliquots a small test dose aλterwards and then measurinμ the response. Such variations arise λrom diλλerences in mass and μrain sensitivity. To determine De usinμ the additive dose method, the curve is extrapolated backwards to zero siμnal intensity and the De will be where the curve intercepts the horizontal dose axis Fiμ. a . In TL datinμ, the

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residual siμnal remaininμ aλter solar bleachinμ, would have to be taken into account as well. It is important to note that, λor both λeldspar and quartz, μrowth curves usually show a linear relationship between the luminescence siμnal and the dose in the early part oλ the curve. Iλ hiμh enouμh doses are administered, however, the siμnal tends to level oλλ, indicatinμ saturation or an exhaustion oλ the luminescence traps.

Figure 6. Me“hods ”sed “o de“ermine “he eq”ivalen“ dose (De). In “he addi“ive dose me“hod (a), incremen“al doses are given “o ”nbleached samples and meas”red. In “he regenera“ive dose me“hod (b), on “he o“her hand, “he samples are zeroed firs“ before incremen“al doses are adminis“ered and meas”red (modified af“er [3]).

. . . Regenerative dose method The reμeneration method diλλers λrom the additive dose method in that the samples are zeroed λirst beλore any laboratory dose is applied. For TL datinμ, previously λired artiλacts, λor example archeoloμical materials or baked sediments, are zeroed by heatinμ. For OSL samples, on the other hand, zeroinμ is achieved by exposure to sunliμht. The zeroed aliquots are then μiven incremental doses as with the additive dose method, preλerably with the doses beinμ chosen to lie above and below the natural siμnal. Normalisation can also be conducted to correct λor

L”minescence Chronology h““p://dx.doi.org/10.5772/58554

inter-aliquot siμnal variations. Siμnals λrom the doses are then plotted to μive a reμenerative μrowth curve. The equivalent dose would be obtained by interpolatinμ the natural siμnal or the unknown siμnal into the curve Fiμ. b . . . . Single aliquot methods versus multiple aliquot methods “s outlined above, when initially developed λor TL datinμ, both the additive dose and reμener‐ ative dose methods involved the use oλ multiple aliquots. With the introduction oλ OSL datinμ, thouμh the possibility oλ usinμ sinμle aliquots was contemplated early [ ], the practice oλ usinμ multiple aliquots was adopted too [ ]. “n inherent assumption when usinμ multiple ali‐ quots is that all the aliquots oλ a μiven sample respond similarly to the dose received. Howev‐ er, this is not what is observed inter-aliqout variations arise λrom a number oλ sources and this necessitates the implementation oλ normalisation to try and address the diλλerences. Quartz in particular appears susceptible to sensitivity chanμes. The diλλerent μrains within any particu‐ lar aliquot would have experienced dissimilar histories within the natural environment and these can include diλλerences in erosion and deposition cycles, episodes oλ heatinμ λrom wildλires or other extreme conditions [ , ]. The heatinμ administered in the laboratory as part oλ the analysis see λurther below also results in sensitivity modiλications that are dissimilar be‐ tween the μrains, and ultimately between the aliquots. Variations in sample mass between aliquots may also be a reason λor diλλerences in behavior between aliquots. The net result oλ these disparities is that they μive rise to diλλerences in sensitivity that contribute to uncertainties in the calculated aμes, even in cases where normalisation is used. Hence, to help address these aspects, there was a desire to develop a method that only utilised a sinμle aliquot. There are a number oλ advantaμes associated with the use oλ sinμle aliquots and these include [ ] i.

when usinμ a sinμle aliquot, to obtain De, the natural siμnal obtained will be compared to the dose response curve oλ the same aliquot. Hence, inter-aliquot variations are eliminated resultinμ in much hiμher precision λor De.

ii.

only a very small amount oλ sample material is required. This is particularly impor‐ tant λor archeoloμical samples that may be oλ limited size.

iii.

normalisation to correct λor inter-aliquot variations in numbers oλ μrains on diλλerent sample discs or variations in sensitivity is not necessary when usinμ a sinμle aliquot.

iv.

the measurement protocol employed with sinμle aliquots which entails preheatinμ, bleachinμ, and irradiation can all be conducted within most modern readers which are automated and it increases precision in addition to reducinμ analysis times.

The λollowinμ section examines procedures used in sinμle aliquot methods. . . . Single-Aliquot Regenerative-dose SAR protocol The introduction oλ sinμle aliquot methods beμan with investiμations that employed the additive dose approach. Eλλorts to use sinμle aliquots λor datinμ quartz had observed that there were sensitivity chanμes associated with repeated preheatinμ oλ the aliquot that was required aλter every successive laboratory dose prior to conductinμ the luminescence measurements.

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Preheatinμ is necessary because it ensures that the distribution oλ trapped electrons aλter administerinμ the laboratory dose is similar to that resultinμ λrom the natural dose [ ]. To correct λor the sensitivity chanμes usinμ the sinμle aliquot additive dose method on λeldspars, Duller [ ] monitored an additional aliquot λor sensitivity chanμes. Galloway [ ] improved on Duller’s [ ] approach by correctinμ the luminescence siμnals usinμ a least squares λittinμ approach usinμ measurements made on the same λeldspar aliquot subsequent to the additive dose irradiation and measurements. This modiλication by Galloway [ ] essentially trans‐ λormed the method into a bona-λide sinμle aliquot protocol. “lternatively, usinμ the additive dose method on quartz, Murray et al. [ ] devised a correction procedure that included additional preheat and stimulation cycles without any additional dose beinμ μiven, the results oλ which were used to λormulate a decay constant. The constant was then used to correct the data λrom the additive dose measurements. “ttempts to use sinμle aliquots with the reμeneration method on λeldspar [ ] and on quartz [ ] had initially concluded that it would not be possible because oλ sensitivity chanμes [ ]. However, to address those sensitivity chanμes, Mejdahl and ”øtter-Jensen [ ] proposed the sinμle-aliquot/ reμeneration–added dose protocol S“R“ to date previously heated materials and Murray [ ] later used the same method on unheated sediments. However, with S“R“, at least two aliquots are required [ ]. Subsequently, a truly sinμle aliquot reμenerative dose S“R protocol was introduced by Murray and Roberts [ ] usinμ sedimentary quartz λrom “ustralia and, with that S“R method, corrections λor the sensitivity chanμes were made by monitorinμ the ° C TL siμnal measured immediately aλter administerinμ a reμeneration dose. “ major methodoloμical breakthrouμh was made when a streamlined version oλ the method proposed by Murray and Roberts [ ] was put λorward by Murray and Wintle [ ] whereby sensitivity chanμes were monitored usinμ a test dose whose siμnal was also meas‐ ured. “s initially proposed by Murray and Wintle [ ], this S“R protocol essentially entailed the λollowinμ sequence Step

Treatmenta

Observed

1

Irradia“e sample wi“h dose, Di

-

2

Prehea“ sample (160-300°) for 10s

-

3

S“im”la“e sample for 100s a“ 125 °C

Li

4

Irradia“e sample wi“h “es“ dose, D“

-

5

Hea“ “o 160°C

-

6

S“im”la“e for 100 s a“ 125°C

7

b

Re“”rn “o 1 and repea“ seq”ence

Ti -

Di is “he regenera“ion dose which gives signal Li whereas D“ is “he “es“ dose which gives signal Ti. The observed signals, Li and Ti are “hen ”sed “o plo“ a c”rve of Li/Ti vs. “he regenera“ion dose, D. a

For “he na“”ral sample, 1=0 and D0=0 Gy.

b La“er modifica“ions s“im”la“e “he sample for 40s (ins“ead of 100s) and an addi“ional s“ep “o op“ically s“im”la“e “he sample for 40s a“ a “empera“”re above “he prehea“ “empera“”re is cond”c“ed af“er s“ep 6 “o red”ce rec”pera“ion [see 26, 62].

Table 1. S“eps in “he SAR pro“ocol as originally proposed by M”rray and Win“le [26].

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Since its oriμinal introduction, the S“R protocol has underμone some minor modiλications Table [ , ] and, over the last - years, the protocol has emerμed as the preλerred method λor routine datinμ oλ both sedimentary and λired materials usinμ both quartz and λeldspar. Further methodoloμical details can be λound in [ , , ]. . . . Single grain analysis Measurement protocols used λor analyzinμ sinμle aliquots can also be adapted λor determininμ paleodoses usinμ individual mineral μrains. Special equipment λor loadinμ and analyzinμ sinμle μrains have been developed that allow multiple sand-sized μrains up to m to be mounted individually in a reμular array that permits automated measurement [ ]. In this λormat, thousands oλ μrains can be analysed in a relatively short period oλ time. “nalyzinμ sinμle μrains makes it possible to recoμnize diλλerences in behaviour between μrains λrom a μiven sample. For instance, it enables the identiλication oλ μrains that have been bleached to diλλerent levels prior to burial because such μrains will yield diλλerent paleodoses. For that reason, sinμle μrain analysis is commonly used to identiλy partial bleachinμ in sediments, especially in λluvial deposits [ ]. . . . Presentation of luminescence paleodose data Once determined, paleodose results can be presented as μrowth curves as in Fiμ. , with the horizontal axis showinμ the dose μiven and the vertical axis showinμ the lumines‐ cence siμnal or nor normalised siμnal . However, λor S“R procedures where multiple determinations can be made on the same sample that yield a ranμe oλ equivalent dose values, individual μrowth curves do not convey all pertinent statistical inλormation. “lternative means that can be used to provide some statistical inλormation include λrequency histoμrams. However, histoμrams do not provide inλormation on precision [ ]. To address that aspect, paleodose data in luminescence datinμ are now commonly presented as radial plots that show both the number oλ De determinations made as well as the relative precision associated with each determination [ ]. In the example oλ a radial plot μiven in Fiμ. , each dot represents an equivalent dose that was determined λor a sinμle μrain usinμ the S“R approach λor a total oλ μrains. Had multiple μrain aliquots been used, each data point would denote an aliquot. “ny straiμht line that passes radially throuμh the oriμin represents a line oλ constant dose. The horizontal axis at the bottom shows the relative error associated with each paleodose calculation, with the precision increasinμ λrom leλt to riμht. The shaded area in the plot [Fiμ. ] denotes the siμma error band centred at the equivalent dose oλ Gy, representinμ the weiμhted-mean oλ all data points. Thus, the band represents a % conλidence level on all aliquots that were analysed. The number oλ data points that lie outside the shaded area are reλlected by the overdispersion oλ the data and can be calculated [ ]. The equivalent dose scale on the riμht is a loμarithmic scale. Overall, radial plots enable investiμators to visualize the dose distributions, allowinμ appropriate data to be tarμeted λor λurther analysis. For instance, they permit investiμators to diλλerentiate between variations in equivalent dose that arise λrom the bleachinμ history and local dose rates λrom those that are caused by intrinsic diλλer‐

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Figure 7. Radial plo“ of eq”ivalen“ dose (De) es“ima“es for 204 single grains from Sample M3T 61.2 m from Lake M”n‐ go, A”s“ralia, ob“ained ”sing “he SAR pro“ocol (redrawn from [66]). Each da“a poin“ represen“s a single grain. Preci‐ sion, shown on “he x-axis, is simply “he reciprocal of “he s“andard error. Hence, as rela“ive error decreases as one moves “o “he righ“, “he precision increases.

ences in luminescence sensitivity oλ the measured aliquots [ ]. “ccordinμly, radial plots have oλten been used to identiλy poorly bleached samples, especially when used to analyze individual μrain paleodoses. Once the paleodose is determined, statistical models used to calculate the aμe include the central aμe model, which calculates the weiμhted mean equiva‐ lent dose λrom a set oλ data points takinμ into account the overdispersion above that associ‐ ated with measurement errors. Similarly, the minimum aμe model μives the equivalent dose associated with the population oλ aliquots or μrains λor sinμle μrain datinμ with the lowest dose. Details on these models can be λound in [ ]. . . Dose rate determination “part λrom the paleodose, an additional element that has to be determined beλore a lumines‐ cence aμe can be calculated is the dose rate. “s outlined earlier, the main isotopes responsible λor the accumulation oλ luminescence enerμy in natural settinμ are the isotopes oλ the uranium and thorium decay chains, potassium and rubidium as well as cosmic radiation. Hence, the total contribution oλ these eλλects have to be evaluated. There are several methods that can be used to determine the total dose rate. One is the concentration approach and with this method, concentrations oλ thorium, uranium, potassium and rubidium in representative samples are measured usinμ an appropriate technique such as neutron activation, atomic absorption spectroscopy ““S , X-ray λluorescence XRF , λlame photometric detection FPD or induc‐ tively coupled plasma mass spectrometry ICP-MS . However, measurement oλ uranium and thorium usinμ this approach can be inaccurate iλ there is disequilibrium [ ].

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Hiμh-resolution μamma ray spectrometry and alpha spectrometry are alternative methods that can be used to measure activities oλ individual radionuclides, includinμ those λrom the thorium and uranium decay chains. Hence, they can be used to measure dose rates whether there is disequilibrium or not. However, extended measurement times could be required and the equipment can be costly [ ]. “nother approach that has been employed to minimise eλλects oλ disequilibrium oλ the thorium and uranium chains is to measure the contribution oλ uranium and thorium usinμ thick source alpha countinμ TS“C and then use ““S, XRF, FPD or ICP-MS to measure potassium. “n alternative procedure is to measure the alpha contribution only usinμ TS“C and determine the beta contribution usinμ a beta particle counter. Whenever possible, the μamma dose rate should be measured on site, especially in settinμs where there is uncertainty about the uniλormity oλ the dose within a cm radius oλ the sample. The recent development oλ powerλul portable μamma–ray spectrometers has made such λield measurements relatively practical [ ]. Other λield measurement options include the use oλ very sensitive synthetic dosimeters such as -“l O C that only need to be buried in the λield λor a λew weeks at the most, as opposed to earlier dosimeters that required burial λor up to a year [ ]. “s described earlier, cosmic-rays also contribute to the dose received by the mineral μrains. This contribution is usually minor but in settinμs where the contributions λrom the radionu‐ clides are low, cosmic contribution can be siμniλicant. Formulae λor evaluatinμ cosmic ray contribution have been provided by Prescott and Hutton [ ]. The eλλect oλ moisture content in the natural settinμ oλ the material beinμ dated is to absorb part oλ the dose that should normally reach the μrain. Consequently, when calculatinμ dose rates, the levels oλ moisture content have to be noted and λactored into the determination. In essence, dry sediment will experience a hiμher dose rate than moist sediment. . . Lower and upper limits for luminescence ages Improvements in luminescence datinμ instrumentation and datinμ protocols have reached a staμe where current OSL methods can be used to date samples deposited as recently as the last λew decades [λor example, ]. The sinμle μrain datinμ method in particular can yield dates with very hiμh precision. Prerequisites λor datinμ such younμ samples include appropriate bleachinμ to remove all previously acquired luminescence enerμy prior to burial as well as the availability oλ μrains that have hiμh luminescence sensitivity [ ]. To optimize the measure‐ ments and increase precision, thermal charμe transλer is minimized in order to increase the siμnal size. Such advances mean that luminescence methods can now produce aμes λrom the last years that are more reliable than those attainable usinμ radiocarbon methods. Cali‐ brated radiocarbon aμes λrom the same period have comparatively larμer uncertainties due to λluctuations in C production [ ]. With reμards to the upper aμe limit attainable usinμ luminescence methods, empirical studies have demonstrated that the storaμe oλ luminescence enerμy throuμh the trappinμ oλ electrons is not a process that can continue indeλinitely within any μiven material because, eventually, the traps do μet exhausted [ , ]. For that reason, luminescence μrowth curves are oλten

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Figure 8. Ill”s“ra“ion of q”ar“z grow“h c”rves cons“r”c“ed ”sing “he SAR pro“ocol (redrawn from [3]). In (a) “he c”rve is

(

)

cons“r”c“ed ”sing a sa“”ra“ing exponen“ial of “he form I (D ) = I 0 I - exp / 0 where I(D) deno“es “he OSL signal com‐ mens”ra“e wi“h “he dose D and I0 is “he maxim”m OSL in“ensi“y “ha“ can be ob“ained. The variable D0 de“ermines “he shape of “he c”rve and in c”rve (a), D0 is 55 Gy. Beca”se c”rve (a) appeared “o ”nderes“ima“e some older ages, in (b) “he sa“”ra“ing f”nc“ion from (a) is combined wi“h a linear f”nc“ion [3]. -D D

represented by saturatinμ exponential λunctions and the λorm oλ the curve determines the maximum luminescence siμnal that can be stored in the mineral μrain beyond which no dose can accumulate eλλiciently. For quartz λor instance, Fiμ. a shows the λast component expressed as a sinμle saturatinμ exponential and, beyond a certain dose, the curve λlattens. Datinμ oλ quartz samples close to saturation > Gy has been demonstrated in some studies to yield OSL aμes that underestimate the true aμe by up to % [λor example, ]. In reality, the absolute aμe limit will be determined by the dose rate, with low dose rates havinμ hiμher aμe limits. The curve in Fiμ. a also shows that the μrowth curve is relatively linear λor low doses, and aμes λrom the linear part oλ the μrowth curve have been shown in numerous studies to be comparable to those obtained usinμ other datinμ methods, λor example, radiocarbon. Gener‐ ally, however, these results indicate that the storaμe oλ luminescence dose in mineral μrains

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has an upper limit beyond which the traps become saturated. This dose level places a limit beyond which the method cannot be applied. For quartz this dose is about Gy. The solution adopted in some studies when workinμ with older aμes [ , ] is to model the lumi‐ nescence μrowth usinμ a combination oλ the saturatinμ λunction and a linear λunction to μive a curve as in Fiμ. b [ ]. “μes in excess oλ ka have been reported λrom quartz usinμ this method [λor example, ]. Feldspar aμes in excess oλ ka obtained usinμ IRSL siμnals have also been reported in a number oλ studies [ ]. However, at such dose levels > Gy the μrowth curve is no lonμer linear such that correction λor anomalous λadinμ usinμ standard procedures [ ] becomes problematic. Overall, however, the indication is that λor both λeldspars and quartz, there is an upper aμe limit beyond which accurate OSL aμes cannot be obtained. The exact limit will ultimately depend on the dose rate.

. Sample collection and preparation: some practical aspects Havinμ looked at the principles oλ luminescence datinμ and the methodoloμical aspects in the precedinμ sections, a topic that needs to be discussed are the types oλ materials that can be dated usinμ luminescence methods. Prior to explorinμ that topic, however, it is imperative to examine aspects oλ the datinμ method that have a bearinμ on the types oλ materials one can date usinμ luminescence techniques. “ccordinμly, this section examines the importance oλ μrain size aλter which sample collection and preparation methods are discussed. . . Importance of grain size For technical reasons, luminescence datinμ is usually conducted on mineral μrains in two broad μrain size cateμories coarse μrains and λine μrains. In the coarse μrain method, μrains in the λine sand cateμory are separated and analyzed. Such μrains would normally receive dose λrom alpha, beta, and μamma radiation. However, because alpha particles can only penetrate the outer m oλ the μrain, the coarse μrains are typically etched usinμ hydroλluoric acid HF to remove the outer rinμ oλ the μrain that experienced alpha radiation. “s a result, methods that date coarse μrains are oλten reλerred to as inclusion datinμ methods [ ]. For quartz inclusion datinμ oλ pottery, particles in the size ranμe m are usually extracted [ ]. For sediment datinμ, on the other hand, coarse μrains representinμ the modal μrain size are normally extracted. For eolian dunes λor instance, μrains in the size ranμe m are usually preλerred [ ]. In λeldspar inclusion datinμ, similar procedures are used to extract μrains in the λine to medium sand size ranμe and etchinμ can also be used to remove alpha particle eλλects. “s a result, when datinμ coarse μrains, the annual dose is calculated by evaluatinμ contributions λrom beta, μamma and cosmic radiation and the aμe equation is modiλied to Luminescence Age =

.

Paleodose D + D + DC

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where D , D and Dc reλer to the beta, μamma and cosmic ray dose contributions respectively [ , ]. When the dose rates are expressed as annual rates, the aμe will be μiven in years. The beta contribution in Equation is λactored by . to account λor the attenuation due to μrain size as well as the etchinμ that removes some parts oλ the μrain that received the beta dose [ , ]. Exceptions to Equation are only those cases where the quartz itselλ has some uranium and thorium within it. “lso λor λeldspar datinμ, where K-λeldspars are usually isolated λrom Na-λeldspars and dated separately, an additional parameter would also have to be included in the denominator in Equation to account λor the internal dose λrom potassium. In λine-μrain datinμ procedures, dated materials are oλten not separated into mineral speciλic concentrations. Rather, polymineral μrains with diameter in the ranμe m λine silt are extracted and analysed. ”ecause oλ their size, alpha particles can penetrate these particles completely and alpha contribution has to be taken into account when calculatinμ the dose rate. “s a result, μeneral aμe equation is modiλied to Luminescence Age =

Paleodose kD + D + D + DC

where D , D , D and Dc reλer to the alpha, beta, μamma and cosmic ray dose contributions respectively. “lternatively, in some studies, λine μrained quartz is extracted λrom the poly‐ mineral mixture oλ λine μrains usinμ procedures outlined below and analyzed separately. There are some studies that have used intermediate size μrains in the ranμe m, which is coarse silt [λor example, ]. For such studies, alpha particle contribution also has to be taken into account when calculatinμ the dose rate. . . Sample collection and laboratory procedures . . . Sample collection When collectinμ samples λor datinμ usinμ luminescence methods, a primary requirement that has to be λulλilled is that the mineral μrains to be analyzed should not be exposed to liμht λrom the time they are initially buried up until the point they are exposed to the stimulatinμ source durinμ measurement. This restriction necessitates the adoption oλ special precautions durinμ sample collection and a number oλ procedures have been devised over the years. For archaeoloμical artiλacts this may entail extractinμ material λrom the interior oλ the artiλact usinμ a drill under saλe liμht conditions. For sediments, however, measures taken include samplinμ at niμht [ , ]. Not only is this an inconvenient method be‐ cause oλ the need to work in the dark, but there is a μreater risk oλ accidentally exposinμ the sample to liμht durinμ the collection [ ]. For sediments that are adequately λirm, an alternative approach is to cut out a block oλ sample λrom the depositional unit beinμ investiμated and transλer it to the laboratory where a portion λor analysis is extracted λrom the sample’s interior [ , ]. “ samplinμ approach that has become a method oλ choice because oλ its ease and relative μuarantee λor retrieval oλ an unadulterated sample is to insert an opaque pipe made oλ metal, PVC or “”S plastic into a λreshly prepared proλile λace [ ]. Once retrieved, the pipe is immediately capped on both ends with an opaque and

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preλerably airtiμht seal. “t the laboratory, sediment at the ends oλ the pipe is removed and the sample λor luminescence measurements is taken λrom the central portion oλ the pipe. In places where depositional units are not directly accessible, drillinμ has also been used to reach tarμeted units and methods that can be used λor such samplinμ are reviewed in [ ]. . . . Sample preparation prior to measurement Once the collected sample has reached the laboratory, it has to be prepared λor analysis and a number oλ procedures have been established dependinμ on the material tarμeted λor analysis. “s outlined in Section . , samples λor luminescence analysis are either measured as λine or coarse μrains. It was also indicated that λor coarse μrains, analysis is usually made on pure mineral separates λor example quartz, or K-λeldspars whereas λor λine μrains, either poly‐ mineral λractions or λine μrained quartz extracts can be used. When datinμ λine μrained sediments such as loess, λor instance it would be preλerable to use the λine μrain procedure whereas λor eolian dune sands, the coarse μrain approach would be more appropriate. In sediments that have equal components oλ λine μrains and coarse μrains, datinμ both λractions would provide a μood mechanism λor comparison as a cross-checkinμ method. For coarse μrained materials, quartz or λeldspar are typically separated usinμ a heavy liquid such as sodium polytunμstate solution. Fiμ. is a λlowchart oλ a separatinμ procedure λor quartz and λeldspar usinμ heavy liquids with successively liμhter or heavier speciλic densities. Prior to separatinμ minerals usinμ the heavy liquid, carbonates and orμanic materials that oλten occur in sediments, and are usually introduced durinμ the postdepositional phase oλ the deposit, are removed usinμ hydrochloric acid and hydroμen peroxide respectively. “dditional inλormation on separation procedures oλ coarse μrains can be obtained λrom [ , ]. For λine μrains, carbonates and orμanic materials are also removed usinμ dilute hydrochloric acid and hydroμen peroxide respectively. Dilute sodium oxalate solution is then added to prevent λlocculation oλ the particles aλter which appropriate μrain sizes are separated usinμ a sedimentation column. Sedimentation columns employ Stoke’s law which states that the velocity oλ a particle’s sedimentation in a λluid also depends on the size oλ the particle. Hence, by extractinμ sediment λrom the column aλter a predetermined time λollowinμ aμitation permits a desired μrain size to be isolated. “s indicated earlier, while λine μrains can be analysed as polymineralic λractions, some studies extract pure quartz λrom the λine μrains by diμestinμ the λeldspars usinμ λluorosilicic acid [λor example, ]. Detailed inλormation on separation procedures oλ λine μrains λor luminescence datinμ have been provided by [ ]. Once separated, coarse μrains quartz or λeldspar or the λine μrains mixed polymineralic or pure quartz are mounted on appropriate sample discs prior to analysis. Typically, the measurement discs are made oλ stainless steel or aluminum and measure around mm in diameter and . mm thick [ ]. To mount coarse μrains, a monolayer oλ the sample is deposited on the disc in dry λorm. Silicone oil can be used to help the sample μrains adhere to the disc. For λine μrain particles, on the other hand, once the desired μrain sizes have been isolated, these are mounted on the discs in a solution oλ acetone, ethanol or water which is then allowed to evaporate, leavinμ the sediment deposited on the disc. In either case, the disc will now be ready λor analysis.

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Figure 9. Separa“ion proced”re for coarse grains ”sing a heavy liq”id. S“ar“ing off wi“h a liq”id of specific gravi“y (s.g.) 2.62 gcm-3, “he sample is separa“ed by cen“rif”ge in“o a frac“ion “ha“ is ligh“er (floa“s) and one “ha“ is heavier (sinks). The frac“ion “ha“ sinks is passed “hro”gh a liq”id of s.g. 2.75 gcm-3 and “he frac“ion “ha“ floa“s will comprise mos“ly q”ar“z or plagioclase while “he sinking frac“ion will comprise heavy minerals, for example, zircon. The frac“ion “ha“ floa“s in “he liq”id of densi“y 2.62 gcm-3 is passed “hro”gh ano“her liq”id of s.g. 2.58 gcm-3. The frac“ion “ha“ sinks will be Na-feldspar whereas “he ligh“er frac“ion is f”r“her separa“ed ”sing a liq”id of s.g. 2.53 gcm-3 in“o K-feldspar and clay.

. What materials can be dated using luminescence methods? For all practical purposes, an important aspect about luminescence datinμ is knowinμ what type oλ materials or sediments can be dated usinμ luminescence methods. Discussions in the precedinμ sections have touched on this topic albeit indirectly. “s detailed earlier, lumines‐ cence methods date materials by measurinμ enerμy that has accumulated in materials called dosimeters. Hence, one prerequisite λor datinμ usinμ the method is that the material to be dated must contain a dosimeter. The second prerequisite is that there has to be an event that reset the enerμy previously stored by the dosimeter to provide a startinμ point λor countinμ the time. In essence, all enerμy stored in the dosimeter will be assumed to have accumulated since that point. “ third requirement λor material to be datable usinμ luminescence methods is that the electron traps in the dosimeter should not be exhausted at the time oλ datinμ because once enerμy storaμe has reached a point oλ saturation, the relationship between time and dose rate breaks down. Hence, the sample λor datinμ has to be younμer than the upper aμe limit that can be attained λor that particular dosimeter and, as indicated earlier, the exact limit ultimately depends on the dose rate too. With these considerations in mind, materials datable with luminescence techniques broadly λall into two main cateμories materials that have been heated and clastic sediments oλ sand and silt size that have been reset zeroed throuμh exposure to solar radiation.

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. . Heated materials “s discussed in an earlier section, luminescence datinμ initially beμan as an archaeoloμical technique that was used λor datinμ materials that had been heated to temperatures adequately hiμh λor example, > °C to expel all electrons λrom their traps. Hence, the heatinμ process provides a startinμ point that can serve as year zero when datinμ such artiλacts. Fired artiλacts such as ancient pottery, tiles, bricks or terracotta λiμures are all examples oλ archeoloμical materials that can be dated usinμ luminescence methods, especially TL, because these materials usually contain dosimeters such as quartz and λeldspar. ”y separatinμ the quartz and datinμ quartz inclusions, or by usinμ the λine μrained components to date polymineralic λractions or quartz separates, aμes can be obtained. Humans are μenerally believed to have discovered the art oλ makinμ pottery durinμ the Neolithic period, which dates back to about yrs aμo in some places [λor example, ], but the art only became widespread about years aμo [ ]. Hence, unless dose rates are very hiμh, most ancient pottery artiλacts are not yet saturated and should be datable usinμ luminescence methods. “part λrom pottery, other heated materials oλ archaeoloμical siμniλicance that can be dated usinμ luminescence methods include burnt λlint and burnt stones that were associated with human settlements and may have been heated to hiμh temperatures. Flint is a sedimentary λorm oλ quartz and hence possesses dosimetric properties [ ]. Paleolithic humans used λlint extensively as a tool λor scrapinμ and λor cuttinμ as well as λor projectile points. Chips or debitaμe leλt over λrom the manuλacture oλ such implements can be λound associated with ancient settlements. Iλ any oλ these tools or chips were at some staμe heated, either deliberately or accidentally durinμ the occupation oλ the site by humans, datinμ the objects usinμ lumi‐ nescence methods will provide a chronoloμy commensurate with the timinμ oλ human habitation. Thus, heated λlint can be a useλul chronometer especially λor timescales beyond those commonly covered by other methods such as radiocarbon [ ]. Other heated μeoloμical materials include stones that were used as pot-boilers’ by some societies prior to the discovery oλ pottery. In some settinμs stones were also used λor constructinμ λireplaces. In both instances, where these previously heated stones contain appropriate minerals they can be dated usinμ luminescence methods [λor example, ]. “ diλλerent class oλ heated materials that can be dated usinμ luminescence methods are μeoloμical materials that have been heated to appropriate temperatures to have zeroed them durinμ the last approximately , years. Such materials include contact-baked sediment that is heated to hiμh temperatures λollowinμ a volcanic eruption. In such cases, the soil can be collected and μrains extracted λor datinμ usinμ either coarse μrain or λine μrain methods [ ]. Iλ the sediment contains larμer clasts such as μravel, constituent quartz or λeldspar μrains can be extracted λrom the pebbles λor analysis. The aμe obtained would be conμruent with the timinμ oλ the volcanic eruption [ ]. “lso associated with volcanic eruptions are the products oλ the eruption itselλ such as lava and ash. The heat associated with the volcanic eruption is suλλicient to zero these products oλ any previously acquired dose, iλ at all, since the lava would mostly be in liquid λorm rather than crystalline state. Fine μrained μlass m extracted λrom volcanic ash has been used in

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some studies to date the eruption [ ]. Other studies have attempted to use minerals λrom the lava instead oλ volcanic ash [λor example, ] Finally, also related to the eλλects oλ heatinμ to reset the luminescence siμnal are materials that have been zeroed by heat emanatinμ λrom the impact oλ a meteorite. The thermal shock associated with such impacts can reach temperatures hiμh enouμh to zero constituent μrains oλ the aλλected μeoloμical material [λor example, ]. . . Dating of sediments reset by sunlight “ class oλ materials that has λostered the rapid development oλ luminescence datinμ methods over the last three decades are clastic sediments that have been zeroed by solar bleachinμ. Since the conλirmation by Huntley et al. [ ] that enerμy λrom sunliμht was capable oλ adequately erasinμ previously accumulated enerμy λrom dosimeters, there have been many applications oλ the method to obtain chronoloμies λrom sedimentary materials, initially usinμ TL and later usinμ OSL. “s outlined above, the prerequisites λor datinμ usinμ luminescence methods which include a presence oλ a dosimeter in the material, the occurrence oλ a bleachinμ episode that erases any previously accumulated enerμy, and the absence oλ saturation in the dosimeters sediment μrains need to be satisλied iλ a material is to be dated. “ number oλ sedimentary materials satisλy these criteria and have been dated usinμ luminescence methods, with some presently constitutinμ λormidable chronoloμical archives oλ environmental chanμe. These include sediments deposited by wind eolian sediments , water-laid sediment, μlacial deposits, and earthquake related sediments. These sediment classes are discussed below under the respective headinμs. In all instances, reλerence to aμes obtained λrom sediments bleached by solar resettinμ denotes burial aμes or time that has elapsed since the last time the sediments were exposed to liμht λrom the sun. . . . Eolian deposits Wind deposited eolian sediments are the sediment oλ choice λor datinμ usinμ luminescence methods. This is because the subaerial transport that the sediment experiences durinμ transportation is expected to provide adequate time to bleach the sediment μrains oλ any previously accumulated enerμy [ ]. While this may not be true in some cases, results μenerally show that in most settinμs, that assumption is valid [ ]. “s a result, this class oλ sediments has provided the majority oλ luminescence aμes reported to date. Eolian sediments μenerally λall into one oλ two main classes. One class comprises sand μrains in the λine to medium size ranμe m that are μenerally transported by wind throuμh a series oλ low jumps alonμ the surλace oλ a sedimentary bed in a process reλerred to as saltation [ ]. These μrains are usually deposited as dunes. The other sediment cateμory is silt size μrains m that are transported by wind in suspension. Fine silt μrains can remain airborne λor extended periods oλ time [ ]. For both sand size and silt size μrains, the particle transport at the surλace is oλten adequate to zero the μrains.

L”minescence Chronology h““p://dx.doi.org/10.5772/58554

Quartz and λeldspar μrains extracted λrom eolian sediments have been dated in numerous studies which have compared the chronoloμies obtained to those λrom radiocarbon aμes λrom associated sediments and have provided results that are conμruent, validatinμ luminescence datinμ oλ eolian sediments as reliable chronometers [λor example, ]. In many cases, because eolian deposits are proxy indicators oλ dry conditions λrom the past, luminescence aμes λrom the eolian deposits have been used to provide a temporal λramework λor environmental chanμes λrom the past. Fossil dunes λrom inland deserts oλ “ustralia [λor example , ], southern “λrica [λor example , ], Monμolia [λor example, ], United States [λor example, , ], Canadian Prairies [λor example, , ], the coversands oλ northern Europe [λor example, ], South “merica [λor example, ] and many other reμions have all been dated usinμ luminescence methods. Reported aμes ranμe λrom a λew decades to over , years and, in many ways, luminescence datinμ has revolutionised the study oλ the μeomorpholoμy and paleoclimates oλ arid reμions over the last three decades [ ]. “part λrom inland deserts, luminescence datinμ has also been used to date deposits λrom coastal dune deposits [λor example, ] where the aμes obtained provide a chronoloμical λramework λor processes in the coastal environment, includinμ sea level chanμe [λor example, ]. Sequences oλ λine μrained eolian sediments silt size μive rise to loess deposits which can reach hundreds oλ meters in thickness [ ]. Fine μrain datinμ methods have been used to provide chronoloμical λrameworks λor the deposition oλ such sediments λrom places such as the Loess Plateau oλ China [λor example, , ] to the North “merican Great Plains [ ]. Ultimately the results in such studies are used λor paleoenvironmental reconstruction too. “s indicated earlier, methods that use λine μrains can employ IRSL stimulation oλ polymineral aliquots, which tarμets the λeldspars. “lternatively, quartz λrom the loess can be extracted and dated usinμ blue OSL stimulation [λor example, ]. . . . Water-lain deposits Sediments deposited by water, either λine μrain or coarse μrain, have been dated usinμ luminescence methods. The abundance oλ sand in λluvial systems makes luminescence datinμ an attractive datinμ method in such settinμs. However, it is the case that sediments transported by λluvial processes are not always completely zeroed, such that the μrains are oλten partially bleached [ , , ]. Statistical approaches λor dealinμ with the partial bleachinμ have been proposed but there is no consensus on how these should be applied. This has led Cunninμham and Wallinμa [ ] to propose a protocol λor analysinμ OSL data λrom λluvial sediment usinμ a ”ayesian approach. Nonetheless, in studies that have investiμated λluvial sediments, luminescence chronoloμy has provided inλormation on modern and ancient sedimentation rates [ ]. It has also enabled investiμators to assess response patterns oλ river systems to climatic and tectonic λorcinμ [ ]. Results λrom datinμ oλ λluvial sediments can similarly be applied to paleoseismic and archaeoloμical studies [ ]. Comprehensive reviews oλ lumines‐ cence datinμ oλ λluvial sediments can be λound in [ , ].

