Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor (Earth and Environmental Sciences Library) 3031547977, 9783031547973

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Earth and Environmental Sciences Library

Anatoly Schreider Mikhail Klyuev Alexandra Sazhneva Andrey Brekhovskikh

Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor

Earth and Environmental Sciences Library Series Editors Abdelazim M. Negm , Faculty of Engineering, Zagazig University, Zagazig, Egypt Tatiana Chaplina, Antalya, Türkiye

Earth and Environmental Sciences Library (EESL) is a multidisciplinary book series focusing on innovative approaches and solid reviews to strengthen the role of the Earth and Environmental Sciences communities, while also providing sound guidance for stakeholders, decision-makers, policymakers, international organizations, and NGOs. Topics of interest include oceanography, the marine environment, atmospheric sciences, hydrology and soil sciences, geophysics and geology, agriculture, environmental pollution, remote sensing, climate change, water resources, and natural resources management. In pursuit of these topics, the Earth Sciences and Environmental Sciences communities are invited to share their knowledge and expertise in the form of edited books, monographs, and conference proceedings.

Anatoly Schreider · Mikhail Klyuev · Alexandra Sazhneva · Andrey Brekhovskikh

Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor

Anatoly Schreider Moscow, Russia

Mikhail Klyuev Moscow, Russia

Alexandra Sazhneva Moscow, Russia

Andrey Brekhovskikh Moscow, Russia

ISSN 2730-6674 ISSN 2730-6682 (electronic) Earth and Environmental Sciences Library ISBN 978-3-031-54797-3 ISBN 978-3-031-54798-0 (eBook) https://doi.org/10.1007/978-3-031-54798-0 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Paper in this product is recyclable.

Introduction

In the middle of the twentieth century, geomagnetic studies became widespread among the methods studying the tectonics of the World Ocean floor, and methods of complex geological and geophysical interpretation of their results were being widely developed. At that time the USA was the leader in this field, where in 1956 a nuclear (proton) magnetometer on transistors was created, the sensor of which was towed in a sealed gondola on a special non-magnetic cable at a considerable distance from an allmetal ship (having a steel magnetic hull), which made it possible to conduct regular geomagnetic studies in the World Ocean. The study of the magnetic field provided vivid confirmation of the hypothesis of ocean floor expansion. Aeromagnetic and hydromagnetic observations revealed linear magnetic anomalies of the ocean floor [1, 2], the origin of which was then associated with the process of formation of a new oceanic crust [3, 4] based on the formation of an inversion magnetically active layer of the ocean floor on the axes of mid-ocean ridges. A comprehensive analysis of the paleo-magnetic information contained in the anomalous magnetic field of the ocean floor has opened wide prospects in the study of the geodynamic evolution of lithospheric plates throughout the geological history of the ocean, as well as in the prediction of mineral deposits through the reconstruction of paleo-geodynamic settings. In the USSR in the late 1960s and early 1970s, several mock-ups of marine nuclear magnetometers were created. Radiometric circuits of magnetometers were realized on electronic tubes. The magnetic field sensor had a signal preamplifier in the towed nacelle. Measurements were made in analogue form, or in conventional units of magnetic field. In the USSR there was no specialized non-magnetic cable allowing to tow the magnetometer sensor behind the stern of a steel vessel and make regular measurements of the magnetic field at operating speeds of research vessels. The electrical cables used for this purpose had low breaking strength and could not withstand the hydro-dynamic tension during the towing of the nacelle, which led to the breakage of their signal cores. All this significantly reduced the reliability of operation of these instruments, and they were not suitable for regular geomagnetic studies of the World Ocean.

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A number of Russian review papers of the last decades mainly describe the stages of creation and development of magnetometers for magnetic field studies on the continents. In the part of the review papers that deals with the oceans, there is almost no information about the contribution (1965–1972) of the P. P. Shirshov Institute of Oceanology of the Russian Academy of Sciences to the establishment of Russian regular magnetic field studies. The contribution (1965–1972) of the Shirshov Institute of Oceanology of the Russian Academy of Sciences to the establishment of the Russian regular geomagnetic studies of the World Ocean carried out by proton magnetometers MM-1 with sensors towed behind the stern of all-metal research vessels is almost completely missing. Thus, it becomes clear that the list of articles cited in this paper only complements numerous studies of various specialists. The development and creation in 1965 of MM-1 magnetometers [5] provided the establishment and the beginning of regular geomagnetic surveys of the P. P. Shirshov Institute of Oceanology of the Russian Academy of Sciences in the World Ocean. On this basis, a domestic technique of magnetic survey by proton magnetometers on transistors with sensors towed on a special power cable behind the stern of all-metal ocean research vessels and geological-geophysical interpretation of geomagnetic information obtained in the process of observations was created. On the basis of geomagnetic data obtained in the World Ocean, important conclusions were made about the deep structure, kinematics and palaeo-geodynamics of various regions of the ocean floor. Their results were published in numerous scientific papers, were included in international geological and geophysical atlases and were used in candidate and doctoral theses. The development of the research opened a new stage in the study of the geodynamics of our planet and the evolution of the main parts of its geospheres, which continues to this day, opening new perspectives for the study of the geological evolution of the Earth.

References 1. Raff A, Mason R (1961) Magnetic survey off the west coast of North America, 32° N. latitude to 42° N. latitude, 40° N. latitude to 52° N. latitude. Geo Soc Am Bull 72:1267–1270 2. Solov’ev ON (1961) Aeromagnetic survey in the area of the Kuril-Kamchatka island arc. App Geophys 29:168–173 3. Vine F, Matthews D (1963) Magnetic anomalies over oceanic ridges. Nature 199:947–949 4. Morley L, Larochelle A (1964) Paleomagnetism as a means of dating geological events. Geochron Canada 8:39–51 5. Verzhbitsky EV, Schreider AA, Isaev EN (1969) Equipment and methods of geomagnetic studies during the 40th and 41st voyages of the R/V “Vityaz”. Oceanology 9(1):187

Contents

1

Geophysical Aspects of Ocean Floor Evolution . . . . . . . . . . . . . . . . . . . 1.1 Prerequisites for the Creation of the Concept of Lithospheric Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Discoveries of the 1950s and 1970s in Marine Geology . . . . . . . . 1.3 Fundamentals of Global Lithospheric Plate Tectonics . . . . . . . . . . 1.4 Evolution of the Oceanic Lithosphere . . . . . . . . . . . . . . . . . . . . . . . 1.5 General Information on the Magnetically Active Layer of the Ocean Floor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6 Scale of Linear Magnetic Anomalies of the Ocean Bottom . . . . . 1.7 Modelling of the Inversion Magnetically Active Layer of the Oceanic Lithosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 2 6 13 17 19 23 27

2

Geochronology of the Eurasian Basin Floor . . . . . . . . . . . . . . . . . . . . . . 2.1 Geomorphology of the Seabed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Identification of Linear Magnetic Anomalies . . . . . . . . . . . . . . . . . 2.3 Charting the Geochronology of the Seabed . . . . . . . . . . . . . . . . . . . 2.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

31 31 34 35 37 38

3

Paleo-Magnetic Anomalies in the Laptev Sea of the Arctic Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

41 44

Kinematic Model of the Eurasian Basin Floor Development . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Aeromagnetic Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Geochronology of the Seabed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

47 47 47 49 52 53

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Contents

Evolution of the Axial Zone of the Mid-Arctic (Gakkel) Ridge in the Upper Neogene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

55 58

Evolution of Oceanic Crustal Parameters of the Amundsen Basin in the Cenozoic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Research Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

61 61 62 65 65

Evolution of Oceanic Crustal Parameters of the Nansen Basin in the Cenozoic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Research Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

69 69 70 72 73

Kinematics of the Polar Area of Lomonosov Ridge Bottom in Arctic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Research Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Paleo-Geodynamic Calculation Results . . . . . . . . . . . . . . . . . . . . . . 8.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

75 75 75 79 80 81

Kinematic Model of the Arlis Spur Breakaway from the Lomonosov Ridge in the Arctic Ocean . . . . . . . . . . . . . . . . . . 9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 Peculiarities of Research Methodology . . . . . . . . . . . . . . . . . . . . . . 9.3 Research Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

83 83 84 85 87 88

10 Kinematic Model of Development of Eastern Areas of the Gakkel Mid-Ocean Ridge in the Eurasian Basin of the Arctic Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Geological Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3 Structure of the Crust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 Calculation of the Splitting Parameters . . . . . . . . . . . . . . . . . . . . . . 10.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

89 89 90 91 94 96 97

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11 Seafloor Kinematics of the Near-Greenland Region of the Eurasian Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 11.2 Seafloor Morphology and Deep Water Drilling Data . . . . . . . . . . . 102

Contents

11.3 Anomalous Gravity Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4 Structure of the Unconsolidated Crust . . . . . . . . . . . . . . . . . . . . . . . 11.5 Structure of the Acoustic Basement . . . . . . . . . . . . . . . . . . . . . . . . . 11.6 Anomalous Magnetic Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.8 Calculation of the Splitting Parameters . . . . . . . . . . . . . . . . . . . . . . 11.9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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103 105 106 106 109 109 112 112

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

About the Authors

Anatoly Schreider graduated from the Faculty of Geology of Moscow State University in 1966. He is Chief Researcher at the Shirshov Institute of Oceanology of the Russian Academy of Sciences, Doctor of Geology and Mineralogy and Professor. The area of scientific interests is geophysics, tectonics and geodynamics of the ocean floor, as well as the magnetic field of bottom oceanic rocks. He is Leading Expert in the field of the chronological scale of linear ocean magnetic anomalies, Laureate of the International Prize “Man of the Sea” of the Sea League of Italy and Author and Co-author of more than 200 scientific publications, including 12 collective monographs. Mikhail Klyuev graduated from the Faculty of General and Applied Physics of the Moscow Institute of Physics and Technology in 1986. He is Senior Researcher at the Shirshov Institute of Oceanology of the Russian Academy of Sciences and Doctor of Physics and Mathematics Sciences. The area of scientific interests is the development of seismic-acoustic methods, geophysical models, interpretations and equipment for studying the structure and objects of the seabed. He has applied research in marine geology, hydro-acoustics and underwater archeology. He is Author and Co-author of more than 100 scientific publications.

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Alexandra Sazhneva graduated from the Faculty of Radio-Technical Systems of the Moscow Institute of Radio-Electronic Equipment in 1995. She is Senior Researcher at the Shirshov Institute of Oceanology of the Russian Academy of Sciences and Doctor of Technical Sciences. She is Specialist in the field of mathematical modeling and analysis of geodynamic processes, magnetic linear anomalies and kinematics of the seabed floor, as well as computer processing of field data. She is Author and Co-author of near 100 scientific publications.

Andrey Brekhovskikh graduated from the Faculty of Geography of Moscow State University in 1975. He is Researcher at the Shirshov Institute of Oceanology of the Russian Academy of Sciences and Doctor of Physics and Mathematics Sciences. He is Specialist in the field of mathematical modeling and analysis of hydro-physical, hydro-dynamic and geodynamic processes, as well as computer processing of field data. He is Author and Coauthor of more than 50 scientific publications.

Chapter 1

Geophysical Aspects of Ocean Floor Evolution

1.1 Prerequisites for the Creation of the Concept of Lithospheric Plates In the 1889 paper by O. Fisher “Physics of the Earth’s Crust”, perhaps for the first time in the development of the concept of mobilism (i.e., horizontal movements of large blocks of the Earth’s crust), the necessity of simultaneous existence of compression and extension structures on the Earth was shown. He attributed the Pacific mobile belt of increased seismicity to compression structures, and stretching structures— stretching structures in Iceland, on the Mid-Atlantic Ridge and other similar structures. As a basis for the geodynamic model of the Earth’s crust development, he took the regularities of movement of lava crusts formed during the cooling of magma in the Kilauea lava lake in Hawaii, and came to the following conclusions: The oceanic crust develops from the outpouring of basalts within stretching zones, such as those located in Iceland and on the axial “plateau” of the Atlantic Ocean, previously known as the Mid-Atlantic Ridge. Additionally, zones of compression found along the periphery of the Pacific Ocean cause the ocean floor to sink beneath island arcs and continental margins. As a result, this pressing of the oceanic crust beneath the continental crust leads to earthquakes along the Pacific Rim. Convective currents within the subcrustal matter are the force propelling the movement of the Earth’s crustal blocks. Thus, 70–80 years before the appearance of fundamental works on the tectonics of lithospheric plates, a model of the development of geological processes on the Earth so close to the modern one was drawn. However, O. Fisher’s ideas were too far ahead of their era, were not appreciated by contemporaries and the geological theory had to be created independently and anew. The next step in the development of the ideas of mobilism was made by the outstanding German geophysicist A. Wegener, who in 1912 substantiated the hypothesis of continental drift. As arguments testifying to continental drift and the breakup © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0_1

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of the once unified supercontinent Pangea, A. Wegener cited the extraordinary similarity of coastline outlines and the same geological structure of continental margins on different sides of the Atlantic Ocean, as well as the commonality of ancient fauna and flora in adjacent areas of the now separated continents and the characteristic distribution of paleo-climatic belts on the surface of modern continents. Unfortunately, with the death of A. Wegener in 1930, his bold hypothesis of continental drift was forgotten. Following A. Wegener, English researcher A. Holmes proposed to explain the movement of continents by the action of forces created by convective flow of hightemperature mantle matter inside the Earth. He also introduced into geology the idea of determining the absolute age of Earth rocks by radioactive isotopes, which helps to reconstruct the chronology of geological events on Earth in the past.

1.2 Discoveries of the 1950s and 1970s in Marine Geology It took a long time before facts were accumulated that confirmed not only the existence of continental drift itself, but also revealed a new phenomenon—the ocean floor sliding and its sinking into the mantle. This occurred in the mid-1950s, and the main role here was played by the results of studying the morphological and geological structure of the ocean floor (including deep-sea drilling data), seismic studies, and paleo-magnetic data. The study of magnetic properties of rocks has shown that rocks containing magnetic minerals (magnetite, titanium-magnetite) are able to “remember” the ancient magnetic field of the Earth. The reconstruction of the characteristics of this field using rock samples from different continents and magnetic anomalies in the oceans led geophysicists to an interesting and important conclusion: over time, the position of all continents on the surface of the Earth changes significantly. But if we arrange the individual continents in such a way that their palaeo-magnetic poles of the late Paleozoic coincide with the modern geographical poles, then the reconstruction of the supercontinent Pangea, the model of which was built by A. Wegener 25 years before the appearance of palaeo-magnetic data itself, was unexpectedly obtained. In the same years, a map of the bottom of the World Ocean was constructed (Fig. 1.1) and the largest underwater ridges (Fig. 1.2) were discovered, girdling the entire Earth and stretching across all the oceans for a distance of up to 60 thousand kilometres. It also turned out that along the crests of these mid-ocean ridges there are deep stretching cracks (rift zones) from which young basalts poured out. In addition, it was found that simultaneously with the movement of continents, some oceans are opening and others are shrinking. The age of the bottom of all the oceans without exception is relatively small, not exceeding 180 million years, while the average age of the continents themselves reaches 3.5–4.5 billion years. In the 1950s, German geologist H. Stille linked the formation of deep-sea troughs with zones of oceanic crust thrusting under the continental crust. As the oceanic crust is underthrusted at a certain depth in the high-temperature mantle layer and

1.2 Discoveries of the 1950s and 1970s in Marine Geology

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Fig. 1.1 Relief of the bottom of the World Ocean (https://avatars.dzeninfra.ru/get-zen_doc/523 4501/pub_62ab10c5419db10068e0783c_62ab2666ba618c2069dce311/scale_1200), modified

Fig. 1.2 Locations of major rift spreading zones (red dashed line) and transform faults (green dashed line) within the mid-ocean ridges of the World Ocean. Subthrust (subduction) zones are shown by black serrated lines (http://johomaps.com/world/worldtecton.html), modified

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additionally heated due to friction, it undergoes melting, giving rise to volcanic centers above the underthrust zones located parallel to the axis of the marginal trench. His idea had predecessors. Back in the mid-1930s, the Japanese scientist K. Wadati, using seismic sounding, first discovered a tilted seismic focal zone extending inland from the deep-sea trough beneath the volcanic centres of the Japanese Islands. Such a fact indicated the connection between the island arcs and possible oceanic lithosphere thrusting along the periphery of the Pacific Ocean. The assumption about the primary and determining role of deep seismic active areas of inclined type in the occurrence of near-surface sources of earthquakes and volcanism above them, which are secondary factors, was made in 1946 by the Russian geologist A. N. Zavaritsky. As a result of the discoveries of the 1950s and 1960s, the hypothesis of continental drift began to revive rapidly, but already at a completely new level. Thanks to the efforts of scientists from different countries of the world, by the end of the 1960s this hypothesis had developed into a coherent concept—the theory of lithospheric plate tectonics. Geophysicists and geologists who studied the structure and development of the ocean floor made a particularly great contribution to its development. In 1961 and 1962, American scientists geologist H. Hess and geophysicist Dietz [1, 2] reiterated the main ideas of O. Fisher about the formation of oceanic crust in mid-ocean ridges, about the youth and expansion of the ocean floor, as well as about the ocean floor dipping into the mantle in the zones of deep-water troughs. In 1963–1964, British and Canadian geophysicists Vine et al. [3, 4] suggested that the banded magnetic anomalies on the ocean floor represent a “record” of inversions of the Earth’s magnetic field in the rocks of the expanding ocean floor, which plays the role of a natural “magnetic tape” in the giant “magnetophone”—the Earth’s lithosphere. On this basis, in 1968, a group of American and French geophysicists (J. Hertzler, X. Le Pichon, etc.) theoretically calculated the age of the ocean floor [5]. It turned out that practically in all areas of the World Ocean the ocean floor was formed relatively recently (only in the Cenozoic and Late Mesozoic times), and the age of the floor increases with distance from the crests of mid-ocean ridges. In 1965, Canadian geologist J. Wilson first drew attention to the fact that the Earth’s rigid shell (lithosphere) is divided into a number of plates delineated by three types of boundaries: rift zones, plate thrust zones and transform faults—a new class of faults arising in the lithosphere during the drift of continents and lithospheric plates along the spherical surface of the Earth [6]. At the same time, the famous English geophysicist E. Bullard for the first time used modern mathematical apparatus and computers to reconstruct the position of drifting continents in past geological epochs [7]. In 1968, the American Le Pichon and Morgan [5, 8] identified the largest lithospheric plates (Fig. 1.3) and calculated the parameters of their motion on the surface of the globe. At the same time American seismologists B. Isaks, J. Oliver, and L. Syks showed that the seismicity of the Earth is completely determined by the movement of lithospheric plates on its surface [9]. In 1970, British geologists J. Dewey and J. Bird first considered the development of the geosynclinal process and the formation of the Earth’s mountain belts from the point of view of the new theory [10]. The Japanese geophysicists S. Uyeda and A.