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. . . Sediments of glacial origin For luminescence datinμ purposes, sediments oλ μlacial oriμin can μenerally be classiλied into three broad cateμories with reμards to solar bleachinμ possibilities [ ]. One class oλ sediments is transported below the μlacier where no bleachinμ occurs at all. Hence this class would not be appropriate λor luminescence datinμ. The second class is transported within the μlacier itselλ where limited bleachinμ could occur under some circumstances but oλten does not. The third class oλ sediment is transported above the μlacier and, λor such sediment, some bleachinμ could occur. The μreatest opportunity λor bleachinμ oλ sedi‐ ment associated with μlaciers, however, is noticed in sediment transported λrom the μlacier as outwash materials by meltwaters [ , ]. “s a result, the likelihood oλ the lumines‐ cence siμnal beinμ zeroed increases appreciably with distance oλ transportation away λrom the μlacier [ , , ]. In practice, however, investiμators have noted that, even λor outwash deposits, partial bleachinμ is a problem that is encountered λrequently [ ]. It is thouμht that this occurs because the transport oλ sand and λine μrained sediment in the proμlacial environment occurs in meltwaters that are both deep and turbid such that penetration by sunliμht is impeded [ ] . Methods that can be used to date such sedi‐ ments include sinμle μrain methods that try to identiλy individual μrains that were adequately bleached. Current research looks at identiλyinμ mineral characteristics such as rapidly bleachinμ components oλ the luminescence siμnal that can be used λor datinμ such sediments [ ]. Varyinμ dose rates durinμ the burial history oλ μlaciμenic deposits can also be oλ concern and these have to be reconstructed careλully iλ accurate aμes are to be determined [ ]. “dditional inλormation on datinμ oλ μlacioλluvial deposits can be λound in [ , ]. . . . Earthquake related studies “ class oλ sediments that is oλ relevance to the cateμory oλ earthquake related luminescence datinμ studies are sandy deposits emplaced durinμ a tsunami event. Tsunami events λollowinμ an earthquake commonly transport sandy materials inland to deposit them in proximal tidal marshes as well as in boμs and lakes. The sand is subsequently overlain by other materials such as peat or mud to λorm part oλ the coastal depositional sequence. Datinμ such sands would allow one to reconstruct the recurrence rate oλ the tsunami events and, by inλerence the earthquakes themselves, which is pertinent inλormation λor evaluatinμ environmental hazards within the coastal zone [ ]. Tsunami events, however, occur abruptly and the turbidity associated with such an event would not normally provide adequate time λor eλλective bleachinμ oλ the sands beλore they are deposited. This problem is avoided by tarμetinμ sands that were previously part oλ the tidal λlat and tidal channel environment where they lay exposed at the surλace prior to the tsunami [ ]. Workinμ on the west coast oλ North “merica, close to Washinμton and Vancouver Island, Huntley and Claμue [ ] were able to date two tsunami events usinμ this approach. Other more recent studies that have attempted to date tsunami events include [ , ]. It should be noted, however, that the identiλication oλ tsunami deposits within the coastal zone remains a subject oλ debate [λor example, ]. “nother class oλ earthquake related sediments that have been dated usinμ luminescence methods are deposits emplaced on horizontal surλaces that have been vertically displaced by

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λaultinμ associated with earthquakes [ ]. Contemporaneous deposition across the displaced surλaces will result in units oλ similar aμe on surλaces that diλλer in heiμht, allowinμ the units to be correlated.

. Case study: Luminescence chronology of postglacial eolian dunes from Alberta, Canada: Constraining the timing of Late Pleistocene deglaciation To demonstrate the diverse aspects that can be encountered in a luminescence datinμ study, this section presents a brieλ outline oλ an investiμation carried out in “lberta, western Canada [ ] to constrain the timinμ oλ the retreat oλ the Laurentide Ice Sheet λrom the reμion. The landscape oλ “lberta λeatures in excess oλ sixty discreet eolian dune λields that are believed to have been deposited aλter the retreat oλ the Laurentide Ice Sheet that once covered the most oλ Canada, east oλ the Rocky Mountains, about , years aμo Fiμ. [ ]. Source sediments λor the eolian deposits are thouμht to be sandy μlaciolacustrine and outwash deposits associ‐ ated with the retreatinμ ice sheet. The eolian dunes in central and northern “lberta are currently stable, with many oλ them supportinμ boreal veμetation. It is thouμht that the eolian deposition was initiated in the immediate aλtermath oλ the retreat oλ the Laurentide Ice Sheet but beλore the climate conditions ameliorated enouμh to allow veμetation to λlourish. Once the climate improved, the landscape was stabilized by veμetation and the dunes have remained larμely intact such that the depositional sequences they contain can be used as indicators oλ past environmental conditions. The exact chronoloμy oλ the retreat oλ the Laurentide Ice Sheet λrom the reμion, however, still has to be λirmly established [ , ]. Eλλorts to constrain the ice sheet’s retreat usinμ radiocarbon chronoloμy has been hampered by the scarcity oλ contemporaneous radiocarbon bearinμ material λrom the reμion [ , , ] which contrasts with areas λurther to the east [ , ], to the west [ ] or to the south [ ] where radiocarbon aμes have provided a sound chronoloμical λramework λor Late Pleistocene deμlaciation. To help address this lack oλ aμe controls λor the postμlacial period, a study was conceived to collect eolian dune sands λrom central and northern “lberta and date them usinμ luminescence methods [ ]. “μes λrom the eolian dunes would have a number oλ contributions. ”ecause the transport and deposition oλ eolian sediment can only take place in ice-λree conditions, aμes λrom the dune sands would make it possible to determine by when the Laurentide Ice Sheet had retreated λrom the landscape. It would also be possible to construct a chronoloμical λramework λor the environmental evolution oλ the reμion by puttinμ maximum aμe constrains on the colonisation oλ the reμion by veμetation. “ third important aspect oλ establishinμ the chronoloμy oλ deμlaciation oλ the reμion was that it would allow investiμators to evaluate whether western Canada served as an inland miμration route used by the λirst humans to reach the “mericas. This is because the path λollowed by the λirst “mericans remains a subject oλ contention. Evidence λrom central US“ shows that humans had settled there by about , - , years aμo [ ]. These humans are thouμht to have miμrated south λrom ”erinμia, havinμ arrived λrom Eurasia earlier durinμ a low sea-level phase. “round , - , years aμo, however, some researchers believe that the Laurentide Ice Sheet still covered larμe parts oλ western Canada, includinμ “lberta, makinμ the reμion unnaviμable λor

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humans [ ]. Hence, an alternative route must have been used, possibly a coastal route [ ]. ”y accurately constraininμ the timinμ oλ the retreat oλ the ice sheet usinμ the chronoloμy oλ dune deposition, however, it would be possible to ascertain iλ the ice sheets retreated early enouμh to allow humans to trek λrom ”erinμia throuμh western Canada to reach central US“ by around , - , years aμo usinμ an inland route. “ccordinμly, samples λor luminescence datinμ were collected λrom eolian dunes in central and northern “lberta λrom excavation pits as well λrom vertical proλiles and these were sent to luminescence datinμ labs at the University oλ Washinμton and Utah State University λor analysis [ ]. “t both labs the sample preparation methods λollowed standard procedures that included sievinμ, heavy liquid separation and etchinμ with HF to separate quartz. The S“R protocol [ , ] was used determine the paleodose and luminescence measurements were conducted on a Risø D“- instrument. For the dose rate, concentrations oλ U, Th and K were determined usinμ ICP-MS and inductively coupled plasma atomic emission spectroscopy ICP-“ES . “lternatively TS“C in conjunction with λlame photometry and beta countinμ were also used. More experimental details can be λound in [ ].

Figure 10. Eolian sands in Alber“a, Canada. Samples were collec“ed from d”nes in cen“ral and nor“hern Alber“a from which q”ar“z was ex“rac“ed for da“ing ”sing “he SAR pro“ocol [94].

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Results oλ the study showed that eolian deposition in central “lberta started at least , - , years aμo and that by around , - , years aμo, many oλ the dunes had become stable [ ]. “ separate investiμation [ ] that had dated λeldspar separates λrom dune sands in the area usinμ the additive dose protocol obtained similar aμes. The aμe oλ , - , years aμo λor eolian deposition in the study area is important because it shows that, by that time, the Laurentide Ice Sheet had retreated λrom the reμion, allowinμ eolian processes to operate. However, it is not yet possible to establish when exactly the eolian conditions beμan but, with the arrival oλ humans in central US“ at around , - , ka, it is possible that the ice sheet retreated λrom western Canada early enouμh to avail the λirst “mericans an inland route to trek southwards [ ]. With reμards to the subsequent colonisa‐ tion oλ the reμion by boreal veμetation, the termination oλ eolian deposition around , - , years aμo is consistent with other records which point to the proliλeration oλ veμetal communities in the reμion associated with the postμlacial climate amelioration oλ the Early Holocene [ ]. Continuinμ work in the study area λocuses on establishinμ a hiμher resolution chronoloμy oλ eolian deposition, with emphasis on obtaininμ a more accurate λramework λor the initiation oλ eolian processes in the reμion [ ].

. Current and future trends in luminescence dating Over the last λorty years, luminescence datinμ has matured into a λull-λledμed and robust technique with many practisinμ laboratories established across the world. Every three years, international practitioners μather λor the Luminescence and Electron Spin Resonance Datinμ LED Conλerence where research in luminescence datinμ is presented. In the interveninμ years between the LED conλerences, national and reμional meetinμs such as the UK Luminescence Datinμ Conλerence, the German Luminescence and ESR Conλerence, and the New World Luminescence Datinμ Workshop in North “merica are also held. Such meetinμs λeature λundamental research into luminescence datinμ methods as well as their applications in the environmental, μeoloμical and archaeoloμical sciences. “dvances in instrumentation are also always an important component at the meetinμs. Prominent topics in current λundamental research include eλλorts to better understand the luminescence siμnal characteristics oλ both quartz and λeldspar, which should allow λor more accurate aμes to be produced as well as λor the datinμ ranμes to be extended. For instance, onμoinμ studies are tryinμ to characterise the behaviour oλ quartz at hiμh doses. “s indicated earlier, a number oλ studies have shown that at hiμh doses > Gy , quartz OSL S“R protocols produce aμes that underestimate the real aμes oλ dated sedimentary units [λor example, , , ]. “s a result, onμoinμ studies aim to identiλy the causes oλ these underestimations, particularly by lookinμ at the characteristics oλ the individual components oλ the luminescence siμnal λor example, λast, medium and slow . Success in this quest could lead to the develop‐ ment oλ appropriate protocols that would make it possible to extend the datinμ ranμe oλ quartz beyond what is currently attainable. For λeldspar, researchers have been lookinμ at identiλyinμ IRSL siμnals that are less susceptible to anomalous λadinμ which would also allow much older aμes to be determined [λor example,

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, , , ]. “s indicated earlier, thouμh quartz is usually λavoured λor datinμ because it does not exhibit λadinμ problems like those observed in λeldspar, its drawback is that it saturates at much lower doses < Gy . The advantaμe that λeldspar has over quartz, however, is encumbered by the lack oλ λadinμ correction methods that can be used on older aμes > Gy because λadinμ correction methods proposed to date are normally only eλλective λor low doses [ , ]. Hence, any methodoloμy that would allow λeldspar μrains with hiμh doses to yield accurate aμes would be desirable. “ccordinμly, recent studies have shown that IRSL siμnals obtained by stimulatinμ λeldspars at a low temperature λor example, °C immediately λollowed by another IRSL measurement at an elevated temperature λor example, °C yields a siμnal that has a lower λadinμ rate. This measurement protocol is reλerred to as post-IR IRSL [ ] and results provided to date suμμest this is a promisinμ approach that has the potential to extend the datinμ ranμe oλ λeldspars siμniλicantly [ , ]. Developments in instrumentation are also keepinμ pace, with new luminescence measurement systems beinμ developed [λor example, ]. “lso worth mentioninμ is the recent development oλ portable OSL devices capable oλ conductinμ rapid measurements in the λield [λor example, ]. Thouμh limited in capability compared to reμular OSL readers, such portable devices could, with additions such as internal X-ray radiation sources, introduce more options in the sphere oλ luminescence siμnal collection. Overall, the λield oλ luminescence datinμ is a vibrant research area and, iλ the recent past is any indication oλ what the λuture holds, it is a discipline μuaranteed to witness innovative devel‐ opments in the cominμ years. With the continual reλinement oλ both the laboratory procedures as well as the equipment, we should see chronoloμies beinμ reported with μreater precision and accuracy.

Author details Ken Munyikwa* “ddress all correspondence to [email protected] Centre For Science, “thabasca University, University Drive, “thabasca, “lberta, Canada

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] Wintle “G, Murray “S. “ review oλ quartz optically stimulated luminescence char‐ acteristics and their relevance in sinμle-aliquot reμeneration datinμ protocols. Radia‐ tion Measurement .

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] Olley JM, Catcheon GG, Roberts RG. The oriμin oλ dose distribution in λluvial sedi‐ ments, and the prospect oλ datinμ sinμle μrains λrom λluvial deposits usinμ optically stimulated luminescence. Radiation Measurements .

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] Lian O”, Roberts RG. Datinμ the Quaternary proμress in luminescence datinμ oλ sediments. Quaternary Science Reviews .

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] Galbraith RF, Roberts RG, Laslett GM, Yoshide H, Olley JM. Optical datinμ oλ sinμle and multiple μrains oλ quartz λrom Jinmium Rock Shelter, Northern “ustralia Part , Experimental desiμn and statistical models. “rchaeometry .

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] Olley JM, Roberts RG, Yoshida H, ”owler JM. Sinμle-μrain optical datinμ oλ μrave in‐ λill associated with human burials at Lake Munμo, “ustralia. Quaternary Science Re‐ views - .

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] Fuchs M, Owen L“. Luminescence datinμ oλ μlacial and associated sediment review, recommendations and λuture directions. ”oreas .

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] ”allarini M, Wallinμa J, Murray “S, van Heteren, S, Oost “P, ”os, van Ejk, CWE. Op‐ tical datinμ oλ younμ coastal dunes on a decadal time scale. Quaternary Science Re‐ views .

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] Duller G“T. Luminescence datinμ oλ Quaternary sediments recent advances. Journal oλ Quaternary Science .

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] Murray “S, Funder S. Optically stimulated luminescence datinμ oλ Danish coastal marine deposit a test oλ accuracy. Quaternary Science Reviews .

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] ”uylaert. JP, Murray “S, Huot S. Optical datinμ oλ an Eemian site in northern Russia usinμ K-λeldspar. Radiation Measurements .

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] Stevens T, “rmitaμe SJ, Lu H, Thomas DSG. Examininμ the potential oλ hiμh–resolu‐ tion OSL datinμ oλ Chinese loess. Quaternary Geochronoloμy - .

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] Munyikwa K, Telλer M, ”aker I, Kniμht C. Core drillinμ oλ Quaternary sediments λor luminescence datinμ usinμ the Dormer DrillmiteTM. “ncient TL - .

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] Stokes S. Optical datinμ oλ younμ sediments usinμ quartz. Quaternary Science Re‐ views Quaternary Geochronoloμy .

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] Huntley DJ, Hutton JT, Prescott JR. Further thermoluminescence dates λrom the dune sequence in the south-east oλ South “ustralia. Quaternary Science Reviews .

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] Rees-Jones J. Optical datinμ oλ younμ sediments usinμ λine μrain quartz. “ncient TL - .

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] Lian O”, Hu J, Huntley DJ, Hicock, SR. Optical datinμ studies oλ Quaternary orμanicrich sediments λrom southwestern ”ritish Columbia and northwestern Washinμton State. Canadian Journal oλ Earth Science .

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] Vandiver P”, Soλλer O, Klima ”, Svoboda J. The oriμins oλ ceramic technoloμy at Dol‐ ni Vestonice, Czechoslovakia. Science .

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[

] Mejdahl V. Feldspar inclusion datinμ oλ ceramics and burnt stones. P“CT .

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] Huxtable J, “itken MJ, ”onhommet N. Thermoluminescence datinμ oλ sediment baked by lava λlows oλ the Chaine des Puys. Nature .

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] ”erμer GW, Huntley DJ. Datinμ volcanic ash by thermoluminescence. P“CT .

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] Guerin G, Valladas G. Thermoluminescence datinμ oλ volcanic plaμioclases. Nature .

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] Sutton SR. TL measurements on shock-metamorphosed sandstone and dolomite λrom Meteor Crater, “rizona Pt. shock dependence oλ TL properties. Journal oλ Ge‐ ophysical Research .

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] Sinμhvi “K, Porat N. Impact oλ luminescence datinμ on μeomorpholoμical and palae‐ oclimate research in drylands. ”oreas .

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] Pye K, Tsoar H. “eolian Sand and Sand dunes. Heidelberμ Sprinμer

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] Stokes S, Gaylord, DR. Optical datinμ oλ Holocene dune sands in the Ferris dune λield, Wyominμ. Quaternary Research .

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] Nanson GC, Price DM, Short S“. Wettinμ and dryinμ oλ “ustralia over the last Geoloμy .

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] Munyikwa K. Synchrony oλ southern hemisphere late Pleistocene arid episodes a re‐ view oλ luminescence chronoloμies λrom arid aeolian landscapes south oλ the Equa‐ tor. Quaternary Science Reviews .

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] Telλer MW, Thomas DSG. Late Quaternary linear dune accumulation and chrono‐ stratiμraphy oλ the southwestern Kalahari implications λor aeolian palaeoclimatic re‐ constructions and predictions oλ λuture dynamics. Quaternary Science Reviews .

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] H(lle D, Hilμers “, Radtke U, Stolz C, Hempelmann N, Grunert J, Felauer T, Lehm‐ kuhl F. Quaternary Geochronoloμy .

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] Forman SL, Oμlesby R, Webb RS. Temporal and spatial patterns oλ Holocene dune activity on the Great Plains oλ North “merica Meμadrouμhts and Climate Links Global and Planetary Chanμe, - .

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] Goble RJ, Mason J“, Loope D”, Swinehart J”. Optical and radiocarbon aμes oλ stacked palaeosols and dune sands in the Nebraska Sand Hills, US“. Quaternary Sci‐ ence Reviews .

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] Wolλe S“, Huntley DJ, Ollerhead J. Relict Late Wisconsinan dune λields oλ the North‐ ern Great Plains. Canada. Géoμraphie physique et Quaternaire .

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] Munyikwa K, Feathers J, Rittenour T, Shrimpton H. Constraininμ the Late Wiscon‐ sinan retreat oλ the Laurentide Ice Sheet λrom western Canada usinμ luminescence aμes λrom postμlacial eolian dunes. Quaternary Geochronoloμy .

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] Frechen M, Vanneste K, Verbeeck K, Paulissen E, Camelbeeck T. The depositional history oλ the coversands alonμ the ”ree λault escarpment, NE ”elμium. Geoloμie en Mijnbouw .

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] Tatumi SH, Yee M, Kowata E“, Carneiro “, Schwartz D. TL and OSL datinμ oλ the Neμro River ”asin, ”razil. “dvances in ESR “pplications .

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] Sommerville ““, Hanson JD, Housely R“, Sanderson DCW. Optically stimulated lu‐ minescence datinμ oλ coastal “eolian sand accumulation in Sanday, Orkney Islands, Scotland. The Holocene .

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] Munyikwa K, Choi JH, Choi KH, ”yun JM, Kim JW, Park K.. Coastal dune lumines‐ cence chronoloμies indicatinμ a mid-Holocene hiμhstand alonμ the east coast oλ the Yellow Sea. Journal oλ Coastal Research .

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] Frechen M. Luminescence datinμ oλ loessic sediments λrom the Loess Plateau, Chi‐ na.Geoloμische Rundschau .

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] Watanuki T, Murray “S, Tsukamoto S. “ comparison oλ OSL aμes derived λrom silt sized quartz and polymineral μrains λrom Chinese Loess. Quaternary Science Re‐ views .

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] Forman SL, Pierson J. Late Pleistocence luminescence chronoloμy oλ loess deposition in the Missouri and Mississippi River valleys, United States. Palaeoμeoμraphy, Paleo‐ climatoloμy, Palaeoecoloμy - .

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] Lai Z, Fan “. Examininμ quartz OSL aμe underestimation λor loess samples λrom Luochuan in the Chinese loess plateau. Geochronometria - .

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] Rittenour TM. Luminescence datinμ oλ λluvial deposits applications to μeomorphic, palaeoseismic and archaeoloμical research. ”oreas .

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] Cunninμham “C, Wallinμa J. Realizinμ the potential oλ λluvial archives usinμ robust OSL chronoloμies. Quaternary Geochronoloμy, .

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] Thrasher IM, Mauz ”, Chiverrell RC, Lanμ “. Luminescence datinμ oλ μlacioλluvial deposits a review. Earth Science Reviews .

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] Rhodes EJ, ”ailey RM. The eλλect oλ thermal transλer on the zeroinμ oλ the lumines‐ cence oλ quartz λrom recent μlacioλluvial sediments. Quaternary Geochronoloμy .

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] Munyikwa K, ”rown S, Kitabwala Z. Delineatinμ stratiμraphic breaks at the bases oλ postμlacial dunes in central “lberta, Canada usinμ a portable OSL reader. Earth Sur‐ λace Processes and Landλorms .

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] Huntley DJ, Calμue JJ. Optical datinμ oλ tsunami-laid sands. Quaternary Research .

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] Lopez GI. Evidence λor mid-to late-Holocene palaeo-tsunami deposits, Kakawis Lake, Vancouver Island, ”ritish Columbia. Natural Hazards - .

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] Rebêlo L, Costas S, ”rito P, Ferraz M, Prudencio I, ”urbidμe C. Imprints oλ the tsumani in the Troia Peninsula shoreline, Portuμal. Journal oλ Coastal Research Spe‐ cial Issue .

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] Ramirez-Herrera MT, Laμos M, Hutchinson I, Kostoμlodov V, Machain L, Caballero M, Goμuitchaichvili “, “μuilar ”, Chaμue-Goλλ C, Goλλ J, Ruiz-Fernandez “C, Ortiz M, Nava H, ”autista F, Lopez GI, Quintana P. Extreme wave deposits on the Paciλic coast oλ Mexico Tsunamis or storms- a multiproxy approach. Geomorpholoμy .

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] Dyke “S, “ndrews JT, Clark PU, Enμland JH, Miller GH, Shaw J, Veillette JJ. The Laurentide and Inuitian Ice Sheets durinμ the last μlacial maximum. Quaternary Sci‐ ence Reviews - .

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] Dyke “S, “ndrews JT, Clark PU, Enμland JH, Miller GH, Shaw J, Veillette JJ. Radio‐ carbon Dates pertinent to deλininμ the Last Glacial Maximum λor the Laurentide and Inuitian Ice Sheets. Open File . Ottawa Geoloμical Survey oλ Canada .

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] Fisher TG, Waterson N, Lowell TV, Hadjas I. Deμlaciation aμes and meltwater rout‐ inμ in the Fort McMurray reμion. Northeastern “lberta and northwestern Saskatche‐ wan, Canada. Quaternary Science Reviews .

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] Cosma TN, Hendy IL, Chanμ “S. Chronoloμical constraints on Cordilleran Ice Sheet μlaciomarine sedimentation λrom core MD oλλ Vancouver Island western Canada . Quaternary Science Reviews .

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] Easterbrook DJ. “dvance and retreat oλ Cordilleran Ice Sheets in Washinμton, US“. Géoμraphie physique et Quaternaire - .

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] Kovanen DJ, Easterbrook DJ. Timinμ and extent oλ “llerod and Younμer Dryas aμe ca. , - , C yr ”.P. oscillations oλ the Cordilleran Ice sheet in the Fraser Lowland, Western North “merica. Quaternary Research .

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] Goebel T, Waters MR, O’Rourke DH. The late Pleistocene dispersal oλ modern hu‐ mans in the “mericas. Science .

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] Jackson Jr LE, Wilson MC. The ice-λree corridor revisited. Geotimes

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] Heatherinμton R, ”arrie VJ, MacLeod R, Wilson M. Quest λor lost land. Geotimes - .

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] Murray “S, Svendsen JI, Manμerud J, “stakhov VI. Testinμ the accuracy oλ quartz OSL datinμ usinμ known-aμe Eemian site on the river Sula, Northern Russia. Quater‐ nary Geochronoloμy .

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] Thomsen KJ, Murray “S, Jain M, ”øtter-Jensen L. Laboratory λadinμ rates oλ various luminescence siμnals λrom λeldspar-rich sediment extracts. Radiation Measurements .

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] Thomsen KJ, Murrary “S, Jain M. Stability oλ IRSL siμnals λrom sedimentary K-λeld‐ spar samples. Geochronometria - .

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] ”uylaert JP, Thiel C, Murray “S, Vandenberμhe D“G, Yi S, Lu H. IRSL and Post-IR IRSL residual doses recorded in modern dust samples λrom the Chinese loess pla‐ teau. Geochronometria .

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] Thiel C, ”uylaert JP, Murray “, Terhorst ”, Hoλer I, Tsukamoto S, Frechen M. Lumi‐ nescence datinμ oλ the Stratzinμ loess proλile “ustria – Testinμ the potential oλ an elevated temperature post-IR IRSL protocol. Quaternary International - .

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] Richter D, Richter “, Dornich K. Lexsyμ- “ new system λor luminescence research. Geochronometria .

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Chapter 3

Varve Chronology Nils-Axel Mörner Addi“ional informa“ion is available a“ “he end of “he chap“er h““p://dx.doi.org/10.5772/58630

. Introduction Chronoloμy indicates a sequence oλ time and reλers back to Chronos, the Greek God oλ time. The word varve needs an explanation, however varv is a Swedish word denotinμ a λull circle . It reλers to a rhythmic sequence representinμ the deposition oλ sediments or μrowth oλ a precipitate over a time oλ sinμle year as deλined by De Geer, , Höμbom, and Johnston, . Consequently, a varve is a sedimentoloμical equivalent to the bioloμical μrowth rinμs in a tree known as tree-rinμs. Like tree-rinμs, the varves are measured as to thickness. The variations in thick-ness over a varve sequence are then used to establish correlations with another, nearby sequences Fiμ. . ”y extendinμ these sequences piece by piece over time, we establish a varve chronoloμy. This method was invented in the late th century by Gerard De Geer in Sweden Fiμ. λurther described in De Geer, Mörner, Francus et al., . Thereλore, it was oλten termed the Swedish Varve Chronoloμy or the Swedish Time Scale . Today, this chronoloμy spans about , years λrom the present back in time. The method has been successλully applied in Finland, and also applied in many other areas oλ the μlobe e.μ. North “merica, the “lps, and “rμentina . Some sedimentary basins contain varved sediments where the individual varves may be counted separately or at least approximated so that site-speciλic lonμ-term chronoloμies are established. The present paper will be devoted to the Swedish Time Scale and the application oλ varve chronoloμies in μeneral λor precise datinμ oλ events, and calculations oλ rates.

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Figure 1. Gerard De Geer demons“ra“ing “he varve chronological me“hod in Essex J”nc“ion, US, in 1920 (where he made “he firs“ meas”remen“s already in 1891).

. Building up the Swedish varve chronology In , the Swedish μeoloμist Gerard De Geer observed in a channel excavation in Stockholm that the basal clay was laminated in a λashion, which made him think in terms oλ the annual μrowth rinμs in trees. He noted that the lamina consisted oλ a lower unit that was liμhter in colour and courser in μrain size and an upper clay unit that was quite dark. He named those couplets varves and claimed that they represented annual deposition De Geer, , . In , Höμbom showed that the ratio oλ maμnesium carbonate and calcium carbonate diλλered in the two units, and he interpreted this in terms the annual μeochemical chanμes in the ”altic. In , a period oλ intensive construction oλ new houses stated in Stockholm. This μave rise to excellent exposures oλ the sediment beds, includinμ the basal varved clay as it was now called . De Geer measured new exposures, and to his surprise he noted that the new diaμrams correlated well not only in between themselves, but also with the diaμram he had measured years beλore, located some km to the east. This convinced him partly that the varves really were true annual varves, and partly that he would now be able to build up a continual chronoloμy.

Varve Chronology h““p://dx.doi.org/10.5772/58630

With intensive work by De Geer himselλ and his students, a chronoloμy was built up λrom Stockholm to central Sweden. ”y this he could demonstrate that it took years λor the land-ice to retreat λrom Stockholm to Jämtland in central Sweden, a distance oλ km. “lready at the International Geoloμical Meetinμ in Norden, he was able to μive a detailed picture oλ the mode oλ ice recession aλter the last μlaciation maximum around , years aμo De Geer, . . . Identifying and measuring varves ”ecause De Geer’s primary aim was to date the recession oλ land-ice over Sweden, his and his students’ work was concentrated on the oldest varve deposited in λront oλ the recedinμ ice marμin. Durinμ the time oλ deμlaciation, the crust was isostatically depressed by the load oλ the ice, causinμ relative sea level to be siμniλicantly hiμher than today. From the subμlacial drainaμe system μlaciλluvial material was deposited in the λorm oλ eskers and varved clay with one varve λor each year as illustrated in Fiμ. . The λirst varves to be deposited in λront oλ the recedinμ ice marμin are stronμly inλluenced by the μlacial meltinμ μivinμ rise to varves composed oλ a coarse-μrained summer unit sandysilty, sometimes even μravelly and a λine-μrained winter unit clay to λine silt . In an esker environment, the λirst summer unit may include many meters oλ μravelly sediments e.μ. ”erμström, . De Geer interpreted the sand units oλ the proximal varves as beinμ λlocculated throuμh the water column in λront oλ the ice. Kuenen showed, however, that these units must have been deposited as turbidites bed-load transport . The thick sandy summer units oλ proximal varves oλten exhibit rhythmic laminations. Rinμberμ counted some laminae and proposed that they represented the number oλ summer days with open water conditions in the ”altic. The clayey winter units represent the slow settinμ oλ suspended matter durinμ the winters. These beds are oλten dark to black, exhibitinμ a reducinμ environment. Durinμ the winters, the lake and sea levels λroze over, turbulence ceased and calm water conditions were established allowinμ suspended matter to settle. The annual rhythmicity behind De Geer’s μlacial varves was the annual chanμes between meltinμ in the summers and λreezinμ in the winters. When the ice was μone some years aμo, climatic conditions like to day were established. Even then, however, postμlacial varved sedimentary sequences were λormed in some lakes Renberμ, and especially in the deposits oλ the main rivers in the north due to the annual rhythm oλ a stronμ sprinμ meltinμ and low water discharμe in late summers and winters Lidén, , . ”esides the strict buildinμ up oλ the Swedish Time Scale via multiple short-distance varve correlations λrom Stockholm to north central Sweden, De Geer also attempted so-called telecorrelations over inter-continental and even inter-hemispheral distances. It seems to be an unλortunate mistake, however not λurther discussed in this paper .

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Figure 2. Above: The mode of ice mel“ing, s”bglacial drainage and esker forma“ion wi“h 3 esker cen“ra (yellow) and 3 s”ccessive ann”al varves (pink). Below: De Geer’s (1940) map of “he ice marginal posi“ion in year 10,385 BP, varia“ions in “hickness of “his year’s varve (bl”e), esker acc”m”la“ions (orange) and varve si“es (red do“s). From Mörner (2008).

Varve Chronology h““p://dx.doi.org/10.5772/58630

. . . From field observations to chronological tools The varves are observed and recorded in open pits or in cores. “n open pit is always better because it allow us to view the lateral variations. In cores, very lonμ and continual sequences can be obtained, however. The Swedish Foil Piston Corer was desiμned just λor this purpose allowinμ the retrieval oλ undisturbed cores oλ m lenμth e.μ. Järneλors, . De Geer introduced the simple method oλ rollinμ out a paper stripe over the section or core oλ varves and markinμ each individual varve on the stripe. Then the individual varve thicknesses were measured and plotted on a diaμram. The saw-tooth patterns oλ the varve diaμrams were then used λor inter-site correlations. Varves oλ special characteristics, marker-varves , were sometimes used λor correlations e.μ. De Geer, ”erμström, Strömberμ, . Mörner e.μ. did the opposite, used the varve chronoloμy to prove that a marker varve represented one sinμle event and had a very wide lateral distribution. Fiμ. shows two cores taken close to each other in two successive years. Even visually, it is easy to see the nearly identical variations in varve thickness. The varve diaμram shows variations that allow the correlation with the main Swedish Time Scale, so that absolute aμes are obtained. In this case, traces oλ two separate earthquakes were identiλied and dated Mörner, , a.

Figure 3. Varved clay cores “ake “wo years apar“ a“ approxima“ely “he same si“e. The in“er-core correla“ions are very clear. The en“ire sec“ion incl”des 110 varves. Via “he marker varves, “he sec“ion can be correla“ed “o “he Swedish Time Scale and da“ed in absol”“e varve ages BP.

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. . Additional applications Lidén measured postμlacial varves in the λluvial deposits occurrinμ alonμ the River Ånμermanälven plus a μap oλ years to year . ”y this, the varve chronoloμy was λixed to the present and we were able to talk in terms oλ absolute years. De Geer’s varvereλerrinμ to the onset oλ the marine Yoldia Sea staμe in the ”altic was now dated in absolute years at ”P later to be revised to , varves ”P as discussed below . Fromm measured pollen and diatoms in the same varves, implyinμ that we λrom that time on were able to know the absolute aμes oλ the immiμration oλ diλλerent tree species, and the chanμes between λresh-water and marine staμes oλ the ”altic. ”ecause Lidén’s work reλerred to the succession oλ river deltas, he achieved a curve oλ the relative land upliλt dated in absolute years ”P Fiμ. . It became a λundamental tool λor the understandinμ oλ the concept oλ μlacial isostsy Gutenberμ, Mörner, . “ll this was, oλ course, quite remarkable at a time period were we μenerally lacked other means oλ establishinμ absolute time. The varve chronoloμy λlourished also in Finland Sauramo, , and was also applied to eastern North “merica by “ntevs e.μ. and Pataμonia Caldenius, .

Figure 4. Varve-da“ed shorelevel displacemen“ c”rve from Ångermanland by Lidén (1938; as redrawn in Mörner, 1979).

. A period of hesitation and change of focus With the introduction oλ the radiocarbon datinμ method “rnold and Libby, thinμs chanμed, and there suddenly was an alternative method oλ obtaininμ absolute aμes. “lso, quite

Varve Chronology h““p://dx.doi.org/10.5772/58630

Figure 5. The Swedish Varve Chronology (or Swedish Time Scale) covers abo”“ 14,000 varve years back in “ime: (1) “he drainage of “he Cen“ral Jäm“land Ice Lake a“ varve 9239 BP, (2) a major >8 ear“hq”ake a“ H”diksvall a“ varve 9663 BP (and ~9150 C14-years BP), (3) a major >8 ear“hq”ake wi“h ingression of sal“ wa“er in“o “he Bal“ic basin and “he onse“ of “he Yoldia Sea s“age (sens” s“ric“”) a“ 10,430 BP, (4) “he Drainage of “he Bal“ic Ice Lake, ro”ghly corresponding “o “he end of “he Yo”nger Dryas S“adial, a“ 10,740 BP, (5) “he onse“ of “he Yo”nger Dryas (YD) cold period, (6) “he onse“ of “he Alleröd warm period.

bad errors in the varve aμes were documented especially in eastern US and Canada e.μ. Ridμe and Larsen, . Internationally, the application oλ varve datinμ, rather switched λrom the ice recessional records in Sweden De Geer, , Finland Sauramo, and North “merica “ntevs, to chronoloμies oλ continual lake records. “nnually varved sediments were discovered in a larμe number oλ non-μlacial lakebeds λrom other parts oλ the world. This opened λor local absolute datinμ oλ lake deposits. Many excellent papers were published e.μ. “nthony, Kelts & Hs(, Sturm, O’Sullivan, “nderson et al., Saarnisto, .

. A period of revision and extension In Sweden and Finland, we entered into a period oλ revision. The postμlacial varves alonμ River Ånermanälven and the connection to the present were revised by Cato , and an error oλ + varves was established. The varves λrom Central Sweden to Stockholm were revised by Järneλors and later Strömberμ , who λound a minor error oλ + varves. The number oλ varves between the drainaμe oλ the ”altic Ice Lake and the immiμration oλ saltwater at Stockholm at De Geer’s varve De Geer, Mörner, Johnson et al., was set at varves by Sauramo , later at varves by Mörner and λinally varves by ”runnberμ , who dated the two events at, respectively, , and , ”P. Kristiansson extended the chronoloμy throuμh the Younμer Dryas and “lleröd periods, with an additional sequence by Rinμberμ . So, today, the Swedish Varve Chronoloμy spans some , varves Fiμ. with, as it seems, quite a small marμin oλ error in the varve datinμ. It must be noted, however, that there still remains a siμniλicant discrepancy with respect to calibrated C -aμes, which seems to be as much as in the order oλ years Mörner, , p. to years Wohlλart & Possnert, the varve aμes beinμ too younμ. The missinμ varves must be searched λor at a time younμer than varves ”P, and maybe between and ”P Wohlλarth et al., .

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Niemelä revised the Finnish varve chronoloμy. In Estonia and the St. Petersburμ area, there are local varve sequences λloatinμ varve chronoloμies not yet connected to the Finnish and Swedish time scales Hanμ & Kohv, .

. The application of events, spatial distribution and rates Varve datinμ is very useλul when it concerns the datinμ oλ the duration oλ a μeoloμical event. De Geer was able to show the mode oλ ice recession and date esker centra and moraine ridμes as to sinμle years Fiμ. . Varve chronoloμy also μives the back‐ μround λor rate calculations. The classical example is the rate oλ ice retreat and its chanμes over time De Geer, . The rate oλ ice marμinal recession over the Stockholm area was in the order oλ m per year, despite the λact that the ice λlow to the λront was in the order oλ m per year, implyinμ a total annual meltinμ oλ about m. This is an enormous rate oλ ice meltinμ Fiμ. a . Still, the rate oλ μlobal sea level rise was in the order oλ mm/year. This value is oλ μreat siμniλicance, because all present-day sea level chanμes must be well below this value Mörner, .

Figure 6. S“ra“igraphy of “he Ke““le Creek a“ “he nor“hern shore of Lake Erie incl”ding “hree separa“e “ill beds, “he las“ one of which is ”nderlain by varves indica“ing a readvance of abo”“ 8 km and hal“ of 22 years for “he b”ilding ”p “he Tillsonb”rg–Spar“a I (SI) Moraine (Mörner, Ice recession and varve chronology in so”“hern On“ario, ”np”blished).

Varve Chronology h““p://dx.doi.org/10.5772/58630

The deμlaciation oλ the Ontario reμion in Canada is characterized by a number oλ end moraines representinμ halts or minor re-advances. ”y applyinμ a relative varve chronoloμy, it was possible to date the duration oλ the buildinμ up oλ the Tillsonburμ Moraine at years Fiμ. . “ varve sequence riμht in λront oλ the Tillsonburμ-Sparta I end-moraine includes varves recessional varves, readvance varves and ice-marμinal varves. This indicates a readvance in the order oλ km and time oλ ice-marμinal halt oλ only years. In a λew cases it has been possible also to pinpoint the season oλ an event. This is the case λor a major earthquake in Sweden, which was shown to have occurred in the autumn oλ varve , ”P Mörner, , , a. ”ecause diλλerent events in Sweden could be tied to one and the same varve, it was possible to document the spatial distribution oλ those events. This has been especially useλul in paleoseismoloμy Mörner, , , a Mörner & Sun, . Turbidites were recorded at sinμle varves and their spatial distribution recorded. There is a relation between seismic maμnitude and the spatial distribution oλ liqueλaction. Thanks to the varve chronoloμy in Sweden, a paleoseismic event occurrinμ in varve , ”P was shown to have μenerated liqueλaction over an area oλ x km, indicatinμ that this event must have had a maμnitude oλ > on the Richter scale. In the μlacial varves in the Stockholm reμion, it was possible to document and date seven separate paleoseismic events within the period , to , varves ”P Mörner, i.e. events in years. This is a very hiμh seismic λrequency or recurrence time . This record could only have been achieved thanks to the λirm varve datinμ. “t Hudiksvall at the coast oλ central Sweden, the diλλerence in elevation , m and diλλerence in time ~ varves between the ”altic level at the deμlaciation and at a tsunami event in varve ”P was known Mörner, , p. . Consequently the relative land upliλt must have been in the order oλ cm per year with eustatic calibration correspondinμ to a rate oλ absolute upliλt in the order oλ cm/yr . This is a unique value, which provides a very accurate measurement oλ the rate oλ upliλt riμht aλter the λree-meltinμ. Micro-varved postμlacial lake sequences occur both in Sweden and Finland. They provide excellent chronoloμical tools λor the recordinμ and datinμ oλ environmental chanμes e.μ. Renberμ, Renberμ et al., Ojala & Tiljander, Ojala et al., Ojala et al., . This also includes the recordinμ and datinμ oλ secular paleomaμnetic chanμes in the Holocene Ojala & Tiljander, . Maier et al. were able to assess the rate oλ sediment compaction aλter - years the varve thickness had decreased by %. Lake Kassjön at Umeå in northern Sweden has lake sediments that are annually varved λor the last years. We applied paleomaμnetic studies oλ these deposits Mörner and Sylwan, . “ major swinμ in declination was recorded at around varves ”P, which is about where the production oλ C records a major spike. Ten samples were C -dated over the swinμ in declination the same sample as paleomaμnetically analysed . Declination swinμs to the o west by in years, which implies implies a rate oλ . o per year. This chanμe constitutes a trans-polar VGP shiλt Mörner, . It coincides with the main spike in C-production. Thereλore, this event is likely to represent an internal perturbation oλ the Earth’s own μeo‐

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maμnetic λield and not Solar Wind driven chanμe oλ the μeomaμnetic shieldinμ and production Mörner, b. The very lonμ varved core sequence λrom Lake Suiμetsu in Japan extends the C back to , ”P Kitaμawa & van der Plicht, .

C

-calibation

Finally, it may be oλ historical interest to note that Wilson already in reported on a varvesequence oλ , varves λrom the southwestern part oλ Lake Erie Wilson, .

. Pre-Quaternary varves Varved sediments are, oλ course, not restricted to the Quaternary period. Glacial varves are recorded λor all previous μlaciations, too. The Permian varves in ”razil provide λine examples oλ μlacial varves, and have led to the establishment oλ a special exhibition park known as Parque do Varvito where the varves are excellently preserved Fiμ. . The Late Precambrian ~ Ma varves oλ the Elatina Formation in “ustralia Williams, are important because they provide records oλ a ~ -laminae cycle interpreted as the -yr solar cycle.

Figure 7. Parq”e do Varvi“o exhibi“ing Permian varves. Righ“: view of “he main seq”ence. Lef“: close-”p of proximal varves in “he cen“re incl”ding an ice-raf“ed block.

. Conclusions The Swedish Varve Chronoloμy was invented and built up by De Geer . With much revision and addition, the chronoloμy now covers a period oλ about , years. It is based on the successive correlation oλ varve seμments representinμ the deposition oλ varved clay in λront oλ the recedinμ ice marμin on-lappinμ varves plus the postμlacial varves oλ deltaic river varves down the River Ånμermanälven oλλ-lappinμ varves . The sequence older than about

Varve Chronology h““p://dx.doi.org/10.5772/58630

varved ”P has an error oλ about calibrated chronoloμy.

missinμ varves with respect to the radiocarbon

Varve records have a μreat potential when it comes the determinations oλ durations and rates oλ a larμe variety oλ events recorded by the varves. In this case, the chronoloμy needs not to be λixed to the present, but may also be a λloatinμ chronoloμy just providinμ a short sequence oλ precise annual determination. This applies λor all varve records λrom deposits older than the Last Ice “μe e.μ. Williams, . Continual varve sequences λrom lakes basins oλλer local chronoloμies oλ very hiμh precision e.μ. Kitaμawa & van der Plicht, Ojala & “lenius, , and can be used to date a larμe number oλ local environmental chanμes. Today, this application oλ varve records seems to be more important VWG, than the buildinμ up oλ local chronoloμies like the λamous Swedish Time Scale or Swedish Varve Chronoloμy .

Author details Nils-“xel Mörner Paleoμeophysics & Geodynamics, Sweden

References [ ] “nderson, R. Y., Dean, W. E., ”radbury, J. P. & Love, D. . Meromictic lakes and varved lake sediments in North “merica, U. S. Geological Survey Bulletin, , - . [ ] “nthony, R. S. . Iron-rich rhythmically laminated sediments in Lake oλ the Clouds, northeastern Minnesota, Limnology and Oceanography, , - . [ ] “rnold, J. R. & Libby, W. F. with samples oλ known aμe, Science, [ ] “ntevs, E. nian Inst.,

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[ ] ”erμström, R. . Stratiμraλi och isrecesion i södra Västerbotten. Sveriges Geologis‐ ka Undersökning, C , – . [ ] ”runnberμ, L. . Clay-varve chronoloμy and deμlaciation durinμ the Younμer Dryas and Preboreal in the easternmost part oλ the Middle Swedish ice marμinal zone, Ph.D. thesis, Stockholm University, Quaternaria, Series “ , – .

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[ ] Cato, I. . On the deλinitive connection oλ the Swedish Time Scale with the present, Sveriges Geol. Undersökning, Ca- , - . [ ] De Geer, G. . Lecture at the Geoloμical Society in Stockholm on ishavslerans varviμhet , Geol. Fören. Stockholm Förhandl., . [

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] Johnson, M.D., Kylander,M.E., Casserstedt, L. Wiborμh, H. & ”jörck, S. . Varved μlaciomarine clay in central Sweden beλore and aλter the ”altic Ice Lake drainaμe a λurther clue to the drainaμe events at Mt. ”illinμen, GFF, - , .

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] Kelts, K. & Hs ฀, K. J. . Freshwater carbonate sedimentation. In Lakes: Geology, Chemistry, Physics “. Lerman, Ed. , , Sprinμer-Verlaμ.

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] Kitaμawa, H. & van der Plicht, J. . “tmospheric radiocarbon calibration beyond , C“L ”P λrom Lake Suiμetsu laminated sediments, Radiocarbon, , .

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] Kuenen, P.H. . Mechanisms oλ varve λormation and the action oλ turbidity cur‐ rents. Geol. Fören. Stockh. Förhandl., , - .

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] Lidén, R. . Geokronoloμiska studier öλver det λiniμlaciala skedet I Ånμerman‐ land, Sveriges Geol. Undersökn., Ca- , - .

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] Lidén, R. . Den senkvartära strandλörskjutninμens λörlopp och kronoloμi i Ån‐ μermanland, Geologiska Föreningens i Stockholm Förhandlingar, , .

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] Maier, ”., Rydberμ, J., ”iμler, C. & Renberμ, I. sediments, GFF, - , .

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] Mörner, N.-“. . Varve Chronoloμy on Södertörn recordinμ and datinμ oλ the "drainaμe" oλ the ”altic Ice Lake and correlation with the Finnish varve chronoloμy, Geologiska Föreningens i Stockholm Förhandlingar, , .

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] Mörner, N.-“. . Varves and varved clays, Encyclopedia of the Earth Sciences, VI“ Sedimentoloμy R.W. Fairbridμe, ed. , .

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] Mörner, N.-“. . The Fennoscandian upliλt and Late Cenozoic μeodynamics μeoloμical evidence, GeoJournal, , .

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] Mörner, N.-“. . Trans-polar VGP shiλts and Earth’s rotation, Geophys. Astro‐ phys. Fluid Dynamics, , .

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] Mörner, N.-“. . Paleoseismicity of Sweden – a novel paradigm. “ contribution to INQU“ λrom its Sub-commission on Paleoseismoloμy, Reno , pp., P&Gprint, Stockholm. IS”N- - .

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] Mörner, N.-“. . Settinμ the λrames oλ expected λuture sea level chanμes, In Evi‐ dence-based Climate Science D.J. Easterbrook, ed. , Chapter , , Elsevier.

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] Mörner, N.-“. a . Drainaμe varves, seismites and tsunamites in the Swedish varve chronoloμy, GFF, - , .

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] Mörner, N.-“. Physics, , -

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] Mörner, N.-“. & Sun., G. . Paleoearthquake deλormations recorded by maμnet‐ ic variables, Earth and Planetary Science Letters, , .

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] Mörner, N.-“. & Sylwan, C. . Detailed paleomaμnetic record λor the last years λrom varved lake deposits in northern Sweden. In Geomagnetism and Paleomag‐ netism F. Lowes et al., Eds. , p. - . Kluwer, Dordrecht.

. Compaction oλ recent varved

. The ”altic ice lake e Yoldia Sea transition, Quaternary Interna‐

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] Niemelä, J. . Die quartäre Sratiμraphie von Tonablaμerunμen und der R(ckzuμ des Inlandseises zwischen Helsinki und Hämeenlinna in F(dλinnland, Geol. Surv. Finland, ”ull. , - .

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] Ojala, “.E.K. & Tiljander, M. . Testinμ the λidelity oλ sediment chronoloμy comparison oλ varve and paleomaμnetic results λrom Holocene lake sediments λrom central Finland, Quaternary Sci. Reviews, , .

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] Ojala, “.E.K. & “lenius, T. . years oλ interannual sedimentation recorded in the Lake Nautajärvi Finland clastic-orμanic varves, Palaeogeogr. Palaeoclim. Palae‐ oecol., , .

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] Ojala, “.E.K., Heinsalu, “., Kauppila, T., “lenius, T. & Saarnisto, M. . Charac‐ taerizinμ chanμes in the sedimentary environment oλ a varved lake sediment record in southern central Finland around cal. yr ”P, J. Quaternary Sci., , .

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] Ojala, “.E.K., Kosonen, E., Weckström, J., Korkonen, S. & Korhola, “. . Season‐ al λormation oλ clastic-bioμenic varves the potential λor palaeoenvironmental inter‐ pretations, GFF, - , .

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] O’Sullivan, G. . “nnually laminated lake sediments and the study oλ Quaterna‐ ry environmental chanμes, Quaternary Sci. Rev., , .

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] Renberμ, I. . Varved lake sediments – μeochronoloμical records oλ the Holo‐ cene, Geologiska Föreningens i Stockholm Förhandlingar, , .

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] Renberμ, I., Seμerström, U. & Wallin, J.-E. . Climatic reλlection in varved slake sediments, In Climate Changes on a Yearly to Millennial Basis N.-“. Mörner & W. Kar‐ lén, Eds. , , Reidel Publ. Co.

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] Ridμe, J.C. and Larsen, F.D. . Re-evaluation oλ “ntevs’ New Enμland varve chronoloμy and new radiocarbon dates oλ sediments GlacialLake Hitchcock, Geol. Soc. Am. Bull., , / .

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] Rinμberμ, ”. . Cyclic lamination in proximal varves reλlectinμ the lenμth oλ summers durinμ the Late Weichsel in southernmost Sweden. In Climate Changes on a Yearly to Millennial Basis N.-“. Mörner & W. Karlén, Eds. , - , Reidel Publ. Co.

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] Rinμberμ, ”. . Late Weichselian clay varve chronoloμy and μlaciolacustrine en‐ vironment durinμ deμlaciation in southeastern Sweden, Sveriges Geol. Undersökning, Ca- , - .

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] Saarnisto, M.

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] Sauramo, M. . Studies on the Quaternary varve sediments in southern Finland, Bull. Comm. Géol. Finlande, , - .

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] Strömberμ, ”. . Late Weichselian deμlaciation and clay-varve chronoloμy in east-central Sweden, Sveriges Geologiska Undersökning, Ca , – .

. Lonμ varve series in Finland, Boreas,

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] Tröλten, P.E. & Mörner, N.-“. . Varved clay chronoloμy as a means oλ record‐ inμ paleoseismic events in southern Sweden, Journal of Geodynamics, , – .

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Chapter 4

Geochronology From The Castelo Branco Pluton (Portugal) Isotopic Methodologies An“”nes Imhr Addi“ional informa“ion is available a“ “he end of “he chap“er h““p://dx.doi.org/10.5772/58686

. Introduction The μeochronoloμy oλ μranitic rocks is a key-issue in the crustal evolution and oroμenic processes. Modern hiμh precision techniques have been used to identiλy relevant μeoloμical episodes. U-Th-Pb chemical datinμ by electron-microprobe EPM“ is a potentially valuable method in monazite-bearinμ rocks. Monazite presents the λundamental conditions required to apply this procedures monazite is a U-Th enriched phase, all Pb monazite is radioμenic its closure temperature has proved to be λairly hiμh, up to º C [ ] and the system remains close [ ]. Monazite presents a hiμher resistance than zircon to radiation damaμe eλλects [ ] and low diλλusion rates [ ]. Diλλerent studies have demonstrated that U-Th-Pb datinμ by EPM“ is an accurate method oλ μeochronoloμy e.μ., [ - ] . U-Th-Pb monazite aμe determination can be obtained in small crystals m , allowinμ the study oλ mineral heteroμeneities, without destruction and preservinμ textural relationships. Microanalytical techniques are an adequate way to study maμmatic and polymetamorphic events reμistered in monazites with zoninμ textures e.μ., [ , - ] . The advantaμes oλ this technique are the hiμh spatial resolution and the possibility to obtain rapidly a larμe number oλ aμes. The main disadvantaμe is the low accuracy, conditioned by Pb content and statistical treatment oλ data. The analytical error λrequently ranμes λrom ± to ± Ma σ λor aμes oλ to Ma, respectively [ ]. However, a statistical treatment oλ homoμeneous aμes promotes a decrease oλ uncertainty to ± – Ma [ ]. “ttemps to constraint the timinμ oλ hiμh-temperature oroμenic processes includinμ crustal meltinμ, metamorphism and deλormation are typically based upon U-Pb aμe analysis oλ accessory minerals such as zircon and monazite. “lthouμh μrowth and recrystallization oλ

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accessory minerals is beinμ increasinμly better understood in the context oλ the host rock petroμenesis [ - ], it remains a diλλicult task to related aμes measured λrom zircon and monazite to speciλic oroμenic events. Zircon is a very robust mineral durinμ maμmatic and metamporphic events. Very slow rates λor U, Th and Pb help ensure that U-Pb aμe and stable isotopic and trace element compositions are preserved durinμ subsequent deep crustal evolution. Conversely, new zircon μrowth associated with tectonic events post-datinμ the initial zircon μrowth typically occurs at very λine spatial scales [ ]. Zircon is capable oλ preservinμ a lonμ history oλ μrowth and modiλication. Monazite also contains valuable chemical and textural inλormation, but tends to recrystallize more readly than zircon [ - ] and thus tend to record aμe and stable isotopic data that are substantially diλλerent λrom that yielded by coexistinμ zircon. ID-TIMS U–Pb aμe λor zircon and monazite is a more accurate and precise methodoloμy and has widely been applied. Uranium decay produces radioμenic Pb Pb and Pb , allowinμ to two independent aμe results- Pb/ U and Pb/ U-and a dependent one- Pb/ Pb [ ]. Data aμes were plotted on the conventional U–Pb concordia diaμrams and the three obtained aμes λrom the same mineral allows a hiμh precision to the U-Pb system. Radioμenic isotope ratios are commonly used as petroμenetic tracers, yieldinμ inλormation on time-inteμrated element λractionation throuμh processes oλ meltinμ, crystallization, metamor‐ phism and contamination. The Rb–Sr datinμ method is based on the behavior oλ two mobile elements and the Rb–Sr isotope systematic oλ iμneous rocks can be easily disturbed by λluid inλiltration or durinμ a thermal event. Isotopic Rb/Sr and Sm/Nd data are petroμenetic indicators. Initial Sr/ Sr isotopic ratio and NdT value oλ maμma are a source siμnature and remain constant durinμ λractionation processes [ ]. Whole rock oxyμen isotope O oλ μranitic rocks will μive inλormations about maμma oriμin and associated maμmatic crystallization and assimilation processes. Generally, maμmas with no supracrustal input have an uniλorm oxyμen isotope ratio that is distinct λrom maμmas that assimilated or were μenerated directly λrom supracrustal sources. However, O can show small variations in the maμmatic diλλerentiation processes [ - ]. The Castelo ”ranco pluton consists oλ λive diλλerent peraluminous μranitic rocks arranμed in a concentrically zoned structure [ ]. This work will present the diλλerent isotopic data U-ThPb, U-Pb, Sr/ Sri, NdT and O obtained in these μranitic rocks to determine their aμe and protolith inλormation.

. Castelo Branco Pluton The Castelo ”ranco μranitic pluton is located within the Central Iberian Zone CIZ , the innermost zone oλ the Iberian Variscan ”elt. This pluton is exposed over an area oλ km , with a mean diameter oλ km, and consists oλ λive late-tectonic Variscan μranitic bodies, intrudinμ the schist-μreywacke complex CXG Fiμ. . In the NE border, it contacts with a medium-μrained biotite μranodiorite oλ ± Ma [ ].

Geochronology From The Cas“elo Branco Pl”“on (Por“”gal) Iso“opic Me“hodologies h““p://dx.doi.org/10.5772/58686

The Castelo ”ranco pluton μenerated a contact metamorphic aureole up to km wide, with metasediments recrystallized as pelitic hornλels in the inner zone, and as micaschists in the outer zone. The schist–μreywacke complex and the μranitic rocks are cut by aplite-peμmatite dikes and quartz veins.

Figure 1. Geographycal se““ing and geological map of “he Cas“elo Branco pl”“on. CXG schis“–greywacke complex; GCB1 m”scovi“e > bio“i“e grani“e; GCB2 bio“i“e > m”scovi“e granodiori“e; GCB3 bio“i“e > m”scovi“e granodiori“e; GCB4 bio“i“e=m”scovi“e grani“e; GCB5 m”scovi“e > bio“i“e grani“e.

The medium-to λine-μrained muscovite > biotite μranite GC” occurs at the pluton´s core and is encircled by a medium-to λine-μrained, sliμhtly porphyritic, biotite > muscovite μranodiorite GC” , surrounded by a medium-to coarse-μrained porphyritic biotite > muscovite μrano‐ diorite GC” , which passes μradually to the medium-to coarse-μrained, porphyritic bio‐ tite=muscovite μranite GC” . Rounded enclaves oλ μranodiorite GC” can be λounded in the μranodiorite GC” and μranite GC” . The boundary oλ the pluton is limited to N and NE by a coarse-μrained muscovite > biotite μranite GC” Fiμ. . The contact between μranite GC” and μranodiorite GC” is sharp, as is the contact between μranites GC” and GC” . The pluton consists oλ λive μranites concentrically distributed oλ Ma ± [ ]. “ll the μranitic rocks λrom the Castelo ”ranco pluton contain quartz, microcline, plaμioclase, biotite, some chlorite, muscovite, tourmaline, monazite, apatite, zircon, ilmenite and rutile. Zircon and monazite are accessory minerals mainly included in apatite, biotite and plaμioclase. Zircon occurs as euhedral crystals, whereas monazites are rounded and easily identiλied by their pleochroic halos. The μranitic rocks GC” , GC” and GC” correspond to three distinct maμmatic pulses derived by partial meltinμ oλ heteroμeneous metasedimentary materials. Granodiorite GC”

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and μranite GC” result by λractional crystallization oλ plaμioclase, quartz, biotite and ilmenite λrom the μranodiorite GC” maμma [ ].

. Analytical methodologies . . U-Th-Pb EPMA The U-Th-Pb monazite aμes were calculated usinμ U, Pb and Th monazite contents determined by electron-microprobe EPM“ . In μeneral, monazite incorporates larμe amounts oλ Th and U durinμ the rock λormation and retains Pb oλ the radioactive decay processes. The obtained aμe will be valid iλ at the time oλ λormation oλ the mineral, initial Pb is practically non-existent and there was no loss oλ Pb, Th and U [ ]. The U, Pb and Th monazite contents oλ representative samples λrom the Castelo ”ranco pluton Fiμ. were determined by electron-microprobe on polished thin sections, in a Cameca SX at the Laboratoire oλ Maμmas and Volcans, University ”laise Pascal Clermont-Ferrand, France . The analytical conditions included an acceleratinμ voltaμe oλ kV and a beam current oλ n“. The standards used were as λollows UO U M , ThO Th M , apatite Ca K , P K , zircon Si K and polysintetic phosphates Y L , La L , Ce L , Pr L , Nd L , Sm L , Gd L . The monazite aμe is directly dependent on the concentrations oλ U, Th and Pb and its detection limit was calculated [ ], with an error oλ σ associated with the uncertainty oλ these elements λor a conλidence level oλ % in the equation decay. The treatment oλ individual analysis, includinμ Th, U and Pb contents oλ each monazite crystals, have been perλomed usinμ a Gw”asic computer proμram providinμ an aμe λor each individual analysis. “ statistical treatment μivinμ the correspondinμ aμe to the studied population and the values oλ the sum oλ squared deviations MSWD is used λor the results validation [ , ]. Iλ the system remained close since the early staμes oλ crystallization, the obtained MSWD value will be less or equal to , whereas iλ the system chanμed λlowinμ throuμh interactions between minerals can promote recrystallization processes, and the MSWD value μreatly increases [ ]. . . U-Pb zircon and monazite ages The U-Pb μeochronoloμical aμes were proceeded with the preparation oλ zircon and monazite concentrates λrom representative samples oλ the Castelo ”ranco pluton. Zircon and monazite separation was carried out by a combination oλ maμnetic separation and heavy liquids. The preparation oλ the selected samples to kμ per sample , included μrindinμ, sievinμ and separation oλ the diλλerent μranulometric λractions. “λter this, a subsample correspondinμ to the λraction below mesh was selected and contains the majority oλ zircon and other accessory minerals. Subsequently, this subsample passed throuμh a maμnetic separator in a vertical position with a maximum speed to separate the more maμnetic minerals e.μ. biotite λrom the remaininμ λraction. Otherwise, the less maμnetic λraction is placed in a μlass ampoule containinμ bromoλorm d= . to recover the heavy concentrated sample which was washed with puriλied water and

Geochronology From The Cas“elo Branco Pl”“on (Por“”gal) Iso“opic Me“hodologies h““p://dx.doi.org/10.5772/58686

GCB1, GCB2, GCB3, GCB4 and GCB5 are “hose in Fig”re 1. Figure 2. U-Th-Pb monazi“e ages from grani“ic rocks of Cas“elo Branco pl”“on.

acetone, and dried in an oven. “λter this, the concentrated sample was separated with methylene iodide d= . and the heavier λraction, which contains zircon and monazite, was washed with acetone and distilled water to eliminate methylene iodide wastes. “t the end, the heavy concentrate sample was passed throuμh a maμnetic separator and diλλerent maμnetic λractions containinμ monazite . to . “ and zircon . “ were obtained. “ll the methodoloμy must be careλully λollowed and will be λundamental λor the quality oλ zircon concordia diaμrams [ - ]. “ consistent zircon concordia diaμram requires non-maμnetic zircon concentrates because maμnetic ones are also rich in uranium, and thereλore become the most likely to lost radioμenic lead and, consequently are more discordant [ ]. Monazite μrains λor U-Pb analysis are selected λrom the concentrated maμnetic λraction and μrains λree oλ cracks and inclusions should be used, like as to selected zircon μrains. Repre‐ sentative crystals oλ zircon and monazite populations are selected by hand-pickinμ, avoidinμ the λractured ones or with inclusions and, iλ possible, oλ inherited cores. However, these inherited cores are not always detectable by binocular or even optical microscope. Selected λrations oλ zircon and monazite were submitted to air-abrasion to prevent λracturation oλ the minerals, remove external portions and possible disturbances [ , ]. The abraded crystals are washed with HNO N , H O and acetone, weiμhted and added "spike" Pb/ U to dissolution processes. Zircon is dissolved with HF +HNO usinμ teλlon

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microcapsules and heated to °C [ ], whereas monazite is dissolved with HCl N in savillex containers on a hotplate. “λter evaporation, HCl . N is added to each microcapsule and savillex containers, and the solution is passed throuμh a HCl ion exchanμe column resin to puriλy U and Pb. Finally, the crystals and blank samples are placed on the λilament by addinμ drops oλ H PO and silica μel. The U–Pb isotopic results λor zircon and monazite were obtained by isotope dilution thermal ionization mass spectrometry ID-TIMS usinμ a Finniμan Mat spectrometer at the Department oλ Geosciences, University oλ Oslo, Norway [ - ]. The initial Pb correction was done usinμ model compositions [ ] and decay constants [ ]. The Isoplot proμram [ ] was used λor the plots and reμression. “ll uncertainties relative to the analyses and aμes are μiven at the σ level. . . Rb-Sr, Sm-Nd and δ O whole rock The Sr and Nd isotope analyses were obtained at the Centro de Instrumentación Cientíλica oλ the University oλ Granada, Spain. Samples were diμested usinμ ultraclean reaμents and analyzed by thermal ionization mass spectrometry TIMS , usinμ a Finniμan Mat spec‐ trometer, aλter chromatoμraphic separation with ion-exchanμe resins [ ]. The standardized ratios Sr/ Sr= . and Nd/ Nd= . and blank values λor Sr and Nd were oλ . and . nμ, respectively. The external precision oλ the method σ was estimated by ten successive samples correspondinμ to diλλerent attacks in the same standard sample WSE [ ]. This value can be considered as a laboratory error, since it includes both the diλλerent attacks and chemical separation oλ the various samples, as well as the instrumental error oλ the determinations. The obtained errors were Sr/ Sr= . ± . σ= . % and Nd/ Nd= . ± . σ= . % . On the analysis, the N”S was used as a standard solution, with a reproducibility λor repeated measurements oλ Sr/ Sr= . ± . σ= . % . The reproducibility obtained λor the La Jolla standard was Nd/ Nd= . ± . σ= . % . The isotopic ratios Rb/ Sr and Sm/ Nd were determined with an accuracy better than ± . % and ± . % σ , respectively. Reμression lines oλ Rb/ Sr versus Sr/ Sr were calculated usinμ the least-squares method [ ], implemented in the Isoplot proμram [ ]. Errors are quoted at the % conλidence level and are σ. The isotopic results oλ O whole rock oλ the λive μranitic rocks were obtained in the Depart‐ ment oλ Earth Sciences, University oλ Western Ontario Canada , usinμ conventional extraction line and triλluoride chlorine as a reactant. This method has an accuracy oλ ± . ‰ and patterns such as quartz and CO laboratory were used.

. Isotopic geochronology . . U-Th-Pb EPMA monazite ages U-Th-Pb contents oλ selected monazite μrains λrom the λive μranitic rocks oλ the Castelo ”ranco pluton were determined by EPM“ and calculated monazite aμes Table I . “ total oλ U-

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Th-Pb analyses EPM“ oλ monazite were obtained λrom the μranitic rocks oλ the Castelo ”ranco pluton. Monazite crystals are homoμeneous and unzoned Fiμ. and a distinct aμe between core and rim was not λound. Thereλore, an individual aμe were considered to the analysed μrains. Monazites λrom GC” present the hiμhest Pb and U contents oλ μranitic rocks λrom the Castelo ”ranco pluton Table I . Monazite aμe data obtained λrom two samples oλ GC” μranite apparently show a μreat dispersion, but iλ the errors obtained are taken into account the aμes are similar. Lead, U and Th averaμe contents λrom monazite crystals oλ μranodiorites GC” and GC” and μranite GC” show variation but within a similar ranμe Table I . Otherwise, monazite λrom μranite GC” contains hiμher Pb and U contents than monazites λrom μrano‐ diorites GC” and GC” and μranite GC” Table .

GCB1, GCB2, GCB3, GCB4 and GCB5 are “hose in Fig”re 1. N – N”mber of analysis. Table 1. EPMA U-Th-Pb monazi“e da“a from grani“ic rocks of “he Cas“elo Branco pl”“on

The obtained results oλ monazite λrom the μranite GC” reveal heteroμeneity, supported by the hiμher MSWD values observed which may be associated with the uncertainties oλ this methodoloμy [ ]. However, they may also be related to the occurrence oλ μeoloμical processes responsible λor the presence oλ some initial Pb in monazite μrains or alteration processes. The U-Th-Pb monazite aμe obtained by electron microprobe is an important alternative μeochronoloμical method, which allows to obtain accurate and similar results to those obtained by isotopic datinμ aμes [ ]. The potentiality oλ this μeochronoloμical methodoloμy increases

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with the application toμheter with other isotopic datinμ methods, such as U-Pb zircon and monazite [ ]. The monazite aμes obtained throuμh U-Th-Pb EPM“ do not allow themselves to evaluate the accuracy oλ obtained aμes because there is concordance between Th-Pb and U-Pb systems. However, the consistency oλ the obtained measurements allows to conclude that a crystal was not siμniλicantly altered or modiλied [ ]. The most recent monazite aμe values obtained by EPM“ may indicate an isotopic discordance leadinμ to a more relatively recent aμe with a smaller ratio Pb/ Th+U [ ]. U-Th-Pb EPM“ monazite aμe correponds to the minimum Pb/ U aμe and maximum Pb/ Th aμe. However, these isotopic disaμreements are not possible to assess by electron microprobe [ ]. Monazites λrom μranites GC” and GC” and μranodiorites GC” and GC” presented the aμes oλ Ma, whereas monazite λrom the μranite GC” tends to be more recent Ma Table . However, the various aμes are similar and within the ranμe oλ the analytical error. The hiμhest MSWD values on monazites λrom μranodiorite GC” and μranite GC” must be associated with a disperion oλ the results, which could be related to the methodoloμy uncer‐ tainty or to a possible μeoloμical or alteration processes. . . U-Pb zircon and monazite ages U–Pb isotopic analyses were carried out on zircon and monazite λrom representative samples oλ the μranitic rocks GC” , GC” and GC” λrom the Castelo ”ranco pluton usinμ the ID-TIMS method [ ]. Granodiorite GC” contains hyaline or colorless zircons, euhedral elonμated prismatic and subhedral crystals with varied size and λorms. Some oλ them contain associated λractures and rare inclusions Fiμ. a . Monazite crystals Fiμ. b are reversely discordant, which can be associated with Paleozoic μeoloμical processes and Pb/ U concordant monazite aμe should be used Table . The reversly concordia can be interpreted as the result oλ the existence oλ some inherited Pb, associated with an excess oλ initial Th [ - ] due to possible inherited zircon cores. For other authors, it could be justiλied with some deμree oλ chanμe [ ] or incomplete dissolution [ ]. Some zircons have inherited cores and were not considered λor the U-Pb aμe. The aμe Pb/ Pb oλ . ± . Ma was obtained λor a more concordant zircon crystal and is similar to the zircon concordia aμe . ± . Ma Fiμ. Table . Monazite λrom μranite GC” plots sliμhtly reversely discordant Fiμ. , a λact commonly linked to Th initial excess, which eventually results in an excess oλ Pb and reverse discordance [ - ]. The Pb/ U ratio is not aλλected by this disequilibrium eλλect and can be used as the closest estimate λor monazite aμe. The concordant monazite oλ μranite GC” yields a Pb/ U aμe . ± . Ma, which overlaps the zircon crystal oλ the μranite GC” Fiμ. Table . Zircons λrom μranodiorite GC” occur as hyaline to sliμhtly pinkish, elonμated prismatic crystals or subhedral crystals with lonμitudinal cracks and occasional inclusions Fiμ. c . Monazite is euhedral with rare inclusions Fiμ. d . Zircon crystals λrom the μranodiorite GC” plot near the concordia, but one oλ them presents a restitic core and deviates λrom the curve

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Figure 3. Selec“ed zircon and monazi“e crys“als from grani“ic rocks of Cas“elo Branco pl”“on. M”scovi“e > bio“i“e gran‐ i“e GCB1: zircon (a), monazi“e (b); bio“i“e > m”scovi“e granodiori“e GCB2: zircon (c) monazi“e (d); m”scovi“e > bio“i“e grani“e GCB5: zircon (e, f).

Fiμ. . So, the concordia aμe was not considered. The concordant zircon yields a Pb/ Pb aμe oλ . ± . Ma Fiμ. Table . The projection oλ monazite λraction is sliμhtly above the concordia curve and μives an aμe oλ . ± . Ma, obtained by Pb/ U ratio Fiμ. Table . The aμe oλ . ± . Ma obtained λrom the concordant zircon crystal should be considered λor the μranodiorite GC” Table .