1.2 Discoveries of the 1950s and 1970s in Marine Geology

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Fig. 1.3 Schematic of the location of the main plates of the Earth’s lithosphere (https://bluffpark backporch.wordpress.com/page/14/), modified

Miyashiro studied in detail the mechanisms of oceanic lithospheric plates dipping into the mantle in the plate thrust zones [11]. Russian scientists have also made a great contribution to the development of the theory of lithospheric plate tectonics. Thus, back in the late 1950s, Kropotkin [12] used paleo-magnetic and geological data to prove the existence of continental drift and convincingly showed that in past geological epochs continental movements did occur. In 1965, V. E. Khain based on the analysis of geological and geophysical data on Antarctica concluded that this continent separated from other continents of the Gondwana group as a result of continental drift [13]. In the late 1960s, A. N. Khramov was able to construct a number of paleo-geographic reconstructions using paleo-magnetic data, showing the positions of continents and oceans in different geological epochs [14]. At the same time, the famous Soviet geologist, Academician A. V. Peive, using a large geological material, suggested that the ophiolitic covers found in many mountain belts of the world represent fragments of the ancient oceanic crust overlain by continental margins [15]. The substantiation of this hypothesis allowed us to get an idea of the structure of the oceanic crust even before ocean drilling. In addition, this idea was an important link in the general chain of evidence for the existence of large-scale movements of individual blocks of the Earth’s crust. In the mid-1970s, A. P. Lisitsyn constructed a refined version of the map of ages of the bottom of the World Ocean using drilling data and magnetic anomalies

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[16]. In addition, he used the changes in sedimentation conditions to determine the directions and rates of oceanic plate shifts. These data, as well as palaeo-geodynamic reconstructions by L. P. Sonenshine and A. Schreider, allowed us to trace the evolution of the oceans throughout the Cenozoic and late Mesozoic [17, 18]. Russian researchers have also made important progress in the application of the theory of lithospheric plate tectonics to the problems of regional geology. V. V. Fedynsky and his colleagues used lithospheric plate tectonics to elucidate the conditions for the formation of oil and gas deposits, and also determined the age of the opening of the mid-ocean ridge system in the northern part of the World Ocean based on magnetic anomalies [19]. A. Schreider, based on the integrated geological and geophysical interpretation of the entire complex of accumulated data on the Indian Ocean, created a modern concept of the evolution of its bottom [20]. This concept is currently used in the world practice of analysing the paleo-geodynamic evolution of the ocean. A. S. Monin and his collaborators carried out numerical simulations of chemicaldensity convection in the Earth’s mantle and obtained convincing theoretical evidence in favour of the reality of this very mechanism of lithospheric plate motion [21]. The solution of the problem of gravitational differentiation of the Earth’s interior and modelling of unsteady chemical-density convection in the mantle made it possible to begin a quantitative study of the geological evolution of the Earth. The results obtained considerably extended the initial framework of the theory of lithospheric plate tectonics and actually turned it into a general theory of the Earth’s geological evolution.

1.3 Fundamentals of Global Lithospheric Plate Tectonics In the XX century, the idea of the shell structure of the Earth—geospheres—was consistently formed, starting with its outer upper shell—the Earth’s crust, then the mantle and ending with the planet’s core. The main process in the evolution of the planet’s interior is the gravitational differentiation of substances of different weights, with denser and heavier ones sinking downwards towards the centre of the planet and less dense ones rising upwards, as a result of which there must be an internal stratification of matter so that deeper shells are composed of denser and heavier materials. The boundaries of the shells were conventionally distinguished by seismic methods by a sharp change in the velocities of elastic wave propagation. Studies have shown that the Earth’s crust is separated from the underlying layers by the Mohoroviˇci´c surface (Mohoroviˇci´c discontinuity), at crossing which there is a jump-like increase in the velocity of elastic waves. The greatest difference in the depth of the boundary position was recorded between the continental and oceanic crust. The average thickness of the continental crust is 35–40 km and more, and of the oceanic crust—5–7 km, and in some axial parts of mid-ocean ridges the crust is almost completely wedged out. The crust is the upper part of the lithosphere.

1.3 Fundamentals of Global Lithospheric Plate Tectonics

7

Thus, the Earth’s outer shell consists of the lithosphere, which includes the Earth’s crust and the upper part of the mantle layer. The thickness of the lithosphere under continents and oceans is different. Within the continents, its thickness increases with increasing age of the basement, reaching a maximum of 300–350 km under the cratons of the northern hemisphere (a craton is a section of the Earth’s crust that does not experience significant folding deformations). The thickness of the lithosphere beneath the oceans also increases naturally in the direction from the axes of the median ridges to the shores of the continents. It is approximately proportional to the square root of the time of oceanic crust formation. In the zone of mid-ocean ridges, the lithosphere is minimal in thickness and in some places even wedges out, while at the boundaries with continents it reaches its maximum—up to 80–100 km. The lithosphere is underlain by the asthenosphere, which can occupy the entire area of the sublithospheric upper mantle down to a depth of 410 km. However, beneath the continents with the deepest “roots” reaching 350–400 km, the asthenosphere accounts for a relatively thin layer of a few tens of kilometres. Seismic sounding has shown that the substance of the asthenosphere is in the solid state, but with rheological properties of the substance (hardness, plasticity, viscosity) different from those of the overlying lithosphere. The special properties of the asthenosphere are explained by the partial melting of its substance, in which fusible rocks are contained in the solid skeleton of refractory ones. The share of such melt may be small—only 1–3%, but it plays an important role as it provides greater plasticity and less viscosity of the asthenosphere substance. Due to these properties, which play the role of “lubrication”, the more rigid and heavy lithosphere moves along it. The existence of the asthenosphere was discovered by the German geophysicist B. Gutenberg by the reduction of elastic wave velocities in it in comparison with the overlying lithosphere. Later, another method of asthenosphere separation—magnetotelluric—was developed by A. N. Tikhonov due to decrease of electrical resistance in the Earth layers. The word “tectonics” literally means “construction” in ancient Greek. In Earth sciences, this term usually refers to the geological structure and patterns of development of the Earth’s crust. Lithosphere is the rocky, i.e. hard and solid, shell of the Earth. It includes not only the Earth’s crust, but also part of the upper mantle, where the mantle matter has cooled so much that it has completely crystallised and become rock. The word “plates” shows that the Earth’s lithospheric shell is broken up into separate blocks whose vertical dimensions are usually much smaller than their horizontal dimensions. Thus, under the concept of lithospheric plate tectonics we will understand such a geological theory that considers the formation, structure and mutual movements of lithospheric plates, accompanied by their deformations, magmatic manifestations and other processes that ultimately lead to the formation of the Earth’s crust and associated minerals. This definition does not say anything about the causes of the movement of lithospheric plates, because this problem is solved by another related theory—geodynamics, the description of which is now beyond our scope. The peculiarity of lithospheric plates is their rigidity and ability to keep their shape and structure unchanged for a long time in the absence of external influences. In order

8

1 Geophysical Aspects of Ocean Floor Evolution

to destroy or deform such a plate, it is necessary to apply additional mechanical stresses exceeding the limit of its strength. With increasing depth, the temperature in the Earth gradually increases. Therefore, the asthenosphere (plastic mantle shell) is usually located beneath the lithospheric plates, the substance of which is already partially melted and characterised by relatively low viscosity. Unlike the lithosphere, the asthenosphere does not have a strength limit and its substance can deform (flow) under the action of even small excess pressures. Under the influence of high hydrostatic pressures prevailing in the Earth’s interior, the melting temperature of silicates increases with depth faster than the temperature of the mantle itself. Consequently, deeper than the asthenosphere, partial melting of mantle matter should no longer occur, although it remains plastic in its properties, resembling a superviscous liquid. The asthenosphere is most pronounced beneath relatively thin oceanic plates, whose thickness usually varies from 3–5 to 80–90 km. Judging by seismic data, under such plates the asthenospheric basement is located at a depth of about 250 km. As a rule, the asthenosphere is not traced under ancient continental plates with thickness of 200–250 km and more. As ice driven by river currents moves along the river during the spring ice drift, the movements of lithospheric plates on the surface of the asthenosphere occur under the influence of convective currents in the mantle. The analogy with ice flow, as we will see, is really very broad here, with the only exception that ice is always lighter than water, whereas lithospheric plates can be heavier than asthenospheric matter. As in the case of ice flow, the individual lithospheric plates can diverge, converge, or slide relative to each other. In the first case, tensile zones with rift cracks along the plate boundaries appear between the plates, in the second case—compression zones accompanied by thrusting of one plate on another, in the third case—shear zones (transform faults) along which the displacement of neighbouring plates occurs. According to the different character of deformations occurring along the plate periphery, three types of plate boundaries are distinguished. The first type includes boundaries along which the lithospheric plates move apart (spreading) to form rift zones. In the oceans, the crests of mid-ocean ridges correspond to these boundaries. On the continents, such boundaries include the East African Rift Zone and the Baikal Rift in Asia. The rift zones of the Red Sea and the Gulf of Aden in the Indian Ocean are examples of rift zones that have been transformed from continental to oceanic zones relatively recently (about 5 million years ago) due to plate movement. The second type includes boundaries along plate thrusting (subduction) zones, when oceanic lithospheric plates are pushed under island arcs or continental margins of the Andean type. These boundaries usually correspond to very characteristic landforms: conjugate structures of deep-water troughs with a chain of volcanic island arcs or the highest mountain massifs. Much less frequently and for a short time, conditions opposite to subduction occur: thrusting of the oceanic lithosphere over the edge of the continental lithosphere—obduction. As a result of such thrusting at the eastern end of the Arabian Peninsula, a section of oceanic lithosphere, more than 500 km long and 100 km wide, was thrust over the continental lithosphere.

1.3 Fundamentals of Global Lithospheric Plate Tectonics

9

The movement of oceanic plates under continents, if it is not compensated by their extension in mid-ocean ridges, usually leads to the gradual closure of the ocean, accompanied by the collision of continents framing it, and to the emergence of a folded belt along the thrust zone. This is how the Alpine-Himalayan mountain belt emerged in place of the ancient Tethys Ocean. The increased seismicity of this region indicates that the process of plate thrusting continues here today, so the Alpine-Himalayan belt can also be considered as a plate boundary of the second type. Detailed studies of mid-ocean ridges have established that their crests and rift valleys do not extend along the ridges continuously, but are as if torn into separate sections by transform faults, along which only purely shear displacements of plates occur. These are the boundaries of plates of the third type. As a rule, transform faults are always located perpendicular to rift fractures. At the same time, only the segments connecting two adjacent rift zones are active fault sections. Outside these sections, no plate displacements along transform faults occur. It should be noted that collision of continental lithospheric plates results in collision, which is accompanied by intense compression and leads to deformation and “crowding” of plate boundary areas in the form of folded mountain structures. The main example is the Himalayan mountain system, which is the result of collision of the southern part of the Eurasian plate with the Indo-Australian plate in the north of Hindustan. The combination of spreading and subduction zones represents a continuous chain of Earth’s seismically active zones, winding more than 100,000 kms across the ocean floor. The interaction of these zones reflects the mechanism of formation and absorption of the lithosphere. The English researcher A. Holmes suggested that this mechanism is based on the process of global convection of molten mantle in the Earth’s interior. The main source of ocean floor expansion is located beneath the lithosphere in spreading zones and is associated with global convection of mantle matter. According to the mechanism of spreading (expansion) of the oceanic crust [22], the upward mantle flow entrains hot asthenospheric matter into the region of lower pressures, where its fusible part becomes molten basaltic magma. The magma is squeezed from the solid skeleton of refractory crystals and localised as magmatic foci near the base of the lithosphere. The oceanic lithosphere above the convective zone is thinning and cracking under the action of upward flows of high-temperature mantle melts, on the one hand, and, on the other hand, under the tensile action of divergent branches of mantle currents. This creates crevices—rift spreading axes, along which molten magmatic lava rises to the bottom surface at a speed of up to 100 m/h. Pouring to the surface, it forms a solidified basalt body—a dike up to 1–3 m wide, oriented along the rift zone. The formation of a dyke in a cleft results in a wedging hydraulic impact on both plates, which, together with the tensile action on them from the divergent convective flows of the mantle, leads to repeated crustal rupture and magma outpouring with the formation of the following dykes and basalt covers. Numerous cycles of molten magma outpourings cause the accumulated overlying basalts to subside.

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1 Geophysical Aspects of Ocean Floor Evolution

Many parallel dikes and overlain basaltic layers are formed, successively forming new areas of the ocean floor on both sides of the rift. Rift zones are seismically active and earthquake sources in the zones are characterized by relatively shallow up to 33 km depth. At the same time, the first displacements in the foci have the character of stretching, which indicates that horizontal displacements of the oceanic lithosphere are taking place to the sides of the axis. Deep-water troughs are zones of interaction between two parts of the oceanic lithosphere and, from the standpoint of the concept of lithospheric plate tectonics, are associated with subduction (thrusting) of one part of the oceanic lithosphere under the other. More ancient, more powerful and heavier oceanic lithosphere is being lowered and pulled under the younger and relatively light lithosphere. The leading edge of the younger lithosphere, buckling out, rises up to the ocean level, exposing some elevated areas of the ocean floor. The uplifted weighted section of the lithosphere going downwards forms a narrow depression in front of the islands— a deep-water trough. On the spherical Earth, the boundary of such interaction of two lithosphere sections forms an arc-shaped bend in the direction of the thrusting lithosphere. Under the action of the subduction process, volcanic centres emerge on the elevated areas of the seabed parallel to the lithosphere thrust line. Over time, some of these centres develop into volcanic islands distributed along an arc bordered on the outer side by a deep-water trough. The movements of lithospheric plates are accompanied by their friction against each other and the occurrence of earthquakes along plate boundaries. Therefore, plate boundaries can be defined not only by geomorphological features, but also by zones of increased seismicity. Different types of boundaries correspond to different earthquake mechanisms. Thus, in oceanic rift zones all earthquakes without exception occur under the crests of mid-ocean ridges. They belong to shallow-focus earthquakes, with focal depths up to 5–10 km, and are characterised by extension mechanisms. In transform faults, the depth of earthquakes sometimes reaches 30–40 km, and their mechanisms are purely shear. Seismically the most active zones are the plate thrust zones. In these zones shallowfocus earthquakes (with focal depth up to 30 km), intermediate (at depths from 30 to 100–150 km) and deep-focus earthquakes (with focal depth up to 600–700 km) occur. The main seismofocal surface of plate thrust zones usually descends at an angle of 30– 50° from the axis of the deep-sea trench under the island arc or continental margin, delineating the body of the part of the oceanic crust subducting into the mantle. Different types of earthquakes occur in the zones of plate thrusting, but among the shallow-focus earthquakes, shear and strike-slip mechanisms predominate, while at medium and great depths, compression mechanisms predominate. Studying the distribution of earthquake epicenters on the Earth’s surface, we can identify 7 major and about the same number of medium-sized lithospheric plates. These are the main ones: African, Eurasian, North American, South American, Pacific, Indo-Australian, Antarctic, Nazca and Cocos plates in the south-eastern part of the Pacific Ocean, Philippine, Arabian, as well as plates bounded by the arcs of the South Sandwich and Lesser Antilles. In addition, the Somali Plate in East Africa, several plates in East and Southeast Asia, and a number of small plates in