Zircon concordia age

GCB1

GCB2

GCB5

309.9 ± 1.1 Ma

-

309.1 ± 0.6

MSWD = 1.11 207

MSWD = 0.11

Pb/206Pb concordan“ zircon age

309.9 ± 1.0 Ma

310.1 ± 0.8 Ma

309.7 ± 0.4 Ma

Pb/235U concordan“ monazi“e age

309.5 ± 0.9 Ma

310.6 ± 1.5 Ma

309.7 ± 0.4 Ma

207

GCB1, GCB2 and GCB5 as in Fig”re 1. Table 2. U-Pb zircon and monazi“e ages of grani“ic rocks from “he Cas“elo Branco pl”“on

Granite GC” contains hyaline and colorless elonμated prismatic zircons and several subhe‐ dral crystals and some sliμhtly rounded, correspondinμ to λractions or λraμmented crystals,

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Figure 4. Selec“ed concordia 207Pb/235U vers”s 206Pb/238U diagrams for zircon and monazi“e of m”scovi“e > bio“i“e grani“e GCB1 and bio“i“e > m”scovi“e granodiori“e GCB2 from “he Cas“elo Branco pl”“on (Error for ellipses are drawn a“ 2σ).

some brownish colourless with inclusions Fiμ. e λ . Monazite is unsual and with rare inclusions. The zircon crystals deλine a discordia line yieldinμ a lower intersect aμe oλ . ± . Ma MSWD= . , similar to the Pb/ Pb concordant zircon aμe . ± . Ma , and an upper intersect aμe oλ about Ma. Concordant monazite has a Pb/ U similar aμe oλ . ± . Ma Table . The averaμe U-Pb aμe obtained λor each μranite λrom the Castelo ”ranco pluton is similar Ma , indicatinμ that they are contemporaneous Table . Zircon λrom μranite GC” is the richest in U content GC” ppm oλ μranitic rocks λrom Castelo ”ranco pluton GC” ppm GC” ppm and with the hiμhest Pb/ Pb ratio GC” GC” GC” . Monazite λrom GC” also presents the hiμhest Pb/ Pb ratio GC” GC” GC” [ ]. Zircon Th/U ratio λrom μranitic rocks oλ Castelo ”ranco pluton ranμes between . – . , correspondinμ to zircons with an iμneous siμnature [ ]. Zircon λrom μranodiorite GC” presents the hiμhest Th/U variation ranμe Th/ U . - . includinμ the values obtained λrom μranodiorite GC” zircon Th/U . - . and μranite GC” Th/U . - . . The selected monazite crystals λrom μranite GC” show the hiμhest variability U and Th/U results includinμ the hiμhest and the lowest value oλ U U – ppm and Th/U ratio . – . λrom the μranitic rocks oλ the Castelo ”ranco pluton. The discordant monazites tend to have hiμher levels oλ Th, identiλied by the hiμhest values oλ Th/U ratio [ ]. However, althouμh hiμh Th values may contribute to the discrepancy associ‐ ated with monazite crystals is not possible to establish a linear correlation between Th/U ratio and the deμree oλ monazites discordance. In some monazite crystals, U-Pb ratio and presented λeatures could have a μreater inλluence on the associated discordance [ ]. The discordance oλ monazite crystals λrom μranite C”G could be associated with Th disequilibrium and U loss, which can be justiλied by possible crystal chanμe, as λound in monazites λrom Suomujärvi

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Complex [ ]. In monazite crystals, there are considerable amounts oλ Pb and Th that could be incorporated and the enrichment or depletion oλ U will depend on λluid composition and associated processes [ ]. The U-Pb monazite and U-Th-Pb isotopic data conλirm that the Castelo ”ranco pluton consists oλ λive concentric late-tectonic Variscan μranitic bodies, which intruded the Cambrian schist – μreywacke. . . Rb-Sr, Sm-Nd and δ O whole rock For Rb-Sr and Sm-Nd isotopic studies, representative samples oλ the λive μranitic rocks λrom the Castelo ”ranco pluton were selected, aλter a detailed μeoloμical λield study, petroμraphic and μeochemical whole rock data interpretation. The Rb/Sr isotopic aμe obtained λor μranitic rocks λrom Castelo ”ranco pluton ± Ma [ ] is lower than the U-Pb zircon and monazite aμes Ma Table , which could be atributed to an openinμ oλ the Rb-Sr system durinμ the metamorphic event associated with late-D μranite intrusions, or λurthermore to the lower temperature oλ Rb-Sr system than U-Pb system [ ]. Initial Sr/ Sr ratios and NdT values were calculated usinμ the U-Pb aμe oλ Ma Table . Petroμraphic and μeochemical characteristics oλ μranodiorite GC” and μranite GC” suμμest that they are related to μranodiorite GC” , and a similar aμe oλ Ma have been considered.

( Sr/86Sr)310 87

GCB1

GCB2

GCB3

GCB4

GCB5

0.7082 – 0.7098

0.7085 – 0.7128

0.7104

0.7078 – 0.7104

0.7120

-3.8 ± 0.2

-1.7 ± 0.4

-0.8

-2.8 ± 0.68

-3.0

1.64 ± 0.12

1.10 ± 0.0

1.11

1.35 ± 0.1

1.56

13.53 ± 0.11

12.27 ± 0.04

12.50

12.75

12.91 ± 0.23

εNd310 TDM O (‰)

18

GCB1, GCB2, GCB3, GCB4 and GCB5 as in Fig”re 1. Table 3. εNd310 and

O da“a of grani“ic rocks from “he Cas“elo Branco pl”“on

18

The Sr/ Sr ratios obtained λor μranite GC” , μranodiorite GC” and μranite GC” are characteristic oλ μranites resultinμ λrom crustal anatexis oλ metasedimentary rocks Table . The Nd and TDM values obtained λor representative samples λrom μranitic rocks oλ Castelo ”ranco pluton were calculated [ ] with a Sm desinteμration constant oλ = . * - year[ ]. To NdT and TDM calculation Nd/ NdCHUR= . and Sm/ NdCHUR= . [ ] and Nd/ NdDM= . and Sm/ NdDM= . [ ] were applied, respectively. Granites GC” and GC” show lower values oλ Nd and hiμher values oλ TDM than μrano‐ diorites GC” , GC” and μranite GC” Table , suμμestinμ that GC” and GC” μranites are not relate to the μranodiorites GC” and GC” and μranite GC” λrom the Castelo ”ranco pluton.

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The diaμram Nd versus Sr/ Sr shows a dominantly crustal oriμin λor all μranitic rocks λrom the Castelo ”ranco pluton. “ll samples plot on the λield IV, indicatinμ that are derived λrom Rb enriched and depleted Sm protholiths Fiμ. a . The scatter oλ Sr/ Sr ratio suμμests that the μranitic rocks were not in complete isotopic equilibrium at the time oλ λormation, which is also supported by an heteroμeneous Nd Fiμ. a .

Figure 5. Selec“ed diagrams of grani“ic rocks from Cas“elo Branco pl”“on: a) εNd310 vers”s (87Sr/86Sr)310; b) 147Sm/144Nd vers”s SiO2. GCB1, GCB2, GCB3, GCB4 and GCB5 as in Fig”re 1.

The obtained results show coherence within each oλ the λive μranitic rocks λrom the Castelo ”ranco pluton with a sliμhtly evolutionary trend λrom hiμher to lower values oλ Sr/ Sr and Nd λrom μranodiorite GC” and GC” to μranite GC” [ ]. Granites GC” and GC” tend to have the most neμative values λor Nd , with variable Sr/ Sr . These distributions suμμest the contribution oλ at least three maμmatic components GC” , GC” and GC” with diλλerent isotopic siμnatures Table Fiμ. a . “ll the data plot within a λield delimited by Nd=− to − and Sr/ Sr= . – . , which indicate derivation λrom crustal material with averaμe Mesoproterozoic mantle extraction aμes Fiμ. a . TDM values oλ μranitic rocks are similar to the TDM data λor schist-μreywacke complex λrom the studied area [ ]. The Sm/ Nd versus SiO diaμram oλ μranitic rocks λrom the Castelo ”ranco pluton shows a positive correlation with an increase oλ Sm/ Nd λrom μranodiorite GC” , to μranodiorite GC” and μranite GC” . Otherwise, μranites GC” and GC” do not present similar variation and plot outside the straiμht line Fiμ. b . Whole rock oxyμen-isotope O values, obtained λor eiμht representative samples oλ μranitic rocks λrom the Castelo ”ranco pluton, ranμe λrom + . to + . ‰ Table . The obtained O values are hiμher than ‰, indicatinμ that the μranitic rocks λrom the Castelo ”ranco pluton correspond to S-type μranites [ ]. There is a proμressive increase oλ O λrom μranodiorite GC” to μranodiorite GC” , μranite GC” and μranite GC” . The O values are also positively correlated with SiO ,

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Li, Rb and neμatively correlated with FeO, Sr and ”a [ ]. In these diaμrams, μranodior‐ ite GC” and GC” and μranite GC” deλine a curvilinear variation trend which is characteristic oλ a maμmatic diλλerentiation process. Granite GC” yields the hiμhest value, which deviates clearly λrom the trend, whereas μranite GC” plots closer, but in averaμe has hiμher O than the trend [ ]. “ system without contamination will present radioμenic isotopic characteristics similar to the oriμinal source, even with the occurence oλ maμmatic diλλerentiation processes [ ]. However, the values oλ O show small variations in the maμmatic diλλerentiation processes, with an increase oλ about to . ‰, increasinμ with the deμree oλ diλλerentiation [ - ]. The O values increase λrom the μranodiorite GC” . ‰ to the μranodiorite GC” . ‰, which is associated with the λractional crystallization process [ ]. These isotopic ratios Sr/ Sr , Nd and O values oλ μranite GC” , μranodiorite GC” and μranite GC” are oλ μranites oriμinated λrom crustal anatexis oλ metasedimentary rocks [ ].

. Conclusions U-Th-Pb monazite aμes λrom μranodiorite GC” and μranite GC” and μranodiorites GC” and GC” have a similar values, ranμinμ λrom Ma. Granodiorite GC” presents a lower value oλ ± Ma, but the diλλerence is insided the analytical error. However, U-Th-Pb monazite aμes λor μranodiorites GC” and GC” and μranite GC” are consistently below about M“, with respect to the aμe oλ ± Ma obtained by ID-TIMS U-Pb zircon and monazite. The most recent aμes obtained by U-Th-Pb monazite EPM“ aμe could be associated to the hiμher levels oλ U and Th and lower Th/U ratio obtained by electron microprobe relatively to those obtained by ID-TIMS, as well as Pb partial loss like as λound in rocks oλ southern India [ ]. The U-Pb zircon and monazite isotopic aμes ID-TIMS are the most accurate. However, U-Th-Pb monazite aμes EPM“ are closer. The μranitic rocks GC” , GC” and GC” correspond to three distinct maμmatic pulses and have a similar aμe oλ ± Ma ID-TIMS U-Pb zircon and monazite . These three μranitic rocks have diλλerent Sr/ Sr , Nd and O values and correspond to three distint maμmatic pulses derived by partial meltinμ oλ heteroμeneous metasedimentary materials.

Acknowledgements Fundinμ was provided to I.M.H.R. “ntunes by the SFRH/”D/ Fundação para a Ciência e a Tecnoloμia, Portuμal.

/

μrant λrom the

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Author details “ntunes Imhr ,

,

“ddress all correspondence to [email protected] Polytechnic Institute oλ Castelo ”ranco and Geo-Environmental and Resources Research Center, Portuμal Neiva “MR, Department oλ Earth Sciences and Geosciences Centre, University oλ Coimbra, Portuμal Silva MMVG, Department oλ Earth Sciences and Geosciences Centre, University oλ Coimbra, Portuμal

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] Kohn MJ, Malloy M“. . Formation oλ monazite via proμrade metamorphic reac‐ tions amonμ common silicates implications λor aμe determinations. Geochim. Cos‐ mochim. “cta , .

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] Kelsey DE, Clark C, Hand M. . Thermobarometric modelinμ oλ zircon and mona‐ zite μrowth in melt-bearinμ systems examples usinμ model metapelitic and meta‐ psammitic μranulites. J. Metam. Geol. , .

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] Corλu F, Hanchar JM, Hoskin PWO, Kinny P. . “tlas oλ zircon textures. In Han‐ char JM, Hoskin PWO Eds . Zircon, Rev. Miner. Geochem. , .

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] “yres JD, Loλlin M, Miller CF, ”arton MD, Coath CD. . In site oxyμen isotope analysis oλ monazite as monitor oλ λluid inλiltration durinμ contact metamorphism ”irch Creek Pluton aureole, White Mountains, Eastern Caliλornia. Geol. , .

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] Harlov DE, Wirth R, Hetherinμton CJ. . The relative stability oλ monazite and huttonite at ºC and MPa metasomatism and the propaμation oλ metastable mineral phases. “m. Mineral. , .

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] Rollinson H. . Usinμ Geochemical Data Evalution, Presentation and Interpreta‐ tion. Lonμman, UK. pp.

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] Taylor Jr HP, Epstein S. . Relationships between O/ O ratios in coexistinμ min‐ erals oλ maμmatic and metamorphic rocks Part I. Principles and experimental re‐ sults. Geol. Soc. “mer. ”ull. , .

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] Cocherie “, “lbarède F. . “n improved U-Th-Pb aμe calculation λor electron mi‐ croprobe datinμ oλ monazite. Geochim. Cosmochim. “cta , .

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] Kroμh TE. . Improved accuracy oλ U–Pb zircon aμes by creation oλ more con‐ cordant systems usinμ an air abrasion technique. Geochim. Cosmochim. “cta , .

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] Tucker RD, Raheim “, Kroμh TE, Corλu F. . Uranium-lead zircon and titanite aμes λrom the northern portion oλ the Western Gneiss Reμion, south-central Norway. Earth Planet. Sci. Lett. , .

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] Davidson “, Van ”reemen O. . ”addedeleyite-zircon relationships in coronitic metaμrabro, Grenville Province, Ontario Implications λor μeochronoloμy. Contrib. Mineral. Petrol. , .

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] Davis DW, ”lackburn CE, Kroμh TE. . Zircon U-Pb aμes λrom the Wabiμoon, Manitou Lakes Reμion, Wabiμoon Subprovince, northwest Ontario. Can. J. Earth Sci. , .

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] Kroμh TE. . “ low contamination method λor hydrothermal decomposition oλ zircon and extraction oλ U and Pb λor isotopic aμe determination. Geochim. Cosmo‐ chim. “cta , .

. Principles oλ isotope μeoloμy. John Willey & Sons, New York.

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] Corλu F, “ndersen T”. . U–Pb aμes oλ the Dalsλjord Campus, SW-Norway, and their bearinμ on the correlation oλ the allochthonous crystalline seμments oλ the Scan‐ dinavian Caledonides. Int. J. Earth Sci. , – .

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] Corλu F. . U–Pb μeochronoloμy oλ the Lekres Group an exotic Early Caledonian metasedimentary assemblaμe stranded on Loλoten basement, northern Norway. J. Geol. Soc. Lond. , .

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] Stacey JS, Kramers JD. . “pproximation oλ terrestrial lead isotope evolution by a two-staμe model. Earth Planet. Sci. Lett. , .

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] Jaλλey “H, FlynnKF, Glendenin LE, ”enthey WC, Esslinμ “M. . Precision meas‐ urement oλ halλ lives and speciλic activities oλ U and U. Phys. Rev., C Nucl. Phys. , .

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] Ludwiμ KR. . Isoplot/Ex version . . “ μeochronoloμical toolkit λor Microsoλt Excel. ”erkeley Geochronoloμy under Special Publication, vol. pp.

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] Montero P, ”ea F. . “ccurate determination oλ Rb/ Sr and Sm/ Nd by in‐ ductively coupled plasma mass spectrometry in isotope μeoscience an alternative to isotope dilution analysis. “nal. Chim. “cta , .

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] Govindaraju K, Potts PJ, Webb PC, Watson JS. . Report on Whin Sill Dolerite WE λrom Enμland and Pitscurrie Microμabbro PM-S λrom Scotland assessment by one hundred and λour international laboratories. Geostand. Newslett. , .

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] Pyle JM, Spear FS, Wark D“, Daniel CG, Storm LC. . Contributions to precision and accuracy oλ monazite microprobe aμes. “m. Mineral. , .

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] Kuiper YD. . Isotopic aμe constraints λrom electron microprobe U-Th-Pb dates usinμ a three-dimensional concordia diaμram. “m. Mineral. , .

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] Schärer U. . The eλλect oλ initial Th disequilibrium on younμ U–Pb aμes the Makalu case, Himalaya. Earth Planet. Sci. Lett. , .

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] Kalt “, Corλu F, Wijbrans JR. . Time calibration oλ a P–T path λrom a Variscan hiμh-temperature low-pressure metamorphic complex ”ayerische Wald, Germany and the detection oλ inherited monazite. Contrib. Mineral. Petrol. , .

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] Williams IS, Claesson S. . Isotopic evidence λor the Precambrian provenance and Caledonian metamorphism oλ hiμh μrade paraμneisses λrom the Seve Nappes, Scan‐ dinavian Caledonides. II. Ion microprobe zircon U-Th-Pb. Contrib. Mineral. Petrol. , – .

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] Poitrasson F, Chenery S, ”land DJ. . Contrasted monazite hydrothermal altera‐ tion mechanisms and their μeochemical implications. Earth Planet. Sci. Lett. , - .

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] “ntunes IMHR, . Mineraloμia, Geoquímica e Petroloμia de rochas μranitóides da área de Castelo ”ranco-Idanha-a-Nova. Unpublished PhD. thesis. University oλ Coimbra, Portuμal, pp.

[

] De Paolo DJ. . Trace elements and isotopic eλλects oλ combined wall rock assimi‐ lation and λractional crystallization. Earth Planet. Sci. Lett. , – .

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] Steiμer RH, Jäμer E. . Convention oλ the use oλ decay constants in μeo and cos‐ mochronoloμy. Earth Planet. Sci. Lett. , .

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] Jacobsen S”, Wasserburμ GJ. . Sm-Nd isotopic evolution oλ chondrites and achondrites. Earth Planet. Sci. Lett. , .

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] Liew TC, Hoλmann “W. . Precambrian crustal components, plutonic associa‐ tions, plate environment oλ the Hercynian Fold ”elt oλ Central Europe indications λrom a Nd and Sr isotopic study. Contrib. Mineral. Petrol. , .

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] Chappell ”W, White “JR. . I-and S-type μranites in the Lachlan Fold ”elt. Trans. R. Soc. Edinb. Earth Sci. , - .

Chapter 5

In situ U-Pb Dating Combined with SEM Imaging on Zircon An Analytical Bond for Effective Geological Recontructions Annamaria Fornelli, Gi”seppe Piccarre“a and Francesca Michele““i Addi“ional informa“ion is available a“ “he end of “he chap“er h““p://dx.doi.org/10.5772/58540

. Introduction In situ U-Pb datinμ combined with SEM imaμes on zircon crystals represent a powerλul tool to reconstruct metamorphic and maμmatic evolution oλ basements recordinμ a lonμ and complex μeoloμical history [ - ]. The development oλ hiμh spatial and mass resolution microprobes e.μ., L“-ICP-MS, SIMS, SHRIMP allows in-situ measurements oλ U–Pb aμes in micro domains smaller than microns [ , ]. The μrowth oλ zircon crystals, evidenced by their internal microtextures, can be easily revealed by SEM imaμinμ by Cathodoluminescence CL and Variable Pressure Secondary Electrons VPSE detectors on separated μrains or in situ within a polished thin rock section [ , , ]. Thereλore it is possible to date diλλerent domains oλ sinμle crystals, which may record maμmatic or metamorphic events oλ the rock’s μeoloμical history [ , ]. In acidic maμmat‐ ic rocks abundant zircon crystals provide precise aμe data about maμma emplacement and oriμin oλ source indicatinμ the μeodynamic context and the pertinence oλ terranes λorm‐ inμ the continental crust. “s reμards the metamorphic context, zircon can potentially preserves multiple staμes oλ metamorphic records owinμ its hiμhly reλractory nature, hiμh closure temperature and slow diλλusion rate oλ Pb, thus it is an ideal mineral λor U-Pb datinμ oλ poly-metamorphic rocks [ , ]. In addition, in situ analyses oλ trace elements such as rare earth elements REE in zircon and between zircon and coexistinμ minerals is useλull to decipher the REE behavior and

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mineral chemistry durinμ metamorphism and to determine metamorphic P-T conditions [ , , ]. In particular, μarnet is one oλ the most important rock-λorminμ minerals in hiμh-μrade metamorphic rocks since it can be also used to constrain metamorphic conditions iλ its composition is combined with that oλ other major minerals such as pyroxene and amphibole [ , ]. Relatively to REE partition in metamorphic rocks μarnet, pyroxene, amphibole and zircon beinμ competitors λor REE partition, represent a useλull tool to outline continental crust evolution. In this paper we present the μeochronoloμical and chemistry data collected in the last ten years in Calabria and Peloritani sectors oλ Italy, utilizinμ the new analytical techniques, useλull to reconstruct the maμmatic and metamorphic history oλ a key sector oλ the South European Variscan ”elt in the peri-Mediterranean area. Metaiμneous and metasedimentary rocks oλ the Calabria-Peloritani Terrane Southern Italy represent a particularity in the South Mediterranean area beinμ connected to “lpine chain Norther Italy throuμh sedimentary “pennines Chain. They rapresent sectors oλ Variscan upper, intermediate and lower continental crust sutured by a thick layer oλ CarboniλerousPermian μranitoids overlapped on “lpine oceanic crust units. Only rocks λorminμ inter‐ mediate and deep crust levels oλ the continental crust were considered in this review. These rock types preserve memory oλ Precambrian to Permian μeoloμical events and in some cases up to Mesozoic times. The available μeochronoloμical data [ - ] toμheter with CL and VPSE imaμinμ and the REE-U-Th distribution in the zircon domains helped to depict the μeoloμical history throuμh the emplacement aμes oλ the protoliths oλ metaiμneous rocks, the contribution oλ the Neoproterozoic-Early Cambrian anatectic melts to produce the protoliths oλ Variscan metaiμneous rocks, the sedimentation aμes oλ the protoliths oλ the metasedimentary rocks the P-T-t path oλ the Variscan metamorphism. In the λollowinμ, an extensive and detailed description oλ utilized analytical techniques was presented toμether with the realized μeoloμical deductions relatively to Calabria-Pelorita‐ ni Terrane.

. Analytical techniques . . Sample preparation The U-Pb aμe data were obtained on zircons directly separated λrom samples or on polished thin rock sections. In the last case, in situ analyses allow to evaluate the micro-domains in which the zircon μrew or was resetted. Separated zircon crystals were selected λrom m and – m λractions extracted λrom about - kμ oλ each rock sample. Crushinμ, heavy liquids, a Carpco and a Frantz maμnetic separators have been used λor mineral separa‐ tion. The clearest, crack-and inclusion-λree zircon μrains were handpicked under binocular microscope and λinally mounted in epoxy resin Fiμ. . Only in the case oλ SIMS analyses, selected crystals were mounted toμether with chips oλ zircon standards Fiμ. , whereas λor L“-ICP-MS analyses external standards were used. Grains were

In si“” U-Pb Da“ing Combined wi“h SEM Imaging on Zircon An Analy“ical Bond for… h““p://dx.doi.org/10.5772/58540

Figure 1. Zircon crys“als separa“ed from a rock sample (a) and placed in a mo”n“ wi“h s“andard crys“als (b).

then polished to halλ their thickness to expose internal structures. In the case oλ selected zircons in thin section, they are chosen also λor their peculiar structural site. . . Zircon imaging “ll crystals were inspected under transmitted liμht and by SEM Scanninμ Electron Micro‐ scope in order to investiμate their morpholoμy and collect hiμh-resolution imaμes unravellinμ the internal microstructures. The λirst observations on zircon crystals were realized by ”SED ”ack-Scattered Electron Detector , in order to examine morpholoμic characters and the possible presence oλ inclusions oλ other minerals. The hiμh-resolution imaμes oλ internal zoninμ patterns oλ zircons were realized by CL Cathodoluminescence and by VPSE Variable Pressure Secondary Electrons detectors, the last used in hiμh vacuum conditions. Operatinμ conditions were an acceleratinμ voltaμe oλ kV with a beam current oλ n“ λor CL imaμes and n“ λor VPSE imaμes. The imaμes obtained by two diλλerent detectors CL and VPSE, Fiμ. are almost completely overlappinμ [ , ]. The most suitable location oλ the spots λor U-Pb analyses was then selected. Zircon μrains were also inspected aλter the isotopic and chemical analyses in order to deλine the precise spot location with respect to internal microstructures Fiμ. . . . In situ U-Pb data acquisition on zircon crystals U-Pb aμe data on zircons were perλormed by L“-ICP-MS, SIMS and SHRIMP techniques. Three techniques produce comparable results with equally accurate U-Pb zircon aμes [ , , ]. However, L“-ICP-MS technique is μenerally preλerred λor the μreater simplicity oλ use, the λaster data capture ca minutes per analysis versus ca minutes per SIMS and SHRIMP analysis see [ ] and because it allows a complete acquisition oλ trace element composition in selected zircon domains.

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Figure 2. The same zircon crys“al inves“iga“ed by Ca“hodol”minescence De“ec“or (CLD) and Variable Press”re Secon‐ dary Elec“rons De“ec“or (VPSED). Wi“h “he permission of Acq”afredda and Fiore (2005).

Figure 3. Images of “he same zircon crys“al ob“ained by BSE (a) and VPSE de“ec“ors (b). In (a) “he cra“ers lef“ by microp‐ robe are clearly visible.

. . . LA-ICP-MS Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry L“-ICP-MS U-Pb data on zircons , , , , , , were perλormed at the CNR-Istituto di Geoscienze e Georisorse Pavia, Italy usinμ a nm “rF excimer laser ablation microprobe Geo-Las Q-Microlas coupled to a maμnetic sector hiμh resolution-ICP-MS Element I λrom Thermo Finniμan .

In si“” U-Pb Da“ing Combined wi“h SEM Imaging on Zircon An Analy“ical Bond for… h““p://dx.doi.org/10.5772/58540

The analyses were carried out in sinμle spot mode and with a spot size oλ approximate‐ ly m. The laser was operated with Hz oλ λrequency and Jcm- oλ λluence. Sixty seconds oλ backμround siμnal and at least s oλ ablation siμnal were acquired. The siμnals oλ masses Hμ, Pb+Hμ , Pb, Pb, Pb, Th and U were acquired in maμnetic scan mode. U is calculated λrom U on the basis oλ the ratio U/ U= . . The and masses were collected in order to monitor the presence oλ common Pb in zircon. In particular, the siμnal oλ Hμ was acquired to correct the isobaric interλerence oλ Hμ on Pb [ ]. The relatively hiμh Hμ backμround, however, hampers the detection oλ low Pb siμnals and, as a consequence, also the calculation oλ small common Pb contribu‐ tion. Generally, the analysed zircons showed siμnals oλ mass elements, which were indistinμuishable λrom the backμround thus no common Pb correction was applied more analytical details in [ ] . “ll λractionation eλλects involvinμ Pb/U ratios e.μ. mass bias and laser induced λractionation were corrected by usinμ the external zircon standard , , Ma [ ] . The same spot size and inteμration intervals were considered on both standard and studied zircons. Durinμ each analytical run reλerence zircon Ma [ ] was analysed toμether with unknowns λor quality control. Data reduction was carried out throuμh the GLITTER soλtware packaμe [ ]. Time resolved siμnals were careλully inspected to detect perturbation oλ the siμnal related to cracks or mixed aμe domains that were avoided in the inteμration intervals. Within the same analytical run, the uncertainty associated to the reproducibility oλ the external standards was propaμated to each analysis see Horstwood et al. and aλter this procedure each aμe determination is considered as accurate within a quoted uncertainty. Correlation coeλλicients λor the Pb/ U and Pb/ U data point uncertainties are calculated simply as a ratio oλ the two uncertainties [ ]. L“-ICP-MS technique also permits a complete acquisition oλ trace element composition in speciλic zircon domains. In this case a dedicated conλiμuration oλ the machine couples a Nd Y“G laser workinμ at nm with a quadrupole ICP mass spectrometer type DRCe λrom Perkin Elmer. For trace element determination the laser was operated at a repetition rate oλ Hz, with pulse enerμy oλ about . mJ and an ablation spot oλ about m in size. N”S NISTand SiO were adopted as external and internal standard, respectively. Data reduction was carried out throuμh the GLITTER soλtware packaμe [ ]. Minimum detection limits at % conλidence level were < - ppm λor the most oλ the elements. Precision and accuracy were assessed on the ”CR- USGS reλerence μlass and are more than % relative. . . . SIMS Secondary Ion Mass Spectrometry SIMS data [ , ] were collected usinμ the Cameca IMSion microprobe CRPGCNRS, Nancy, France . Primary O – ion beam was accelerated at kV with an intensi‐ ty that ranμed between and n“ and λocused on a – m diameter area, providinμ

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a mean secondary ions yield oλ cps/n“/ppm. Each spot was analysed λor min, aλter a presputerrinμ oλ min. “n empirical relationship between UO+/U+ and Pb+/U+ was deλined λrom all the measurements perλormed on the standard parts oλ each sample mount in order to determine the relative sensitivity λactor λor Pb and U used λor samples [ ]. “lso in this case zircon , , Ma, [ ] is the reλerence standard. Correction λor common lead was made measurinμ the Pb amount. The common lead composition was calculated at Pb/ Pb measured aμes, usinμ Stacey and Kramers model [ ]. The Pb/ Pb ratios ranμe in most case λrom , to more than , , and thus the com‐ mon Pb composition chosen λor correction is not hiμhly critical. Further inλormation on instrumental conditions and data reduction procedures are λound in [ ]. Errors include the analytical statistical error, the error associated with the common lead correction and the systematic error associated with the U/Pb calibration procedure [ ]. “s reμards the ion microprobe analyses we used Pb/ U aμes λor all the data instead oλ Pb/ U aμes, which are more sensitive to common lead contribution, beinμ the Pb ion siμnal about ten times lower than the Pb ion siμnal [ ]. . . . SHRIMP Sensitive High Resolution Ion MicroProbe SHRIMP data were collected [ , ] usinμ procedures based on those described by [ ]. “ . n“, kV primary beam oλ O -ions was λocused to a probe oλ c. m diameter. Positive secondary ions were extracted λrom the sample at kV, and the atomic and molecular species oλ interest analysed at c. mass resolution usinμ a sinμle ETP electron multiplier and peak switchinμ. The Pb isotopic composition was measured directly, without correction λor the small mass dependent mass-λractionation c. . % per a.m.u. . Interelement λractionation was corrected usinμ the TEMOR“ II reλerence zircon, usinμ a Pb/U-UO/U power law calibration equation [ ]. The uncertainty in the Pb/U calibration was , %. Pb, U and Th concentrations were measured relative to SL reλerence zircon. Common Pb corrections were very small most< . ppm total Pb , so all were made assuminμ that the common Pb was all laboratory contamination oλ ”roken Hill μalena Pb composition Pb/ Pb= . , Pb/ Pb= . , Pb/ Pb= . [ ] . Corrections λor the plots and isotopic data table were made usinμ Pb. Corrections λor the calculation oλ mean Pb/ U aμes used Pb, assuminμ the analyses to be concordant. “μes were calculated usinμ the constants recommended by the IUGS Subcom‐ mission on Geochronoloμy [ ]. “ll collected data were traited by the soλtware packaμe Isoplot/Ex . [ ]. This soλtware was used λor the concordia test and the probability oλ concordance calculation, per‐ λormed λor each analytical spot λrom Pb/ U and Pb/ U ratios. The Isoplot/Ex . soλtware was also used to construct Concordia, possible discordia lines and probability density plots and to calculate the mean concordia aμes λor data clusters deλined on the basis oλ i statistical siμniλicance, ii the visual appearance on the Concordia plot, iii the peak distribution alonμ the probability density plot, and iv the correspondence with speciλic internal microstructures oλ zircon.

In si“” U-Pb Da“ing Combined wi“h SEM Imaging on Zircon An Analy“ical Bond for… h““p://dx.doi.org/10.5772/58540

. Geological setting of case study The Calabria-Peloritani Terrane CPT represents an exotic terrane λormed by a PreMesozoic basement consistinμ oλ diλλerent tectonic units aλλected by Variscan metamorphism and stacked durinμ the “lpine oroμenesis [ - ]. It carries the cristalline Massiλs oλ Calabria Sila, Serre and “spromonte and Peloritani Mountains in Sicily Fiμ. . In the λollowinμ, we describe the μeoloμical and petroloμical λeatures oλ the λour considered tectonic units representinμ portions oλ middle and lower continental crust. Many samples λrom the diλλerent rock types in each unit were considered with the aim to reconstruct and date the μeoloμical events recorded by zircon μrains. The mineraloμical composition oλ the all cited samples and their relative spectrum oλ U-Pb zircon aμes are reported in Table . Their exact localization is indicated in Fiμ. . Four tectonic units were considered alonμ the CPT λrom North to South Fiμ. The Mandatoriccio Complex outcroppinμ in Sila Massiλ represents intermediate continental crust and consists mainly oλ metapelites, meta-arenites, acidic metavolcanites and metabasites with rare intercalations oλ marbles and orthoμneisses crosscutted by abundant aplite and peμmatite veins [ - ]. Metasediments show a static porphyroblastic μrowth mainly oλ biotite, μarnet, andalusite, staurolite and muscovite [ - ]. Recently, clockwise P–T paths have been constrained λor siliciclastic metasediments oλ this complex. Peak-metamorphic conditions oλ ca. °C and . GPa are reported λor the lower structural levels oλ the Mandatoriccio Complex and they were reached at Ma U-Th-Pb aμes in monazite, [ ] durinμ Variscan post-oroμenic extension. The Castagna Unit outcroppinμ in the central part oλ Calabria, consists oλ paraμneisses, micaschists, auμen μneisses, Variscan μranitoids and minor amphibolites, quartzites, calcsilicate rocks and marbles [ , ]. It includes metamorphic rocks equilibrated under μreens‐ chist to amphibolite λacies conditions in Variscan times and reworked by “lpine tectonics [ , , ]. The Sila Unit occupies wide areas in Sila and Serre Massiλs. In the Serre the section oλ Variscan crust consists, λrom the bottom to the top oλ i - km thick lower crustal rocks, ii an about km-thick layer oλ μranitoids [ ] emplaced ~ Ma aμo U-Pb convention‐ al zircon data, [ , ] , and iii amphibolite to sub-μreenschist λacies metamorphic rocks oλ the upper crust. The μeochronoloμical λeatures oλ the lower portion recordinμ Variscan amphibolite-μranulite λacies metamorphism and representinμ a λraμment oλ deep crust were considered. This section includes λrom the bottom a λelsic and maλic μranulites with rare meta-peridotites and metapelites, b miμmatitic metapelites with interleaved metabasites, rare marbles and auμen μneisses. The metabasic rocks λrom the lower part oλ the section toμether with the auμen μneisses λrom the upper part oλ the section bear memory oλ preVariscan maμmatism Table . The Aspromonte-Peloritani Unit APU outcrops in Southern Calabria and Eastern Sicily Fiμ. it consists oλ auμen μneisses, micaschists, biotite paraμneisses with minor amphib‐

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olites and marbles. “ pre-Variscan oriμin oλ protoliths oλ auμen μneisses at Ma was suμμested by spot U-Pb zircon aμes [ , , ]. “ccordinμ to [ ] the timinμ oλ hiμhμrade metamorphism accompanied by partial meltinμ in paraμneisses, was sinchronous at Ma with the intrusion oλ protoliths oλ auμen μneisses. The metamorphic rocks are diλλusely intruded by late-Variscan peraluminous μranitoids [ - , ], sometimes aλλect‐ ed by “lpine metamorphism. P–T estimates λor the Variscan tectono-metamorphic evolution indicate T around – °C and P oλ about . – . GPa [ , ]. The evolution oλ the “PU provides crustal thickeninμ durinμ early-middle Variscan collisional staμes, λollowed by crustal thinninμ, μranitoid intrusion and unrooλinμ durinμ late-Variscan extensional staμes [ ]. The collected data in Southern Italy μive constraints about the complex maμmatic and metamorphic history oλ South European Variscan Chain in the peri-Mediterranean area. Maμmatic and metamorphic events are recorded in the considered rocks λrom Late-Neopro‐ terozoic-early Cambrian to Permian times. In the λollowinμ, the μeoloμical history is punctually depicted.

Figure 4. – Geological ske“ch map of CPT wi“h “he indica“ion of considered samples in fo”r differen“ s“r”c“”ral ”ni“s.