1.3 Fundamentals of Global Lithospheric Plate Tectonics

11

the Southwest Pacific (e.g., the plates of the Fiji Seamount Plateau, the New Guinea Sea), etc., should be identified as independent. It is noteworthy that many plates include both continental massifs and the oceanic lithosphere sealed to them. For example, the African plate includes the continent of Africa itself and the adjoining eastern halves of the Central and South Atlantic, the western parts of the Indian Ocean floor, as well as parts of the Mediterranean and Red Sea floor. Here again, the analogy with ice is appropriate. The thick continental lithosphere, which goes deep into the mantle and is covered by a light continental crust, can be compared to an iceberg, while the relatively thinner oceanic lithosphere can be compared to pack ice fields soldered to an iceberg. In addition to plates of mixed continental-oceanic structure, there are plates consisting only of oceanic lithosphere with oceanic crust on the surface. These include the Pacific, Nazca, Cocos and Philippine plates. Euler’s theorem is usually used to quantitatively describe the movements of lithospheric plates on the spherical surface of the Earth. Applied to the problem of determining the parameters of the motion of rigid spherical shells of lithospheric plates on the surface of the globe, this theorem states that at any given moment of time, any such motion can be represented by the rotation of the plate with a certain angular velocity relative to the axis passing through the centre of the Earth and some point on its surface (the plate rotation pole). In the process of studying the tectonic structure of the ocean floor, an interesting regularity has emerged. It turned out that almost all rift faults are oriented to the corresponding poles of plate rotation, while the associated transform faults are always perpendicular to these directions. Consequently, the network of rift and transform faults arising between two sliding plates is always oriented along meridians and latitudinal circles drawn from the pole of mutual rotation of the plates. It also follows from Euler’s theorem that the rate of mutual displacement of two lithospheric plates will change with distance from the pole of rotation according to the law of the sine of the latitude of a given point, counted from the same pole of rotation of the plates. Data on the location of striped linear magnetic anomalies on the ocean floor are commonly used to determine the velocities of lithospheric plate motions. These anomalies, as it is now established, are born in the rift zones of the oceans due to magnetisation of basalts poured into them by the magnetic field that existed on the Earth at the time of basalt outpouring. But, as is known, the geomagnetic field from time to time changes its direction to the exact opposite. Therefore, the basalts poured out in different periods of geomagnetic field inversions are magnetised in opposite directions. Due to the ocean floor movement in the rift zones of mid-ocean ridges, the older basalts are always moved away from these zones at large distances, and together with the ocean floor, the Earth’s ancient magnetic field “frozen” in basalts is also moved away from them. The oceanic crustal extension together with differently magnetised basalts usually develops strictly symmetrically on both sides of the rift fault. The associated magnetic anomalies are also located symmetrically on both slopes of mid-ocean ridges and surrounding abyssal basins. Consequently, magnetic anomalies can now be used to determine the age of the ocean floor and the rate of its extension in rift zones. However,

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1 Geophysical Aspects of Ocean Floor Evolution

this requires knowing the age of individual inversions of the Earth’s magnetic field and comparing these inversions with the magnetic anomalies observed on the ocean floor. The age of magnetic inversions was determined by palaeo-magnetic studies of reliably dated strata of basalt covers and sedimentary rocks (initially, these studies were carried out only on the continents, then they were confirmed by drilling the ocean floor). By comparing the obtained scale with magnetic anomalies on the ocean floor, it was possible to determine the age of the oceanic crust in most of the ocean areas of the World Ocean (Fig. 1.4). The Earth’s magnetic field is also characterised by an inclination directly related to geographic latitude. By measuring it in a rock, we determine the geographic latitude of the place where the rock was formed and the minimum distance that the lithospheric plate containing it should have travelled. Thus, scientists were able to quantitatively calculate the motion parameters of adjacent plates. By determining the parameters for two plates first, and then for the third plate paired with one of the previous ones, it is possible to gradually involve all major lithospheric plates in the calculation and determine the mutual movements of the entire ensemble of lithospheric plates on the Earth’s surface. Outside Russia, such calculations were performed by J. Minster and his colleagues, and in Russia by Yu. Minster and his colleagues, and in Russia— Galushkin and Schreider [20, 23, 24]. As a result, it became clear that the ocean floor is moving with maximum speed in the southeastern part of the Pacific Ocean

Fig. 1.4 Age map of the World Ocean floor and chrones of linear magnetic anomalies (http://joa chim.cl/geologia/html2/003tectonica_de_placas/001_deriva_continental.htm), modified

1.4 Evolution of the Oceanic Lithosphere

13

(near Easter Island). Up to 18 cm of new oceanic crust is being built up here every year. On geological scales it is very little, as only for 1 million years in this way a strip of young ocean floor up to 180 km wide is formed, and on each linear kilometre of the rift zone for the same time about 360 km3 of basaltic lavas are poured out. The same calculations showed that Australia is moving away from Antarctica at a rate of about 7 cm per year, and South America from Africa at a rate of about 4 cm per year. North America is moving away from Europe at a much slower rate of 2.2–2.3 cm per year. The Red Sea is expanding even more slowly—by 1.5 cm per year (accordingly, less basalts are also poured out here—only 30 km3 for each linear kilometre of the Red Sea rift in a million years). But the speed of “collision” of India with Asia reaches 5 cm per year, which, by the way, explains the deformations of the Hindu Kush, Pamir and Himalayas that are developing literally before our eyes. These deformations create an exceptionally high level of seismic activity in the entire region (the tectonic influence of the collision of India with Asia is reflected far beyond the plate collision zone itself, extending as far as Baikal). Deformations of the Greater and Lesser Caucasus are caused by the pressure of the Arabian plate on this region of Eurasia, but the rate of plate convergence here is much slower—only 1.5–2 cm per year. Therefore, the seismic activity of the region is also lower here. The importance of these calculations is extremely great, because it allows us to quantitatively estimate the present-day tectonic activity of the Earth and the volume of magmatic outpourings in modern rift zones. In addition, by successively combining one-age magnetic anomalies with each other, using this technique we can build very accurate reconstructions of the position of continents and oceans for past geological times, as well as determine the paleo-depths of the ancient oceans and the rates of moving apart or moving up their ocean floor. Many such reconstructions have been constructed by Scotese [25] for the entire time interval of existence of magnetic anomalies on the modern ocean floor, i.e., from the late Mesozoic to the present day. For older geological epochs, paleo-geographical reconstructions using paleomagnetic data for the continents can be built only approximately. This is due to the fact that all oceanic plates formed earlier than the Late Jurassic have already had time to sink into the mantle under the modern or ancient plate thrust zones, and, consequently, no magnetic anomalies older than 180 Ma have been preserved on the ocean floor.

1.4 Evolution of the Oceanic Lithosphere The analysis of geological and geophysical data indicated that in the places of origin and formation of new oceanic crust at the spreading axes the thickness of the Earth’s crust is insignificant. When the newly formed relatively thin basaltic crust begins to move away from the spreading axis, a part of the magmatic source contents moves away from the axis under it and together with it, which eventually solidifies and crystallises into rock. As a result, the thickness of the young crust increases and reaches 5–7 km at the first stage of its formation.

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1 Geophysical Aspects of Ocean Floor Evolution

The basaltic crust forms the basis of the oceanic lithosphere, which is expanding in width and thickness. Away from the spreading axis, refractory rocks of the asthenosphere and mantle matter left after basaltic magma emission grow on the base of the young lithosphere in the process of crystallisation. The older the oceanic lithosphere is, the more heavy and iron-rich mantle rocks, released from convective horizontal flows beneath the lithosphere, have time to accrete to it from below. Under the most ancient areas of the bottom, formed in the Jurassic time (more than 160 million years ago), at the borders with the continents, the thickness of the oceanic lithosphere reaches 80 and more kilometres. In some sense, the process of crystallisation of mantle components at the base of the lithosphere is similar to the thickening of ice in freezing bodies of water, when ice crystals grow up from below to the ice shell during their phase transformation from water. With time, the lithosphere cools, becomes heavier, and its density increases on average. Moving away from the spreading axis, the plate sinks deeper and deeper into the underlying asthenosphere and. Therefore, the ocean depth above the lithosphere thrust zones (near the continents or island arcs) should be the greatest. During the time from birth to the approach to the continents, sediments are deposited on top of the basaltic crust. If their accumulation is uniform in time, the further away from the spreading axis, the more of them should accumulate. The average thickness of the ocean sedimentary layer is assumed to be 0.5–1 km. At the spreading axes, sediments are practically absent, while in areas closer to the ocean margins, sediments are also replenished by materials brought from land by wind and river runoff. In the oldest parts of the oceanic crust at the continental foothills, the thickness of sediments can reach 5–10 km and more, and under their weight the oceanic lithosphere sinks even deeper into the asthenosphere. In this case, it is natural to expect that its heavier sections at the ocean margins are more easily pushed under the oncoming lighter and less powerful continental plate. The results of seismic tomography show that in the thrust zones the oceanic lithospheric plate sinking to a depth of 60–80 km moves at an angle of 10–30° to the horizon. As the lithospheric rocks move further into the depths, with increasing depth pressure, they become compacted, and the plate dip trajectory becomes steeper. At depths of more than 500–600 km and more, the plate movement continues along a horizontal trajectory, where it eventually finally melts and disappears. The introduction of the seismic tomography method into the practice of geophysical research has made it possible to discover evidence of the existence of mantle convection on a global scale, which forms the basis of the concept of lithospheric plate tectonics. The method involves computer synthesis of seismic wave parameters from many thousands of earthquakes that have occurred in different parts of the planet. Areas of increased and decreased velocities of elastic wave propagation have been detected in the Earth’s mantle at different depths, corresponding to areas of compaction and decompaction of mantle matter—its cooling and heating as a consequence of mantle convection. Interpretation of tomography results also indicates that oceanic lithosphere absorption occurs directly under continental-ocean boundaries and in the regions of island arcs. In these places, the oceanic lithosphere is pulled by the downward mantle

1.4 Evolution of the Oceanic Lithosphere

15

flow to the depth where it is compacted at high pressures. The compacted plate sinks even deeper into the high-temperature mantle shell, where it is further melted. Near Kamchatka, the oceanic lithosphere tightens to a depth of up to 1200 kms and then disappears altogether. In other areas of the planet, the lithosphere sinks even deeper. At the same time, complex geodynamic interpretation of seismic-tomographic data made it possible to detect ancient subduction zones that died out more than 150 million years ago. Within the framework of this approach, it is possible to trace the sinking of ancient plates down to the transition zone between the lower mantle and the Earth’s outer core, i.e. to a depth of 2900 km. According to seismic tomography data, it appears that subduction initiates the main geodynamic processes, and the distribution of lithospheric plates determines the pattern of convection currents in the Earth’s mantle. Unlike thermal convection in the atmosphere, both molten mantle matter and cooled large-scale lithospheric fragments circulate together in mantle convection. Such circulation leads to the fact that the weighted part of the unbroken plate, which is sinking into the mantle under the action of gravity, pulls the rest of the plate from the subduction zone to the spreading axis. In this case, the pulling effect can lead to plate rupture or breakaway in the thinnest and weakened part of the plate in the vicinity of the spreading axis. As a result, rifts are formed by means of which basaltic lava is transported from magmatic centres beneath the lithosphere to form a new crustal section. Subduction of the lithospheric plate in subduction zones under the weight of the submerged part of the plate triggers mantle convection—the basis of geodynamic evolution. The sequence of ocean floor expansion and absorption can be compared to a conveyor belt moving continuously from rift zones of mid-ocean ridges to deep-sea troughs at the edge of continents and returning in the mantle again to the spreading axis to repeat the evolutionary cycle. On the marginal side of the ocean in subduction zones, the same lithosphere sinking into the mantle layers in the region of ultrahigh pressures is compacted and sinks even deeper, thus causing convective movements in the Earth’s mantle. A comparison of the convective circulation of the Earth’s atmosphere and mantle shows that their mechanisms are opposite. The atmosphere is characterised by thermal convection, the main driving force of which is the rise of air due to heating from below. The warmer and lighter air streams are relatively narrow jets and therefore rise upwards with greater velocity. Having cooled from above, they then descend over large areas at a much slower speed. Mantle convection, on the other hand, occurs due to gravitational sinking of heavy and cold lithospheric plates into the lower mantle at a rate of up to 10 cm/year. In other places of the mantle layer, the mantle substance is rising, but at a slower rate, close to the average spreading rate (5–6 cm/year). We cannot exclude the possibility that the latter is a consequence of the fact that the rising mantle jets apparently cover the entire global system of spreading zones, which is one and a half times more extended than subduction zone systems. In the works of A. S. Monin and O. G. Sorokhtin it was assumed that convection in heated mantle layers is caused by the process of chemical-density differentiation of Earth rocks, leading to the formation of a system of layers—geospheres—with the

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1 Geophysical Aspects of Ocean Floor Evolution

core of the highest density in the centre of the Earth and the lowest density in the nearsurface layer. It was assumed that it occurs only in the least intensive and therefore more stable forms—single-cell (opposite region of rise and region of sinking of mantle matter) and double-cell (if with closed cells—two regions of rise and equator of sinking, if with open cells—equator of rise and two regions of sinking). Variants of convection forms transient between them are called bifurcations. It is not excluded the possibility that at present the global tectonic structure of the Earth’s face may be the result of the manifestation of bifurcated convection with open cells of the tennis ball type, the seam on which—the equator of ascent—is represented by the global line of mid-ocean ridges. In this context, one “flap” of the tennis ball contains North and South America and Antarctica, and the other flap contains Africa, Eurasia and Australia. During the period of the Pangea foremass 285–195 Ma, the mantle had a singlecell structure. All continental blocks were apparently located in one hemisphere with the centre above the mantle jet sinking pole. At the same time, Pangaea was surrounded by subduction zones from almost all sides. During the period of transition from one-cell to two-cell mantle convection of the Earth—bifurcation—the disintegration of Pangea and the formation of the present-day appearance of the Earth took place. Numerical experiments revealed the possibility of existence of less stable multicellular forms of convection accompanied by the appearance of the second zone of mantle matter uplift. The peculiarities of the phase transition of individual components of mantle matter at the boundary between the upper and lower mantle (at a depth of about 670 km) and, in particular, additional heating or cooling of mantle rocks leads to a jump-like change in their density and the appearance of positive or negative buoyancy, tending to return the boundary to its initial state. This creates a barrier effect for the vertical component of convective motions near the 670 km boundary. Taking into account this effect, L. I. Lobkovsky et al. proposed a model of two-tier thermochemical convection in the Earth’s mantle. The driving force of such convection is the gravitational differentiation of mantle matter in the lower mantle, which leads to the subsidence of heavy components of mantle rocks and the rise of light ones. It is accompanied by the accumulation of relatively heavy rocks at the lower boundary of the upper mantle as a result of the process of eclogitisation of the oceanic lithosphere in subduction zones (when downward convective flows with cooled and metamorphically altered mantle rocks descend into the upper mantle together with the lithosphere). Convection can be two-tiered, when cells in the lower and upper mantle develop independently, without exchange of matter across their phase boundary, or single-tiered, characterised by breakthroughs of matter across the phase boundary both from below and above. Numerical experiments within the framework of this convection scheme revealed, on the one hand, giant plumes rising from the mantle-core boundary, decaying in the vicinity of the phase boundary into “daughter” upper mantle regional plumes. Heavy eclogite masses (heavy rocks consisting of garnet, pyroxene, quartz and rutile) sinking in subduction zones together with lithospheric plates are trapped at the same phase boundary of 670 km, forming huge lenses of heavy material. Reaching the critical mass of the lens of heavy rocks causes them to flow into the lower mantle

1.5 General Information on the Magnetically Active Layer of the Ocean Floor

17

down to the Earth’s core, causing additional perturbations that also participate in the formation of giant plumes. The objectivity of the processes of spreading and subduction of the ocean floor is confirmed by the materials of deep-water drilling of the World Ocean floor from the special drilling ships “Glomar Challenger” and “JOIDES Resolution”. No rocks with the age of more than 180 million years were found in the cores. The age of the Earth exceeds 4 billion years, and the existence of the Earth’s ocean is apparently 3 billion years old. The absence of such old rocks in the ocean is explained by the continuous renewal of the Earth’s crust in the process of spreading and subduction of lithospheric plates. Therefore, the maximum age of the Earth’s crust under the ocean is determined not by the age of the Earth, but by the time of movement of the newly formed crust from the spreading axes to the zones of plate subduction under continental margins and massifs of island arcs with velocities ranging from the first millimetres to one or two tens of centimetres per year. Intensive geological and geophysical studies of the bottom of the World Ocean have made it possible to explain important geomorphological features of the bottom development within the concept of lithospheric plate tectonics.

1.5 General Information on the Magnetically Active Layer of the Ocean Floor In the 1950s, magnetic scientists found that many rocks during their formation acquired magnetisation along the direction of the geo-magnetic field at the time of rock formation. In many cases, this magnetisation has remained unchanged to this day. By summarising such studies in different regions of the Earth, it is possible to reconstruct the history of the geomagnetic field as a whole, and by it to reproduce the evolution of the motion of the investigated crustal areas. Paleo-magnetic studies have shown that the ability to magnetise is possessed by rocks containing grains of ferromagnetic substances, in such minerals as hematite magnetite, titanomagnetite, ilmenite, pyrrhotite and some iron hydroxides. The largest and most stable is the thermally stable magnetisation, which is acquired by a hot but cooling ferromagnet at the moment when its temperature passes through the Curie point. Such magnetisation is acquired in cooling lavas, so that the eruptive rocks appear to be the keepers of the imprints of the parameters of the geomagnetic field that existed at the moment of cooling of basalts after their formation. The application of modern methods of paleo-magnetic, petrological, X-ray, and geochronological analyses of rocks led to important results, one of which is the construction of a paleo-magnetic scale of geological time based on the alternation of epochs of normal and reversed polarity of the geomagnetic field. In addition, the palaeo-latitudes of continental blocks of the Earth’s crust and their orientation relative to the geographic poles in different time periods were determined, which made it possible to reconstruct their mutual movements.

18

1 Geophysical Aspects of Ocean Floor Evolution

Within the framework of the ocean floor sliding mechanism, basalts smelted from the mantle in rift zones should acquire normal or reverse magnetisation during their cooling in one or another epoch of the geomagnetic field polarity, respectively. When the oceanic crust is moving apart, its basaltic material should imprint in its basaltic material the strips of direct and reverse magnetisation of the oceanic crust parallel to the strike of the axes of the mid-ocean ridges on which these crustal sections were formed. The degree of symmetry of their location relative to these axes depends on the speed of pushing of the newly formed cortex in each direction from the spreading axis. Therefore, the main characteristic feature of the ocean floor magnetic field structure is the existence of the world system of linear magnetic anomalies (Figs. 1.5 and 1.6). They represent a system of alternating bands of positive (forward) and negative (reverse) magnetic polarity in the horizontal measurement plane (close to the bottom or noticeably elevated above it), stretched along the spreading axes symmetrically on both sides of them [26]. Vine et al. [3, 4] were the first to link the origin of linear magnetic anomalies of the ocean floor with the process of formation of new oceanic crust and lithospheric plates, assuming the inversion nature of magnetisation of the magnetically active layer of the ocean floor. The sources of anomalies are formed at the structural boundaries of lithospheric plates and then move as part of the magnetoactive layer of rigid lithospheric plates along the spherical surface of the Earth. In this aspect, the magneto-active layer is an effective bottom thickness that accumulates the residual magnetic field of the bottom rocks, and forms linear bottom magnetic anomalies in the horizontal measurement plane. Since the linear magnetic anomalies of the ocean floor carry information about the state of the Earth’s magnetic field at the time of formation of the inversion magnetically active layer of the ocean floor, the anomalies themselves can be called palaeo-magnetic. Let us summarise their main parameters, properties and interpretations. The strip structure of magnetic anomalies on the ocean floor was first discovered in the North Pacific Ocean in the middle of the last century by Russian magnetologist O. N. Solov’ev and American geophysicists R. Mason and A. Raff (Solov’ev 35; Mason 36). They recorded narrow, 30–60 km wide, parallel bands of alternating positive and negative magnetic anomalies with intensity within 500 nTl. Similar results were subsequently obtained in many other areas of the World Ocean, including the Arctic and the Red Sea. The width of the magnetic anomaly bands and the duration of the epochs of geomagnetic field polarity were used to determine the ocean floor spreading rates varying from a maximum of 12–18 cm/year (East Pacific Rise) to a minimum of 0.4–0.6 cm/year (Arctic and southwestern Indian Ocean). The boundaries of magnetic anomaly bands (as well as lines parallel to them) can be considered as lines of the same age of the oceanic crust—isochrones. The data from the analysis of cores from deep ocean bottom drilling wells drilled from the board of the special drilling vessel “Glomar Challenger” allowed us to perform a direct verification of ocean bottom age determinations known from magnetic anomalies. In those boreholes that completely penetrated through the sediments and reached the underlying basalt cover, the age of the lowest sediment layer immediately adjacent to the

1.6 Scale of Linear Magnetic Anomalies of the Ocean Bottom

19

Fig. 1.5 In-situ measurements of linear bottom magnetic anomalies using a magnetometer via the benthic, surface and over-water methods

basalt base was determined by the micro-palaeontological method. It turned out that the age of basal sediments obtained from drill cores agrees well with the age obtained from the interpretation of linear magnetic anomalies. To reconstruct the epochs of the geomagnetic field polarity in the distant past, the strip magnetic anomalies of the ocean floor proved to be a convenient form of information presentation.

1.6 Scale of Linear Magnetic Anomalies of the Ocean Bottom Paleo-magnetic studies of stratigraphic sequences of rocks on continents and in ocean bottom sediments contributed to the confirmation of the scientific ideas of Vine and Matthews [3]. Based on the complex analysis of magnetic anomalies, these studies allowed us to create a magneto-chronological scale (time scale of inversions of the Earth’s Main Magnetic Field) and the associated scale of linear magnetic anomalies of the ocean floor—the scale of paleo-magnetic anomalies.

20

1 Geophysical Aspects of Ocean Floor Evolution

Fig. 1.6 Linear bottom magnetic anomalies (measured and calculated) relative to the mid-ocean ridge axis (a) and their displacement in the transform fault (b)

The polarity of the Earth’s Main Magnetic Field is called normal (straight) when the north end of the compass arrow points north and is inclined downwards at the north magnetic pole and upwards at the south magnetic pole. A local variation of this inclination indicates the presence of rocks with reversed magnetisation and the polarity is considered reversed (in both hemispheres). Changes in the polarity direction of the Earth’s Main Magnetic Field by 180° are recorded in rocks, which is the physical basis of magneto-stratigraphy. Polarity inversions are recorded simultaneously by all forming rocks capable of preserving palaeo-magnetic information, and magneto-stratigraphic subdivisions do not change with time. The period of inversions averages about 0.5–1 million years, and the inversion itself takes on average about 5 thousand years, as established by detailed palaeomagnetic studies of transition zones [27]. For this reason, the resolving power of magneto-stratigraphy cannot be better than the latter figure. Sometimes the Earth’s Main Magnetic Field experiences short-term variations, which are characterised by polarity changes reaching 180°. The time interval between two consecutive inversions of the geomagnetic field polarity is considered as an interval (time interval) of one or another stable polarity. Linear magnetic anomalies of the ocean floor (called palaeo-magnetic anomalies)

1.6 Scale of Linear Magnetic Anomalies of the Ocean Bottom

21

are the most important source of information about the inversions of the Earth’s Main Magnetic Field during the Meso-Cenozoic time. The main reason for the high reliability of marine magnetic survey data is the continuity of geodynamic processes leading to the formation of new oceanic crust along the structural boundaries of lithospheric plates. The alternation of forward and reverse polarity intervals, captured in the inversion magnetically active layer of the ocean floor, is responsible for the observed palaeo-magnetic anomalies. The palaeo-magnetic anomalies observed on the profiles are in some cases complicated by anomalies of other nature (irregularities in the relief of magnetically active rocks, discontinuous tectonics, etc.). The sequence of inversions of the Earth’s magnetic field, analysed by comparing the ages and paleo-magnetic data of the Earth’s crustal rocks, as well as taking into account the regularities of the spatial distribution of linear oceanic magnetic anomalies, formed the basis for the time scale of paleo-magnetic anomalies. The practice of recognising (on the basis of model ideas about spreading) palaeo-magnetic anomalies allowed us to select and number those of them that are most stable in all oceans. These anomalies are included in the scale of palaeo-magnetic anomalies (Table 1.1). One of the first versions of the chronological scale of linear magnetic anomalies of the ocean floor was the scale of Soh [28] for the time interval of about 3.3 Ma. Later studies made it possible to construct the scales of palaeo-magnetic anomalies up to the age of about 170 Ma, which corresponds to the most ancient parts of the ocean floor [27, 29, 30]. Further improvement of the geochronological interpretation methodology, application of astronomical dating, and use of the cubic spline apparatus to determine the duration of polarity intervals made it possible to create in 1992 the scale [31], which structurally belongs to the modern generation of scales. Reference profiles were selected on the East Pacific Bottom Rise, the Austral-Antarctic and Chilean Bottom Rises, as well as in the South Atlantic and North Pacific bottom regions. These areas are characterised by the absence of major restructuring of ocean floor spreading systems over significant periods of time. The work [32] represents a further development of the Cenozoic scale of palaeomagnetic anomalies. In it, the mathematical apparatus of multiple optimisation based on nonlinear Lagrangian functions is applied to the kinematic characteristics of the East Pacific Rise, the Chile Ridge, the mid-oceanic ridge in the northern, central and southern Atlantic, and the southeastern Indian mid-oceanic ridge. Currently, there are two systems for labelling chrons. The first is represented by the names of authors (e.g., Brunhes, Matuyama, Gauss, Gilbert, etc.). Brunhes, Matuyama, Gauss, Gubio, Gilbert). These names are recommended and used for global correlation of stratigraphic subdivisions. The second system is based on numbered linear magnetic anomalies of the ocean floor—palaeo-magnetic anomalies. In this case, the number 1 denotes the palaeo-anomaly above the axial zone of mid-ocean ridges, where the youngest portion of the new oceanic crust is formed. Chron 0 corresponds to the present day. The numbers with the index “n” were correlated with directly (normally) magnetised blocks of the inversion magnetically active

22

1 Geophysical Aspects of Ocean Floor Evolution

Table 1.1 Direct polarity intervals in the scale of linear magnetic anomalies of the ocean floor (chronological scale of linear magnetic anomalies of the ocean bottom) I

II

III

I

II

III

I

II

III

C1n

0.000

0.779 C6Cn.1n

23.151

23.415 M7n

128.500 128.600

C1r.1n

0.986

1.053 C6Cn.2n

23.621

23.800 M8n

129.050 129.300

C2n

1.789

2.010 C6Cn.Zn

23.015

24.144 M9n

129.600 129.800

C2r.1n

2.219

2.250 C7n.1n

24.808

24.863 M10n

130.200 130.500

C2An.1n

2.613

3.083 C7n.2n

24.922

25.282 M10N.1n

131.000 131.200

C2An.2n

3.158

3.256 C7Ar

25.606

25.764 M10N.2n

131.300 131.600

C2An.Zn

3.363

3.599 C8n.1n

25.946

26.061 M10N.3n

131.700 131.900

C3n.1n

4.096

4.208 C8n.2n

26.098

26.618 M11n.1n

132.000 132.700

C3n.2n

4.354

4.542 C9n

27.056

28.066 M11n.2n

133.050 133.100

CZn.Zn

4.743

4.835 C10n.1n

28.365

28.642 M11An.1n 133.400 133.600

C3n.4n

4.968

5.230 C10n.2n

28.718

28.909 M11An.2n 133.700 134.000

CZAn.1n

5.912

6.157 C11n.1n

29.663

29.930 M12n.1n

134.100 134.300

CZAn.2n

6.291

6.595 C11n.2n

30.037

30.380 M12n.2n

134.800 134.900

CZBn

6.971

7.131 C12n

30.771

31.179 M12An

135.000 135.200

CZBr.1n

7.177

7.212 C13n

33.058

33.545 M13n

135.400 135.600

CZBr.2n

7.388

7.423 C15n

34.655

34.940 M14n

135.900 136.200

C4n.1n

7.482

7.615 C16n.1n

35.343

35.526 M15n

136.700 137.300

C4n.2n

7.705

8.144 C16n.2n

35.685

36.341 M16n

137.900 139.700

C4r.1n

8.302

8.335 C17n.1n

36.618

37.473 M17n

140.400 140.800

C4An

8.796

9.140 C17n.2n

37.604

37.848 M18n

142.600 143.100

C4Ar.1n

9.359

9.444 C17n.3n

37.920

38.113 M19n.1n

143.600 143.700

C4Ar.2n

9.739

9.806 C18n.1n

38.426

39.552 M19n.2n

143.800 144.600

C5n.1n

9.913 10.064 C18n.2n

39.631

40.130 M20n.1n

145.100 145.300

C5n.2n

10.107 11.168 C19n

41.257

41.521 M20n.2n

145.400 146.000

C5r.1n

11.274 11.323 C20n

42.536

43.789 M21n

146.700 147.600

C5r.2n

11.714 11.770 C21n

46.264

47.906 M22n.1n

148.200 149.500

C5An.1n

12.189 12.337 C22n

49.037

49.714 M22n.2n

149.600 149.650

C5An.2n

12.443 12.666 C23n.1n

50.778

50.946 M22n.3n

149.700 149.750

C5Ar.1n

12.918 12.945 C23n.2n

51.047

51.743 M22An

150.400 150.500

C5Ar.2n

13.006 13.047 C24n.1n

52.364

52.663 M23n.1n

150.700 151.100

C5AAn

13.203 13.338 C24n.2n

52.757

52.801 M23n.2n

151.300 151.350

C5ABn

13.488 13.676 C24n.3n

52.903

53.347 M24n.1n

152.100 152.500

C5ACn

13.851 14.175 C25n

55.904

56.391 M24n.2n

152.900 152.950

C5ADn

14.264 14.638 C26n

57.554

57.911 M24An

153.200 153.300

C5Bn.1n

14.800 14.891 C27n

60.920

61.276 M24Bn

153.500 153.900

C5Bn.2n

15.039 15.164 C28n

62.499

63.634 M25n

154.100 154.300 (continued)

1.7 Modelling of the Inversion Magnetically Active Layer of the Oceanic …

23

Table 1.1 (continued) I

II

C5Cn.1n

16.039 16.341 C29n

III

I

II 63.976

III

64.745 M25An.1n 154.500 154.700

I

II

III

C5Cn.2n

16.378 16.551 C30n

65.578

67.610 M25An.2n 154.800 154.850

C5Cn.3n

16.624 16.807 C31n

67.735

68.737 M25An.3n 154.900 154.950

C5Dn

17.399 17.748 C32n.1n

71.071

71.338 M26n.1n

155.050 155.150

C5En

18.433 18.906 C32n.2n

71.587

73.004 M26n.2n

155.250 155.300

C6n

19.157 20.211 C32r.1n

73.291

73.374 M26n.3n

155.400 155.500

C6An.1n

20.586 20.771 C33n

73.619

79.075 M27n

155.700 155.850

C6An.2n

21.013 21.302 C34n.1n

83.500 114.900 M28n

156.000 156.200

C6AAn

21.701 21.782 C34n.2n

115.100 120.400 M29n.1n

156.300 156.450

C6AAr.1r 22.041 22.128 M2n

121.000 123.700 M29n.2n

156.500 156.550

C6AAr.2r 22.315 22.347 M4n

124.000 124.750 M29n.3n

156.600 156.650

C6Bn.1n

22.436 22.588 M5n

126.800 127.750 M29n.4n

156.700 156.750

C6Bn.2n

22.639 22.886 M6n

128.300 128.400 M30n.1n

156.800 157.200

I—Chron, subchron; II and III—beginning and end of the direct polarity interval of one million years

layer of the ocean floor responsible for the paleo-magnetic anomalies, the numbers with the index “r” correspond to inversely magnetised blocks, and the combination of these indices correspond to intermediate forms (Table 1.1; Fig. 1.4). The specific extents of the zones of one or another polarity vary in time. Because of these variations, an interval consisting of a sequence of several polarity zones represents a “personal signature” of the period under consideration. It can be correlated with a similar sequence of zones elsewhere on the Earth—on the continents and in the oceans. None of the existing versions of the palaeo-magnetic anomaly scale is perfect, as its construction is in constant development. One of the main factors in improving the scale should be recognised as the further development of deepwater drilling and the whole complex of geological and geophysical studies associated with it.

1.7 Modelling of the Inversion Magnetically Active Layer of the Oceanic Lithosphere The study of oceanic magnetic anomalies within the framework of the concepts of lithospheric plate tectonics is based on the model ideas about the inversion magnetically active layer, which composes the ocean floor and is represented by rocks whose residual magnetisation significantly exceeds that induced by the modern magnetic field.