Kfs+Bt+Opx+Cpx+Qtz

Tur 37b Quartz-monzodiorite dike (Fornelli et al., 2011a) [7] Tur 76A mafic granulite (Muschitiello, 2012) [24]

Grt3 mafic granulite (Fornelli et al., 2014) [22]

Opx+Pl+Bt+Amph

Tur 46 metabasite interleaved with migmatitic metapelites (Fornelli et al., 2011a) [7]

Pl+Grt+Bt+Opx+Qtz+Kfs

Pl+Opx+Grt+Amph+Bt

Opx+Pl+Bt

Pl+Opx+Cpx+Amph

Qtz+Pl+Kfs+Grt+/-Bt

Qtz+Pl+Kfs+Sil+Bt+Grt+/-Crd

Tur 32 metabasite interleaved with felsic granulites (Fornelli et al., 2011a) [7]

Tur 49 meta-quartz-diorite (Fornelli et al., 2011a) [7]

GO 182 migmatitic metapelite (Micheletti et al., 2008) [17] Tur 17 felsic granulite (Micheletti et al., 2008) [17]

Pl+Amph+Opx+Cpx

MFS 3 metagabbro (Micheletti et al., 2008) [17] Tur 3 restitic metagreywacke (Micheletti et al., 2008) [17] Grt+Pl+Opx+Amph+Bt

Qtz+Kfs+Pl+Bt+/-Ms+/-Grt+/-Sil

MINERALOGICAL COMPOSITIONS

GO 100 augen gneiss (Micheletti et al., 2007) [16]

Sila Unit CALABRIA

609±29

744±20

595±12

2502±19, 2404±92, 1760±46, 752±6, 617±23, 575±4, 572±6, 571±4

INHERITED AGES

537±15, 505±11

593±14, 564±17

574±18

584±24, 506±21

552±9, 545±4, 539±7, 537±4

NEOPROTEROZOICCAMBRIAN MAGMATISM

466±15, 436±15

483±12, 464±12, 451±11, 418±14

457±13, 438±13

483±9

453±19

494±14, 462±7

345±4, 298±10, 295±9, 291±6, 285±17, 278±6 357±11, 334-300 (n=8)

380±11 347±3 (n=10) 319±3 (n=7) 296±4 (n=5) 370±6 (n=3) 340±7 (n=2) 321±3 (n=9) 300±3 (n=6) 279±8, 277±7 382±9 318±5 (n=2) 303±4 (n=4) 294±4 (n=3) 279±10 368±11, 367±9 323±5 (n=3)

377±5 282±5 (n=4) 325±9, 316±9,308±9, 297±4 (n=4), 275±8 395±9 280±2 (n=18) 329±14 286±4 (n=8)

ORDOVICIANDEVONIANSILURIAN LOWER PERMIAN AGES AGES

260±6, 252±8

249±4

257±7

263±8, 231±5

POST LOWER PERMIAN AGES

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MINERALOGICAL COMPOSITIONS Bt+Grt+And+St+Ms/-Crd+/-Sil

LL61b2 micaschist (Langone, 2008) [20]

Qtz+Kfs+Pl+Ms+/-Bt

Qtz+Pl+/-Ms+/-Kfs+/-Bt

Mandatoriccio Complex CALABRIA

GO 95 fine grained leucocratic gnei (Micheletti et al., 2011) [18] GO 82 mylonitic pegmatite (Micheletti et al., 2011) [18]

Qtz+Kfs+Pl+Bt+/-Ms

GO 35 augen gneiss (Micheletti et al., 2007) [16] GO 39 fine leucocratic leucocratic gneiss (Micheletti et al., 2011) [18] Qtz+Kfs+Pl+Ms+/-Bt

Qtz+Kfs+Pl+Bt+/-Ms

MINERALOGICAL COMPOSITIONS

GO 6 augen gneiss (Micheletti et al., 2007) [16]

Castagna Unit CALABRIA

2506±43 - 604±24 (n=30)

INHERITED AGES

801±19, 633±14

2069±52, 588±17, 566±16 858±17, 632±15, 631±16

2216±56, 748±6, 621±5, 585±5

INHERITED AGES

587±14- 511±13 (n=8)

485±13 – 428±10 (n=8)

NEOPROTEROZOIC- ORDOVICIANDEVONIANCAMBRIAN SILURIAN LOWER PERMIAN MAGMATISM AGES AGES

NEOPROTEROZOIC- ORDOVICIANDEVONIANCAMBRIAN SILURIAN LOWER PERMIAN MAGMATISM AGES AGES 562±5, 556±5, 548±5, 464±4 547±4,543±4, 542±5, 541±7, 515±10 556±16, 552±16, 544±16 533±11 (n=4) 473±14, 459±10, 302±12, 302±8, 413±9 296±9, 294±8, 287±9, 286±7, 285±7, 282±7, 281±7, 275±8, 275±7 (n=2), 274±8 547±3 (n=4), 521±12, 452±13, 437±10, 345±9 509±14, 504±12, 494±14 425±11 297±9, 291±8, 279±8, 278±7

POST LOWER PERMIAN AGES

268±8

259±4 (n=6)

265±6, 261±6, 259±11

POST LOWER PERMIAN AGES

118 Geochronology - Me“hods and Case S“”dies

Kfs+Qtz+Pl+Bt+/-Ms

MV-15 augen gneiss (Williams et al., 2012) [23] FIU-7 paragneiss (Williams et al., 2012) [23] GC-5 trondhjemite (Fiannacca et al., 2008) [23]

Table 1. U-Pb concordan“ da“a on zircon in “he s“”died rocks from CPT con“inen“al cr”s“ Qtz+Kfs+/-Bt+/-Ms+/-Chl

MINERALOGICAL COMPOSITIONS

2013±1, 1140±10

INHERITED AGES

2455±9 – 634±14 (n=12) 2672±9 – 611±6 (n=46) 2446±14, 626±18

NEOPROTEROZOICCAMBRIAN MAGMATISM

549±5 – 528±7 (n=10) 566±15 – 535±4 (n=10)

578±10 - 516±4 (n=11)

550±8 – 536±8 (n=7)

577±10, 568±10, 566±13, 550±16, 527±12 548±16, 531±15, 526±15, 522±15 566±14, 548±14, 517±15

NEOPROTEROZOICCAMBRIAN MAGMATISM

ORDOVICIANSILURIAN AGES

491±12

456±21

446±13

ORDOVICIANSILURIAN AGES

DEVONIANLOWER PERMIAN AGES

324±2, 314±4 (n=9) 309±2

300±4 (n=12)

391±10, 365±11, 324±13, 279±12

DEVONIANLOWER PERMIAN AGES

POST LOWER PERMIAN AGES

259±11, 258±11, 252±10, 247±10

POST LOWER PERMIAN AGES

[n]: see reference list Qtz: quartz; Pl: plagioclase; Kfs: K-feldspar, Grt: garnet, Bt: biotite, Ms: muscovite, Amph: amphibole, Crd: cordierite, Opx: orthopyroxene, Cpx: clinopyroxene, Sil: sillimanite, And: andalusite, St: staurolite Mean concordia ages are indicated in bold.

Ta-Pu1-2-3, Ta-Cs, Tao Felsic porphyroids and andesites (Trombetta et al., 2004) [15] ID-TIMS data

Lower Domain PELORITANI

Pl+Qtz+Kfs+Bt+Ms+/-Sil

Qtz+Bt+Pl+/-Grt+/-Sil

Qtz+Kfs+Pl+Bt+/-Ms+/-Sil

FIU-11 augen gneiss (Williams et al., 2012) [23]

PELORITANI

Pl+Qtz+Kfs+Bt+Ms+/-Sil

VSG-1 leucogranodiorite (Fiannacca et al., 2008) [19] 3242±13 - 607±5 (n=13)

2457±45, 2447±45, 2223±21, 2081±11, 997±22, 953±22 940±23, 769±19,759±21, 706±18 2358±16, 873±25, 654±18, 614±7

Hbl+Pl+/-Bt+/-Qtz

Qtz+Kfs+Pl+Bt+/-Ms

917±26, 614±10, 611±11, 597±10, 586±10 623±18, 617±17, 565±16

Qtz+Kfs+Pl+Bt+/-Ms

CALABRIA

ADR 5 augen gneiss (Micheletti et al., 2007) [16] ADR 18 augen gneiss (Micheletti et al., 2007) [16] AS53 amphybolite (Grande, 2009) [21]

INHERITED AGES

MINERALOGICAL COMPOSITIONS

Aspromonte-Peloritani Unit

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Geochronology - Me“hods and Case S“”dies

. . Geological reconstructions inferred from U-Pb spot data . . . Recognizable Gondwana pertinence Memory oλ the maμmatic Proterozoic events widely occurs in the rocks oλ the CalabriaPeloritani Terrane as inherited aμes preserved in detrital zircons or xenocrystic cores sur‐ rounded by younμer overμrowths Fiμ. .

Scale bar: 50 μm

Figure 5. CL images of zircons showing de“ri“ic charac“ers (a-b-c-d) and xenocrys“ic cores (e-f). No“e “he yo”nger over‐ grow“hs in e and f.

The zircon aμes revealed in the diλλerent rock-types oλ the described units are detailed in the λollowinμ • Metaμranitoids auμen μneisses belonμinμ to “spromonte-Peloritani, Castaμna and Sila Units havinμ Fortunian-Ediacaran protoliths Table preserve inherited zircon aμes coverinμ a time span oλ Ma and Ma [ , ]. In addition, they show SmNd model aμes ranμinμ λrom to Ma [ ] • Granulite λacies metabasic rocks oλ the Sila Unit record two Neoproterozoic inherited aμe ± Ma and ± Ma despite their maμmatic mantle oriμin in the NeoproterozoicCambrian times [ ] • Metasediments λrom the lower and upper crust oλ the Sila Unit preserve memory oλ old events at , , and Ma obtained as upper intercepts oλ U-Pb discordia lines isotopic dilution method in [ , ] . Furthermore they show Nd model aμes oλ Ma [ ] and Ma [ ]

In si“” U-Pb Da“ing Combined wi“h SEM Imaging on Zircon An Analy“ical Bond for… h““p://dx.doi.org/10.5772/58540

• “mphibole bearinμ-micaschists λrom Mandatoriccio Unit preserve xenocrystic cores old up to ± Ma [ ] • “mphibole bearinμ-μneisses λrom “spromonte-Peloritani Unit preserve inherited aμes λrom Ma to Ma [ ] • In Eastern Sicily ortho-and para-μneisses belonμinμ to “PU show clusters oλ Proterozoic aμes around Ma, Ma and Ma and some aμes at , and Ma were also obtained [ ]. Still in Eastern Sicily Lower domain Ordovician porphyroids preserve inherited aμes at Ma and Ma upper intercepts oλ U-Pb discordia lines ID-TIMS analyses in [ ] . Meta-andesites associated with these porphyroids contain older zircons dated at and Ma [ ]. The inherited zircon aμe patterns in Calabria rocks indicate Gondwana domain pertinence. In particular, the similarities in aμe and chemistry oλ the protoliths oλ Calabria auμen μneisses with the acidic maμmatites λrom “nti-“tlas Moroccan domain point to a source derived λrom a reworkinμ oλ the West “λrican Craton W“C [ ] showinμ similarities with other European Cadomian terranes [ - ]. In λact, analoμous inherited aμe patterns occur in other sectors oλ European Variscides [ ] Southern ”ritish Islands, “rmorica Massiλ and Massiλ Central in France, ”radant Massiλ ”elμium , Iberian Massiλ Spain and Portuμal and ”ohemian Massiλs Czech Republic . The distribution oλ these aμes suμμests Cadomian pertinence with West “λrican Craton aλλinity. “ccordinμ to [ ], the inherited zircon aμe patterns in the auμen μneisses and paraμneisses λrom “spromonte-Peloritani Unit in the Sicily bear evidence, on the whole, oλ East “λrican provenance owinμ to aμe cluster in the ranμe Ma reveled in this area. These authors evidence stronμ similarities between Sicily terranes and those oλ other areas in the Eastern Mediterranean reμion as Southern Israel, Jordan and “rabia and suμμest an East “λrican provenance as several pieces oλ basements in Mediterranean area, like Turkey, Greece, Sardinia and Cyclades [ ]. Considerinμ the whole set oλ inherited zircon aμes in Calabria and Sicily, we can suμμest that a both East and West “λrican provenance was eλλective in Southern Italy as happened in other Mediterranean areas where pre-Variscan basements, startinμ with Neoproterozoic, are considered as derived λrom both East and West Gondwanan cratonic sources [ , ]. The presence oλ detritic components havinμ West and East “λrican oriμin was reveled by inherited zircon aμes acquired with diλλerent techniques in many samples λrom diλλerent domains oλ Calabria and Sicily terrains, revealinμ the eλλectiveness oλ U-Pb zircon data. . . . Neoproterozoic-Cambrian bimodal magmatism In situ U-Pb datinμ perλormed in metaiμneous rocks on zircon crystals showinμ euhedral morλoloμy and a typical undisturbed oscillatory zoninμ [ ] Fiμ. has evidenced a wide‐ spread Neoproterozoic-Cambrian bimodal maμmatism in an older basement oλ CalabriaPeloritani Terrane. Evidences oλ basic and acidic maμmatism are diλλused in Calabria λrom Sila Massiλ up to Sicily Fiμ. in metabasic rocks, auμen μneisses, λine-μrained leucocratic μneisses and amphibolites Table , [ - , , , ] .

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Figure 6. Ca“hodol”minescence images of zircons in me“abasic rocks, a”gen gneisses, fine grained le”cocra“ic gneiss‐ es and amphyboli“ic gneisses showing charac“eris“ic oscilla“ory zoning in“erpre“ed as indica“ive of “heir magma“ic ori‐ gin. Scale bar: 50 μm

Zircons λrom samples oλ metaμabbro and λrom samples oλ metabasites interbedded with λelsic μranulites and miμmatitic metapelites oλ the lower crust oλ the Serre Massiλ belonμinμ to Sila Unit were dated [ , ]. In all samples domains dated Ma n= showinμ maμmatic oscillatory zoninμ and hiμh Th/U ratio . - . are present Fiμ. . These domains

In si“” U-Pb Da“ing Combined wi“h SEM Imaging on Zircon An Analy“ical Bond for… h““p://dx.doi.org/10.5772/58540

show λractionated REE patterns interpreted as λormed in absence oλ μarnet considered as Variscan metamorphic phase [ , ]. On this basis a maμmatic oriμin oλ the zircons indicatinμ the aμe oλ protoliths in the time ranμe Ma was suμμested [ , ]. So, a basic maμmatism in Calabria occurred in Neoproterozoic times in an older basement, as happened in many oλ the so-called Cadomian blocks widespread λrom Western “lps to Turkey [ ]. This basic maμmatism records tholeiitic and calc-alkaline aλλinities and, due to the association with a thick pile oλ metasediments, seems to be connected with a mature? maμmatic arc in oroμenic context [ ]. Zircon μrains λrom seven samples oλ biotitic auμen μneisses and two samples oλ λine-μrained leucocratic μneisses cominμ λrom the “spromonte-Peloritani samples , Sila sample and Castaμna samples Units in Calabria [ , ] and Eastern Sicily [ ] are considered. These μneisses are intimately associated with metasediments aλλected by Variscan metamorphism, but their zircon domains do not bear memory oλ this event, preservinμ only Pre-Cambrian/ Silurian aμes [ , , ]. Only one sample GO , Table preserves Devonian-Lower Permian aμes interpreted as resetted aμes due to thermal input oλ λluids relased by Late-Variscan plutonites [ ]. In the Calabria auμen and λine μrained leucocratic μneisses, the majority oλ the concordant aμes λorms a statistically siμniλicant cluster averaμinμ at Ma n= aμes λrom to Ma mainly related to euhedral crystals without discontinuity between core and rim havinμ U contents ranμinμ λrom to ppm and Th/U ratios mostly comprised between . and . one domain analysed λor REEs produces a hiμhly λractionated pattern and a distinct neμative Eu anomaly [ ] interpreted as primary maμmatic characters accordinμ to [ ] or as recrys‐ tallized domains with memory oλ primary maμmatic zircons [ ]. The moderate variability and the hiμh values oλ Th/U ratios seem to be more compatible with precipitation λrom a hybrid maμma precursor oλ the auμen μneisses [ ] havinμ mantle and crustal oriμin. Discordia lines with lower intercepts comprised between Ma and Ma have been also calculated considerinμ the discordant data [ ]. The auμen μneisses λrom Peloritani Mountains contain zircon μrains μivinμ aμes around Ma includinμ two kinds oλ zircon domains havinμ U contents oλ ppm Th/U= . - . and ppm Th/U= . - . interpreted as suμμestive oλ maμmatic and detritic oriμin, respectively [ ]. On this basis [ ] suμμest that the protoliths oλ auμen μneisses were the hostinμ metasediments in which similar aμes were detected. This acidic maμmatic activity dated around Ma seems to be diλλused in the CalabriaPeloritani basement successively than basic maμmatism described above. Chemistry oλ the auμen μneiss indicates that their protoliths derived λrom shoshonitic to hiμhK calc-alkaline μranitoids related to a post-collisional staμe [ , ], probably at the transition λrom compressional to extensional tectonics or even aλter the tectonic collapse oλ an intracon‐ tinental oroμen [ ]. The emplacement aμe obtained λrom the protoliths oλ all μranitic μneisses in CPT and their μeochemical aλλinity share similarities with the μranitoids widespread at the Northern edμe oλ the West “λrican Craton, especially in Morocco [ - ], “lμerian Tuareμ Shield [ ] and Mauritania [ ]. In λact, voluminous hiμh-K calc-alkaline plutonism charac‐

123

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Geochronology - Me“hods and Case S“”dies

Figure 7. CL and VPSE images of selec“ed zircons showing Ordovician-Sil”rian ages in fine grained le”cocra“ic gneisses (a), me“agabbros (b, c) and res“i“ic me“agreywake (d). Scale bar: 50 μm.

terize the λinal staμes oλ Panaλrican oroμeny in Northern marμin oλ the West “λrican Craton as well as in almost all the Cadomian Units alonμ the present “lpine-Mediterranean mountain belts [ , ]. In the period – Ma, acidic maμmatism was diλλused at the transition λrom an active compressive-transtensive to a passive extensional continental marμin with extension and development oλ λoreland basins [ ]. It is noteworthy that acidic and basic maμmatism oλ Neoproterozoic-Lower Cambrian times, in Calabria-Peloritani Terrane, is diachronous beinμ maλic maμmatic activity - Ma older than the acidic one [ - , ] both maμmatic activity monitored the tectonic evolution oλ Panaλrican oroμen λrom compressional to collapse staμes [ ]. . . . Ordovician–Silurian tectono-thermal activity Ordovician-Silurian aμes data ranμinμ λrom ± to ± Ma have been recorded in auμen μneisses, λine-μrained leucocratic μneisses and μranulite-λacies metabasites λrom Calabria Table [ - , , ]. In these rock-types the Ordovician-Silurian aμes represent clusters connected to a recrystallization event beinμ the protoliths Neoproterozoic-Cambrian in oriμin. These aμes were measured on cores displayinμ irreμular and patchy microstructures some‐ times stronμly luminescent Fiμ. a-b or on overμrowths surroundinμ older cores Fiμ. c-d . Owinμ to the textural λeatures oλ zircons, the Ordovician-Silurian aμes seem related to a tectonothermal event as an eλλect oλ recrystallization see [ , ] producinμ an isotope resettinμ at that time. One sample oλ auμen μneiss sample GO , Table λrom Sila Unit interleaved with the miμmatitic metapelites shows two Ordovician aμes at ± Ma and ± Ma as a Rb-Sr isochron at ± Ma determined in miμmatitic metapelites [ ]. In addition Ordovician– Silurian detritic population oλ zircon occurs in the Mandatoriccio micaschists in Mandatoriccio Complex sample LL b , Table . In Peloritani Mountains an intermediate-acidic maμma‐ tism in Ordovician times was revealed by [ ] analysinμ zircons with maμmatic textures λrom porphyroids and meta-andesites dated at ca. – Ma. “ look at the European Variscan Chains in which Ordovician-Silurian aμes have been detected reveals that λrom Iberian Massiλs to Carpathians several acidic and maλic products are related to a diλλusely Ordovician maμmatic activity [ ]. “ccordinμ to [ , , ] riλtinμ phases in the Early and Middle Palaeozoic prepared the openinμ oλ basins separatinμ the λuture Variscan

In si“” U-Pb Da“ing Combined wi“h SEM Imaging on Zircon An Analy“ical Bond for… h““p://dx.doi.org/10.5772/58540

basement λrom Gondwana. Iλ a tectono-metamorphic phase was responsible oλ maμmatic activity in Ordovician-Silurian times recorded in Variscan λraμments oλ European Chain, then also the U-Pb zircon aμes determined in Calabria-Peloritani rocks can be reλerred to the same phase. Nevertheless, it cannot be excluded that these aμes miμht result λrom rejuvenation due to the openinμ oλ U–Pb radioμenic system with partial loss oλ Pb durinμ the Variscan meta‐ morphism [ , ]. “lternatively, accordinμ to the model proposed by [ ], these aμes can be related to an Eo-Variscan activity started in Silurian-Ordovician times. . . . Variscan orogenesis Devonian-Lower Permian times The investiμated basement λorminμ continental crust units oλ Calabria and Sicily was aλλected by Variscan metamorphism and maμmatism [ , ] as shown by Rb-Sr and Sm-Nd isotopic μeocronoloμy [ , ]. U-Pb zircon aμe data can be utilized to evidence these μeoloμical processes realized under hiμh temperature conditions in λact zircon has very hiμh closure temperature λor U-Th-Pb isotopic system > °C in [ - ] then only hiμh-T metamorphic and maμmatic conditions can be monitored throuμh U-Pb zircon data. Zircons oλ amphibolitic λacies paraμneisses and micaschists λrom Mandatoriccio Complex in Calabria [ ] and λrom “spromonte-Peloritani Unit in Sicily [ ], respectively, do not evidence Variscan aμes owinμ to their low temperature metamorphic conditions around °C [ , ] . Zircon is uneλλicient in these rock types to record μeoloμical events under low temperature conditions. This λact is conλirmed in the auμen μneisses λrom Castaμna and “spromonte-Peloritani Units low-medium μrade Variscan metamorphism where aμes younμer than ~ Ma in Calabria [ ] and ~ Ma in the Sicily [ ] were not detected. Maλic and λelsic μranulites toμether with miμmatitic metapelites λrom Sila Unit in Calabria show many U-Pb zircon aμes ranμinμ λrom ~ Ma to ~ Ma [ , ] testiλinμ the stronμ eλλiciency oλ hiμh μrade metamorphism in Variscan times that, in part, masks the oriμinal Neoproterozoic-Cambrian aμes. Zircons λrom these rock types record domains with oscillatory zoninμ μenerated by dissolu‐ tion/re-precipitation or crystallization in presence oλ melts [ , ] toμether with lobate structurless μrey or luminescent rims invadinμ older cores metamorphic re-crystallization in [ ] Fiμ. . The evaluation oλ zircon textural λeatures on which spot aμes were determined constrains step by step the Variscan metamorphic trajectory oλ the lower crust oλ the Sila Unit. Distinct U-Pb zircon aμe clusters were determined Table i a λew aμes λrom Ma to Ma ii data points around Ma iii zircon aμes clusterinμ at Ma iv aμes around Ma v several aμes in the ranμe Ma. Considerinμ the P-T evolution oλ the lower crust oλ the Sila Unit representinμ a λraμment oλ Variscan continental crust, the revealed cluster aμes were interpreted in the λollowinμ [ ] a.

The aμes λrom Ma to Ma indicate phases oλ crustal thickeninμ durinμ the proμrade metamorphism λrom amphibolite to μranulite λacies

b.

The cluster at Ma represents the metamorphic peak at T= °C and P= . GPa under μranulite λacies conditions in the lower part oλ the continental crust section

125

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c.

The aμe peaks at , and Ma Table Fiμ. date the decompression phases. In particular, the cluster at Ma in the μranulites coincide with the aμe oλ basic Variscan maμmatism determined on zircons oλ a quartz-monzodioritic dike dated at Ma sample Tur b, Table , Fiμ. a . The λirst decompression staμe was accompanied by partial meltinμ in the hosted rocks as shown by zircon domains with oscillatory zoninμ crystallized by partial melt Fiμ. . The aμe peak at about Ma dates a λurther decom‐ pression phase and probably the end oλ anatexis in the μranulites as testiλied by successive homoμeneous and luminescente rims oλ zircons with aμes around Ma in which the Variscan cycle stoped [ ].

Figure 8. VPSED images of selec“ed Variscan zircons. See “he oscilla“ory zoning domains s”rro”nded or invaded by loba“e s“r”c“”rless grey or l”minescen“ rims. Scale bar: 50 μm.

Durinμ the crustal thinninμ and decompression, emplacement oλ huμe Late-Variscan calcalkaline μranitoids occurred between the upper and lower crustal portions oλ the Sila Unit Fiμ. at about Ma aμo as showed by Rb-Sr isotopic aμes [ ] and U-Pb zircon aμes in μranodorities and tonalities oλ the Serre batholite [ ], in the Castaμna Unit as showed by U-Pb datinμ oλ zircons in a peμmatitic dike sample GO , Table , Fiμ. b and in CPU as showed by U-Pb zircon aμes λrom peraluminous maμmatites [ ] Table . The μeoloμical evolution oλ the continental crust in Calabria was detailed utilizinμ the precious textures oλ zircons and the U-Pb zircon data the reconstructed scenario is conλirmed by the comparison with similar metamorphic evolution oλ other lower crust λraμments λrom the South European Variscides croppinμ out in the West Mediterranean areas [ ].

In si“” U-Pb Da“ing Combined wi“h SEM Imaging on Zircon An Analy“ical Bond for… h““p://dx.doi.org/10.5772/58540

Figure 9. Magma“ic zoning (VPSE images) in Variscan magma“i“es. Scale bar: 50 μm.

“ limitation oλ the U-Pb spot analyses on zircon is the spot size in λact the auμen μneisses interleaved with the miμmatitic metasediments oλ the lower crust oλ the Serre Calabria show a thin recrystallized rim clearly shown by the cathodoluminescent imaμes but undatable λor the small size. Speculatively, these thin rims have been interpreted as λormed durinμ the Variscan metamorphism by [ ], but their precise aμes are not known. . . . Post lower Permian events Few and scattered zircon aμes comprised between ± Ma and ± Ma [ ] Table , Fiμ. were measured in the μranulites oλ the Sila Unit and in metamorphites and maμmatites oλ the Castaμna Unit. These aμes have been interpreted as eλλect oλ a recrystallization event assisted by λluids [ , , ]. “ comparison with Variscan basements λrom Corsica [ ] and Western “lps as the Ivrea zone [ , ] show similar cluster aμes interpreted as precursor siμnals oλ the openinμ oλ the Tethys Ocean. “n analoμous interpretation can be adopted λor the Calabria rock types associated to domains λormed durinμ the openinμ oλ Tethys Ocean. However, it can not be excluded that these aμes in Calabria miμht be connected to openinμ oλ U-Pb isotopic system oλ zircon due to “lpine tectonism [ ], in λact the studied rocks belonμ to tectonic units stacked durinμ the construction oλ “lpine chain and are aλλected by “lpine shear zones [ , ].

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Geochronology - Me“hods and Case S“”dies

Scale bar: 50μm Figure 10. VPSED images of selec“ed zircons showing pos“ Lower-Permian ages.

. Conclusions The reconstruction oλ the pressure-temperature-time P-T-t evolution oλ crustal sections is λundamental to understandinμ many tectonic processes. This task, particulary diλλicult in the case oλ polymetamorphic rocks, requires the combination oλ metamorphic petroloμy and μeochronoloμy oλ diλλerent mineral phases that potentially can record more than one μeoloμical event. Zircon has been larμely used λor this role in hiμh-μrade terrains because its U-Pb system is able to retain the memory oλ polyphase evolution even at relatively hiμh temperatures λor its hiμhly reλractory nature, hiμh closure temperature and slow Pb diλλusion rate. Zircon is an ideal mineral λor U–Pb datinμ oλ poly-metamorphic rocks [ , , , ]. In addition, the precise and accurate datinμ oλ the retroμrade metamorphism is crucial λor understandinμ the exhumation history oλ the ancient metamorphic basements. Obviously, spot U-Pb zircon data in maμmatites λormed under hiμh temperature conditions, constrains the timinμ oλ maμma emplacement and brinμ liμht on the μeoloμical context in which the maμmatism explicated. The case study presented in this paper shows as in situ zircon datinμ linked with determined P-T conditions could constrain the evolution oλ the Calabria-Peloritani Terrane, a crucial λraμment oλ Southern European Variscan ”elt. In the last ten years the advances in analytical capabilities have permitted in-situ investiμation oλ complex zircon μrains that allow us to reconstruct the μeoloμical history λrom Neoprotero‐ zoic-Cambrian to post Permian times in Southern Italy. In Fiμ. a histoμram and a probability density curve oλ the U-Pb spot zircon aμes collected in CPT are reported showinμ the larμe number oλ determinations in a wide time interval λrom “rchean to Triassic aμes. The collected data are interpreted as suμμestive oλ Neoproterozoic detrital input λrom cratonic areas oλ Gondwana testiλied by inherited zircons diachronic bimodal basic and acidic maμmatism between and Ma, relative to an active tectonic marμin settinμ riλtinμ and openinμ oλ Ordovician-Silurian basins siμned by consistent cluster aμes around Ma correspondinμ to acidic and intermediate volcanic activity porphyroids and metaandesites in Peloritani Mountains Variscan μranulite λacies metamorphism and pervasive partial meltinμ in deep crustal rocks oλ the Sila Unit precursor siμnals oλ the Tethys evolution showed by post Permian zircon domains.

In si“” U-Pb Da“ing Combined wi“h SEM Imaging on Zircon An Analy“ical Bond for… h““p://dx.doi.org/10.5772/58540

Figure 11. His“ogram and probabili“y densi“y c”rve for U-Pb concordan“ da“a on zircon (n=491) from CPT (Tab.1). Ref‐ erences: [7, 15-24].

Author details “nnamaria Fornelli*, Giuseppe Piccarreta and Francesca Micheletti *“ddress all correspondence to annamaria.λ[email protected] Dip. di Scienze della Terra e Geoambientali, Università deμli Studi di ”ari “ldo Moro, Italy

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] “nμì G, Cirrincione R, Fazio E, Fiannacca P, Ortolano G, Pezzino “. Metamorphic evolution oλ preserved Variscan upper crust in the “lpine Calabria-Peloritani Oro‐ μen southern Italy structural and petroloμical constraints λrom the Serre Massiλ metapelites. Lithos , .

[

] Geisler T, Schalteμμer U, Tomaschek F. Re-equilibration oλ zircon in aqueous λluids and melts. Elements , – .

[

] Fornelli “, Pascazio “, Piccarreta G. Diachronic and diλλerent metamorphic evolution in the λossil Variscan lower crust oλ Calabria. International Journal oλ Earth Sciences b , .

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[

] Caμμianelli “ and Prosser G. Modellinμ the thermal perturbation oλ the continental crust aλter intraplatinμ oλ thick μranitoid sheets a comparison with the crustal sec‐ tions in Calabria Italy . Geoloμical Maμazine , .

[

] Handy MR and Zinμμ “. The tectonic and rheoloμical evolution oλ an attenuated cross section oλ the continental crust Ivrea crustal section, southern “lps, northwest‐ ern Italy and southern Switzerland. Geoloμical Society oλ “merica ”ulletin , – .

[

] Gardien V, Lardeaux JM, Ledru P, “llemand P, Guillot S. Metamorphism durinμ late oroμenic extension insiμhts λrom the French Variscan belt. ”ulletin Société Géoloμi‐ que France , – .

[

] Lardeaux J, Ledru P, Daniel I, Duchene S. The Variscan French Massiλ Central-a new addition to the ultra-hiμh pressure metamorphic club’ exhumation processes and μeodynamic consequences. Tectonophysics , – .

[

] Rossi P, Cocheri “, Fanninμ CM, Deloule E. Variscan to eo-“lpine events recorded in European lower-crust zircons sampled λrom the French Massiλ Central and Corsica, France. Lithos , – .

[

] Giacomini F, ”omparola RM, Grezzo C, Guldbransen H. The μeodynamic evolution oλ the Southern European Variscides constraints λrom the U/Pb μeochronoloμy and μeochemistry oλ the Palaeozoic maμmatic-sedimentary sequences oλ Sardinia Italy . Contribution to Mineraloμy and Petroloμy , – .

[

] Lu M, Hoλmann “W, Mazzucchelli M, Rivalenti G. The maλicultramaλic complex near Finero Ivrea-Verbano Zone . II. Geochronoloμy and isotope μeochemistry. Chemical Geoloμy , – .

[

] Peressini G, Quick JE, Siniμoi S, Hoλmann “W, Fanninμ M. Duration oλ a larμe maλic intrusion and heat transλer in the lower crust a SHRIMP U-Pb zircon study in the Ivrea-Verbano Zone Western “lps, Italy . Journal oλ Petroloμy , – .

[

] Schalteμμer U and Gebauer D. Pre-“lpine μeochronoloμy oλ the Central, Western and Southern “lps. Schweiz Mineral Petroμr Mitteilunμen , – .

[

] Katayama I, Maruyama S, Parkinson CD, Terada K, Sano Y. Ion micro-probe U–Pb zircon μeochronoloμy oλ peak and retroμrade staμes oλ ultrahiμh-pressure metamor‐ phic rocks λrom the Kokchetav massiλ, northern Kazakhstan. Earth and Planetary Sci‐ ence Letters - , – .

[

] Hermann J, Rubatto D, Korsakov “, Shatsky VS. Multiple zircon μrowth durinμ λast exhumation oλ diamondiλerous, deeply subducted continental crust Kokchetav Mas‐ siλ, Kazakhstan . Contributions to Mineraloμy and Petroloμy , - .

[

] Moller “, O’”rien PJ, Kennedy “, Kroner “. Polyphase zircon in ultrahiμh-tempera‐ ture μranulites Roμaland, SW Norway constraints λor Pb diλλusion in zircon. Jour‐ nal oλ Metamorphic Geoloμy , – .

In si“” U-Pb Da“ing Combined wi“h SEM Imaging on Zircon An Analy“ical Bond for… h““p://dx.doi.org/10.5772/58540

[

] Wu Y and Zhenμ Y. Genesis oλ zircon and its constraints on interpretation oλ U-Pb aμe. Chinese Science ”ulletin , .

[

] Liati “. Identiλication oλ repeated “lpine ultra hiμh-pressure metamorphic events by U–Pb SHRIMP μeochronoloμy and REE μeochemistry oλ zircon the Rhodope zone oλ Northern Greece. Contributions to Mineraloμy and Petroloμy , .

[

] Liu Y, Gao S, Hu Z, Gao C, Zonμ K, Wanμ D. Continental and oceanic crust recy‐ clinμ-induced melt–peridotite interactions in the Trans-North China Oroμen U–Pb datinμ, Hλ isotopes and trace elements in zircons λrom mantle xenoliths. Journal oλ Petroloμy - , .

[

] McClelland WC, Power SE, Gilotti J“, Mazdab FK, Wopenka ”. U-Pb SHRIMP μeo‐ chronoloμy and trace-element μeochemistry oλ coesite-bearinμ zircons, North-East Greenland Caledonides. Geoloμical Society oλ “merica, Special Paper , Ultrahiμhpressure Metamorphism Deep Continental Subduction, .

[

] Mcclelland WC, Gilotti J“, Mazdab FK, Wooden JL. Trace-element record in zircons durinμ exhumation λrom UHP conditions, North-East Greenland Caledonides. Euro‐ pean Journal oλ Mineraloμy , .

[

] Chen RX, Zhenμ YF, Xie L. Metamorphic μrowth and recrystallization oλ zircon dis‐ tinction by simultaneous in situ analyses oλ trace elements, U–Th–Pb and Lu–Hλ iso‐ topes in zircons λrom ecloμite-λacies rocks in the Sulu oroμen. Lithos , – .

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Chapter 6

Layered Pge Paleoproterozoic (LIP) Intrusions in the N-E Part of the Fennoscandian Shield Isotope Nd-Sr and 3 He/4He Data, Summarizing U-Pb Ages (on Baddeleyite and Zircon), Sm-Nd Data (on Rock-Forming and Sulphide Minerals), Duration and Mineralization T. Bayanova, F. Mi“rofanov, P. Serov, L. Nerovich, N. Yekimova, E. Ni“kina and I. Kamensky Addi“ional informa“ion is available a“ “he end of “he chap“er h““p://dx.doi.org/10.5772/58835

. Introduction There are about Palaeoproterozoic layered maλic-ultramaλic bodies in Finland, most oλ which occur in a rouμhly east–west-trendinμ, kmlonμ belt known as the TornioNa.ra.nka.vaara ”elt “lapieti et al. Voμel et al. Iljina & Hanski . The belt Fiμ. extends λor a λew kilometres into Sweden Tornio intrusion , and λor several tens oλ kilometres into the Russian Karelia Olanμa complex . Toμether the intrusions make up the Southern, or Fenno-Karelian ”elt, FK” Mitroλanov et al. . In the NE oλ the province, the Northern, or Kola ”elt K” strikes northwestwards λor about km Fiμ. . It includes more than ten isolated layered maλic-ultramaλic bodies that are mostly ore-bearinμ Mitroλanov et al. . The central part oλ the Kola ”elt has been suμμested to be part oλ a triple junction typical oλ intraplate riλtinμ Pirajno and is occupied by the Moncheμorsk Layered Complex with a λairly complete ranμe oλ ore types Cr, Cu, Ni, Co, Ti, V, Pt, Pd, Rh . The western and eastern arms oλ the triple junction are composed oλ larμe anorthosite-troctolite Main Ridμe, Pyrshin, Kolvitsa intrusions Fiμ. . The most typical PGEbearinμ layered pyroxenite-norite-μabbroanorthosite intrusions oλ the Kola ”elt e.μ. Mt Generalskaya, Moncheμorsk Layered Complex, Fedorovo-Pansky are conλined to boundaries between early Proterozoic riλts which were in-λilled with volcano-sedimentary rocks overlyinμ the “rchaean basement Schissel et al. Mitroλanov et al. . In these cases, similar to

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Geochronology - Me“hods and Case S“”dies

those in Finland, the intrusive rocks underwent relatively low-μrade local metamorphism and preserve cumulus and intracumulus minerals.

Figure 1. Generalized geological map of “he nor“heas“ern par“ of “he Bal“ic Shield and “he loca“ion of Paleopro“erozo‐ ic mafic layered in“r”sions (Mi“rofanov e“ al., 2005).

Convincinμ arμuments in support oλ the mantle plume hypothesis, either as shallow plumes’ λrom c. km or deep plumes’ λrom the core – mantle boundary have been put λorward λor relatively younμ well-preserved Palaeozoic and recent larμe iμneous provinces LIPs Coλλin & Eldhom Heaman Ernst & ”uchan French et al. . Voluminous maμmatism is considered to be related to mantle plumes that occurred throuμhout the Precambrian Condie Pirajno . The best records oλ a plume source are Cu, PGE, Ti,

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

V and Fe. “ll the above-mentioned rock types, metals, host riλt-associated volcanic rocks and maλic dykes are λound in the relatively recently described East Scandinavian Palaeoproterozoic Larμe Iμneous Province LIP Iljina & Hanski with a total area oλ more than km Fiμ. . In Finland, these μeoloμical complexes have been widely studied “lapieti et al. Huhma et al. Voμel et al. Hanski et al. and the data were su marized by Iljina & Hanski . Only a λew publications on similar Russian complexes oλ the ”altic Shield have been written or translated into Enμlish Papunen & Gorbunov et al. ”alashov et al. ”ayanova & ”alashov ”ayanova “melin et al. Sharkov et al. Mitroλanov et al. Mitroλanov & ”ayanova Chashchin et al. Schissel et al. Mitroλanov et al. , . This chapter presents a brieλ μeoloμical description oλ the Russian maλic-ultramaλic intrusions oλ the ”altic Shield and associated mineralization. It λocuses on new U–Pb TIMS and Sm–Nd μeochronoloμical data which constrain timinμ oλ maμmatic pulses and the duration oλ the emplacement oλ Cr, Cu, Ni, Ti and PGE-bearinμ layered intrusions oλ the Kola ”elt. Nd, Sr and He-isotope data help deλine μeodynamic models λor a lonμ-lived early Precambrian mantle source expressed either in a larμe mantle diapir or multiple plume processes λor one oλ the earliest clearly identiλiable old intraplate LIPs and its metalloμeny.

. The Monchepluton, intrusions of the main ridge Monchetundra and Chunatundra and adjacent intrusions — Monchegorsk layered complex The Moncheμorsk Layered Complex Fiμ. has lonμ been the subject oλ detailed investiμation due to the exploitation oλ rich Cu–Ni ores oλ the Monchepluton Papunen & Gorbunov Chashshin et al. Smolkin et al. . The complex is located at a triple junction Fiμ. where weakly metamorphosed early Proterozoic riλt-related rocks and deep-seated “rchaean rocks metamorphosed at μranulite to amphibo ite λacies become contiμuous at the modem erosion level. The Monchepluton is an S-shaped body with an area oλ c. km . It consists oλ two parts which probably represent independent maμma chambers. The northwestern and central parts oλ the Monchepluton NKT Mts Nittis, Kumuzhya and Travyanaya and Mt Sopcha are mainly composed oλ non-metamorphosed ultramaλic rocks, which λrom bottom-up are represented by a – mthick basal zone oλ quartz-bearinμ norite and μabbronorite, arzburμite – m , alternatinμ harzburμite and orthopyroxenite – m , orthopyroxenite – m with chromitite lenses Mt Kumuzhya and – m-thick Cu–Nibearinμ dunite-harzburμite layers Mt Sopcha, horizon’ . The total thickness oλ the NKT intrusion expands southwards λrom – m and culminates at Mt Sopcha m. The southeastern part oλ the Monchepluton NPV Mts Nyud, Poaz and Vurechuaivench consists mainly oλ – m-thick maλic rocks basal quartz-bearinμ μabbronorite and norite up to m , melanocratic norite with lenses oλ olivinebearinμ harzburμite and norite, orebearinμ critical horizon’ with xenoliths, olivine-λree mesocratic and leucocratic norite and μabbronorite, μabbronorite, leucoμabbro, anorthosite with PGE mineralization Mt Vure‐ chuaivench .

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”oth parts oλ the Monchepluton NKT and NPV chambers have a trouμh-like shape with a nearhorizontal λloor and λlanks dippinμ southwestwards at an anμle oλ – °. The complex is underlain by the “rchaean μneiss and miμmatite, and overlain by the Sumi rocks oλ the Imandra-Varzuμa riλt near Mt Vurechuaivench . The intrusive rocks oλ the Monchepluton are cut by veins oλ basic to intermediate peμmatites and diorite, and by dolerite and lamprophyre dykes.

Figure 2. Geological map of “he Monchegorsk layered complex (Smolkin e“ al. 2004).

The synμenetic disseminated Cu–Ni ore occurs in layers and is usually spatially conλined to the layers oλ olivine-bearinμ rocks. The ore location is controlled by the primary structural elements oλ the intrusions. It also may be λound in the upper and basal parts oλ the intrusions. The mineralization is related to the coarse-μrained peμmatoid rocks. Occurrences oλ synμenetic and nest-disseminated ore with bedded, lens-shaped and stock-like λorms are locally conλined

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

to the parts oλ the intrusions where λine-μrained and irreμular-μrained rocks, peμmatoids and rocks related to the intrusion critical horizon’ are widely developed. The distribution oλ the two last-mentioned rock varieties may in some cases serve to reveal ore-controllinμ zones. Exploitable Cu–Ni–PGE deposits oλ veined epiμenetic ores in the Monchepluton are conλined to the systems oλ steeply dippinμ shear λractures trendinμ NNE and dippinμ SSE, which trace the primary structural elements oλ the intrusion μeometry oλ intrusive blocks, primary jointinμ, etc. . The main ore-controllinμ elements in the occurrences oλ epiμenetic strinμerdisseminated ores are the zones oλ tectonic dislocations marked by schistose and blastomylo‐ nitized rocks. Most λavourable λor the concentration oλ injected strinμer-disseminated ores are the places where the tectonic zones pass alonμ the bend oλ the contact between rocks sharply diλλerent in physico-mechanical properties, λor example between ultramaλic rocks and “rchaean μranite-μneiss. The epiμenetic sulphide Ni– Cu ores oλ the complex tend to occur in bodies with a mainly NE strike and SW plunμe. The rocks oλ the Monchepluton were dated earlier by U–Pb methods on zircons and badde‐ leyite at the Geoloμical Institute KSC R“S ”ayanova and at the Royal Ontario Museum laboratory in Canada “melin et al. with a μood converμence oλ results see below . These aμes λall in the ranμe oλ – Ma and λavour the correlation oλ the Monchepluton maλicultramaλic layered series with the maλic layered series oλ the second intrusive phase oλ the Fedorovo-Pansky massiλ. In both intrusions, the main phase melts have produced Cu–Ni–PGE economic mineralization where base metals predominate, but the portion oλ platinum in the PGE disseminated occurrences is at least %. The ore bodies within the ultramaλic rocks oλ the Monchepluton Papunen & Gorbunov et al. are considerably richer than those oλ the Fedorov block deposit Schissel et al. . However, the deposits oλ the Moncheμorsk reμion have already been mined out, while the Fedorovo-Pansky Complex is now beinμ careλully investiμated λor λuture development. Extensive areas oλ the Moncheμorsk ore reμion are occupied by amphibolite-λacies hiμhpressure μarnet-bearinμ μabbronorite-anorthosite and anorthosite with numerous conλorma‐ ble and cuttinμ veins oλ leucoμabbro and peμmatoid rocks. These are the intrusions oλ the Main Ridμe and Lapland-Kolvitsa μranulite belts Pyrchin, etc. located within stronμly metamor‐ phosed country rocks. The rocks oλ the intrusions are insuλλiciently studied by modern μeoloμical and petroloμical methods, but have been investiμated by mininμ companies because oλ the presence oλ hiμh PGE and V–Ti concentrations. The Monchetundra intrusion is separated λrom the Monche‐ pluton by a thick a λew hundreds oλ metres blastomylonite zone with a μarnet-amphibole mineral association Smolkin et al. . Reμional shear zones cut and transλorm the primary monolith-like shape oλ the intrusion composed oλ rouμhly layered leucocratic maλic rocks. This results in the lens-like morpholoμy oλ the intrusions. “vailable U–Pb isotope aμes oλ these anorthosites λall in a wide time interval Mitroλanov & Nerovich ”ayanova . The zircons derived λrom maμmatic plaμioclase yield an aμe varyinμ λrom – Ma λor diλλerent intrusions. “ λew μenerations oλ metamorphic zircons yield an aμe oλ multistaμe metamorphism that took place , and Ma Mitroλanov & Nerovich .

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Geochronology - Me“hods and Case S“”dies

. Monchegorsk layered complex, isotope data Ten samples oλ – kμ were collected λor U–Pb datinμ. “ccessory baddeleyite and zircon were better preserved in drill core samples than in outcrops. The oldest rocks studied are peμmatites oλ μabbronorite composition, which are associated with the ore-bearinμ sulphide veins λrom the basal zone oλ Mt Travyanaya and the critical horizon’ Mt Hyud, Terassa deposit . Two baddeleyite and three zircon populations were examined λrom these rocks. “ll the crystals were unaltered. ”addeleyite μrains are up to m lonμ and liμht brown in colour. Zircons are prismatic and isometric, up to m in size, and λeature narrow iμneous zoninμ and various hues oλ brown. U and Pb concentrations are hiμh, which is typical oλ peμmatite. “ U–Pb aμe obtained on the λive zircon and baddeleyite populations is ± Ma, MSWD= . the lower intersection oλ the discordia and the concordia is at ± Ma, indicatinμ Palaeozoic lead losses Fiμ. “, Table . This aμe is comparable with that oλ ± Ma obtained λor μabbronorite oλ Mt Nyud, and with a zircon aμe λor the norite oλ Mt Travyanaya Fiμ. ”, Table . “ U–Pb aμe on baddeleyite and zircon recently obtained λor the coarse-μrained μabbronorite oλ Mt Vurechuaivench λoothills now considered as a PGE-bearinμ reeλ is ± Ma, beinμ very similar to that λor the Fedorovo-Pansky μabbronorite Fiμ. C, Table . To determine the aμe oλ the Sopcheozero chromite deposit located within the Dunite ”lock oλ the Monchepluton, cross-cuttinμ dykes were analysed. The Dunite ”lock is composed oλ rocks poor in accessory minerals. The dykes are assumed to be associated with intrusive maλic rocks oλ the Monchepluton and are thouμht to have intruded the Dunite ”lock rocks beλore they had cooled. Thus the aμe oλ the dykes would constrain the minimum aμe limit oλ the Dunite ”lock and Sopcheozero deposit λormation. For U–Pb datinμ, a sample was collected λrom ”orehole at a depth oλ – m, λrom a coarse-μrained μabbronorite dyke cuttinμ the ultramaλic rocks oλ the Dunite ”lock. ”addeleyite, two zircon populations and rutile were used λor datinμ. ”rown transparent plate-like baddeleyite μrains oλ up to – m in size are well preserved. Liμht-ink zircons oλ up to m in size have μood outlines and thin zoninμ. The U–Pb aμe on zircon and baddeleyite is ± Ma, MSWD= . the lower intersection oλ the discordia with the concordia is at ± Ma Fiμ. D, Table . The point λor the rutile has a near concordant value oλ c. . Ga that reλlects the time oλ its λormation. “ similar U–Pb aμe ± Ma has also been obtained on zircon λrom a coarse-μrained μabbronorite dyke λrom ”orehole Fiμ. E, Table . The μabbronorite dyke cuts the ultramaλic rocks oλ the Dunite ”lock, thereλore the Dunite ”lock must be older than the Monchepluton. Small intrusions and dykes oλ the Moncheμorsk Layered Complex were considered by most μeoloμists to have the same aμe as the Monchepluton. In order to veriλy these relationships, diorite oλ the Yarva-Varaka intrusion was studied. Three zircon types and baddeleyite were selected λrom a sample oλ quartz diorite and μranophyric hypersthenes diorite collected in the upper part oλ the Yarva-Varaka section. Stubby prismatic, pink-brown zircons oλ up to m in size were divided by their colour hues into three populations. In i mersion view, they are multi-zoned. ”addeleyite μrains and λraμments are prismatic in habit, liμhtbrown coloured

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

and up to m in size. “ U–Pb aμe obtained on λour points is ± Ma, MSWD= . lower intersection is at zero, indicatinμ recent lead losses Fiμ. F, Table .

the

The Ostrovsky intrusion also belonμs to the series oλ small maλic-ultramaλic intrusions oλ the Moncheμorsk Layered Complex. It was considered to correlate in aμe with the Monchepluton and was interestinμ as a tarμet λor Cu–Ni prospectinμ. “ sample λor U–Pb datinμ was taken λrom maλic peμmatite veins in the middle part oλ the upper μabbronorite zone Mt Ostrov‐ skaya . The peμmatite body is > m-thick, up to m lonμ and has a complex morpholoμy, with sinuous contacts with the coarseμrained sliμhtly amphibolized host piμeonite μabbronorite. The sample is dominated by coarseμrained to peμmatoid μabbronorites with a poikilitic texture, made up mostly oλ calcic plaμioclase and amphibolized clinopyroxene. The kμ sample produced two types oλ baddeleyite and two types oλ zircon. ”addeleyite μrains oλ type are up to m in size, with a deep-brown colour and λlattened and tabular structure. Larμer, up to m baddeleyite μrains oλ type were λound within a λrinμe oλ metamict zircon and were exposed to aeroabrasion λor minutes in order to remove the metamict λrinμe. Zircons are prismatic, up to m in size, and are subdivided into liμht brown and brown varieties. Zircons show well-developed joints and thin zoninμ in i mersion view. The U–Pb isochron aμe on two baddeleyite and two zircon points is ± Ma, MSWD= . and the lower intersection oλ the discordia with the concordia is at ± Ma Fiμ. G, Table . To establish aμe correlations between the μabbronorite oλ the Monchepluton and the anortho‐ site oλ the Main Ridμe intrusion, rock samples oλ the Monchetundra and Chunatundra intrusions were studied. The Monchetundra intrusion has a complex structure and an overview oλ μeoloμical and μeochronoloμical investiμations is μiven by Smolkin et al. . It includes the upper zone comprised mainly oλ amphibolized μabbronorite and μabbro-anorthosite, and the lower zone, which consists oλ μabbronorite, norite and plaμiopyroxenite drilled by the deep borehole M- . The middle part oλ the upper zone, which contains a prominent horizon oλ sliμhtlyaltered medium to coarse-μrained μabbronorite with trachytoid texture, was sampled λor U–Pb datinμ. The sample yielded three zircon types. Prismatic acicular crystals up to m in size and their brown λraμments were divided into three types by colour. In i mersion view, multi-zoninμ, mineral inclusions, stronμ jointinμ, corrosion oλ the surλace and spotted uneven μrain colour are observed. The U–Pb aμes Fiμ. H, Table on zircon λrom trachytoid μabbronorite are ± Ma, MSWD= . and ± Ma, Fiμ. I, Table MSWD= ”ayanova & Mitroλanov . “ sample was also taken λrom the rocks oλ the diλλerentiated series oλ the Chunatundra intrusion. Zircons λrom medium-μrained leucoμabbro with trachytoid texture were divided into λive types. Four types are up to m isometric λraμments oλ brown and pink colour, whereas the last λraction is represented by up to m twinned pinkishbrown zircons with adamantine lustre. The U–Pb isochron plotted on λive points has the upper intersection with the concordia at ± Ma, MSWD= . and the lower intersection is at zero Fiμ. J, Table . This aμe is close to the aμe obtained on maμmatic zircon λrom anorthosite oλ the Pyrshin

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Geochronology - Me“hods and Case S“”dies

intrusion Mitroλanov & Nerovich

and on zircons λrom later anorthositic injections oλ

the LLH Fedorovo-Pansky Complex .

Figure 3. U–Pb concordia diagrams for zircon, baddeleyi“e and r”“ile from differen“ rocks of “he Monchegorsk Layered Complex.

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

(ppm)

(mg)

No

Weight

Sample

Concentration

Pb isotopic composition1 Pb

206

Pb

207

206

Pb

U

204

Pb

206

Pb

Pb

208

Pb

Isotopic ratios2 207

Pb

235

U

206

Age2 (Ma)

Pb

207

Pb

U

206

Pb

238

( cri“ical horizon , M“. Ny”d Monchepl”“on, gabbronori“e (М-2); from Bayanova, 2004) 1 (bd)

0.70

93.1

198.8

9432

6.0586

103.8300

10.4643

0.4636

2495

2 (bd)

0.40

170.8

364.4

3589

5.9833

50.7070

10.3199

0.4574

2494

3

0.40

117.4

183.1

4590

6.0153

1.8703

9.8274

0.4359

2492

4

0.80

187.9

308.4

13664

6.1169

1.9750

9.4740

0.4227

2483

5

0.50

152.2

252.5

5300

6.0842

1.8994

9.2129

0.4125

2477

1

0.30

308.3

504.8

5778

6.0202

2.3805

10.0760

0.4458

2497

2

0.35

185.4

319.8

8358

6.0582

2.7721

9.9277

0.4402

2493

3

0.40

264.5

441.6

23762

6.1006

2.2929

9.7814

0.4342

2491

4

0.40

434.8

793.1

6273

6.0541

3.2613

9.7060

0.4314

2489

(marginal zone, M“. Travyanaya Monchepl”“on, nori“e (M-1); from Smolkin e“ al., 2004)

(V”rech”aivench Foo“hills Monchepl”“on, coarse-grained me“agabbronori“e (М-42); presen“ s“”dy) 1 (bd)

0.80

150.1

271.4

2982

6.3099

3.2054

9.23762

0.43446

2393

2 (bd)

0.65

65.1

122.6

2080

6.5863

2.7920

8.13574

0.40516

2295

3

0.75

137.4

288.5

911

6.4805

2.3018

5.75090

0.34208

2228

(D”ni“e block, Monchepl”“on, coarse-grained gabbronori“e dyke c”““ing ”l“ramafic rocks, hole 1586 (М-14); from Bayanova, 2004) 1(bd)

0.50

5.3

10.3

1307

5.7748

12.4320

10.5720

0.4684

2494

2

0.80

358.7

309.2

13360

6.1029

0.5312

9.8622

0.4391

2486

3

0.60

321.8

362.1

3791

6.0407

0.7838

9.3919

0.4199

2479

4(r”)3

1.30

7.5

4.5

28

1.7085

0.8077

5.7139

0.3328

2022

(D”ni“e block, Monchepl”“on, coarse-grained gabbronori“e dyke c”““ing ”l“ramafic rocks, hole 518 (M-12); from Smolkin e“ al., 2004) 1

0.45

221.4

409.6

2152

5.9237

3.5776

9.6682

0.4303

2487

2

0.30

321.7

542.6

11260

6.1264

2.2049

9.4976

0.4249

2478

3

0.50

164.9

302.4

1952

5.9508

2.5602

8.9806

0.4031

2472

(M“. Yarva-Varaka, diori“e (М-38); from Bayanova, 2004) 1 (bd) 1

0.50

32.9

70.0

5615

6.0158

53.309

10.419

0.4608

2497

2

0.80

310.5

515.4

2587

5.9089

2.9118

10.420

0.4597

2501

3

1.40

151.8

262.7

4840

5.9895

3.1873

10.242

0.4519

2501

151

Geochronology - Me“hods and Case S“”dies

(ppm)

(mg)

No 4

Weight

Concentration Sample

152

0.70

Pb isotopic composition1 Pb

206

Pb

207

206

Pb

U

273.2

472.5

204

4590

Pb

206

Pb

Pb

208

Pb

5.9970

3.1828

Isotopic ratios2 207

Pb

235

206

U

(Ma)

Pb

207

Pb

U

206

Pb

238

10.217

Age2

0.4518

2497

(Os“rovsky in“r”sion, gabbronori“e-pegma“i“e (М-7); from Bayanova, 2004) 1 (bd)

0.45

28.6

63.9

1820

6.162

29.610

9.350

0.4311

2405

2 (bd)

0.55

36.3

83.7

3380

6.346

42.038

9.210

0.4248

2389

3

0.45

336.4

694.8

9420

6.378

3.797

8.471

0.3953

2407

4

0.35

89.1

187.6

3700

6.375

2.942

7.756

0.3667

2384

1

0.50

110.9

172.9

8690

6.0591

1.9737

10.0171

0.444092

2493

2

0.35

37.7

61.0

1122

5.7260

2.2170

9.82794

0.436123

2492

3

0.25

168.3

277.7

6350

6.0914

1.8221

9.15540

0.409417

2479

4

0.30

122.6

213.5

6159

6.2294

1.9243

8.64155

0.395489

2439

(Monche“”ndra, “rachy“oid gabbronori“e (М-55); from Smolkin e“ al., 2004)

(Monche“”ndra, “rachy“oid gabbronori“e (М-54); from Smolkin e“ al., 2004) 1

0.50

308.9

494.5

9172

6.0283

2.4881

10.47020

0.46359

2503

2

0.35

374.3

587.5

18868

6.0791

2.2742

10.40220

0.46050

2496

3

0.40

72.8

118.6

6833

6.0271

2.5023

10.25210

0.45405

2498

4

0.25

206.3

333.1

7831

6.0324

2.1148

9.90668

0.44177

2499

5

0.45

196.6

311.9

14844

6.1123

1.9269

9.74196

0.43412

2484

(Ch”na“”ndra, “rachy“oid anor“hosi“e (М-16); from Bayanova, 2004) 1

0.20

80.3

138.4

2710

6.020

3.404

10.216

0.4589

2471

2

2.05

122.83

214.1

4420

6.144

3.293

9.999

0.4527

2455

3

0.30

141.3

251.0

5140

6.137

3.291

9.831

0.4443

2461

4

0.60

92.7

169.4

7860

6.148

2.970

9.388

0.4228

2467

5

0.20

46.5

86.1

1090

5.805

3.242

9.262

0.4180

2463

All ra“ios are correc“ed for blanks of 0.08 ng for Pb и 0.04 ng for U and for mass discrimina“ion of 0.12±0.04%.

1

2

Correc“ion for common Pb was de“ermined for “he age according “o S“acey and Kramers (1975).

3

Correc“ed for iso“ope composi“ion of ligh“ cogene“ic plagioclase: 206Pb/204Pb=14.041±0.005, 207Pb/204 Pb=14.581±0.007, Pb/204Pb=35.58±0.02.

208

Table 1 U-Pb baddeleyi“e (bd), zircon and r”“ile (r”) iso“ope da“a from “he Monchegorsk Layered Complex.

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

. The Fedorovo-Pansky complex The Fedorovo-Pansky Layered Complex Fiμ. outcrops over an area oλ > km . It strikes northwestwards λor > km and dips southwestwards at an anμle oλ – °. The total rock sequence is about – km thick. Tectonic λaults divide the complex into several blocks. The major blocks λrom west to east Fiμ. are known as the Fedorov, the Lastjavr, the Western Pansky and the Eastern Pansky Mitroλanov et al. . The Fedorovo-Pansky complex is bordered by the “rchaean Keivy terrane and the Palaeoproterozoic Imandra-Varzuμa riλt. The rocks oλ the complex crop out close to the “rchaean μneisses only in the northwestern extremities, but their contacts cannot be established due to poor exposure. In the north, the complex borders with the alkaline μranites oλ the White Tundra intrusion. The alkaline μranites were recently proved to be “rchaean with a U–Pb zircon aμe oλ ± Ma ”ayanova Zozulya et al. . The contact oλ the Western Pansky ”lock with the Imandra-Varzuμa volcanosedimentary sequence is mostly covered by Quaternary deposits. However, drillinμ and excavations in the south oλ Mt Kamennik reveal a stronμly sheared and metamorphosed contact between the intrusion and overlyinμ Palaeoproterozoic volcano-sedimentary rocks that we interpret to be tectonic in oriμin. The Fedorovo-Pansky Complex comprises predominantly μabbronorites with varyinμ proportions oλ maλic minerals and diλλerent structural λeatures. From bottom up, the composite layered sequence is as λollows • Marμinal Zone – m oλ plaμioclase–amphibole schists with relicts oλ massive λine‐ μrained norite and μabbronorite, which are reλerred to as chilled marμin rocks • Taxitic Zone – m that contains orebearinμ μabbronoritic matrix Ma, see below and early xenoliths oλ plaμioclasebearinμ pyroxenite and norite – Ma, see below . Synμenetic and maμmatic ores are represented by Cu and Ni sulphides with Pt, Pd and “u, and Pt and Pd sulphides, bismuthotellurides and arsenides • Norite Zone – m with cumulus interlayers oλ harzburμite and plaμioclase-bearinμ pyroxenite that includes an interμranular injection Cu–Ni–PGE mineralization in the lower part. The rocks oλ the zone are enriched in chromium up to ppm and contain chromite that is also typical oλ the rocks oλ the Penikat and Kemi intrusions Finland derived λrom the earliest maμma portion Iljina & Hanski . ”asal Cu–Ni–PGE deposits oλ the Fedorov ”lock have been explored and prepared λor licensinμ Schissel et al. Mitroλanov et al. . • Main Gabbronorite Zone c. m that is a thickly layered stratiλied’ rock series Fiμ. with a – m thinly layered lower horizon LLH at the upper part. The LLH consists oλ contrastinμ alteration oλ μabbronorite, norite, pyroxenite and interlayers oλ leucocratic μabbro and anorthosite. The LLH contains a reeλ-type PGE deposit poor in base-metal sulphides. The deposit is now beinμ extensively explored Mitroλanov et al. . “ccordinμ to the λield investiμations Latypov & Chistyakova , the LLH anorthositic layers have been intruded later, as shown by cuttinμ injection contacts. This is conλirmed by a zircon U– Pb aμe λor the anorthosite oλ ± Ma see below .

153

154

Geochronology - Me“hods and Case S“”dies

• Upper Layered Horizon ULH between the Lower and Upper Gabbro Zones. The ULH consists oλ olivine-bearinμ troctolite, norite, μabbronorite and anorthosite Fiμ. . It comprises several layers oλ rich PGE Pd-Pt ore poor in base-metal sulphides Mitroλa‐ nov et al. . The U–Pb aμe on zircon and baddeleyite oλ the ULH rocks oλ ± Ma see below is the younμest amonμ those obtained λor the rocks oλ the FedorovoPansky Complex.

Figure 4. General geological map of “he Fedorovo-Pansky Layered Complex (Mi“rofanov e“ al. 2005).

. Fedorovo-Pansky complex, isotope data Several larμe samples were selected λor the U–Pb datinμ oλ the Fedorovo-Pansky Complex. “ kμ sample oλ medium-and coarse-μrained μabbronorite was collected λrom the Lower Layered Horizon in the Eastern Kievey area. The separated zircons are transparent with a vitreous lustre. “ll the μrains were divided into three types Pan- –reμular bipyramidalprismatic crystals oλ up to m Pan- –λraμments oλ prismatic crystals Pan- –pyramidal apices oλ crystals oλ – m. In i mersion view, all the zircons display a simple structure with λine zoninμ and cross jointinμ. The discordia plotted on three points yields the upper intersection with the concordia and the U–Pb aμe at ± . Ma, MSWD= . . The lower intersection oλ the discordia with the Concordia is at zero and reλlects modern lead losses Fiμ. “, Table . The same zircon sample was analysed in the Royal Ontario Museum laboratory in Canada the obtained U–Pb zircon

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

aμe is . ± . Ma “melin et al. that is somewhat older than ours. The aμe obtained is interpreted as the time oλ crystallization oλ the main μabbronorite phase rock Mitroλanov et al. Mitroλanov & ”ayanova . Sm–Nd datinμ on ortho-and clinopyroxene, plaμioclase and whole-rock minerals extracted λrom the same μabbronorite μave an aμe oλ ± Ma, MSWD= . ”alashov et al. . Three zircon populations oλ prismatic habit and liμht-yellow colour were separated λrom PGEbearinμ μabbro-peμmatite LLH . The zircons λrom sample P- are stubby prismatic crystals with sharp outlines, about m in size. The crystals show cross-cracks and apparent zoninμ in i mersion view. The zircons λrom samples D- and D- are multi-zoned pinkish λraμments oλ prismatic crystals with adamantine lustre and and m in size. The U–Pb zircon aμe oλ ± Ma, MSWD= . Fiμ. “, Table was obtained λrom three points one concordant and two lyinμ in the upper part oλ the isochron. The lower intersection oλ the discordia with the concordia c. Ma indicates lead loss associated with the Palaeozoic tectonic activation oλ the eastern ”altic Shield and the development oλ the μiant Khibina and Lovozero intrusions oλ nepheline syenites Kramm et al. . Zircons λrom the μabbro-peμmatite are λound to have hiμher U and Pb concentrations than those λrom the μabbronorite. Three zircon and two baddeleyite populations were separated λrom a sample collected λrom the Upper Layered Horizon in the Southern Suleypahk area. “ll the zircons λrom anorthosite are prismatic, liμht-pink-coloured with vitreous lustre. In i mersion view, they are zoned and λractured. “ population oλ bipyramidal-prismatic zircons Pb- is made up oλ elonμate crystals. Sample Pb- contains zircons oλ round-ellipsoidal habit and sample Pb- contains transparent λlattened crystal λraμments oλ up to . m in size. The separated baddeleyite crystals λirst recorded in the anorthosite were subdivided into two varieties, deep-brown and brown. “ll the μrains are λraμments oλ transparent baddeleyite crystals oλ m in size, without selvaμes and inclusions. “ U–Pb isochron plotted λrom three zircons and two baddeleyites intersects the concordia with an aμe oλ ± Ma, MSWD= . Fiμ. ”, Table . The lower intersection oλ the Discordia with the concordia records recent lead loss. The position oλ the baddeleyite points is nearconcordant, while zircon points Sample P - are above the concordia due to uranium loss. This aμe ± Ma is considered to constrain the oriμin oλ latephase anorthosite because, as shown by Heaman & LeCheminant , baddeleyite is co monly μenerated in residual melts. The U–Pb zircon aμe oλ the early barren orthopyroxenite λrom the Fedorov ”lock, ± Ma, is believed to be the time oλ emplacement Fiμ. C, Table . The U–Pb aμe oλ ± Ma Fiμ. D, Table , obtained λrom zircon λrom barren olivine μabbro, is interpreted as the time oλ crystallization. The last Cu–Ni–PGE-bearinμ taxitic μabbronorite λrom the Fedorov ”lock Fiμ. E, Table yielded a U–Pb zircon aμe oλ ± Ma Nitkina . Ihe coeval Sm-Nd isotope aμes have been oblained usinμ rock-λorminμ minerals λrom the same rork oλ the Fedorovo-Pansky massiλ Fiμ. , Table .

155

156

Geochronology - Me“hods and Case S“”dies

Figure 5. U–Pb concordia diagrams for “he Wes“ern-Pansky (a, b) and Fedorov (c, d, e) Blocks of “he Fedorovo-Pansky Complex.

SampleNo

Weight

Concentration

(mg)

(ppm) Pb

Pb isotopic composition1

Isotopic ratios2

Age2 (Ma)

U

206

Pb

206

Pb

206

Pb

204

Pb

207

Pb

208

Pb

207

Pb

235

U

206

Pb

207

Pb

U

206

Pb

238

(Wes“ern-Pansky Block, gabbronori“es (Pan-1); from Bayanova, 2004) 1

3.30

95.0

144

11740

6.091

3.551

10.510

0.4666

2491

2

1.90

70.0

142

10300

6.100

4.220

9.135

0.4061

2489

3

1.60

84.0

144

6720

6.062

3.552

10.473

0.4650

2491

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

SampleNo

Weight

Concentration

(mg)

(ppm) Pb

Pb isotopic composition1

Isotopic ratios2

Age2 (Ma)

U

206 204

Pb

206

Pb

207

Pb

206

Pb

Pb

208

Pb

207

Pb

235

U

206

Pb

207

Pb

U

206

Pb

238

(Wes“ern-Pansky Block, gabbropegma“i“e (P-8); from Balashov e“ al., 1993) 1

5.90

95.0

158

3240

5.991

3.081

10.435

0.4681

2471

2

7.30

181.0

287

8870

6.161

2.260

10.092

0.4554

2465

3

1.25

125.0

200

3400

6.012

2.312

10.082

0.4532

2468

0.5352

2438

(Wes“ern-Pansky Block, anor“hosi“e (P-6); from Bayanova, 2004) 1

0.75

218.0

322

5740

6.230

3.263

11.682

2

0.10

743.0

1331

3960

6.191

3.151

9.588

0.4393

2438

3

0.20

286.0

577

2980

6.021

3.192

8.643

0.3874

2474

4 (bd)

1.00

176.0

396

14780

6.290

63.610

9.548

0.4380

2435

5 (bd)

0.26

259.0

560

3360

6.132

54.950

9.956

0.4533

2443

(Fedorov Block, or“hopyroxeni“e (F-3); from Ni“kina, 2006) 1

0.75

48.0

60.9

825

4.9191

1.3039

10.0461

0.44249

2504

2

0.80

374.0

598.6

4588

6.0459

1.9650

9.6782

0.43153

2484

3

0.85

410.2

630.2

4521

6.0281

1.6592

9.5667

0.42539

2488

4

1.00

271.0

373.1

2552

5.9916

1.2393

9.4700

0.42406

2476

(Fedorov Block, olivine gabbro (F-4); from Ni“kina, 2006) 1

1.80

725.3

1322.8

14649

6.1121

3.8177

10.0132

0.44622

2484

2

2.00

731.3

1382.8

8781

6.1522

3.5517

9.4306

0.42454

2467

3

1.95

680.9

1374.0

7155

6.2645

3.6939

8.7401

0.40155

2433

(Fedorov block, PGE-bearing gabbronori“e (F-2); from Ni“kina, 2006) 1

0.30

498.0

833.4

2081

5.9502

2.2111

9.49201

0.42493

2477

2

0.65

513.8

932.2

5274

6.1519

2.6371

9.1373

0.41378

2458

3

0.55

583.2

999.3

3194

6.1132

2.0528

8.9869

0.40832

2452

4

0.80

622.5

1134.5

4114

6.1161

2.1914

8.6638

0.39165

2460

All ra“ios are correc“ed for blanks of 0.1 ng for Pb and 0.04 ng for U and for mass discrimina“ion of 0.17 ± 0.05%.

1

Correc“ion for common Pb was de“ermined for “he age according “o S“acey and Kramers (1975).

2

Table 2 U-Pb baddeleyi“e (bd) and zircon iso“ope da“a from “he Wes“ern-Pansky and Fedorov Blocks of “he FedorovoPansky Complex.

157

158

Geochronology - Me“hods and Case S“”dies

Figure 6. Mineral Sm–Nd isochrons for rocks and rock-forming minerals of “he Fedorov Block of “he Fedorovo-Pansky Complex.

Sample No

Concentration

Isotopic ratios

(ppm) Sm

Nd

Sm/144Nd

147

143

TDM

Sm-Nd

εNd (2.5Ga)

(Ga)

(Ma)

3.05

2521±42

-1.73

2.94

2516±35

-1.53

3.18

2482±36

-2.50

Nd/144Nd

or“hopyroxeni“e (F-3) WR

0.32

1.17

0.1648

0.512196±12

Opx

0.12

0.38

0.2228

0.513182±16

Cpx

2.21

7.67

0.1745

0.512349±17

Pl

0.26

1.62

0.0960

0.511071±29 olivine gabbro (F-4)

WR

0.63

2.80

0.1357

0.5115488

Opx

0.23

0.72

0.1951

0.51255515

Cpx

0.83

2.28

0.2187

0.51294716

Pl

0.24

1.77

0.0815

0.51067714

PGE-bearing gabbronori“e (F-2) WR

0.42

1.66

0.1537

0.51180720

Pl

0.41

2.88

0.0865

0.51070914

Cpx

1.78

5.73

0.1876

0.5123878

Opx

0.13

0.33

0.2323

0.51308840

Table 3 Sm-Nd iso“ope da“a on whole rock and mineral separa“es of “he Fedorov Block of “he Fedorovo-Pansky Complex.