24

1 Geophysical Aspects of Ocean Floor Evolution

The ideas about the formation of the oceanic crust, in terms of the ideas of the bottom expansion, were first formulated by Deitz [1] and Hess [2], who developed the idea of continental drift [33, 34] and assumed that the new oceanic crust is continuously formed in a narrow spreading zone along the axes of mid-ocean ridges as a result of magmatic processes. The study of the magnetic field gave confirmation to the hypothesis of the ocean floor expansion—linear magnetic anomalies were detected [35, 36], which are the result of the formation of the new oceanic crust with an inverse magnetically active layer. The first and fundamental model of the magneto-active layer within the concept of lithospheric plate tectonics was the model of Vine and Matthews [3]. In this model, the magnetically active layer is formed in the axial zone of the mid-ocean ridge due to the deep hot material rising to the surface. The material (basalts), rising to the depths where its temperature becomes below the Curie point, fixes magnetisation in the direction of the actual terrestrial magnetic field, and then is carried away in opposite directions from the mid-ocean ridge by the horizontal motion of the plates. In the presence of the geomagnetic field inversion, the rocks of the magnetically active layer will acquire alternating magnetisation as a result of the bottom expansion. In this case, the inversion blocks will be symmetrically located with respect to the expansion axis. The most important advantage of the model is that the authors used for the first time a model of a layer in which there were no vertical boundaries between rocks of different compositions with sharply contrasting magnetic susceptibility. In their model, the magnetic susceptibility is constant, while the direction of the residual magnetisation In changes. Further accumulation of actual material, including data from bottom magnetic surveys, led to the improvement of the model. The model [37] assumes that the magnetically active layer is formed by the introduction of dikes normally distributed with a certain dispersion with respect to the spreading axis. At the same time, the dikes themselves are as if supply channels for lava flows. The outpouring lavas add magnetic material, distributing it normally relative to the supply channel with a certain dispersion. Each dike carries the same amount of material. When the material flowing out of the supply channel solidifies, a surface is formed whose cross section is described by the corresponding Laplace function. Under the conditions of stationarity of the process, taking into account the known build-up rate of the magneto-active layer, its power (band width) will be kept constant. Thus, there is a basis to assume that the lower and upper boundaries of the layer are conformal. A survey of the actual material according to this more advanced model, which includes consideration of dike and lava mechanisms, allowed us to establish that the size of the transition zone (the zone of inversion in linear distances) is close to 1–2 km, and the width of the zone of formation of the magnetically active layer is close to 3.5 km. In order to explain the asymmetry of a number of anomalies after poleward adjustment, a two-layer model of magnetically active rocks of the oceanic lithosphere was developed [38–40]. In it, the upper layer is relatively thin, has a narrow transition zone, and is composed of extrusive rocks. The lower layer is thicker, composed of intrusive complexes, and cools more slowly, having a wider transition zone. Its slope is different from that of the upper zone and is controlled by the behaviour

1.7 Modelling of the Inversion Magnetically Active Layer of the Oceanic …

25

of the Curie isotherm in the vertical section of the lithosphere. The resulting nonrectangular geometry of the inversion sections, different widths and slopes of the transition zones are responsible for the asymmetry of the anomaly shape. The data of [26, 41, 42] show that the anomalies decrease in amplitude with distance from the ridge axis and reach their minimum values at a distance of about 800 km from the axis of the East Pacific Rise, 200 km from the axis of the Mid-Atlantic Ridge and 80 km from the axis of the Carlsberg Ridge. The study of the spatial distribution of the magnetic characteristics of basalts of the Atlantic and Pacific oceans, obtained mainly as a result of dredging, has shown that the magnitude of the natural residual magnetisation of basalts decreases naturally with distance from the axis of the mid-ocean ridges, but more sharply than the amplitudes of magnetic anomalies. The interval of sharp decrease of magnetisation, approximately by an order of magnetisation, occurs at a distance of about 100 km from the axis of the Mid-Atlantic Ridge and 400 km from the axis of the East Pacific Rise. Starting from these distances, a rather low value of the residual magnetisation value of 2–5 A/m is preserved. Studies of the magnetic properties of oceanic basalt samples have shown that the process of low-temperature oxidation is widely developed in them, during which titanium-magnetites of basalts transform into titanium-maghemites [43–45]. The consequence of this process is a decrease in the residual magnetisation and an increase in the Curie point. It is the processes of low-temperature oxidation of titaniummagnetites that explain the sharp decline in magnetisation (up to 1/3 of its initial value over a time period of about 0.5 Ma [46]. Vine and Matthews [3] considered that the layer of magnetically active ocean rocks covers the entire upper part of the lithosphere up to the Curie isotherm, which in their opinion lies at a depth of about 20 km. In the next pa6o te [6], the authors considered a layer with a thickness of 8 km, which corresponded to the crustal thickness for the studied region of the Juan de Fuca Ridge, where the model calculations were made. The authors obtained that the magnetisation in the layer could be 1.25 A/m (or 2.5 A/m for the axial block of the ridge). In 1966, Vine [47] further limited the thickness of the layer, reducing it to the thickness of seismic layer 2 (1.5–2 km). The study of magnetic and mineralogical properties of basalts in the rift zone by Irving et al. [43] suggested that the thickness of the magnetically active layer of the Mid-Atlantic Ridge is only about 200 m. The best agreement between the observed and model curves over local relief inhomogeneities was achieved under the assumption that the rock magnetisation for the profile along the spreading axis is 30 A/m, for the profile along Anomaly 4 (6.5 Ma, 12 A/m), and for the profile along Anomaly 5 (9.5 Ma, 7 A/m). Taking the magnetisation along the strike of the blocks constant, the estimate of the vertical thickness of the magnetically active layer averages 400 m. According to the model of Blakely [48], magnetically active rocks consist of two layers whose magnetic properties acquire two differences during formation. The upper layer consists of lava flows and pillow lavas, and is highly magnetic with narrow transition zones. The lower layer consists of dykes and is less magnetic with a wide transition zone.

26

1 Geophysical Aspects of Ocean Floor Evolution

The study of the magnetic properties of the oceanic crust and, first of all, the study of the values of residual magnetisation of rock samples have shown that the magnetisation values of 4–5 A/m accepted in the models of the magnetisation of rocks of layer 2a do not always agree with the research data. Thus, in pa6o te [49], an average magnetisation value of 3.74 A/m without correction for the magnetic latitude of the drilling site was obtained using data from 55 deepwater drilling wells. In a somewhat earlier work by Harrison [50], such a correction was introduced and the average magnetisation of 2.41 A/m was obtained from the data of 50 boreholes. Fox and Opdyke [51] studied 10 modified basalt samples from the Mid-Atlantic Ridge, in which they found a very low magnetisation of 0.44 A/m (it should be said that one sample was intensely magnetised up to 4.26 A/m). In general, the available material testifies to the metamorphism of rocks from the bottom of layer 2 and its low magnetisation [52]. These prerequisites led T. Francis to the model of serpentinisation of a significant in thickness layer of the upper mantle of a slowly expanding ridge. According to his model, the mantle under the ridge axis is located at depths of about 3 km below the bottom surface. Its high temperature and the presence of magmatic channels cause the seismic velocity to decrease to 7.2 km/s. At a small distance from the axis (2– 4 km), normal discharges begin to form [53], through which sea water penetrates into the crust and cools it. The discharges themselves penetrate to depths of up to 8 km below the bottom surface, contributing to water penetration into the mantle and serpentinisation of its rocks. The T. Francis model is similar to the model [54], but differs by more intensive serpentinisation development, leading to the appearance of a synchronous serpentinite layer in contrast to the alternating serpentinised and non-serpentinised mantle sections of E. Bonatti and J. Honnores with different degrees of regularity. T. Francis suggests that serpentinised rocks of the mantle should contribute to the magnetic anomalies of the ocean. It was mentioned above that the possibility of serpentinised rocks contributing to the anomalous ocean magnetic field was suggested earlier [41]. However, the difference of the T. Francis model is that he gives a quantitative estimate of the position of the serpentinisation region with respect to the spreading axis. According to his estimation, serpentinisation of rocks occurs in the interval of 5–10 km from the axis. If the magnetisation process is more or less synchronous with the serpentinisation process, it can be estimated that the magnetisation lag of serpentinised mantle rocks relative to pillow lavas will be 0.15–1.5 Ma for velocities of 1–3 cm/year. Significant progress in the study of magnetically active properties of ocean floor rocks has improved and developed modelling concepts of the inversion magnetically active layer of the ocean. It is due to modelling that it is now possible to successfully identify linear paleo-magnetic anomalies of the ocean (Fig. 1.6a). At the same time, the analyses show that our knowledge of the vertical and horizontal structure of the magneto-active layer is somewhat limited. This is the main obstacle to the widespread introduction of compositionally complex models into the practice of calculations of theoretical palaeo-magnetic anomalies. By virtue of the equivalence principle, the real inversion magneto-active layer of the ocean floor can be replaced, in terms of the observed paleo-magnetic anomalies, by an effective magneto-active layer of this

References

27

or that configuration, depth, thickness, etc. [55]. These circumstances, as well as the presence of individual features of paleo-magnetic anomalies on specific observation profiles, are the basis for the use of single-layer models with zero transition zones between different polar blocks in the overwhelming number of studies, despite the fact that modern computational techniques have practically no obstacles in recreating on models any complex processes of formation of the magnetically active lithospheric shell and calculating theoretical magnetic anomalies adequate to the observed ones using these models. The problem of restoring the magnetisation of the magnetically active layer from the anomalous magnetic field of the ocean is reduced to the inverse problem of geophysics—determination of the distribution and intensity of sources by the field generated by them. Due to the impossibility of solving this inverse problem by analytical methods, it is necessary to use numerical methods. For this purpose, it is necessary to determine the parameters of the model under consideration, taking into account the data of earlier studies, to compile an algorithm for solving the problem and implement it in the form of a programme, with the possibility of presenting the obtained results in a convenient format. Thus, the following stages can be distinguished in the modelling of the magnetoactive layer: . construction of a model of the magnetically active layer, which agrees with the main provisions on its real structure and allows simplifying calculations; . development of a mathematical method for solving the inverse problem for the selected model; . implementation of the numerical solution algorithm, as well as carrying out calculations for idealised data obtained from the solution of the direct problem in order to verify the correctness of the results; . carrying out calculations for real profiles and evaluating the results obtained.

References 1. Dietz R (1961) Continent and ocean basin evolution by spreading of the sea floor. Nature 190:854–857 2. Hess H (1962) The history of ocean basins. In: Petrological studies: a volume in honour of A.F.Buddington. Geological Society of America, N.Y., 509–620 3. Vine F, Matthews D (1963) Magnetic anomalies over oceanic ridges. Nature 199:947–949 4. Morley L, Larochelle A (1964) Paleomagnetism as a means of dating geological events. Geochronol Can 8:39–51 5. Le Pichon X, Heirtzler J (1968) Magnetic anomalies in the Indian Ocean and sea-floor spreading continents. J Geophys Res 73(6):2101–2117 6. Wilson J (1965) A new class of faults and their bearing on continental drift. Nature 207:343–347 7. Bullard E, Everett J, Smith A (1965) The fit of continents around Atlantic. Symphosium on continental drift. Phil Trans Roy Soc Lond 258(1088):41–51 8. Rises MW (1968) Trenches, great faults, and crustal blocks. J Geophys Res 73(6):1959–1982 9. Isaks B, Oliver J, Syks L (1968) Seismology and the new global tectonic. J Geophys Res 75(18):5855–5899

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10. Dewey J, Bird J (1970) Mountain belts and the new global tectonics. J Geophys Res 75(14):2625–2647 11. Uyeda S, Miyashiro A (1974) Plate tectonics and the japanese islands: a synthesis. Geol Soc Am Bull 85:1159–1170 12. Kropotkin PN (1969) The problem of continental drift (mobilism). IZV USSR Acad Sci Phys Earth 3:3–18 13. Khain VE (1973) General geotectonics, 2nd edn. Nedra, Moscow, 511 p 14. Khramov AN (1967) Paleomagnetism: principles, methods and geological applications of palaeomagnetology. In: Khramov AN, Sholpo LE (eds) Nedra Leningr. Department, Leningrad, 251 p 15. Peyve AV (1969) Oceanic crust of the geological past. Geotectonics 4:5–23 16. Lisitsyn AP (1974) Sedimentation in the oceans. Nauka, Moscow, 215 p 17. Zonenshain LP, Savostin LA (1979) Introduction to geodynamics. Nedra, Moscow, 311 p 18. Schreider AA (1989) Paleoceanological study of the anomalous geomagnetic field of the Indian Ocean. Dissertation for the degree of Doctor of Geology and Mineralogy. Sciences. USSR Academy of Sciences, Institute of Oceanology named after P.P. Shirshov. P. P. Shirshov Institute of Oceanology, Moscow, 395 p 19. Fedynsky VV, Sorokhtin OG, Ushakov SA (1974) Dynamics of lithospheric plates and the origin of oil fields. Dokl USSR Acad Sci 214(6):1407–1410 20. Schreider AA (2001) Geomagnetic studies of the Indian Ocean. Nauka, Moscow, 319 p 21. Monin AS (1977) History of the earth. Nauka, Leningrad, 228 p 22. Bodvarsson, G. and Walker, GPL (1964) Crustal Drift in Iceland // The Geophysical J Roy Astron Soc 8:285–300 23. Minster J, Jordan T (1978) Present-day plate motions. J Geophys Res 83(B11):5331–5354 24. Galushkin YI (2007) Modelling of sedimentary basins and assessment of their oil and gas content. Moscow State University named after M. V. Lomonosov. Lomonosov Moscow State University, Moscow, Nauch. Mir, 456 p 25. Scotese CR (1985) The assembly of Pangea: middle and late paleozoic paleomagnetic remits from North America. Ph.D. Thesis. University of Chicago, Dept. of the Geophysical Sciences, Mar 1985, 339 p 26. Heirtzler JR, Dickson GO, Herron et al (1968) Marine magnetic anomalies, geomagnetic field reversals, and motions of the ocean floor and continents. J Geophys Res 73(6):2119–2136 27. Harland WB, Armstong RL, Cox AV et al (1989) A geologic time scale 1989. Cambridge University Press, Cambridge, 263 p 28. Cox A, Doell R, Dalrymple G (1963) Geomagnetic polarity epochs and pleistocene geochronometry. Nature 198:1049–1051 29. Kent D, Gradstein F (1986) Jurassic to recent chronology. Geology of North America, Boulde Colorado, pp 45–50 30. Handschumacher DW, Gettrust JF (1985) Mixed polarity model for the Jurassic quiet zones; new oceanic evidence of frequent pre-M25 reversals. EOS Trans Am Geophys Union 66(46):867 31. Cande S, Kent D (1992) A new geomagnetic polarity time scale for the Late Cretaceous and Cenozoic. J Geophys Res 97:13917–13951 32. Huestis S, Acton G (1997) On the construction of geomagnetic timescales from non-prejudicial treatment of magnetic anomaly data from multiple ridges. Geophys J Int 129:176–182 33. Wegener A (1922) Die Entstehung der Kontinente und Ozeane [The origin of continents and oceans] (in German) 34. Du Toit A (1937) Our wandering continents: an hypothesis of continental drifting. Oliver and Boyd, Edinburgh, 366 p 35. Solov’ev ON (1961) Aeromagnetic survey in the area of the Kuril-Kamchatka island arc. Appl Geophys 29:168–173 36. Raff A, Mason R (1961) Magnetic survey off the west coast of North America, 32° N latitude to 42° N latitude, 40° N latitude TO 52° N latitude. Geol Soc Am Bull 72:1267–1270

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37. Atwater T, Mudie J (1973) Detailed near-bottom geophysical study of the Gorda Rise. J Geophys Res 78(35):8665–8686 38. Cande S, Kent D (1976) Constraints imposed by the shape of marine magnetic anomalies on the magnetic source. J Geophys Res 81(23):4157–4162 39. Kidd R (1977) The nature and shape of the sources of marine magnetic anomalies. Earth Planet Sci Lett 33:310–320 40. Arkani-Hamed J (1989) Thermoviscous remanent magnetisation of oceanic lithosphere inferred from its thermal evolution. J Geophys Res 94(B12):17421–17436 41. Schreider AA, Valyashko GM, Nazarova EA (1976) Magnetic heterogeneity of the bottom of the troughs of the north-western part of the Indian Ocean. Oceanology 1:105–112 42. Pechersky DM, Nazarova EA, Lykov AV (1977) Magnetism and some problems of the structure and development of the Earth’s crust and upper mantle. Izvestia AS USSR Phys Earth 11:85–98 43. Irving E (1970) The mid-atlantic ridge at 45° N oxidation and magnetic properties of basalt: review and discussion. Can J Earth Sci Geol 7:1528–1538 44. Ozima M, Larson E (1970) Low- and high-temperature oxidation of titanomagnetite in relation to irreversible changes in the magnetic properties of submarine basalts. J Geophys Res 75(5):1003–1017 45. Lowrie W et al (1973) The magnetic properties of deep sea drilling project basalts from the Atlantic Ocean. Earth Planet Sci Lett 17:338–349 46. McDonald K (1977) Near-bottom magnetic anomalies, asymmetric spreading, oblique spreading, and tectonics of the mid-atlantic ridge near lat 37° N. GSA Bull 88(4):541–555; Wilson T (1965) A new class of faults and their bearing on continental drift. Nature 207:343–347 47. Vine F (1966) Spreading of the ocean floor: new evidence. Science 154(3755):1405–1415 48. Blakely R (1976) An age-dependent, two-layer model for marine magnetic anomalies. Geophys Pacific Ocean Basin Margin 19:227–234 49. Lowrie W (1977) Intensity and direction of magnetisation in oceanic basalts. J Geol Soc 133(1):61–82 50. Harrison C (1976) Magnetisation of the oceanic crust. Geophys J Roy Astron Soc 47(2):257– 283 51. Fox P, Opdyke N (1973) Geology of the oceanic crust: Magnetic properties of oceanic rocks. J Geophys Res 78:5139–5154 52. Harrison C (1987) Marine magnetic anomalies—the origin of the stripes. Ann Rev Earth Planet Sci 15:505–543 53. Laughton A, Searle R (1979) Tectonic processes on slow spreading ridges. Deep Drilling Res Atlantic Ocean Ocean Crust 2:15–32 54. Bonatti E, Honnorez J (1976) Sections of the earth’s crust in the equatorial atlantic. J Geophys Res 81(23):4104–4116 55. Strakhov VN (1981) Some issues of the theory of interpretation of the results of geomagnetic measurements in the ocean. In: Magnetic anomalies of the oceans and new global tectonics. Nauka, Moscow, pp 20–60

Chapter 2

Geochronology of the Eurasian Basin Floor

The Arctic Ocean (AO) consists of the Amerasian and Eurasian basins, separated from each other by the Lomonosov Ridge. On the Eurasian side, the Eurasian Basin is bounded by the shelf areas of the Laptev, Kara and Barents Seas. The Eurasian Basin differs from the Amerasian Basin in that it contains a modern active mid-ocean ridge (Fig. 2.1), the main link of which is known in the literature as the Nansen, Gakkel or Gakkel-Nansen mid-ocean ridge, or as the Mid-Arctic Ridge [1–4]. The questions of the evolution of the Eurasian basin floor of the Arctic (or Arctic [1] and others) Ocean have been discussed in the literature to date [2, 5–16]. Geomagnetic studies were carried out, as a rule, by aeromagnetic expeditions of different countries. This kind of research by the international scientific community in the last half a century allowed obtaining a significant amount of information about the anomalous magnetic field of the Eurasian basin and, first of all, about the linear magnetic anomalies of the Nansen and Amundsen basins (sometimes called sub-basins [11]). Geodetic referencing of the results of aeromagnetic observations in the last half a century was carried out in different studies using different navigation systems, and different scales of linear magnetic anomalies were used in the geohistorical interpretation of the data. Therefore, an important task of the present work was to clarify the identification of linear magnetic anomalies of the Eurasian basin from the standpoint of the most modern version of the geochronological scale and to restore on this basis the features of the kinematics of the basin floor development.

2.1 Geomorphology of the Seabed Ice coverage of the water area makes it difficult to collect data on the geological structure of its bottom. There is no full confidence that geological samples brought aboard research vessels are not products of ice drift. Ice conditions also limit the possibility of obtaining data during drilling. Among the data on deep-water drilling and their © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0_2

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Fig. 2.1 Bathymetric map of the Eurasian basin of the Arctic Ocean [17, 18, 36], modified

interpretation, the materials presented in domestic studies [19–21] occupy an important place. Taking them into account, a comprehensive geological and geophysical analysis of the available data on potential fields and, first of all, on the anomalous magnetic field of the water area, makes it possible to answer a number of important questions about the stages of development of the Eurasian basin. The surface of the Mid-Arctic Ridge in the Laptev Sea lies at depths of 2–3 km, while the bottom of the adjacent abyssal plains to the north-west (Amundsen Basin) and south-east (Nansen Basin) is located at depths of 3–4 km. Towards the Siberian shelf, the ridge itself and its rift valley are increasingly covered [11, 22]. To the south of 78.5° N the ridge structure covered with sediments according to seismic data has a width of 50–60 km with a relative depth of the rift valley incision of about 5 km. According to seismic data, it can be traced between 128° and 131° E to 77.5° N, where it is sharply interrupted by a fault [2, 23]. In the central part of the Eurasian Basin, the depth of the rift valley of the MidArctic Ridge is somewhat shallower at 4.0–4.2 km with a width of about 15 km. Near Greenland, the rift valley is 4.5–5.0 km deep and 10–20 km wide. About 200 km from Greenland, the ridge is interrupted by a transform fault. Further south, the Lena Trough serves as a continuation of the axial zone. The southern limit of the Lena Trough and the entire modern spreading system of the Arctic Ocean is the Svalbard transform fault, along which the Mid-Arctic and Mid-Atlantic ridges join [2, 23]. According to gravity calculations, the crustal thickness beneath the Mid-Arctic Ridge is approximately 1.5 km less than that observed beneath other mid-ocean ridges. The Eurasian basin also includes the Amundsen Basin (between the Lomonosov Ridge and the spreading axis of the Mid-Arctic Ridge), the Lincoln Basin (between

2.1 Geomorphology of the Seabed

33

the Maurice-Jesup Rise and the Lomonosov Ridge), the Nansen Basin (between the spreading axis of the Mid-Arctic Ridge and the Eurasian shelf), and the Sofia Basin (between the Ermak Rise and Svalbard). The Nansen and Amundsen deep-water basins [2, 15] are composed of oceanic crust about 10 km thick with a thick (up to 2–3 km) sedimentary layer, and their maximum bottom depths approach 4 km. Aeromagnetic observations [2, 8–12, 14, 16] have been intensively carried out in the Eurasian basin over the last half century (Fig. 2.2) and have provided information on the distribution of magnetic anomalies in it. According to the results of the studies, the Mid-Arctic Ridge, including the axial spreading zone, is characterised by linear magnetic anomalies with amplitudes typically less than 500 ntl with wavelengths up to 30 km (Fig. 2.3). The axial magnetic anomaly reaches values of 2000 ntl in the west of the ridge and is low amplitude in almost all other areas. Comparative analysis of the accumulated data of geomagnetic surveys indicates a number of inconsistencies in the survey materials of different authors for the same areas, which hinders the increase in the detail of the representation of the magnetic field features, primarily in electronic form for the purposes of digitisation and binding to the spatial grid. In addition, the works use versions of the geochronological scale of linear magnetic anomalies of different authors of different years (e.g., [24–26]), also the parameters of the inversion magnetoactive layer are not the same in different studies. For example, the thickness of the inversion magnetically active layer varies more than ten times, from 2 km [10, 27] to 0.1 km [11], which together with the use of different versions of linear magnetic anomaly scales is directly reflected in the drawing of theoretical magnetic anomalies and often complicates the comparative analysis of magnetic fields from different works.

Fig. 2.2 Examples of aeromagnetic survey routes of the Eurasian basin according to [2, 28, 31] with the results of [8–10, 12, 14], modified. Isobaths are shown in bold figures in km according to [34]. The numbers of aeromagnetic survey routes correspond to the numbers of profiles with anomalous magnetic field curves along the survey routes in Fig. 2.3

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Fig. 2.3 Examples of profiles with anomalous magnetic field curves along the survey routes and identified paleo-magnetic anomalies A1–A26 based on the calculations of linear magnetic anomalies in the model of ocean floor expansion from the viewpoint of lithospheric plate tectonics in the Laptev Sea (a), in the near-pole region and in the Greenland region (b) (based on data [3, 8–12, 22, 28–31, 35], modified). The profile numbers correspond to the route numbers in Fig. 2.2

This led to the need for a detailed comparative analysis of the results of various studies with the subsequent selection of those that were used to construct a modern version of the electronic map of the anomalous magnetic field, reconstruct the geochronology of the seafloor and conduct a comprehensive geohistorical analysis of the materials from the perspective of lithospheric plate tectonics. Note that for the identification of linear magnetic anomalies and all kinematic calculations, the geochronological scale from [26] is used in the present work. Examples of aeromagnetic survey routes covering the Mid-Arctic Ridge and adjacent basins are presented in Fig. 2.2.

2.2 Identification of Linear Magnetic Anomalies Comparison of observed and theoretical magnetic anomalies in the model of ocean floor expansion allowed a number of domestic and foreign studies (the most notable of which are [2, 8–12, 14, 16]) to identify paleo-magnetic anomalies A1–A25 in the Eurasian basin. At the same time, paleo-anomalies A1–A5 are confined to the top and slopes of the mid-Arctic ridge, and older paleo-anomalies are observed in the area of the adjacent Amundsen and Nansen basins. Paleo-anomalies 24A, 24B, as well as 24u, 24o, 25u, 25o, etc. identified in a number of works do not have nomenclature designations in the most modern version of the linear magnetic anomaly scale [26] used in the present work. The analysis of these models and map schemes of [10–12, 29] shows that in them the axes of

2.3 Charting the Geochronology of the Seabed

35

paleo-anomaly 24A, 24o, 25u practically coincide with the axis of paleo-anomaly 25 in [9, 14]. The identification of this and other palaeo-anomalies in [9, 14] is supported by a significant amount of factual material, good models and seems to us the most reasonable to date. With this in mind, we re-identified palaeo-anomalies 24A, 24o, 25u as A25, and the palaeo-anomalies 25 (e.g., in [29]) and 25o (e.g., in [30]) following it in precedence were re-identified as A26. The palaeo-anomalies from [31] and a number of other works were also re-identified in the direction of greater antiquity.

2.3 Charting the Geochronology of the Seabed Based on the calculations of theoretical linear magnetic anomalies in the model of ocean floor expansion from the perspective of lithospheric plate tectonics, we traced (and, if necessary, revised) the palaeo-magnetic anomalies of the Cenozoic sequence starting from A26 and their corresponding polarity chrons. Following the results of [2, 8–12, 14, 16], we considered the chrons to be the most reliable for the entire water area, the oldest model elements of which were the blocks of the inversion magnetically active layer model C1n (0–0.781 Ma), C2An.3n (3.330–3.596 Ma), C5n.2n (9.984–11.056 Ma), C6n (18.748–19.722 Ma), C13n (33.157–33.705 Ma), C18n.2n (39.698–40.145 Ma), C20n (42.301- 43.432 Ma), C24n.3n (53.416–53.983 Ma), C25n (57.101–57.656 Ma), C26n (58.959–59.237 Ma). When digitising the polarity chrons, we used a unified principle [32] of their separation as corresponding to the oldest parts of the blocks of the corresponding polarity in the model of the inversion magnetically active layer of the ocean with the use of a unified geochronological scale [28]. All of the above allows us to draw up a new scheme of geochronology of the Eurasian basin floor (Fig. 2.4). The chron diagram shows the chronological lines corresponding to these oldest parts of the blocks, excluding the chron C1 line, which corresponds to the modern spreading axis of the Mid-Arctic Ridge (mid-oceanic Gakkel Ridge), is shown by points along the centreline of the modern rift valley and has an age of 0 Ma. The complex interpretation of all available geological and geophysical information listed in the literature references to the present work allows us to believe that before the time of paleo-anomaly A26 there was a vast area of stretching and development of basaltic volcanism on the Arctic margin of Eurasia, continental rifting in which led to the detachment from the Eurasian continental margin of its fragment—the Lomonosov Ridge. The detachment marked the beginning of the Eurasian basin opening, accompanied by the formation of linear magnetic anomalies on the spreading axis of the mid-Arctic ridge (or mid-oceanic Nansen Ridge, mid-oceanic Gakkel Ridge, mid-oceanic Gakkel-Nansen Ridge) starting from the time of palaeo-magnetic anomaly A26. The chron lines on either side of the spreading axis (dotted line) have been labelled as 2A (3.596 Ma), 5 (11.056 Ma), 6 (19.722 Ma), 13 (33.705 Ma), 18 (40.145 Ma), 20 (43.432 Ma), 24 (53.983 Ma), 25 (57.656 Ma), 26 (59.237 Ma). The calculations

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Fig. 2.4 Geochronology of the Eurasian basin floor according to Fig. 2.3 and taking into account information from [2, 8–11, 14, 22, 27, 30, 31, 33], modified. Isobaths in hundreds of metres according to [33]

of bottom expansion rates were carried out along 7 profiles relatively evenly spaced along the ridge length with an inter-profile distance of about 300 km. At the junction of this spreading system with a similar Norwegian-Greenlandic system, a magmatism outbreak (Ermak hot spot) occurred later than the formation of palaeo-anomaly A21, creating the Maurice Jesup-Yermak plateau between the Lomonosov Ridge and Svalbard. Until the time of palaeo-anomaly A18 the bottom expansion was going at a rate of more than 2 cm/year, then the bottom expansion starts to slow down and in the interval of palaeo-anomalies A18-A6 these rates do not exceed 1 cm/year. After that, the expansion starts to accelerate towards the present day and exceeds the rate of 1.2 cm/year with some general decrease in the intensity of bottom expansion in the eastern direction. Note that the average rate of seafloor expansion over the interval of almost 60 Ma was close to 1.3 cm/year, which allows us to refer the Mid-Arctic Ridge to the category of very slowly expanding mid-ocean ridges [35]. These circumstances made it difficult to confidently identify specific palaeo-magnetic anomalies (the amplitude of many anomalies rarely exceeds 100 ntl, which leads to the necessity [2] to identify tsunaments of anomalies in some areas (e.g., A4–A5; A17–A18, etc.). In general, the bottom expansion occurs in the direction orthogonal to the strike of the ridge axial zone. Kinematic calculations using a unified geochronological scale [28] confirm the conclusions of numerous previous studies that the new oceanic crust in the Amundsen Basin was growing more intensively than in the Nansen Basin. The latter circumstance is associated in the literature with changes in the geodynamic regime [1, 35]. According to known sources, in the early Oligocene, Greenland becomes part of the North American lithospheric plate, the Fram Strait opens, bottom spreading in the Labrador Sea stops, and the Maurice-Jesup-Yermak Plateau begins to split (e.g., [1, 2, 28–31]).

2.4 Conclusions

37

In conjunction with these events, a complex rift system was formed on the shelf of the Laptev Sea, which most likely has a connection with the Mid-Arctic Ridge, but the latter is separated from it by a fault. The development of this system continues at present, as evidenced by the current seismic activity of its structures. The southern limit of the spreading axes in the Laptev Sea is parallel 77.5° N. A very important task of subsequent studies is to substantiate and reliably search for a continental rift structure genetically connected with the continental continental extension of the MidArctic Ridge. Equally important studies should reveal the real pattern of transform faults cutting the bottom of the Eurasian basin. These faults are not shown in Fig. 2.4 because they differ from each other in different works, look differently and their position requires significant clarification in the future on the basis of more detailed study grids.

2.4 Conclusions A comprehensive geological and geophysical analysis of information on the anomalous magnetic field in the Eurasian basin of the Arctic Ocean was carried out. Modelling of the inversion magnetically active layer of the oceanic crust was an important tool of such analysis. As a result of the analysis, the identification and spatial position of palaeo-magnetic anomalies were clarified, which allowed us to significantly update the geochronology of the Eurasian basin floor and identify a number of stages in the evolution of its floor. At the first Cretaceous-Paleogene stage before the beginning of the formation of palaeo-anomaly A26, the Eurasian margin underwent a significant development of stretching processes that turned into rifting. In the process of rifting, weakened zones and associated fractures of rifting were born, along which some of the 60 Ma, the Siberian continental margin began to break away with the formation of the Lomonosov Ridge. At the second stage of evolution, rifting turned into spreading, and the rate of expansion of the new oceanic crust in the interval of paleo-anomalies A26–A24 (59–53 Ma) was more than 2.5 cm/year. At the same time, the northern flank of the Mid-Arctic expanded more intensively than the southern flank. The third stage was characterised by further progressive deceleration of the bottom expansion process, the minimum of which with expansion rates of about 1 cm/year occurred during the formation of paleo-anomalies A13–A6 (30– 20 Ma). The fourth stage of new oceanic crust growth began later than the time of palaeo-anomaly A6 and is characterised by some intensification of expansion at rates up to 1.2 cm/year. The average rate of seafloor expansion over the interval of almost 60 Ma was close to 1.3 cm/year, which allows us to categorise the Mid-Arctic Ridge as slowly expanding.