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

. Analytical U-Pb, Sm-Nd, Rb-Sr methods U–Pb TIMS method with Pb/ U tracer. Followinμ the method proposed by Kroμh , the samples were dissolved in stronμ % hydroλluoric acid at a temperature oλ – °C over – days. In order to dissolve λluorides, the samples were reacted with . N HCl at a temperature oλ °C λor – hours. To determine the isotope composition oλ lead and concentrations oλ lead and uranium, the sample was divided into two aliquots in . N HCl, and a mixed Pb/ U tracer was added. Pb and U were separated on an “G × , – mesh anion exchanμer in Teλlon columns. The laboratory blank λor the whole analysis was < . – . nμ λor Pb and . – . nμ λor U. “ll isotopic determinations λor zircon and badde‐ leyite were made on Finniμan M“Tand MI -T mass spectrometers and the Pb isotopic composition was analysed on a secondary-ion multiplier on a Finniμan M“Tin ion countinμ mode. The measurements oλ the Pb isotopic composition are accurate to . % Finniμan M“Tand . % MI -T when calibrated aμainst N”S SRMand SRMstandards, respectively. The U and Pb concentrations were measured in sinμleλilament mode with the addition oλ H PO and silica μel usinμ the method Scharer & Gower Scharer et al. . Pb and U concentrations were measured within the temperature ranμes oλ – and – °C, respectively. “ll oλ the isotopic ratios were corrected λor mass discrimination durinμ the static processinμ oλ replicate analyses oλ the SRMand SRMstandards . ± . % λor the Finniμan M“Tand . ± . % per a.m.u. . The errors in the U–Pb ratios were calculated durinμ the statistical treatment oλ replicate analyses oλ the IGFM- standard and were assumed equal to . % λor Finniμan M“Tand . % λor MI -T. Iλ the actual analytical errors were hiμher, they are reported in the table oλ isotopic data. Isochrons and sample points were calculated Squid and Isoplot proμrams Ludwiμ , . The aμe values were calculated with the conventional decay constants λor U Steiμer & Jaμer , all errors are reported λor a siμma level. Corrections λor co mon Pb were made accordinμ to Stacey & Kramers . Corrections were also made λor the com‐ position oλ Pb separated λrom synμenetic plaμioclase or microcline iλ the admixture oλ co mon Pb was > % oλ the overall Pb concentration and the Pb/ Pb ratios were < . Pb/ U tracer λor sinμle μrains. U-Pb TIMS method with based U-Pb method λor sinμle μrain accessory minerals usinμ ion-exchanμe chromatoμraphy. Handpicked crystals are λirst treated in ultrasonic bath λor cleaninμ in spirit or in acetone, and then in N nitric acid, heated λor about minutes on a warm ranμette, and λinally are three times λlushed with recurrent puriλication water. Chemical mineral decomposition is perλormed in teλlon bombs with addinμ to mcl oλ mixed Pb/ U tracer usinμ T. Kroμh method in concentrated nitric acid durinμ to days at a temperature oλ ° . “λter complete decomposition, the column eλλluent is evaporated on a warm raμette, and then drops oλ . N chlorohydric acid are added. The sample is placed to the thermostat λor to hours at a temperature oλ ° λor homoμenization. Lead and uranium are separated λor isotope investiμations usinμ ion-exchanμe chromatoμraphy in columns with Dowex IX mesh resin. Lead is eluted with drops oλ . N chlorohydric acid when also one drop oλ . N phosphoric acid is added, and the solution is evaporated on a raμette down to mcl. Uranium is eluted separately λrom lead with drops oλ water with one drop oλ . N phosphoric acid added, and evaporated

159

160

Geochronology - Me“hods and Case S“”dies

on a raμetter down to mcl. “ll chemical procedures are carried out in the ultraclean block with blank Pb and U contamination oλ ca. - pμ, and ca. - pμ respectively. The measure‐ ment oλ Pb and U isotope composition and concentrations is perλormed on Re bands at sevenchannel mass-spectrometer Finniμan-M“T RPG , on collectors, with Pb and Pb measured at a temperature oλ ° in an ion countinμ mode usinμ a multiplier or quadrupole RPG accessory. Silicaμel is used as an emitter. U concentrations are detected at a temperature oλ ° usinμ a collector and a multiplier in a mixed statically dynamic mode. When U concentrations are neμliμible, the multiplier or quadrupole RPQ accessory is applied in a dynamic mode. “ll the measured isotope ratios are adjusted λor mass-discrimi‐ nation obtained when studyinμ parallel analyses oλ SRMand SRMstandards to be . ± . %. The coordinates oλ points and isochrone parameters are calculated usinμ proμrams by K. Ludwiμ , . “μes are calculated in accordance with the accepted values oλ uranium decay constants Steiμer and Jμer, , with errors beinμ indicated on a b level. The J. Stacey & J. Kramers model is used to adjust numbers λor the admixture oλ co mon lead. Isotope Sm/Nd method. In order to deλine concentrations oλ samarium and neodymium, the sample was mixed with a compound tracer Sm/ Nd prior to dissolution. It was then diluted with a mixture oλ HF+HNO or+HClO in Teλlon sample bottles at a temperature oλ °C until complete dissolution. Further extraction oλ Sm and Nd was carried out usinμ standard procedures with twostaμe ion-exchanμe and extraction-chromatoμraphic separation usinμ ion-exchanμe tar «Dowex» × in chromatoμraphic columns employinμ . N and . N HCl as an eluent. The separated Sm and Nd λractions were transλerred into nitrate λorm, whereupon the samples preparations were ready λor mass-spectrometric analysis. Measurements oλ Ndisotope composition and Sm and Nd concentrations by isotope dilution were perλormed usinμ a multicollector mass-spectrometer in a Finniμan M“T RPQ in a static mode usinμ Re +Re and Ta+Re λilament. The measured reproducibility λor ten parallel analysis oλ Nd-isotope composition λor the standard La Jolla= . ± was < . % σ . The same reproducibility was obtained λrom parallel analyses oλ the Japanese standard Ji Nd = . ± . The error in Sm/ Nd ratios oλ . % σ , the averaμe oλ seven measures, was accepted λor statistic calculations oλ Sm and Nd concentrations usinμ the ”CR standard. The blanks λor laboratory contamination λor Nd and Sm are . and . nμ, respectively. Isochron parameters were developed λrom proμrams oλ Ludwiμ , . The reproducibility oλ measurements was ± . % σ λor Sm/Nd ratios and ± . % σ λor Nd-isotope analyses. “ll Sm/ Nd and Nd/ Nd ratios were normalized to Nd/ Nd= . and adjusted to Nd/ Nd. . usinμ the La Jolla Nd standard. The Nd T values and model TDM aμes were calculated usinμ the currently accepted parameters oλ CHUR Jacobsen & Wasserburμ Nd/ Nd= . and Sm/ Nd= . and DM Goldstein & Jacobsen Nd/ Nd= . and Sm/ Nd= . . Sm-Nd method λor studyinμ suphides. The chemical and analytical treatment oλ sulphide minerals pyrite, pentlandite, chalcopyrite, etc. λor Sm-Nd study is perλormed λollowinμ a modiλied technique Yekimova as compared to the conventional one Zhuravlyov et al. . To decompose sulphides, a mineral weiμht to mμ is mixed with a Sm/ Nd

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

tracer solution, treated with aqua reμia Cl+HNO until complete decomposition, and evaporated dry. “λterwards, this is transλormed to chlorides throuμh evaporatinμ the sample in . - N l. “λter the λractional acid decomposition, the dry residue is dissolved in ~ ml . N HCl, and total REEs are separated λrom the solution via cation-exchanμe chromatoμra‐ phy. “ stepwise elution method is applied to . and . N HCl in a chromatoμraphic column with cation-exchanμe resin Dowex x mesh . The separated REE λraction is evaporated dry, dissolved in . N HCl, and loaded to the second column with KEL-F solid ion-exchanμe resin HDEHP. The resin is used to separate Sm and Nd. The selected Sm and Nd λractions are evaporated to μet prepared λor λurther mass-spectrometric analysis. “ll the measurements oλ the Nd isotope composition and Sm and Nd concentrations usinμ an isotope dilution technique were perλormed at a seven-channel solid-phase mass-spectrometer Finniμan-M“T RPQ in a static double-band mode in collectors usinμ Ta+Re λilaments. Re λilaments were used as ionizers, and the sample was applied to the Ta λilament with a diluted the H PO microdrop beinμ deposited on beλorehand. The reproducibility error λor eleven Nd isotope composition determinations oλ La Jolla= . ± σ, N= has been within . % σ . The same error was obtained when measurinμ λorty-λour parallel analyses oλ a new Japanese standard, JNdi = . ± σ, N= . The error in Sm/ Nd ratios is accepted λor the static calculation oλ the Sm and Nd concentrations in ”CR- to be . % σ , which is an averaμe oλ seven measurements. The blank intralaboratory contamination in Nd and in Sm is . nμ and . nμ respectively. The measured Nd isotope rations were normalized per Nd/ Nd= . , and recalculated λor Nd/ Nd in LaJolla= . aλterwards. The isochron parameters were computed usinμ K. Ludwiμ proμrams Ludwiμ , . The decompositions constants are as per Steiμer . The Nd parameters λor a one-staμe model were calculated usinμ [De Paolo ], and λor a two-staμe model usinμ Liew & Hoλmann . Isotope Rb/Sr method. The samples and minerals were all treated with double distilled acids HCl, HF and HNO and H O distillate. “ sample oλ – mμ dependinμ on Rb and Sr contents was dissolved with ml oλ mixed HF and HNO in corked teλlon sample bottles and leλt at a temperature oλ about °C λor one day. The solution was then divided into three aliquots in order to determine Rb and Sr isotope compositions and concentrations. These were measured by isotope dilution usinμ separate Rb and Sr tracers. Rb and Sr extraction was perλormed by eluent chromatoμraphy with «Dowex» tar × – mesh . N and . N HCl served as an eluent. Tar volumes in the columns were c. and c. sm . The separated Rb and Sr λractions were evaporated until dryness, λollowed by treatment with a λew drops oλ HNO . Sr isotope compositions and Rb and Sr contents were measured by a MI-T Ukraine mass spectrometer in the two-ribbon mode usinμ Re λilaments. The prepared samples were deposited on the ribbons in the λorm oλ nitrate. Sr isotope composition in all the measured samples was normalized to a value oλ . reco mended by N”S SRM. Errors on Sr isotope analysis conλidence interval oλ % do not exceed . %, and those oλ Rb–Sr ratio determination are oλ . %. ”lank laboratory contamination λor Rb is . nμ and λor Sr . nμ. The adopted Rb decay constant oλ Steiμer & Jaμer was used λor aμe calculations.

161

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Geochronology - Me“hods and Case S“”dies

. Geological setting and petrography features of Monchetundra massif The Monchetundra intrusion belonμs to Northern Kola belt and has a northwestwardly elonμated oval shape with a total area oλ ca. sq. km Fiμ. . The lenμth oλ the intrusion is ca. km, and the width varies λrom to km. From east and southeast, the Monchetundra intrusion is separated λrom the Monchepluton intrusion by a thick mass oλ blastocataclasites and blastomilonites, and λrom west by the Viteμuba-Seidozero λault. The shape oλ the intrusion is also compared with a lopolith. The intrusion μenerally plunμes south-westwards, but in its central part the layerinμ and trachytoid elements occur near-horizontally, dippinμ towards the axial part oλ the intrusion. The maximum vertical thickness oλ the Monchetundra intrusion cross-section exceeds km Fiμ. .

Figure 7. Schema“ic geological map of “he cen“ral and so”“heas“ern par“s of “he Monche“”ndra in“r”sion (compiled by L.I. Nerovich on “he ma“erials of Cen“ral Kola Expedi“ion OAO, Geological Ins“i“”“e KSC RAS wi“h addi“ions and amendmen“s).

“ccordinμ to the results oλ the μeoloμical and petroμraphic study carried out on the principles oλ cumulative stratiμraphy Eules, Cawthorn, Irvine, , the maλic and ultramaλic rocks oλ the Monchetundra intrusion have been divided into three zones. The rock sequence oλ the lower zone Fiμ. varies λrom olivinite to leucocratic norite. The lower zone is domi‐ nated by norites with quite a wide distribution oλ pyroxenites and olivinites, which are co mon in the south-eastern λlank oλ the intrusion. Minor are harzburμites and μabbronorites. Ortho‐ pyroxene and olivine cumulates prevail in the cumulative stratiμraphy oλ the lower zone. The rocks oλ the middle zone represent northwestwardly elonμated strinμs at the exposed surλace oλ the eastern and western λlanks oλ the intrusion Fiμ. and compose a siμniλicant part oλ the

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

cross-section in the boreholes. The rock sequence oλ the middle zone ranμes λrom troctolite and olivine μabbronorite to anorthosite. Contrast layerinμ is more typical oλ the western λlank oλ the intrusion. The lower zone is dominated by trachytoid medium-μrained μabbronorite with plaμioclase-pyroxene and minor plaμioclase cumulates. The rocks oλ the upper zone make up the central part oλ the intrusion Fiμ. .

. Petrographical features rocks of the Monchetundra massif In terms oλ composition, the rocks oλ the upper zone ranμe λrom plaμioperidotites to μabbro‐ norite-anorthosites and μabbro-anorthosites. The contrast oλ the rocks increases northwest‐ wards. Massive coarse-μrained auμite-piμeonite and auμite-enstatite varieties oλ μabbronoriteanorthosites and leucoμabbronorites, μabbro-anorthosite and leucoμabbro prevail in the upper zone. The leucoμabbro apparently represents an individual intrusive phase since there are xenoliths oλ leucocratic varieties oλ μabbronorites in the μabbro-anorthosites and leucoμabbros oλ the upper and middle part oλ the Hipiknyunchorr Mt. slopes. The rocks oλ the upper zone correspond to plaμioclase cumulates poikilitic inclusions oλ plaμioclase are typically observed in the pyroxenes and olivines. Minor are plaμioclase-pyroxene and plaμioclase-olivine cumulates. Poikilitic inclusions oλ cumulus plaμioclase in pyroxenes and olivines are λound even in such melanocratic rocks as plaμioperidotites oλ the upper zone. Thus, the lower zone oλ the Monchetundra intrusion consists oλ orthopyroxene and olivine cumulates, the middle zone oλ pyroxene-plaμioclase and plaμioclase cumulates, and the upper zone mainly oλ plaμioclase cumulates. Massive coarse-μrained meso-leucocratic, mesocratic, and rarely melanocratic amphiboleplaμioclase rocks are co mon in the southeastern and southwestern parts oλ the Monchetundra intrusion Fiμ. . These rocks are mainly thouμht to be altered varieties oλ leucoμabbro, μabbroanorthosite, and μabbro. Only relic clinopyroxene rarely shows well-preserved primary iμneous λeatures. The observed relic μabbro-ophytic and poikiloophytic structures indicate that the rocks are close to the leucoμabbro and μabbro-anorthosite oλ the upper zone. However, secondary alteration oλ the rocks stronμly hampers their investiμation. The internal structure oλ the Monchetundra intrusion displays siμniλicant lateral heteroμeneity. The deμree oλ diλλerentiation tends to increase λrom the eastern λlank oλ the intrusion south‐ wards λor the lower zone and westwards λor the middle and upper zones . This implies a possibility to λind PGE mineralization not only at the junction oλ the Monchetundra and Monchepluton intrusions eastern and southeastern λlanks oλ the intrusion that has mainly been investiμated, but also in the rocks oλ the southwestern, western, and northwestern λlanks oλ the intrusion. The Monchetundra intrusion was earlier λound to contain a level oλ noble metal mineralization conλined to the norite and pyroxenite oλ the lower zone Grokhovskaya et al., Smolkin et al., . In , the exposed central and southeastern parts oλ the Monchetundra intrusion that are mainly composed oλ the upper zone rocks and oλ the middle zone rocks in

163

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Geochronology - Me“hods and Case S“”dies

the eastern and western λlanks, were sampled λor a μeochemical analysis. “ μeochemical sample oλ kμ was taken λor analysis. The rocks were analyzed λor PGE, “u and “μ usinμ atomic absorption method at the “nalytic Laboratory λor noble metals oλ the Geoloμical Institute KSC R“S. The resultant local anomalies oλ noble metals were conλirmed by minera‐ μraphic methods. The polished samples were studied with scanninμ electron microscope LEOat the Physical “nalysis Laboratory oλ the Geoloμical Institute KSC R“S. The analysis oλ the μeochemical data has shown that the local μeochemical anomalies are mainly concentrated within the western slope oλ Mt. Monchetundra. The only exception is Mt. Hipiknyunchorr, where increased Pd content is observed alonμ the whole intersection λrom east to west. On the whole, λor the massive μabbroids oλ the upper zone, and λor the dike and veins oλ the intrusion, oxide mineralization that is oλten accompanied by synμenetic chalco‐ pyrite and epiμenetic chalcosine-bornite-chalcopyrite masses, is more typical. It correlates with a sliμht increase in Pd and rarely “u content. “ sliμht increase in Pd content is also reμistered in the chlorite-amphibole schists aλter μabbroids adjacent to the shear-λault displacement planes. No noble-metal minerals themselves have been λound in the above-discussed cases. Hiμher concentrations oλ valuable components and noble-metal minerals are established in the trachytoid μabbronorite oλ the middle zone at the western λlank oλ the intrusion. The mineralization traced λor over km has been clearly associated with the top oλ the middle zone in terms oλ structure and litholoμy. It points out the stratiλorm character oλ mineralization, similar oλ sulphides ores at Sudbury Li, Naldrett, .

. Isotope — U-Pb data on zircon and baddeleyite from Monchetundra The aμe oλ the lower zone has about established in Pentlandite μorμe the contact zone between Monchepluton and Monchetundra . The trachytoid μabbronorite oλ the middle zone emplaced – ± Ma and ± Ma ”ayanova et al., . The μabbro-anorthosite oλ the upper zone was previously dated to have an aμe oλ ± Ma Mitroλanov et al., that within error was conλirmed by the investiμations carried out within the present project ± Ma, Fiμ. “, Table . The aμes oλ ± Ma and ± Ma obtained on baddeleyite that as a primary iμneous mineral allows reliably establishinμ the time oλ crystallization corroborate the μeoloμical evidence oλ the earlier emplacement oλ the upper zone leucoμabbronorite and μabbronorite-anorthosite based on the xenoliths λound in the μabbro-anorthosite Fiμ. ”-C, Table . Thus, accordinμ to the U-Pb isotope study, two injection phases have been established λor the upper zone oλ the Monchetundra intrusion an earlier ± Ma, ± Ma and a later ± Ma, ± Ma one. The aμes oλ ± Ma Fiμ. D, Table indicate the time oλ the earliest rock alterations and within error coincides with the alteration aμe oλ the other Early Proterozoic μabbro-anorthosite intrusions Mitroλanov et al., . “ discordant aμe oλ ± Ma Fiμ. E, Table , however, may indicate the presence oλ rocks oλ diλλerent aμe amonμ stronμly amphibolized μabbroids. The ranμe oλ aμes λor the Monchetundra intrusion conλirms its polychronous nature and lonμ-term evolutional history, and is close to that λor the Fedorovo-Pansky Complex ”alashov et al., Mitroλanov et al., ”ayanova et al., , .

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

Figure 8. U–Pb concordia diagrams for zircon, baddeleyi“e and r”“ile from differen“ rocks of “he Monchegorsk Layered Complex.

165

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Geochronology - Me“hods and Case S“”dies

No.

Weight of portion,

Concentration,

Mg

ppm

Pb isotope composition

206

Pb

U

Pb/

204

Pb

206

Pb/

207

Pb

206

Pb/

208

Pb

Isotope ratios and age Ma**

207

Pb/

235

U

206

Pb/

238

U

207

Rho

Pb /

206

Pb

Coarse-grained massive gabbro-anor“hosi“e, sligh“ly amphibolized, wes“ern slope of M“. Khippikny”nchorr (

-4)

1

0.30 (bd)

62.2

138.3

3759

6.1220

35.850

9.64313

0.437144

2456

0.97

2

0.10 (bd)

45.5

107.9

4982

6.1556

48.241

9.12187

0.413717

2455

0.95

3

0.50 (zr)

348.4

634.6

7223

6.191

1.6275

7.88063

0.357735

2453

0.84

4

0.20 (zr)

216.8

420.0

562

5.7009

5.5664

9.06935

0.430759

2376

0.78

Medi”m-“o-coarse-grained le”cogabbronori“e, so”“heas“ern slope of M“. Monche“”ndra (1/106) 1

0.50 (bd)

110.7

244.9

1478

5.9187

23.690

9.504470

0.429716

2460

0.94

2

0.35 (bd)

152.6

359.1

3510

6.1640

35.011

9.119096

0.413367

2441

0.95

3

0.50 (bd)

60.5

136.8

830

5.5615

13.663

8.820570

0.400447

2453

0.91

4

0.20 (bd)

98.0

246.4

1539

6.3461

24.580

8.368770

0.382377

2437

0.83

Medi”m-“o-coarse-grained gabbronori“e-anor“hosi“e, so”“heas“ern slope of M“. Monche“”ndra (7/106) 1

0.25 (bd)

94.5

114.8

86

3.3003

2.2134

9.92226

0.450763

2500

0.70

2

0.20 (bd)

57.6

123.1

570

5.5602

11.459

9.08165

0.417879

2430

0.93

3

0.25 (bd)

30.1

67.9

557

5.6496

8.0718

8.19067

0.385383

2392

0.88

Medi”m-“o-coarse-grained massive me“amorphosed le”cogabbro, wes“ern slope of M“. Khippikny”nchorr (

-3)

1

0.35 (bd)

145.6

385.9

9943

6.6849

24.354

7.82654

0.368090

2326

0.94

2

0.40 (zr)

132.2

245.9

2892

6.4701

1.7904

7.68813

0.362228

2347

0.91

3

0.25 (zr)

296.5

590.4

10687

6.4780

1.7975

7.18160

0.340041

2382

0.94

4

0.20 (bd)

22.9

96.0

3075

6.4669

27.545

4.69641

0.232147

2351

0.86

0.15 (zr)

38.3

73.6

3640

5.2862

7.1653

11.6136

0.453251

2706

5

Medi”m-“o-coarse-grained massive me“amorphosed gabbro, wes“ern slope of M“. Khippikny”nchorr (

0.96 -5)

1

0.20(zr)

442.9

674.4

11730

6.1317

1.3673

8.96466

0.401310

2477

0.95

2

0.20(zr)

110.7

187.1

4750

6.0548

1.6944

8.67071

0.389643

2482

0.85

3

0.30(zr)

717.3

1260.8

8770

6.1474

1.4718

7.83127

0.357492

2469

0.96

4

0.20(zr)

238.8

453.0

6557

6.2417

1.7384

7.67200

0.351541

2437

0.9

No“es: ra“ios correc“ed “o “he free-r”nning con“amina“ion 0.08 ng for Pb and 0.04 ng for U and “o mass-discrimina“ion of 0.12±0.04 %. ** Correc“ion “o admix“”re of coμmon lead made for “he age acc. “o “he model by S“acey and Kramers (S“acey, Kramers, 1975). Table 4 Iso“ope U-Pb (ID-TIMS) da“a for baddeleyi“e (bd) and zircon (zr) from “he rocks of “he Monche“”ndra in“r”sion.

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

. Pentlandite gorge Monchetundra and Monchepluton : Isotope U-Pb age on single zircon and baddeleyite and Sm-Nd data on rock-forming and sulfides minerals from plagiopyroxenites Pentlandite μorμe is a very important part oλ Monchetundra massiλ so it is a contact place with Moncheμorsk intrusions Smolkin et al., . From plaμiopyroxenites oλ outcrops about kμ were separated accessory minerals-baddeleyite and zircon were very small sizes about m and about - mμ. ”addeleyite μrains are black and dark brown were separated by types due to sizes. Zircon μrains are brown and were a λraμment oλ the crystals and subdi‐ vided onto types on sizes. Isotope U-Pb datinμ presented in Fiμ. “, Table and all points lie near the concordant with aμe . ± . Ma which reλlect oriμin oλ plaμiopyroxenite. The λinal maμmatic activity in Monchetundra massiλ connected with μabbro peμmatite rocks. “bout kμ oλ the rocks were taken λor U-Pb sinμle zircon datinμ. “ll zircon λrom separation procedures ”ayanova et al., were subdivided into types due to colored. Grains oλ zircon are pink and have sliμhtly rounded and corroded λeatures with m in sizes. “ll zircon population in CL transmission are characterized by invisible zonetions and was separated into intensively oλ color on three types to U Pb datinμ. Sinμle zircon λrom μabbro-peμmatite on UPb isochron yielded . ± . Ma and reλlect the aμe oλ crystallization oλ the rock Fiμ. ”, Table .

Figure 9. U-Pb concordia diagrams from Pen“landi“e gorge (Monche“”ndra massif) on: a-zircon (1-3, 6) and baddeley‐ i“e (4, 5) from plagiopyroxeni“e; b-zircon from gabbro-pegma“i“e.

167

168

Geochronology - Me“hods and Case S“”dies

From plaμiopyroxenites oλ Pentlandite μorμe were separated rock-λorminμ minerals Cpx and Opx, Pl and sulλides Po to Sm-Nd datinμ. “ll ±

Ma Fiμ.

, Table

with positive

minerals yielded Sm-Nd isochron aμe with

Nd=± . and model TDM aμe –

Ma . Two points

oλ sulphides – mixture oλ sulλides and pyrrhotine toμether with rock-λorminμ minerals have shown less error in Sm-Nd datinμ and possibilities usinμ sulphides in datinμ oλ layered PGE intrusions Yekimova et al.,

. Value

Nd

T is positive and considered as a result oλ depleted

mantle reservoir DM .

№ Weight Concentration mg

Isotopic composition1)

Isotopic ratios and age in

%

Ma2)

Dis

(ppm) Pb/

206

Pb

U

204

Pb

206 206

Pb/238U±2σ

207

Pb/235 U±2σ 207Pb/206Pb±2σ

Pb/238U 207Pb/235U ±2σ

±2σ

Pb/

207

Pb±2σ

206

Plagiopyroxeni“e, zircon (1-3, 6) and baddeleyi“e (4, 5) 1

0.099

25.45

38.49

1056.1

0.473±0.002 10.713±0.059

2

0.093

25.46

30.49

975.1

0.472±0.002 10.687±0.059

3

0.085

43.19

68.43

1084.9

0.472±0.002 10.684±0.049

4

0.010

60.65

67.39

257.0

0.472±0.008 10.683±0.188

5

0.010

60.07

69.55

414.1

0.467±0.007 10.588±0.178

6

0.076 271.47 286.32

859.2

0.465±0.003 10.509±0.086

0.1644±0.000 6 0.1642±0.000 6 0.1643±0.000 4 0.1640±0.001 0 0.1640±0.001 0 0.1638±0.000 9

2496±11 2499±14 2501±8

0.2

2493±11 2496±14 2499±9

0.2

2491±10 2496±11 2500±6

0.4

2493±40 2496±44 2499±18 0.2

2473±39 2488±42 2500±16 1.1

2463±15 2481±20 2495±14 1.3

Gabbro-pegma“i“e, zircon 1

0.15

61.20

96.42

1709.4

2

0.05

130.84 225.37

1594.9

3

0.08

10.31

460.6

28.13

0.4562±0.003 3 0.3953±0.002 9 0.3650±0.003 1

10.003±0.074

8.678±0.080

8.011±0.070

0.1590±0.000 3 0.1592±0.000 9 0.1599±0.000 3

2423±18 2435±18 2445±4

0.9

2147±16 2304±21 2447±14 12.2

1361±12 1846±16 2447±5 44.4

The ra“ios are correc“ed for blanks of 1 pg for Pb and 10 pg for U and for mass discrimina“ion 0.12 ± 0.04%.

1)

Correc“ion for common Pb was de“ermined for “he age according “o S“acey and Kramers (1975).

2)

Table 5 Iso“ope U-Pb da“a on zircon and baddeleyi“e from differen“ rocks of Monche“”ndra massif.

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

Figure 10. Iso“ope Sm-Nd mineral isochrone for rock-forming and s”lphides minerals from plagiopyroxeni“es of Pen‐ “landi“e gorge.

Sample

Concentration (ppm)

Isotope ratios

№

Sm

Nd

147

P-1/109 WR

0.678

2.090

0.17617

0.512377±19

P-1/109 Po

0.018

0.095

0.11710

0.011381±59

P-1/109 S”lf

0.032

0.123

0.15607

0.512015±43

P-1/109 Cpx

1.048

3.230

0.19614

0.512687±33

P-1/109 Opx±Cpx

1.095

3.374

0.19018

0.512586±16

P-1/109 Pl

0.090

0.523

0.10363

0.511171±26

Sm/

144

Nd

143

Nd/

144

TDM (Ga)

εNd (2.5 Ga)

3192

±1.2

Nd

Average s“andard val”es: N=11 (La Jolla:=0.5118336); N=100 (JNdi1:=0.51209815). Table 6 Iso“ope Sm-Nd da“a on rock-forming and s”lphides minerals from Pen“landi“e gorge.

. Specific features of the isotope investigation of the intrusions U-Pb TIMS , Sm-Nd, and Rb-Sr methods have been applied in this work λor diλλerent purposes.

169

170

Geochronology - Me“hods and Case S“”dies

The U-Pb concordia and isochron method has been used to deλine the aμe oλ the rocks. The values obtained on zircons and baddeleyites λrom the same sample usually lie at the isochron Table , indicatinμ a similar aμe oλ maμma crystallization and subsequent transλormations. Coordinates oλ baddeleyites are near the concordia line. The method however encounters the obstacle that maλic rocks contain very λew zircon and baddeleyite μrains. Samples oλ tens oλ kiloμrams yield only a λew milliμrams oλ these minerals. The Sm-Nd system is not an accurate μeochronometer ~ - % . However, the Sm-Nd isochron method can allow the establishment oλ crystallization times λor maλic rocks on major rockλorminμ minerals orthopyroxene, clinopyroxene, and plaμioclase . It is especially important λor datinμ rocks with synμenetic ore minerals and sulphides. For example, this method has been used to determine λor the λirst time the aμe ± Ma oλ the early ore body in the Penikat Cu-Ni-PGE deposit oλ the Finland Southern belt that has economic importance Yekimova et al., . Layered intrusions

Age (Ma) U-Pb

εNd(T) @ Sm-Nd

U/Pb age

Northern belt M“. Generalskaya gabbronori“e

2496±101 (2505±1.6)2

anor“hosi“e

2446±10

2453±421

-2.3

2492±313

-1.4

2489±4917

+1.2

1

Monchepl”“on M“. Travyanaya, nori“e

2507915;

D”ni“e block, gabbronori“e dyke

2506±1015; 2496±1415

Ny”d Terrace, gabbronori“e

2500514

Ny”d Terrace, gabbronori“e

2493±71 (2504±1.5)2

V”rech”aivench Foo“hills, me“agabbronori“e

2497±2115 Main Ridge

Monche“”ndra, gabbro

2463254; 245345

Monche“”ndra, gabbronori“e

2505±614; 2501±814

Monche“”ndra, plagiopyroxeni“e

2502.3±5.917; 2445.1±1.717

Ch”na“”ndra, anor“hosi“e

2467±715

Os“rovsky in“r”sion, gabbronori“e-pegma“i“e

24451115 Fedorovo-Pansky Complex

or“hopyroxeni“e

2526±612

2521 ± 4213

-1.7

olivine gabbro

2516±712

2516 ± 3513

-1.4

magne“i“e gabbro

2498±5

6

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

Layered intrusions

Age (Ma)

εNd(T) @

U-Pb

Sm-Nd

U/Pb age

gabbronori“e

2491±1.5 (2501±1.7)

2487±517

-2.1

C”-Ni PGE-bearing gabbronori“e

2485±912

2482 ± 3613

-2.4

PGE-gabbro-pegma“i“e

2470±97

PGE-anor“hosi“e

2447±127

2444±777

-2.0

2439±298

-1.2 -2.4

7

2

Imandra lopoli“h gabbronori“e

2446±397(2441±1.6)2

gabbro-diori“e-pegma“i“e

24404

nori“e

243776

le”cogabbro-anor“hosi“e

2437116

granophyre

2434156

olivine gabbronori“e (dyke)

239556

monzodiori“e dyke

2398216

6

Southern belt Kivakka, olivine gabbronori“e

2445±27

L”kk”laisvaara, pyroxeni“e

2439±11 (2442±1.9)

2388±59

Tsipringa, gabbro

2

2441±1.2

B”rakovskaya in“r”sion, gabbronori“e

2449±1.1

2

Kovdozero in“r”sion, pegma“oid gabbronori“e

243696

7

2

8 8

2430±26

-1.1

2365±90

8

-2.0

Finnisn group Koi“elainen

2433±89

Koilismaa

2436±5

Nyaryankavaara

2440±1610

-2.0

2410±649

-1.6

2426±38

-1.4

10

Penika“

Akanvaara

24374911

24377

242349

11

16

11

-2.1

1. Bayanova e“ al., 1999

7. Balashov e“ al., 1993

13. Serov e“ al., 2007

2. Amelin e“ al., 1995

8. Amelin, Semenov, 1996

14. Bayanova & Mi“rofanov, 2005

3. Tols“ikhin e“ al., 1992

9. H”hma e“ al., 1990

15. Bayanova e“ al., 2009

4. Vrevsky, Levchenkov, 1992

10. Alapie“i e“ al., 1990

16. Yekimova e“ al., 2011

5. Mi“rofanov e“ al., 1993

11. Hanski e“ al., 2001

17. Presen“ s“”dy (single U-Pb zircon-

6. Bayanova, 2006

12. Ni“kina, 2006

baddeleyi“e da“a)

Table 7 S”mmary of U-Pb and Sm-Nd geochronology for layered in“r”sions loca“ed in “he eas“ern Bal“ic Shield.

171

172

Geochronology - Me“hods and Case S“”dies

For the maλic-ultramaλic intrusions oλ the Kola belt, the Sm-Nd aμes overlap because oλ hiμh errors, but are commonly close to the U-Pb TIMS data on zircon and baddeleyite.

Sample

Concentration

No

(ppm) Sm

Nd

Isotopic ratios

147

Sm/144Nd

143

εNd

TDM

(2.5 Ga)

(Ga)

87

Rb/86Sr

87

Sr/86Sr(±2σ)

@2.5 Ga

Nd/144Nd

(±2σ) Monche“”ndra MT-10, medi”m-

0.483

1.913

0.152689

0.51192533

-0.36

2.81

0.00495

0.7039±2

S-3464, gabbronori“e 1.147

5.362

0.129320

0.511449±14

-2.30

2.91

0.00534

0.7042±2

Pan-1, gabbronori“e 0.762

3.293

0.139980

0.511669±7

-2.00

2.98

0.00135

0.7032±1

Pan-2, gabbronori“e 0.423

1.662

0.153714

0.51180720

-2.50

3,18

0.00174

0.7029±2

F-4, olivine gabbro

0.629

2.801

0.135695

0.5115488

-1.53

2.94

0.00144

0.7029±2

F-3, or“hopyroxeni“e 0.318

1.166

0.164803

0.512196±12

-1.73

3.05

0.00205

0.7033±2

2.156

10.910

0.119130

0.511380±3

-2.00

2.88

0.00339

0.7046±3

M-1, q”ar“z nori“e

1.750

8.040

0.131957

0.511493 ±3

-1.51

2.91

0.01053

0.7034±9

H-7, gabbronori“e

0.920

4.150

0.134055

0.511537 ±4

-1.37

2.90

0.00227

0.7037±2

grained pyroxeni“e M“. Generalskaya

Fedorovo-Pansky in“r”sion

Imandra lopoli“h 6-57, gabbronori“e Monchepl”“on

Table 8 Iso“ope Sm-Nd and Rb-Sr da“a for rocks of “he layered Paleopro“erozoic in“r”sions.

It is also important to stress that the Sm-Nd method provides valuable petroloμical and μeochemical markers Nd T and TDM. The Nd shows the deμree oλ mantle maμma source depletion, while TDM indicates an approximate aμe oλ the mantle protolith Faure, . The Rb-Sr whole rock and mineral isochron method is mostly valuable λor datinμ unaltered λelsic iμneous rocks and metamorphic amphibolite-λacies associations Faure, . In this work, in Rb-Sr isotope values λor the rocks Fiμ. , Table are considered to have only a petroloμical implication. Toμether with speciλic trace elements Cu, Ni, Ti, V, and LREE , Nd . Ga , REE, Nd-ISr Fiμ. , Table , and He/ He Table data, the values oλ initial Sr/ Sr ISr, . Ga indicate an enriched mantle reservoir . billion years aμo which is comparable with the modern EM-I Hoλmann, .

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

Figure 11. Iso“ope εNd-ISr plo“ of rocks from “he Nor“hern (Kola) Bel“ layered in“r”sions. Grey colo”r in “he diagram shows EM-1 reservoir plo““ed for “he layered in“r”sions of “he Kola Penins”la based on “he Sm-Nd and Rb-Sr iso“ope da“a given in Table 8.

Не10-6

4

Hole No/sampling depth (m)

Rock, mineral

µcm3/g

Не/3Не106

4

Low Mantle contribution**%

Monche“”ndra hole, 765/905,9

Clinopyroxene

163.00

4.76

0.21

hole, 765/905,9

Or“hopyroxene

21.00

4.76

0.21

hole, 765/985,3

Amphibole

97.00

4.76

0.21

hole, 765/985,3

Clinopyroxene

115.00

5.00

0.20

o”“crop, MT-5

Gabbro

1.30

2.00

0.41

Fedorovo-Pansky in“r”sion hole, Ki-16/6

Amphibole

81.00

9.10

0.11

hole,

Or“hopyroxene

9.90

12.80

0.08

Ilmeni“e

43.90

16.50

0.06

а-14/1

o”“crop, No 9 Monchepl”“on, M“. Sopcha hole, 995/315

Olivini“e, rock

17.00

6.25

0.16

hole, 995/315

Olivine

25.00

5.88

0.17

hole, 995/315

Or“hopyroxene

31.00

6.25

0.16

hole, 995/315

Plagioclase

47.00

5.56

0.18

hole, 995/315

Magne“i“e

132.00

4.35

0.23

hole, 904/102

D”ni“e, rock

218.00

1.47

0.68

hole, 904/102

Olivine

115.00

1.35

0.74

hole, 1651/244,9

Chromi“i“e, ore

56.00

1.43

0.70

hole, -1651/373,5*

D”ni“e-Bronzi“i“e

28.00

0.83

1.20

hole, -1622/7*

Chromi“i“e, ore

2.80

0.69

1.44

Monchepl”“on, d”ni“e block

173

174

Geochronology - Me“hods and Case S“”dies

4

Не10-6

Rock, mineral

hole, -1646/450*

D”ni“e

2.20

1.29

0.77

hole, -1651/373.5*

D”ni“e-Bronzi“i“e-con“ac“

0.13

0.60

1.68

µcm3/g

4

Не/3Не106

Low Mantle

Hole No/sampling depth (m)

contribution**%

No“e: errors are according “o “he calc”la“ion me“hod (Tols“ikhin and Mar“y, 1998). *S“ep wise hea“ing experimen“ (frac“ion ”nder “he “empera“”re 1300C). **Man“le componen“s are given from val”e 4He/3He 0.55×104 (solar heli”m from lower man“le reservoir), Tols“ikhin and Mar“y (1998). Table 9 Iso“opic 4 е/ 3 е ra“ios of PGE layered in“r”sions of “he Bal“ic Shield.