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24. Cande SC, Kent DV (1995) Revised calibration of the geomagnetic polarity time scale for the Late Cretaceous and Cenozoic. J Geophys Geophys Res 100(B4):6093–6095 25. Gradstein F, Ogg J, Smith A et al (2006) A geological time scale 2004. CUP, 503 p 26. Gradstein F, Ogg J, Schmitz M, Ogg G (2012) The geologic timescale 2012. Elsevier, 1139 p 27. Engen O, Gjengedal L, Faleide J et al (2009) Seismic stratigraphy and sediment thickness of the Nansen Basin, Arctic Ocean. Geoph J Int 176:805–821 28. Schreider AA, Sazhneva AE, Klyuev MS, Brekhovskikh AL, Rakitin IY, Zuev OA (2019) Bottom kinematics of the subgreenland region of the Eurasian basin. Oceanology 59(2):282– 291 29. Lutz R, Franke D, Berglar K et al (2018) Evidence for mantle exhumation since the early evolution of the slow spreading Gakkel Ridge, Arctic Ocean. J Geodyn Geodyn 118:154–165 30. Berglar K, Franke D, Lutz R et al (2016) Initial opening of the Eurasian Basin, Arctic ocean. Front Earth Sci 4A:91, 14 31. Schreider AA, Sazhneva AE, Klyuev MS, Brekhovskikh AL (2019) Kinematic model of the development of the regions east of the mid-oceanic Gakkel Ridge in the Eurasian basin of the Arctic Ocean. Oceanology 59(1):143–152 32. Schreider AA (1988) On the principles of axes of linear paleo-magnetic anomalies of the ocean. In: Proceedings of all-union proceedings of science Shk. marine geology, vol 2. Izvo IOAN, Moscow, 109 p 33. www.topex.ucsd.edu/cgi-bin/get_srtm15.cgi (2021) 34. White R, Minshull T, Bickle M, Robinson C (2001) Melt generation of very slow_spreading oceanic ridges: constraints from geochemical and geophysical data. J Petrol Petrol 42:1171– 1196 35. Srivastava S (1985) Evolution of the Eurasian Basin and its implication to the motion of Greenland along the Nares Strait. Tectonophysics 114:29–53 36. https://ocean.ru/index.php/scientific-directions/morskaya-geologiya-i-geokhimiya/item/584sozdanie-geomodelej-relefa-dna-i-osadochnoj-tolshchi

Chapter 3

Paleo-Magnetic Anomalies in the Laptev Sea of the Arctic Ocean

An important area of Arctic research is the study of the palaeo-geodynamics of the Arctic Ocean. The Eurasian basin, where the only modern active mid-Arctic ridge in the Arctic Ocean is located, plays a significant role. In the west it meets the MidAtlantic Ridge, and in the east it continues into the Laptev Sea, where it overlaps with sediments in the area of the continental slope and is not further distinguished. The Laptev Sea itself is located between the northern coast of Siberia in the south, the Taimyr Peninsula, Severnaya Zemlya Islands in the west and the Novosibirsk Islands in the east. The northern boundary of the Sea has no clear configuration and includes part of the Amundsen and Nansen Basins and a segment of the Mid-Arctic Ridge separating them. The geological and geophysical study of the Laptev Sea segment of the Eurasian basin plays an important role in reconstructing the features of the geodynamic development of the eastern Arctic Ocean floor. Research by the international scientific community over the last half century has provided information on the morphology of the seafloor topography, sedimentary cover, crustal structure and anomalous potential fields of the Laptev Sea and adjacent areas. At the same time, it should be noted that the ice coverage of the Arctic Ocean, including the Laptev Sea area, makes it difficult to collect data on the geological structure of the bottom. There is no full confidence that geological samples brought aboard research vessels are not products of ice drift. Ice conditions severely limit the possibility of obtaining data from deep-sea drilling. Paleo-geodynamic reconstructions of the Laptev Sea segment are either very schematic or do not include it in their consideration (e.g., [1]), which is primarily due to imperfect data on the bottom chronology. Under these conditions, only a comprehensive analysis of the available geological and geophysical data makes it possible to answer a number of important questions about the stages of development of the Laptev Sea segment of the World Spreading System, which is the subject of the present work. The surface of the Mid-Arctic Ridge in the Laptev Sea lies at depths of up to 2–3 km, while the bottom of the adjacent troughs to the north-west (Amundsen © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0_3

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Basin) and south-east (Nansen Basin) is located at depths of 3–4 km. Towards the Siberian shelf, the ridge itself and its rift valley are increasingly buried in sediments. The northern side of the Amundsen Basin is the Lomonosov Ridge, which [2] is a continental remnant of the Siberian shelf that was broken off during the linear phase of spreading by the Mid-Arctic Ridge and moved hundreds of kilometres northward to the north pole. The width of the ridge can reach 100 km and more. In the Laptev Sea segment, the ridge extends northward from the shelf of the Novosibirsk Islands and now its surface lies at depths of up to a kilometre and more. According to seismic data, the structure of the Mid-Arctic Ridge can be traced eastwards between 128° and 131° E and 77.5° N, where it is sharply interrupted by the Khatanga fault [3]. Under the Mid-Arctic Ridge, gravity calculations indicate that the crustal thickness is about 1.5 km less than that observed under other midocean ridges. Evidence of recent volcanic activity within its boundaries has also been obtained [4]. Aeromagnetic observations in the Eurasian basin [5–11] provided information on the distribution of magnetic anomalies in the Laptev Sea. According to them, the Mid-Arctic Ridge is characterised by linear magnetic anomalies. The axial magnetic anomaly reaches 2000 nTl only in the west and is characterised by a significantly smaller amplitude in almost all other areas (e.g., [7]). Comparison of the observed and theoretical magnetic anomalies in the model of bottom extension ([7] and others). allowed us to identify palaeo-magnetic anomalies C1–C25. All authors testify that the horizontal displacements relative to each other of palaeo-magnetic anomalies and bottom structures do not exceed 10–30 km, the drawing of transform faults in different works does not coincide in position and strike. The direction of the faults is 70° [5], 45° [3], 30° [12], or even 120° [13]. The most modern version of the geomagnetic-based chronology of the bottom of the Laptev Sea segment of the Eurasian basin, covering the Mid-Arctic Ridge and the adjacent Amundsen and Nansen Basins, is presented in Fig. 3.1. For compact presentation of the material in the scheme, the chron numbers are given without the index “c”. The most important difference from the previous schemes is the identification of palaeo-anomaly C25 in the Amundsen Basin in the present study based on the materials of [6]. It was established on the basis of the correlation of observed and theoretical magnetic anomalies in the model of bottom expansion away from the spreading axis. In calculations of theoretical magnetic anomalies and in the identification of paleo-magnetic anomalies based on the modelling results ([7] and others), the most modern version of the paleo-magnetic anomaly scale [14] was used, developing the work of [15]. Comparison of the spatial position of the C25 anomaly with the position of the boundary between continental and oceanic crust (Fig. 3.1) from [1] (taking into account the data of studies [3, 12, 13]) indicates that the boundary is located on the periphery of chron C25r (57.656–58.959 Ma). Since the boundary marks the transition from continental crust to crust born during spreading, the beginning of oceanic crust formation in the Laptev Sea segment can be dated to about 59 Ma.

3 Paleo-Magnetic Anomalies in the Laptev Sea of the Arctic Ocean

43

Fig. 3.1 Magnetic geochronology of the seafloor in the area of the Laptev Sea segment of the Eurasian basin. Symbols: 1—spreading axis (according to [3, 7]), 2—chron ages C1-C25 (according to [7] taking into account [1, 3, 6, 9–11]), 3—boundary between continental and oceanic crust (according to [1] taking into account [3, 6, 12, 13]), 4—isobaths in hundreds of metres. Modified

The boundary itself is spatially close to the position of isobaths 2.0–2.5 km from the near-pole region to 79° N. Bottom spreading occurs in the direction orthogonal to the strike of the ridge axial zone. Kinematic calculations indicate that in the interval of palaeo-anomalies C25–C13, the bottom spreading proceeded at rates of about 0.9–1.2 cm/year. In the interval of palaeo-anomalies younger than C13, the rates do not exceed 0.6 cm/ year with a general decrease in the rates of the bottom expansion in the eastern direction. These circumstances sharply complicate the confident identification of specific palaeo-magnetic anomalies and lead to the necessity to identify anomaly tsunaments (e.g., C4–5, C17–19, etc.). Paleo-geodynamic calculations of the Eulerian pole and rotation angle, using the indicated boundary between oceanic and continental crust as an isochrone, allowed us to estimate for the first time the position of the opening pole of the Laptev Sea segment of the Eurasian basin. At the position of the Eulerian pole at the point with coordinates 70.03° N. 134.09° E, the opening angle is 16.34°. The pole is spatially gravitating to the area of existence of the previously known Cenozoic finite opening poles of the Eurasian basin, the compilation of which is given in [1]. Thus, as a result of these studies, the main paleo-geodynamic events in the Laptev Sea segment of the Eurasian basin of the Arctic Ocean have been reconstructed.

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Based on a complex geological and geophysical analysis of the anomalous magnetic field, continental rifting about 59 Ma led to the detachment of its fragment, the Lomonosov Ridge, from the Eurasian continental margin. The detachment marked the opening of the Laptev Sea segment of the Eurasian basin, accompanied by the formation of linear magnetic anomalies on the spreading axis of the mid-Arctic ridge starting from the time of Chron C25o. The spreading axis was graphed in the eastern direction in time, extending the space of the oceanic crust toward the Siberian shelf. The spreading rates in the interval of palaeo-anomalies C25–C18 were about 1.2 cm/ year, and since Chron C13 they have decreased to 0.6 cm/year. In conjunction with these events, a complex rift system was formed on the shelf of the Laptev Sea, which most likely has a connection with the Mid-Arctic Ridge, but the latter is separated from it by the Khatanga Rift [3, 7, 12]. The development of these shelf structures continues at present, as evidenced by their modern seismic activity. The southern limit of spreading axes in the Laptev Sea is parallel to 77.5° N. A very important task of subsequent studies is to substantiate and reliably search for a continental rift structure genetically related to the continental extension of the Mid-Arctic Ridge.

References 1. Glebovsky VE, Kaminsky VD, Minakov AN et al (2006) History of the Eurasian Arctic Ocean basin formation based on the results of geohistorical analysis of the anomalous magnetic field. Geotectonics 4:21–42 2. Jokat W, Weigelt E, Kristoferstn Y et al (1995) New insights into the evolution of the Lomonosov Ridge and the Eurasian basin. Jeophys J Int 122:378–392 3. Sekretov S (2002) Structure and tectonic evolution of the south Eurasia basin, Arctic Ocean. Tectonophysics 351:193–243 4. Edwards M, Kurras G, Tolstoy M et al (2001) Evidence of recent volcanic activity on the ultraslow spreading Gakkel ridge. Nature 409:808–811 5. Karasik AM (1981) Some peculiarities of geohistorical analysis of the anomalous magnetic field in the conditions of slow expansion of the ocean floor (on the example of the Eurasian basin of the Arctic Ocean). In: Magnetic anomalies of the oceans and new global tectonics. Nauka, Moscow, pp 162–174 6. History of the Eurasian Arctic Ocean basin formation according to the results of geohistorical analysis of the anomalous magnetic field. Geotectonics 4:21–42; Russian Arctic Geotraverses. Proc VNIIOkeangeologiya 220:172 7. Schreider AA (2004) Linear magnetic anomalies of the Arctic Ocean. Oceanology 44(5):768– 777 8. Gaina C, Roest W, Muller D (2002) Late Cretaceous-Cenozoic deformation of northeast Asia. Earth Planet Sci Lett 197:273–286 9. Kristoferson Y (1990) Eurasia basin, vol 1. Geology of North America, Boulder, Colorado, pp 365–378 10. Taylor P, Kovacs L, Vogt P, Johnson G (1981) Detailed aeromagnetic investigations of the Arctic basin, 2. J Geophys Res 86(7):6323–6333 11. Vogt P, Taylor P, Kovacs L, Johnson G (1979) Detailed aeromagnetic investigation of the Arctic basin. J Geophys Res 84(3):1071–1089 12. Drachev S, Kaul N, Biliaev V (2003) Eurasia spreading basin to Laptev shelf transition: structural pattern and heat flow. Geophs J Int 152:688–698

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13. Andieva ES (2008) Tectonic position and main structures of the Laptev Sea. Petroleum Geol Theor Pract 3:1–28 14. Gradstein F, Ogg J, Schmitz M, Ogg G (2012) The geologic timescale 2012. Elsevier, 1139 p 15. Schreider AA (1992) Magnetism of the oceanic crust and linear palaeo-magnetic anomalies. Phys Earth 6:59–70

Chapter 4

Kinematic Model of the Eurasian Basin Floor Development

4.1 Introduction The Arctic Ocean consists of the Amerasian and Eurasian basins, separated by the Lomonosov Ridge. From the Eurasian side, the Eurasian basin is bounded by the shelf areas of the Laptev, Kara and Barents Seas. The Eurasian Basin differs from the Amerasian Basin in that it contains a modern active mid-ocean ridge (Fig. 4.1), the main link of which is known in the literature as the Nansen, Gakkel or Gakkel-Nansen mid-ocean ridge, or as the Mid-Arctic Ridge [1–3]. The Eurasian basin includes the Amundsen Basin (between the Lomonosov Ridge and the spreading axis of the Mid-Arctic Ridge), the Lincoln Basin (between the Maurice-Jesup Rise and the Lomonosov Ridge), the Nansen Basin (between the spreading axis of the Mid-Arctic Ridge and the Eurasian shelf) and the Sofia Basin (between the Ermak Rise and Svalbard). The Nansen and Amundsen deep-water basins [2–5] are composed of oceanic crust about 10 km thick with a thick (up to 2–3 km) sedimentary layer, and their maximum bottom depths approach 4 km. The issues of the Eurasian basin floor evolution of the Arctic (or Arctic [1] and others) ocean are still discussed in the literature and examples of such discussion are given in [2–10 and others]. An important role in the process of such an analysis is assigned to the data of aeromagnetic observations.

4.2 Aeromagnetic Studies Aeromagnetic observations, many references to which are cited in [3, 8], have been intensively carried out in the Eurasian basin over the last half century and have provided information on the distribution of magnetic anomalies in it. According to the results of the studies, the Mid-Arctic Ridge, including the axial spreading zone, is characterised by linear magnetic anomalies with amplitudes typically less © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0_4

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Fig. 4.1 Bathymetry of the Eurasian basin of the Arctic Ocean [11], modified

than 500 ntl with wavelengths up to 30 km. The axial magnetic anomaly reaches values of 2000 ntl in the west of the ridge and is of low amplitude in other areas. A comparative analysis of the accumulated data of geomagnetic studies indicates a number of inconsistencies in the survey materials of different authors for the same areas, which makes it difficult to increase the detail of representation of the magnetic field features, primarily in electronic form [3, 8]. In addition, the papers use versions of the geochronological scale of linear magnetic anomalies of different authors of different years, also the parameters of the inversion magnetically active layer are not the same in different studies (the relevant literature references are given in [3, 8]). This led to the need for a detailed comparative analysis of the results of various studies with subsequent selection of those that were used to construct a modern version of the electronic map of the anomalous magnetic field and to reconstruct the geochronology of the seafloor and conduct a comprehensive geohistorical analysis of the materials from the perspective of lithospheric plate tectonics [8]. Note that for

4.3 Geochronology of the Seabed

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Fig. 4.2 Scheme of geochronology of the Eurasian basin bottom (according to [8], modified)

the identification of linear magnetic anomalies and all kinematic calculations in the present work, the geochronological scale from [12] is used. When digitising the polarity chrons in the study [8], a single principle [7] was used to identify them as corresponding to the oldest parts of the blocks of the corresponding polarity in the model of the inversion magnetically active layer of the ocean with the use of a single geochronological scale (in this case, the most modern version of the scale from [12] is used). All of the above allows us to draw up a new scheme of geochronology of the Eurasian basin floor (Fig. 4.2). A comprehensive geological and geophysical analysis of this scheme is the subject of this paper.