. Summary and conclusions . . Total duration of magmatic activity, timing and multi-stages The larμest and richest ore deposits oλ the Monchepluton, Monchetundra and FedorovoPansky Complexes have been careλully studied by μeochronoloμical methods. The layered or diλλerentiated series oλ maλic-ultramaλic rocks, λrom troctolite to leucoμabbroanorthosite, and synμenetic Cu-Ni-PGE ores oλ the Monchepluton λormed within the time interval oλ max to min Ma. Without analytical errors, the time interval is λrom Ma to Ma. Some researchers Smolkin et al., suμμest that the Vurechuaivench part oλ the pluton, composed oλ μabbroids and anorthosites containinμ PGE deposits, is an independent maμma chamber and that the aμe oλ rock and synμenetic PGE ore emplacement is ± Ma. The Fedorov ”lock oλ the Fedorovo-Pansky Complex represents an independent maμma chamber, the rocks and ores oλ which diλλer siμniλicantly λrom those oλ the Western Pansky ”lock Schissel et al., Nitkina, Serov et al., . The early maμmatic activity about . Ga maniλested itselλ in the μabbronorite oλ the Monche‐ tundra ± Ma and ± Ma and Mt. Generalskaya ± Ma . The maμmatic activity that resulted in the λormation oλ anorthosite took place about and Ma. It also contributed to the layered series oλ the Chunatundra ± Ma and Mt. Generalskaya ± Ma , Monchetundra μabbro ± Ma ± μabbro-anorthosite and peμmatoid μabbronorite oλ the Ostrovsky intrusion ± Ma . The Imandra lopolith is the younμest larμe layered intrusion within the Kola ”elt. It varies λrom the other intrusions oλ the Kola ”elt both in its emplacement aμe and its metalloμeny. There are λive U-Pb zircon and baddeleyite aμes λor the rocks oλ the main maμmatic pulse represented by norite, μabbronorite, leucoμabbro-anorthosite, μabbrodiorite, and μranophyre all λormed within the interval λrom to Ma. Thus, several eruptive pulses oλ maμmatic activity have been established in the complex intrusions oλ the Kola ”elt, includinμ at least λour pulses or phases in the Fedorovo-Pansky

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

Complex a Ma barren pulse, and three ore-bearinμ oλ Ma, Ma, and Ma. For similar intrusions oλ the Fenno-Karelian ”elt, λor example, Penikat intrusion in Finland, λive maμmatic pulses varyinμ only in μeochemistry have been distinμuished λrom the same deep chamber Voμel et al., Iljina & Hanski, . “ total duration λor maμmatic processes oλ over unexpected λor many researchers.

million years in the Kola ”elt intrusions is

The multi-phase maμmatic duration oλ the Fenno-Karelian ”elt intrusions was short-term and took place about . Ga years aμo. However, there are only a λew U-Pb precise aμe estimations λor the Fenno-Karelian ”elt intrusions Iljina & Hanski, . “ joint Russian-Finnish research collaboration intended λor datinμ the intrusions oλ the both belts has recently been initiated. It is expected that the research will result in updatinμ the knowledμe about the timinμ and duration oλ the Paleoproterozoic ore-λorminμ intrusions on the ”altic Shield. The Kola results underline that the layerinμ oλ the intrusions with thinly-diλλerentiated horizons and PGE reeλs was not contemporaneous or synμenetic with each intrusion deλininμ its own metalloμentic trends in time and space. . . Metallogeny features The Palaeoproterozoic maμmatic activity in the eastern ”altic Shield is associated with the λormation oλ widespread ore deposits Cu-Ni ±PGE , Pt-Pd ±Rh, ±Cu, Ni, “u , Cr, Ti-V Richardson & Shirey, Mitroλanov & Golubev, . On the Kola Peninsula, economic Cu-Ni ±PGE deposits are known in the Moncheμorsk ~ Ma and Pechenμa ~ Ma type intrusions. In the Monchepluton the Moncheμorsk type , synμenetic disseminated Cu-Ni ±PGE ore bodies oλ maμmatic oriμin are conλined to basal parts oλ maμmatic chambers Papunen & Gorbunov, , while massive rich redeposited ores in the veined bodies oλ the Monchepluton bottom as well as beyond it oλλset bodies also contain a relatively hiμh portion oλ platinum amonμ platinum-μroup elements. They are associated mainly with ca. Ma maμnesia-rich maλic-ultramaλic rocks with Nd . Ga values varyinμ λrom- to- . In comparison, Cu-Ni ±PGE ores oλ the Pechenμa type intrusions that are not discussed are related to the Ma μabbro-wehrlite rocks with Nd . Ga values varyinμ λrom ± to ± Hanski et al., Mitroλanov & Golubev, . The basal ores oλ the Fedorovo deposit are λirst oλ all valuable λor platinum-μroup elements Pt, Pd, Rh , but nickel, copper and μold are also oλ economic importance here Schissel et al., . Pt-Pd ±Cu, Ni, Rh, “u reeλ-type deposits and ore occurrences oλ the Vurechuaivench Foothills Monchepluton and Western Pansky ”lock Fedorovo-Pansky Complex seem, in terms oλ μenesis, to be associated with peμmatoid leucoμabbro and anorthosite rocks enriched in latestaμe λluids. Portions oλ this maμma produce additional injections oλ ca. Ma Vurechuai‐ vench , ca. Ma the Lower, Northern PGE reeλ , and ca. Ma the Upper, Southern PGE reeλ oλ the Western Pansky ”lock and PGE-bearinμ mineralization oλ the Mt. Generalskaya intrusion . These nonsimultaneous injections are quite close in terms oλ composition, preva‐ lence oλ Pd over Pt, ore mineral composition Mitroλanov et al., , and isotope μeochemistry

175

176

Geochronology - Me“hods and Case S“”dies

oλ Sm-Nd and Rb-Sr systems. The Nd values λor the rocks under consideration vary λromto- , which probably indicates a sinμle lonμ-lived maμmatic hearth. Chromium concentration > ppm is typical μeochemical λeature oλ the lower maλicultramaλic rocks oλ the layered intrusions oλ the ”altic Shield “lapieti, Iljina & Hanski, . The chromite mineralization is known in the basal series oλ the Monchepluton, Fedor‐ ovo-Pansky Complex, Imandra lopolith Russia , Penikat and Narkaus intrusions Finland and in chromite deposits oλ the Kemi intrusion Finland and Dunite ”lock Monchepluton, Russia . On the contrary, Fe-Ti-V mineralization oλ the Mustavaara intrusion Finland tends to most leucocratic parts oλ the layered series, and to leucoμabbro-anorthosite and μabbrodiorite oλ the Imandra lopolith Russia and Koillismaa Complex Finland . Thus, PGE-bearinμ deposits oλ the reμion are represented by two types the basal and the reeλlike ones. “ccordinμ to modern economic estimations, the basal type oλ deposits is nowadays more preλerable λor mininμ, even iλ the PGE concentration - ppm is lower compared to the reeλ-type deposits > ppm . ”asal deposits are thicker and contain more platinum, copper and, especially, nickel. These deposits are accessible to open pit mininμ. . . Isotope-geochemistry and geodynamic significance Maμmatic processes since the Palaeoproterozoic . Ga have aλλected almost the whole reμion oλ the East-Scandinavian Kola-Lapland-Karelian province and a mature continental crust λormed . Ga in the Neoarchaean Gorbatschev & ”oμdanova, . Thick up to km basaltic volcanites oλ the Sumian aμe . - . Ga in Karelia, Kola and northeast Finland cover an area oλ μreater than . km . In the north, maμmatic analoμues oλ these volcanic rocks are represented by two belts oλ layered intrusions and numerous dyke swarms Vuollo et al., , Vuollo & Huhma, . This toμether composes a sinμle time-and space-related meμacyclic association, the East-Scandinavian Larμe Iμneous Province LIP . “ll the maμmatic units oλ the province coverinμ a huμe area show similar μeoloμical, compositional and metalloμenic λeatures Coλλin, Eldholm, . Reμional μeoloμical settinμs indicate anoroμenic riλt-like intraplate arranμements involvinμ volcano-plutonic belts connectinμ diλλerent domains oλ the Paleoarchaean Kola-LaplandKarelia protocontinent. This resembles early advection extensional μeodynamics oλ passive riλtinμ that is typical oλ intraplate plume processes Pirajno, . Geochemical and isotope-μeochemical data shed liμht on λeatures oλ deep maμma source λor the LIP rocks. TDM values Faure, are approximately the aμe oλ the depleted mantle reservoir DM with sliμhtly enriched Sm-Nd ratios. The TDM values lie within the interval oλ . - . Ga. The Nd values vary λrom- . to- . and similar ISr values . - . obtained λor discrete layered intrusions λorm a narrow ranμe oλ enriched compositions. It is diλλicult to arμue λor a local crustal contamination and we suμμest that the maμmas producinμ diλλerent rocks oλ the LIP layered intrusions were derived λrom a sinμle homoμenous mantle source enriched both with typically maμmatic ore elements Ni, TI, V, and Pt and lithophile elements includinμ liμht REE. To some extent, this reservoir is comparable with the modern EM- source Hoλmann, .

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

Isotope He/ He ratio is also a reliable isotope tracer oλ mantle plume processes Tolstikhin & Marty, ”ayanova et al., , Pirajno, . Their use in studyinμ Precambrian rocks and requires special case. Table shows recent helium isotope data λor the rocks and minerals oλ the Kola ”elt intrusions. The data indicate that the He/ He isotope ratios oλ n x correspond to those oλ the upper mantle and diλλer λrom those oλ the crust n x and lower mantle n x Tolstikhin & Marty, . The helium isotope data tend to λavour a source dominated by mantle derived maμmas with only local crustal contamination. “ccordinμ to the available data Campbell, Condie, Vuollo et al., ”leeker, Ernst & ”uchan, ”leeker, Ernst, ”ayanova et al., present study , the peak oλ the maλic-ultramaλic maμmatic activity oλ the Kola-Karelian, Superior and Wyominμ provinces has been estimated at ~ . Ga. Fiμure presents an attempt to demonstrate some reconstruction oλ the “rchaean supercontinent embodyinμ these three provinces oλ Europe and North “merica Heaman, ”leeker, Ernst, Ernst, . Trends oλ the Kola and Fenno-Karelian ”elts oλ . - . Ga layered intrusions are show with the intraplate nature interpreted λrom the results oλ the present study.

Figure 12. A new correla“ion for “he S”perior, Karelia and Hearne cra“on. The de“ailed fi“ is based on s”ccessf”l ma“ching of several shor“-lived magma“ic even“s, a“ ca. 2450 Ma (Ma“achewan), ca. 2217 Ma (Nipissing (N) and Karja‐ li“ic (K) sills), and ca. 2110 Ma (Mara“hon), as well as correla“ion of “he cover seq”ences (see “ex“). Kola is likely par“ of “his correla“ion as par“ of a grea“er Karelia cra“on. The Wyoming cra“on likely origina“ed from “he re-en“ran“ wes“ of “he Hearne cra“on. No“e “ha“ o”r recons“r”c“ion s”ccessf”lly places “he ca. 3.5 Ga Si”r”a gneiss of Karelia (diamond symbol; E”rope’s oldes“ rocks ) along s“rike of similar age cr”s“ in “he Hearne cra“on. Arrows indica“e par“ of “he long-dis“ance “ranspor“ of magma “o feed “he Nipissing and Karjali“ic sills (Bleeker, Erns“, 2006).

177

178

Geochronology - Me“hods and Case S“”dies

The LIP layered intrusions are directly related to the ”altic Shield metalloμeny Mitroλanov & Golubev, . The > Ma duration and multiphase history oλ the Kola ”elt layered maλic intrusions i.e., . -to . Ga has been shown here. It has also been underlined that the younμer intrusions oλ the Fenno-Karelian ”elt Fiμ. cluster at . Ga Iljina & Hanski, . The partially asynchronous evolution oλ these two belts, that are thouμht to be arms oλ a mantle plume, is now beinμ examined in more detail as a λollow-up to this study within the λramework oλ Russian-Finnish and Canadian research collaboration Ernst, . “ number oλ new U-Pb and Sm-Nd isotope data were obtained λor Monchetundra massiλ oλ Moncheμorsk ore reμion and various rocks oλ the maλic layered intrusions oλ the Kola ”elt ”altic Shield , includinμ those which bear PGE, Ni-Cu and Ti-V mineralization. “ surprisinμly lonμ period oλ multiphase maμmatic activity, λrom to Ma about million years , resulted in the intrusion oλ larμe-scale ore-bearinμ intrusions oλ the Kola ”elt. Maμmatism continued until about Ma and μenerated wide-spread dykes and small-scale intrusions. These results contrast with the published data indicatinμ short-term evolution interval ~ Ma λor similar intrusions oλ the Fenno-Karelian ”elt Iljina & Hanski, . The two belts oλ maλic layered intrusions oλ the ”altic Shield the Kola and Fenno-Karelian belts , toμether with the surroundinμ volcanic rocks and dyke swarms, compose the Palaeo‐ proterozoic East-Scandinavian Larμe Iμneous Province LIP with an area oλ more than . km . The petroloμical-μeodynamic interpretation proposed by the present paper oλ the LIP is a product oλ a vast lonμ-lived plume is based on the enriched isotope characteristics oλ the maμmas and also the larμe volume and widespread distribution oλ the maμmas. The is acknowledμe that alternatives involvinμ super-lonμ duration oλ the homoμenous deep-seated maμma sources are possible.

. Discussion . . Specific features of the isotope investigation of the intrusions The U–Pb concordia and isochron method has been used to deλine the aμe oλ crystallization oλ the rocks. The values obtained on zircons and baddeleyites λrom the same sample usually lie at the isochron, indicatinμ a similar aμe oλ maμma crystallization and subsequent transλorma‐ tions. Coordinates oλ baddeleyites are near the Concordia line. However, the method encoun‐ ters the obstacle that maλic rocks contain very λew zircon and baddeleyite μrains. Samples oλ tens oλ kiloμrams yield only a λew milliμrams oλ these minerals. In order to compare our U–Pb results

isochron points , some samples were sent to the

Royal Ontario Museum Laboratory in Canada. The data obtained there “melin et al. aμree with ours within error. The Sm–Nd system is not an accurate μeochronometer c. – % . However, the Sm–Nd isochron method can allow the establishment oλ crystallization times λor maλic rocks on major rock-λorminμ minerals olivine, orthopyroxene, clinopyroxene and plaμioclase . It is especially

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important λor datinμ rocks with synμenetic ore minerals. For example, this method has been used to determine λor the λirst time the aμe ± Ma oλ the early ore body in the FedorovoPansky Cu–Ni–PGE deposit oλ the Kola Peninsula that has economic importance Serov et al. . For the maλic-ultramaλic intrusions oλ the Kola belt, the Sm–Nd aμes overlap because oλ hiμh errors, but are co monly close to the U–Pb TIMS data on zircon and baddeleyite. They are especially valid λor the marμinal λast-crystallizinμ rocks oλ the Taxitic Zone oλ the FedorovoPansky Complex, where the early barren orthopyroxenite and μabbro have the λollowinμ aμes ± Ma and ± Ma Sm–Nd method and ± Ma and ± Ma U–Pb method , respectively. The ore-bearinμ norite oλ the Fedorov ”lock yielded an aμe oλ ± Ma Sm– Nd method and ± Ma U–Pb method accordinμ to Nitkina and Serov et al. . It is also important to stress that the Sm–Nd method provides valuable petroloμical and μeochemical markers Nd T and TDM. The Nd shows the deμree oλ mantle maμma source depletion, while TDM indicates an approximate aμe oλ the mantle protolith Faure . The Rb–Sr whole rock and mineral isochron method is mostly valuable λor datinμ unaltered λelsic iμneous rocks and metamorphic amphiboliteλacies associations Faure . In our work, Rb–Sr isotope values λor the rocks are considered to have only a petroloμical implica‐ tion. Toμether with speciλic trace elements Cu, Ni, Ti, V and LREE , Nd . Ga and He/ He data, the values oλ initial Sr/ Sr ISr [ . Ga] indicate an enriched mantle reservoir . billion years aμo which is comparable with the modern EM-I. . . The timing, pulsation and total duration of magmatic activity The larμest and richest ore deposits oλ the Monchepluton and Fedorovo-Pansky complexes have been careλully studied by μeochronoloμical methods. The layered or diλλerentiated series oλ maλicultramaλic rocks, λrom troctolite to leucoμabbroa‐ northosite, and synμenetic Cu–Ni–PGE ores oλ the Monchepluton λormed within the time interval oλ max – min Ma. Without analytical errors, the time interval is λrom – Ma. Some researchers Smolkin et al. suμμest that the Vurechuaivench part oλ the pluton, composed oλ μabbroids and anorthosites containinμ PGE deposits, is an independent maμma chamber and that the aμe oλ rock and synμenetic PGE ore emplacement is ± Ma. The Fedorov ”lock oλ the Fedorovo-Pansky Complex represents an independent maμma chamber, the rocks and ores oλ which diλλer siμniλicantly λrom those oλ the Western Pansky ”lock Schissel et al. . The km-thick rock sequence, λrom the Marμinal Zone to the Lower Gabbro Zone, is a layered or diλλerentiated synμenetic series oλ relatively melanocratic pyroxenite-norite-μabbronorite-μabbro dated at ± and ± Ma. The Taxitic Zone is penetrated by concordant and cuttinμ Cu–Ni–PGEbearinμ μabbronorite Fedorovo deposit oλ the second pulse oλ maμmatic injection, which is sliμhtly younμer ± Ma. The Western Pansky ”lock λrom the Main Gabbronorite Zone, without the Lower Layered Horizon and probably without the upper part above m , can also be considered a sinμle synμenetic series oλ relatively leucocratic, mainly olivine-λree μabbronorite-μabbro crystallized

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within the interval oλ – – ± Ma. In the lower part oλ the ”lock there are Norite and Marμinal zones. The Marμinal zone contains poor disseminated Cu–Ni–PGE mineralization. This rock series can be correlated with certain parts oλ the Monchepluton and the Fedorov ”lock. The – m-thick Lower Layered Horizon LLH is prominent because oλ its contrastinμ structure with predominant leucocratic anorthositic rocks. The exposed part oλ the horizon strikes λor almost km and can be traced in boreholes down to a depth oλ m Mitroλanov et al. . ”y its morpholoμy, the horizon seems to be part oλ a sinμle layered series. Never‐ theless, there are anorthositic bodies that in outcrop show cuttinμ contacts and apophyses Latypov & Chistyakova the cumulus plaμioclase compositions in the rocks oλ the horizon are diλλerent λrom those in the surroundinμ rocks and the aμe oλ the PGE-bearinμ leucoμabbro-peμmatite, which is precisely deλined by concordant and near-concordant U–Pb data on zircon as ± Ma, is sliμhtly younμer than the aμes oλ the surroundinμ rocks e.μ. ± . Ma . The LLH rocks, especially the anorthosite and the PGE mineralization, probably represent an independent maμmatic pulse. The upper part and olivine-bearinμ rocks oλ the Western Pansky ”lock and the anorthosite oλ the Upper Layered Horizon ULH with the Southern PGE Reeλ have been poorly explored. They diλλer λrom the main layered units oλ the ”lock in rock, mineral and PGE mineralization composition Mitroλanov et al. . Until now, only one reliable U–Pb aμe ± Ma has been obtained λor the PGE-bearinμ anorthosite oλ the block, which may represent another PGEbearinμ maμmatic pulse. The early maμmatic activity oλ about . Ga maniλested itselλ in the μabbronorite oλ the Monchetundra ± and ± Ma and Mt Generalskaya ± Ma . The maμmatic activity that resulted in the λormation oλ anorthosite took place about and Ma. It also contributed to the layered series oλ the Chunatundra ± Ma and Mt Generalskaya ± Ma , Monchetundra μabbro ± Ma, Mitroλanov et al. and peμmatoid μabbronorite oλ the Ostrovsky intrusion ± Ma. The Imandra lopolith is the younμest larμe layered intrusion within the Kola ”elt. It varies λrom the other intrusions oλ the Kola ”elt both in its emplacement aμe and its metalloμeny. There are λive U–Pb zircon and baddeleyite aμes λor the rocks oλ the main maμmatic pulse represented by norite, μabbronorite, leucoμabbro-anorthosite, μabbrodiorite and μranophyre all λormed within the interval λrom – Ma. Thus, several eruptive pulses oλ maμmatic activity have been established in the complex intrusions oλ the Kola ”elt, includinμ at least λour pulses or phases in the Fedorovo-Pansky Complex a – Ma barren pulse and three ore-bearinμ oλ – , and Ma. For similar intrusions oλ the Fenno-Karelian ”elt, λor example, the Penikat intrusion in Finland, λive maμmatic pulses varyinμ only in μeochemistry have been distinμuished λrom the same deep chamber Iljina & Hanski . “ total duration λor maμmatic processes oλ over Ma in the Kola ”elt intrusions is unex‐ pected λor many researchers. The multi-phase maμmatic duration oλ the Fenno-Karelian ”elt intrusions was short-term and took place about . Ga years aμo. However, there are only a λew U–Pb precise aμe estimations λor the Fenno-Karelian ”elt intrusions Iljina & Hanski

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

. “ joint Russian– Finnish research collaboration intended λor datinμ the intrusions oλ the both belts has recently been initiated. It is expected that the research will result in updatinμ the knowledμe about the timinμ and duration oλ the Palaeoproterozoic ore-λorminμ intrusions on the ”altic Shield. The Kola results underline that the layerinμ oλ the intrusions with thinly-diλλerentiated horizons and PGE reeλs was not contemporaneous or synμenetic , with each intrusion deλininμ its own metalloμentic trends in time and space. . . Metallogenic implications The Palaeoproterozoic maμmatic activity in the eastern ”altic Shield is associated with the λormation oλ widespread ore deposits Cu–Ni ±PGE , Pt–Pd .Rh, ±Cu, Ni, “u , Cr, Ti–V Mitroλanov & Golubev Richardson & Shirey . On the Kola Peninsula, economic Cu–Ni +PGE deposits are known in the Moncheμorsk c. Ma and Pechenμa c. Ma type intrusions. In the Monchepluton the Moncheμorsk type , synμenetic disseminated Cu–Ni +PGE ore bodies oλ maμmatic oriμin are conλined to basal parts oλ maμmatic chambers Papunen & Gorbunov , while massive rich redepos‐ ited ores in the veined bodies oλ the Monchepluton bottom as well as beyond it oλλset bodies also contain a relatively hiμh portion oλ platinum amonμ PGE. They are associated mainly with c. Ma maμnesium-rich maλic-ultramaλic rocks with Nd . Ga values varyinμ λrom to . In comparison, Cu–Ni ±PGE ores oλ the Pechenμa type intrusions, that are not dis‐ cussed, are related to the Ma μabbro-wehrlite rocks with Nd . Ga values varyinμ λrom+ to+ Hanski et al. Mitroλanov & Golubev . The basal ores oλ the Fedorovo deposit are λirst oλ all valuable λor platinum-μroup elements Pt, Pd, Rh , but nickel, copper and μold are also oλ economic importance here Schissel et al. . The ore-λorminμ maμmatic and post-maμmatic processes are closely related to the Taxitic Zone μabbronorite oλ ± Ma maμmatic pulse. Pt–Pd ±Cu, Ni, Rh, “u reeλ-type deposits and ore occurrences oλ the Vurechuaivench Foothills Monchepluton and Western Pansky ”lock Fedorovo-Pansky Complex seem, in terms oλ μenesis, to be associated with peμmatoid leucoμabbro and anorthosite rocks enriched in late-staμe λluids. Portions oλ this maμma produce additional injections oλ c. Ma Vurechuaivench , c. Ma the Lower, Northern PGE reeλ and c. Ma the Upper, Southern PGE reeλ oλ the Western Pansky ”lock and PGE-bearinμ mineralization oλ the Mt Generalskaya intrusion . These nonsimultaneous injections are quite close in terms oλ compo‐ sition, prevalence oλ Pd over Pt, ore mineral composition Mitroλanov et al. , and isotope μeochemistry oλ Sm–Nd and Rb–Sr systems. The Nd values λor the rocks under consideration vary λrom to , which probably indicates a sinμle lonμ-lived maμmatic hearth. Chromium concentration . ppm is a typical μeochemical λeature oλ the lower maλicul‐ tramaλic rocks oλ the layered intrusions oλ the ”altic Shield “lapieti Iljina & Hanski . The chromite mineralization is known in the basal series oλ the Monchepluton, Fedor‐ ovo-Pansky Complex, Imandra lopolith Russia , Penikat and Narkaus intrusions Finland and in chromite deposits oλ the Kemi intrusion Finland and Dunite ”lock Monchepluton,

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Russia . On the contrary, Fe–Ti–V mineralization oλ the Mustavaara intrusion Finland tends to most leucocratic parts oλ the layered series, and to leucoμabbro-anorthosite and μabbrodiorite oλ the Imandra lopolith Russia and Koillismaa Complex Finland . Thus, PGE-bearinμ deposits oλ the reμion are represented by two types the basal and the reeλlike ones. “ccordinμ to modern economic estimations, the basal type oλ deposits is nowadays more preλerable λor mininμ, even iλ the PGE concentration – ppm is lower compared to the reeλ-type deposits > ppm . ”asal deposits are thicker and contain more platinum, copper and, especially, nickel. These deposits are accessible to open pit mininμ. . . Petrological and geodynamic implications Maμmatic processes since the Palaeoproterozoic . Ga have aλλected almost the whole reμion oλ the East Scandinavian Kola-Lapland-Karelian province and a mature continental crust λormed . Ga in the Neoarchaean Gorbatschev & ”oμdanova . Thick up to km basaltic volcanites oλ the Sumian aμe . – . Ga in Karelia, Kola and NE Finland cover an area oλ > km . In the north, maμmatic analoμues oλ these volcanic rocks are repre‐ sented by two belts oλ layered intrusions and numerous dyke swarms Vuollo et al. Vuollo & Huhma . This toμether composes a sinμle time-and space-related meμacyclic association, the East Scandinavian Larμe Iμneous Province LIP . “ll the maμmatic units oλ the province coverinμ a huμe area show similar μeoloμical, compositional and metalloμenic λeatures. Reμional μeoloμical settinμs indicate anoroμenic riλt-like intraplate arranμements involvinμ volcanoplutonic belts connectinμ diλλerent domains oλ the Palaeoarchaean Kola-LaplandKarelia protocontinent. This resembles early advection extensional μeodynamics oλ passive riλtinμ that is typical oλ intraplate plume processes Pirajno . Geochemical and isotopeμeochemical data shed liμht on λeatures oλ deep maμma source λor the LIP rocks. TDM values Faure are approximately the aμe oλ the depleted mantle reservoir DM with sliμhtly enriched Sm–Nd ratios. The TDM values lie within the interval oλ . – . Ga. The Nd values vary λrom- . to+ . and similar ISr values . – . obtained λor discrete layered intrusions λorm a narrow ranμe oλ enriched compositions. It is diλλicult to arμue λor a local crustal contamination and we suμμest that the maμmas producinμ diλλerent rocks oλ the LIP layered intrusions were derived λrom a sinμle homoμenous mantle source enriched both with typically maμmatic ore elements Ni, TI, V and Pt and lithophile elements includinμ liμht REE. To some extent, this reservoir is comparable with the modern EM- source Hoλmann . Isotope He/ He ratio is also a reliable isotope tracer oλ mantle plume processes Tolstikhin & Marty ”ayanova et al. Pirajno . Their use in studyinμ Precambrian rocks requires special care. Table shows recent helium isotope data λor the rocks and minerals oλ the Kola ”elt intrusions. The data indicate that the He/ He isotope ratios oλ n × – correspond to those oλ the upper mantle and diλλer λrom those oλ the crust n × and lower mantle n × Tolstikhin & Marty . The helium isotope data tend to λavour a source dominated by mantle-derived maμmas with only local crustal contamination.

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“ccordinμ to the available data Campbell Condie Vuollo et al. ”leeker Ernst & ”uchan present study , the peak oλ the maλic-ultramaλic maμmatic activity oλ the Kola-Karelian, Superior and Wyominμ provinces has been estimated at c. . Ga. Fiμ. presents an attempt to demonstrate some reconstruction oλ the “rchaean supercontinent embodyinμ these three provinces oλ Europe and North “merica Heaman ”leeker, Ernst, . Insert “ shows trends oλ the Kola and Fenno-Karelian ”elts oλ . – . Ga layered intrusions with the intraplate nature interpreted λrom the results oλ the present study. The LIP layered intrusions are directly related to the ”altic Shield metalloμeny Mitroλanov & Golubev . The Ma duration and multiphase history oλ the Kola ”elt layered maλic intrusions i.e. . – . Ga has been shown here. It has also been underlined that the younμer intrusions oλ the Fenno-Karelian ”elt clustre at . Ga Iljina & Hanski . The partially asynchronous evolution oλ these two belts, that are thouμht to be arms oλ a mantle plume, is now beinμ examined in more detail as a λollow-up to this study within the λramework oλ Russian-Finnish research collaboration. . Relationship oλ Pt-Pd provinces with larμe iμneous provinces, LIP hot plume λields Larμe iμneous provinces or LIPs, by Campbell, Griλλiths, as derivatives oλ deep mantle plume or asthenospheric upwellinμ processes were minutely discussed in May in China at the International Continental Volcanism Conλerence Yi-μanμ Xu, . “ special LIP μroup alonμ with alkaline, komatiite, λelsic ones, is represented by maλic intraplate continental provinces or maλic LIPs, by ”leeker, Ernst, composed oλ thick riλtoμene sedimentary and volcanic rocks coμenetic with dike swarms and maλic-ultramamλic intrusions. Grachyov , Pirajno , ”oμatikov et al. cite main μeoloμical, μeophysical, and μeochemical λeatures oλ μeoloμical processes within LIPs related with deep mantle plumes. Takinμ into account experience oλ studyinμ ancient Precambian areas where most μeoloμical and μeophysical λeatures oλ μeoloμical units, bodies, and rock compositions λail to be pre‐ served, Felix P. Mitroλanov proposed the λollowinμ indicators oλ various rank λor intraplate maλic LIPs • presence oλ μravitational anomalies caused by a crust-mantle layer in the crust bottom • riλtoμene anoroμenic structural ensemble with maniλestations oλ multipath λault tension tectonics identiλied by the distribution oλ μrabens and volcanic belts, elonμated dike swarms, and radial belts oλ intrusions • lonμ duration, polystaμe and pulsatinμ nature oλ tectonics and maμmatism, continental discontinuities and erosion with early staμes oλ tholeiite-basalt trappean , boninite-like and subalkaline maμmatism in the continental crust, and possible closinμ staμes oλ the Red Sea spreadinμ maμmatism • intrusive sills, lopoliths, sheet-like bodies, larμe dikes and dike swarms. The intrusions are oλten layered, beinμ diλλerent λrom rocks typical oλ subduction and spreadinμ zones in terms oλ nature ”leeker, Ernst, , with trends oλ thin diλλerentiation or layerinμ , with limited development oλ intermediate and λelsic rocks, oλten with leucoμabbro and anorthosite ends and abundant peμmatoid maλic varieties

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• typical mantle μeochemistry oλ rocks and ores, isotope mantle tracers Os/ Os, He/ He

Nd/ Nd, Sr/ Sr,

• maλic intracontinental LIPs acco modate larμe orthomaμmatic Cr, Ni, Cu, о, PGE ±“u , Ti, V deposits. The Palaeoproterozoic East-Scandinavian Larμe Iμneous Province LIP with a modern area oλ ca. , , km occupies the eastern part oλ the ”altic or Fennoscandinavian Shield which basement is represented by the mature “rchaean μranulite and μneiss-miμmatite crust λormed > Ma. Main λeatures oλ the structure and description oλ co mercial Pt-Pd and Cu-Ni-PGE deposits are μiven in modern publications oλ F. Mitroλanov, Ye. Sharkov, V. Smolkin, “. Korchaμin, T. ”ayanova, S. Turchenko, etc. It is worth notinμ certain preserved μeoloμical and μeophysical λeatures oλ this ancient Palaeoproterozoic ore-bearinμ maλic LIP. Geophysical survey demonstrated the lower part oλ the Earth crust in the eastern part oλ the shield to be represented by a transitional crust-mantle layer Vp= . - . km/s . Deep xenoliths in the Kandalaksha explosion pipes elevated λrom this layer have the compositions oλ μranulite and μarnet anorthosite with an aμe oλ Ma typical oλ most bodies in the province Verba et al., . This shows that masses oλ deep matter arose not only in the λorm oλ volcanic, dikes, and intrusions, but also emplaced to the crust bottom in the course oλ vast underplatinμ Mitroλanov, . The outcropped part oλ the province continues under the platλorm cover in the northern part oλ the Russian platλorm in the λorm oλ vast Palaeoproterozoic ”altic-Central Russian wide arc, or intracontinental oroμen Mints, . This certainly expands lonμ-term co mercial opportunities oλ the province. “noroμenic autonomous pattern oλ μrabens, dike swarms and belts rays oλ intrusive bodies independent λrom the structure oλ the enclosinμ “rchaean μneiss-miμmatite λrame, is prominent in the Geoloμical Map oλ the Fennoscandian Shield . The studied intru‐ sions with deposits and prospects compose elonμated belts rays , e.μ. northwesttrendinμ Kola belt in the northern part oλ the province, and northeasttrendinμ Fenno-Karelian belt with the concentration oλ intrusions in the well-known Moncheμorsk ore node ”ayanova et al., . In the Early Palaeoproterozoic Ma epoch oλ the lonμ history oλ the LIP evolution, a λew staμes separated by breaks conμlomerates sedimentation and maμmatism have been distinμuished. The Sumi Ma staμe was principle in the metalloμeny oλ Pt-Pd ores related to the intrusive siliceous hiμhly Mμ boninite-like and anorthositic maμma‐ tism Mitroλanov, Sharkov, . Such ore-bearinμ intrusions λormed earlier in the Kola belt Fedorov-Pana and other intrusions Ma and later in the FennoKarelian belt Ma , accordinμ to ”ayanova et al., Mitroλanov et al., Ekimova et al., . “ number oλ new U–Pb and Sm–Nd isotope data were obtained λor various rocks oλ the maλic layered intrusions oλ the Kola ”elt ”altic Shield , includinμ those which bear PGE, Ni–Cu and Ti–V mineralization. “ surprisinμly lonμ period oλ multiphase maμmatic activity, λrom – Ma about Ma , resulted in the intrusion oλ larμe-scale ore-bearinμ

Layered Pge Paleopro“erozoic (LIP) In“r”sions in “he N-E Par“ of “he Fennoscandian Shield... h““p://dx.doi.org/10.5772/58835

intrusions oλ the Kola ”elt. Maμmatism continued until about Ma and μenerated widespread dykes and small-scale intrusions. These results contrast with the published data, indicatinμ short-term evolution interval c. Ma λor similar intrusions oλ the FennoKarelian ”elt Iljina & Hanski . The two belts oλ maλic layered intrusions oλ the ”altic Shield the Kola and Fenno-Kareli‐ an belts , toμether with the surroundinμ volcanic rocks and dyke swarms, compose the Palaeoproterozoic East Scandinavian Larμe Iμneous Province LIP with an area oλ > km . The petroloμicalμeodynamic interpretation proposed by this chapter oλ the LIP is a product oλ a vast lonμlived plume is based on the homoμenous and enriched isotope characteristics oλ the maμmas and also the larμe volume and widespread distribution oλ the maμmas. It is quite possible, and λully consistent with our observations, that the μeochemical siμnatures oλ the LIP maμmas may well have been in part inherited λrom the subcontinental lithosphere, as described recently based on Osisotope characteristics λor the ”ushveld maμmas Richardson & Shirey .

Acknowledgements We thank to D.Wasserburμ λor Pb artiλicial spike, J. Ludden λor and Temora standards, F. Corλu, V. Todt and U. Poller λor assistance in the establishinμ oλ the U-Pb method λor sinμle zircon and baddeleyite μrains. The authors would like to thank the λollowinμ L. Koval λor baddeleyite, zircon, rock-λorminμ and sulphides minerals separation λrom rock samples L. Laylina λor baddeleyite and zircon analyses usinμ a Cameca MS- and λor takinμ imaμes oλ baddeleyite crystals N. Levkovich λor the chromatoμraphic separation oλ U and Pb λor analyses by mass spectrometry at the Geoloμical Institute, Kola Science Center, Russian “cademy oλ Sciences. The studies were supported by the Russian Foundation oλ ”asic researches RF”R , projects no. - , OFI-M- - , IGCP-SID“and Proμram Department oλ Earth Sciences R“S no. , .

Author details T. ”ayanova, F. Mitroλanov, P. Serov, L. Nerovich, N. Yekimova, E. Nitkina and I. Kamensky *“ddress all correspondence to tamara@μeoksc.apatity.ru Geoloμical Institute oλ the Kola Science Centre, Russian “cademy oλ Sciences GI KSC R“S , “patity, Russia

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