4.3 Geochronology of the Seabed Based on the calculations of theoretical linear magnetic anomalies in the ocean floor expansion model, we traced (and, if necessary, revised) the palaeo-magnetic anomalies of the Cenozoic sequence starting from A26 and their corresponding polarity chrons. Following the results of [3, 8–10, 13], we considered the chrons to be the most reliable for the entire water area, the oldest model elements of which were the blocks of the model of the inversion magnetically active layer C1n (0–0.781 Ma), C2An.3n (3.330–3.596 Ma), C5n.2n (9.984–11.056 Ma), C6n (18.748–19.722 Ma), C13n (33.157–33.705 Ma), C18n.2n (39.698–40.145 Ma), C20n (42.301–43.432 Ma), C24n.3n (53.416–53.983 Ma), C25n (57.101–57.656 Ma), C26n (58.959–59.237 Ma). The chron diagram shows the chronological lines corresponding to these oldest parts of the blocks, excluding the chron line C1, which corresponds to the modern spreading axis of the Mid-Arctic Ridge (mid-oceanic Gakkel Ridge), and has an age of 0 Ma. A comprehensive interpretation of all available geological and geophysical

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information listed in the literature references [3, 8] suggests that before the time of paleo-anomaly A26, there was an extensive area of stretching and development of basaltic volcanism on the Arctic margin of Eurasia, continental rifting in which led to the detachment of its fragment, the Lomonosov Ridge, from the Eurasian continental margin. The breakaway marked the beginning of the opening of the Eurasian basin, accompanied by the formation of linear magnetic anomalies on the spreading axis of the midArctic ridge (or mid-oceanic Nansen ridge, mid-oceanic Gakkel ridge, mid-oceanic Gakkel-Nansen ridge), starting from the time of the palaeo-magnetic anomaly (or, for short, palaeo-anomaly) A26. Therefore, the task of the present work was to clarify, update, and sometimes add new data to the spreading velocity distribution of the Eurasian basin using the most modern version of the geochronological scale from [12] and to reconstruct the features of the basin floor kinematics on this basis. Comparison of the observed and theoretical magnetic anomalies in the model of the ocean floor expansion allowed us to identify C1–C26n chrons in the Eurasian basin [3, 8]. As a result of a complex geological and geophysical analysis, it was possible to compile a modern version of the seafloor geochronology presented in Fig. 4.2. In this case, the lines corresponding to the most ancient blocks of the inversion magnetoactive layer model, in order to simplify the captions in Fig. 4.2, were labelled as 2A (3.596 Ma), 5 (11.056 Ma), 6 (19.722 Ma), 13 (33.705 Ma), 18 (40.145 Ma), 20 (43.432 Ma), 24 (53.983 Ma), 25 (57.656 Ma), 26 (59.237 Ma). The modern spreading axis of the Mid-Arctic Ridge is shown by dots. Estimated determinations of spreading velocities between the above chrones in the Amundsen, Nansen, Lincoln and Ermak basins allowed us to get an idea of the kinematics of the Mid-Arctic Ridge in the Eurasian basin of the Arctic Ocean. The calculations were carried out along 20 profiles relatively evenly spaced along the length of the ridge. The time domain of calculations of interval spreading rates varied from 1.5 to 13.9 Ma, and the average value of the calculated interval was 5.7 Ma. The graphs (Figs. 4.3 and 4.2) show polynomial approximations with equations and values of approximation reliability R2. The closer its value is to 1, the more accurately the selected function approximates the used measurement data. The practice of measurement results processing shows that a good result should be considered as finding an approximating function with reliability coefficient R2 > 0.8 (at the same time, an excellent approximation result is achieved at R2 > 0.9). Analyses of numerous literature sources indicate that bottom spreading occurs in the direction orthogonal to the strike of the ridge axial zone at each temporal stage of its development. Kinematic calculations using the most modern version of the geochronological scale [12] confirm the conclusions of numerous previous studies that the build-up of new oceanic crust in the Amundsen Basin was more intense than in the Nansen Basin and allow us to estimate this intensification at 11% ± 4% (Fig. 4.4). An important point is the overall decrease in the spreading scale from west to east from an average rate of 0.84 cm/year ± 0.34 cm/yr to an average rate of 0.47 cm/year ± 0.29 cm/year. At the same time, the average spreading rate for the last 60 Ma for the entire area of

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Fig. 4.3 Spreading velocities on the northern flank of the Mid-Arctic Ridge. The positions of the calculated points are timed to the midpoints of the calculated intervals. Polynomial approximations with equations and significance values are presented vertical bars show the error of the obtained values in each calculation interval, and horizontal bars provide an opportunity to present the time intervals of the performed calculations

seafloor spreading in the Eurasian basin based on more than 200 determinations was found to be close to 0.62 cm/year ± 0.32 cm/year. In correlation with bottom expansion in the Eurasian basin, a complex rift system was formed on the shelf of the Laptev Sea, which most likely has a connection with the Mid-Arctic Ridge, but the latter is separated from it by a fault. The development of this system continues at the present time, as evidenced by the modern seismic activity of its structures [3]. The southern limit of the spreading axes in the Laptev Sea is parallel 77.50 N. It is very important to identify a continental rift structure genetically related to the continental extension of the Mid-Arctic Ridge and to study

Fig. 4.4 Spreading velocities on the southern flank of the mid-arctic ridge the other notations are the same as in Fig. 4.3

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Fig. 4.5 Asymmetry of new oceanic crust buildup on the flanks of the mid-arctic ridge a polynomial approximation with equation and significance value is presented

the associated paleo-geodynamic parameters on the basis of calculations and analyses of instantaneous, interval and finite Eulerian poles. Analysis of the crustal build-up asymmetry graph on the flanks of the Mid-Arctic Ridge (Fig. 4.5) shows that earlier 40 Ma, the northern flank was building up more intensively than the southern flank, but the build-up intensity was decreasing towards the present day. And with time, about 25 Ma, new oceanic crust began to build up on the southern flank more than 20% more intensively than on the northern flank. Somewhat earlier, 10 Ma, spreading began to approach the symmetric spreading that is characteristic of its process at present. Judging by the predicted values of the approximation curve, the spreading character will remain so for about 10 Ma.

4.4 Conclusion As a result of a comprehensive geological and geophysical analysis of numerous materials on the anomalous magnetic field in the Eurasian basin of the Arctic Ocean, the identification and position of paleo-magnetic anomalies were revised on the basis of modeling the inversion magnetically active layer of the oceanic crust using the most modern scale of linear magnetic anomalies. This analysis allowed us to significantly update the geochronology of the Eurasian basin floor and identify a number of stages in its evolution. At the first Cretaceous-Palaeogene stage, before the beginning of the formation of palaeo-anomaly A26, the Eurasian margin underwent a significant development of stretching processes that turned into rifting. In the process of rifting, weakened zones and associated fractures of rifting were laid down, along which the Siberian continental margin began to be torn away about 60 Ma with the formation of the Lomonosov Ridge. At the second stage of evolution, rifting turned into spreading,

References

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and the rate of new oceanic crust accretion in the interval of palaeo-anomalies A26– A24 (59–53 Ma) was more than 1.5 cm/year. At the same time, the northern flank of the Mid-Arctic was growing more intensively than the southern flank. The third stage was characterised by a progressive slowdown of the bottom expansion process, the minimum of which with spreading rates up to 0.3 cm/year occurred at the time of formation of paleo-anomalies A13–A6 (30–20 Ma). The fourth stage of new oceanic crust expansion started later than the time of palaeo-anomaly A6 and is characterised by some increase in spreading rates up to 0.6 cm/year.

References 1. Khain VE (2001) Tectonics of continents and oceans. Scientific World, 606 p 2. Shipilov EV, Lobkovsky LI, Shkarubo SI, Kirillova TAII, Kirillova TA (2021) Geodynamic conditions in the conjugation zone of the Lomonosov Ridge and the Eurasian basin with the continental margin of Eurasia. Geotectonics 5:3–26 3. Schreider AA (2004) Linear magnetic anomalies of the Arctic Ocean. Oceanology 44(5):768– 777 4. Ivanov VA, Pokazeev KVV, Schreider AA (2008) Fundamentals of oceanology. SPb., Lan, 576 p 5. Trukhin VI, Pokazeev KV, Kunitsyn VE, Shreider AA (2004) Fundamentals of ecological geophysics. SPb., Lan, 384 p 6. Lobkovsky LI, Verzhbitsky VE, Kononov MV, Schreider AA, Garagash IA, Sokolov SD, Tuchkova MI, Kotelkin VD, Vernikovsky VA (2011) Geodynamic model of the Arctic region evolution in the late Mesozoic-Cenozoic and the problem of the outer boundary of the Russian continental shelf. Arctic Ecol Econ 1:104–115 7. Schreider AA (1988) On the principles of axes of linear palaeo-magnetic anomalies of the ocean. In: Theses of reports of the 111th all-union school of marine geology, vol 2. Izvo IOAN, p 109 8. Schreider AA, Brekhovskikh AL, Sazhneva AE, Klyuev MS, Galindo-Zaldivar H, Rakitin IY (2021) Geochronology of the Eurasian basin floor. Prots Geos 59, 3(29):1227–1305 9. Schreider AA, Sazhneva AE, Klyuev MS, Brekhovskikh AL, Rakitin IY, Zuev OA (2019a) Bottom kinematics of the subgreenland region of the Eurasian basin. Oceanology 59(2):282– 291 10. Schreider AA, Sazhneva AE, Klyuev MS, Brekhovskikh AL (2019b) Kinematic model of the development of areas east of the mid-oceanic Gakkel Ridge in the Eurasian basin of the Arctic Ocean. Oceanology 59(1):143–152 11. https://www.severe-weather.eu/global-weather/arctic-sea-ice-melt-minimum-2021-fa/ 12. Gradstein F, Ogg J, Schmitz M, Ogg G (2012) The geological timescale 2012. Elsevier, 1139 p 13. Gaina C, Nikishin F, Petrov E (2015) Ultraslow spreading, ridge relocation and compressional events in the East Arctic region: a link to the Eurekan orogeny? Arktos A 16:11

Chapter 5

Evolution of the Axial Zone of the Mid-Arctic (Gakkel) Ridge in the Upper Neogene

The bottom relief, formed as a result of tectonomagmatic processes on the spreading axis of the Mid-Arctic Ridge, subsequently undergoes changes under the influence of bottom spreading [1]. Therefore, a comparative analysis of the same-age seafloor areas on its slopes carries information about the peculiarities of the geodynamic process of the Eurasian basin seafloor formation. The reconstruction of the parameters of the new oceanic crust build-up on the spreading axes in the Arctic Ocean allows us to evaluate the peculiarities of the geodynamic process responsible for the evolution of the Eurasian basin of the Arctic Ocean [2–23]. In this regard, the study of the bottom relief surface of the axial zone of the mid-oceanic Gakkel Ridge is in the process of formation, especially since geophysical methods are constantly improving [24–29]. Geological and geophysical work in the Arctic Ocean has been carried out intensively since the middle of the last century, and the main references to the published results of studies carried out in the period before the introduction of modern systems of geographic positioning of observation points and collection of geological and geophysical data are presented in [11, 30, 31]. In this connection, an international digital elevation model of the Arctic Ocean floor (The international bathymetric chart of the Arctic Ocean—IBCAO) has been created in recent years as part of the work of the Arctic Scientific Committee [13, 32]. For the Arctic, regional constructions currently use the ETOPO 2 global digital elevation models [33], which combine land topography and ocean bathymetry derived from the compilation of numerous regional data. Among their ranks, the modern version of IBCAO has a resolution often better than 0.5 × 0.5 km. Note that in this regard, all kinematic constructions in the present work are carried out using the most modern version of the geochronological scale of linear magnetic anomalies from [12]. Ice coverage of the water area makes it difficult to collect data on the geological structure of its bottom. There is no full confidence that geological samples brought aboard research vessels are not products of ice drift. Ice conditions limit the possibility of obtaining data during deep-water drilling. Under these conditions, a comprehensive geological and geophysical analysis of the available data on potential fields and, © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0_5

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first of all, on the anomalous magnetic field of the water area allows us to answer a number of important questions about the stages of its development. The Eurasian Basin is bounded by the continental margins of Eurasia, Greenland and the Lomonosov Ridge. It is separated from the Norwegian-Greenland basin by the Fram Strait, located between Greenland and Svalbard, and is bounded in the east by the shelf of the Laptev Sea and in the south by the shelf of the Barents and Kara Seas. [34–36]. The basin stretches for a distance of about 2000 km and has a width of about 900 km. In the middle part of the Eurasian basin lies the spreading midoceanic Gakkel Ridge, which divides it into two basins (Figs. 2.1 and 4.1): Nansen, bounded by the Eurasian Shelf, and Amundsen, adjacent to the Lomonosov Ridge. The general relief of the bottom of these basins is formed by abyssal plains gently sloping away from the axis of the Gakkel Ridge with depths up to 4 km and more [37, 38]. In the central part of the basin, the depth of the rift valley of the Mid-Arctic Ridge is somewhat shallower at 4–4.2 km with a width of 15–50 km. Close to Greenland, the rift valley is 4.5–5 km deep and 12–30 km wide. About 200 kms from Greenland, the ridge is interrupted by a transform fault. Further south, the Lena Trough, which runs at an angle to the mid-ocean ridge, serves as a continuation of the axial zone. The southern limit of the Lena Trough and the modern spreading system of the Arctic Ocean is the Spitsbergen Transform Fault, along which the Mid-Arctic and Mid-Atlantic Ridges join [21, 31]. The dotted line shows the tracing (Fig. 5.1) of the characteristic forms between the bottom relief profiles along chrons 2a N to the north and chrons 2a S to the south of the spreading palaeo-axis (see text). The Nansen and Amundsen deep-water basins [11, 21, 31, 39–43] are composed of oceanic crust about 10 km thick with a thick (up to 2–3 km) sedimentary layer, and the maximum bottom depths approach 4 km. Under the Mid-Arctic Ridge, according to gravity calculations, the crustal thickness was about 1.5 km less than that observed under other mid-ocean ridges [6, 44]. Evidence of recent volcanic activity within its boundaries has also been obtained. Statistical analysis of the bottom topography data (Fig. 5.2) indicates the geomorphological features of the paleo-middle valley of the ridge during chron C2An.3n (3.330–3.596 Ma). Figure 5.3 shows that the surface of the spreading axis at that time has an asymmetric dome-like shape centred at 40 meridian E, its minima are located closer to the Eurasian and Greenland shelves and occur at 20 and 100 meridian E. The relative height of the dome exceeds 100 m at a wavelength of a thousand kilometres. The relative height of the dome exceeds 100 m at a wavelength of a thousand kilometres. The presence of the dome may be related to the fact that in the interval of meridians 160–165 the supply of magmatic material was more intense and exceeded by about 50% the same in the subGreenland and Laptev Sea areas. The profile of residual relief (Fig. 5.4) obtained after exclusion of the regional component clearly shows local magmatic formations with a relative amplitude of 20–80 m and a wavelength along the profile of up to 10 km. Most likely, they are associated with sporadic slot volcanism responsible for the formation of new oceanic crust in the process of bottom extension. Against this background, significant volcanic-magmatic formations with a relative height of up to several hundred metres

5 Evolution of the Axial Zone of the Mid-Arctic (Gakkel) Ridge …

57

Fig. 5.1 Bottom topography (in hundreds of metres) along chron C2An.3n (3.330–3.596 Ma) north (2a-N) and south (2a-S) of the modern spreading axis (according to [21, 39, 40]) in a west-to-east direction (km)

Fig. 5.2 Predicted bottom topography profile (hundreds of metres) along the spreading axis (km) for chron time C2An.3n (3.330–3.596 Ma). The palaeo-axis spreading depths were obtained by adding the profile data presented in Fig. 5.1 and dividing the total results by two

Fig. 5.3 Relief profile (hundreds of metres) along the palaeo-axis (km) of spreading for chron time C2An.3n (3.330–3.596 Ma) calculated using the moving average method for a window size of 40 km and a sliding step of 1 km

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Fig. 5.4 Residual relief profile obtained by subtracting from the data of Fig. 5.3 the data of Fig. 5.2

are noted to the west of the 40th meridian E. They are most likely associated with volcanic-magmatic formations. They are most likely associated with central-type volcanic apparatuses, whose foci are separated from each other at a distance of up to 150 km and reflect additional portions of the incoming material of the new oceanic crust in the area of three limb-shaped protrusions of the hot magmatic material dome. Thus, as a result of these studies, it was possible for the first time to reconstruct the bottom configuration on the palaeo-spreading axis of the Eurasian basin of the Arctic Ocean for the time of chron C2An.3n (3.330–3.596 Ma). It is revealed that the surface of the spreading axis along the strike has an asymmetric dome-shape centred on the 40 E meridian, its minima are located closer to the Eurasian and Greenland shelves and fall on the 20 and 100 E meridians. The relative height of the dome exceeds 500 m at a wavelength of a thousand kilometres. Against the background of this general pattern, local magmatic formations with a relative amplitude of 20–80 m and a wavelength along the profile of up to 10 km, associated with magma melting and formation of new oceanic crust by slit-type eruptive apparatuses, are clearly traced. At the same time, west of 40 meridian E, three significant volcano-magmatic formations with a relative height of up to several hundred metres are observed, associated with the pulsation character of extrusive volcanism of the central type, the sources of which are separated from each other at a distance of up to 200 km. At the same time, east of the 100th meridian E, the input of new oceanic crust material is more uniform. The data obtained are very important in the process of reconstructing the evolution of the Eurasian basin and allow us to present the peculiarities of the process of building up new oceanic crust there during the Upper Neogene.

References 1. Khain VE (2001) Tectonics of continents and oceans. Scientific World, Moscow, p 606 2. Rekant PV, Petrov OV, Kashubin SN et al (2015) History of the sedimentary cover formation in the deep-water part of the Arctic basin according to the data of seismic studies of the MOU-OGT. Reg Geol Metall 64:11–30

References

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3. Berglar K, Franke D, Lutz R et al (2016) Initial opening of the Eurasian basin, Arctic Ocean. Front Earth Sci 4A:91, 14 4. Dossing A, Hansena T, Olesen A (2014) Gravity inversion predicts the nature of the Amundsen basin and its continental borderlands near Greenland. Earth Planet Sci Lett 408:132–145 5. Dossing A, Hopper J, Olesen A (2013) New aero-gravity results from the Arctic: linking the latest Cretaceous-early Cenozoic plate kinematics of the North Atlantic and Arctic Ocean. Geochem Geophys Geosyst 14:22 6. Edwards MH, Kurras GJ, Tolstoy M, Bohnenstiehl DR, Coakley BJ, Cochran JR (2001) Evidence of recent volcanic activity on the ultraslow-spreading Gakkel ridge. Nature 409:808–812 7. Ehlers B, Jokat W (2009) Subsidence and crustal roughness of ultra-slow spreading ridges in the northern North Atlantic and the Arctic Ocean. Geophys J Int 177:451–462 8. Engen O, Gjengedal L, Faleide J et al (2009) Seismic stratigraphy and sediment thickness of the Nansen basin, Arctic Ocean. Geoph J Int 176:805–821 9. Gaina C, Medvedev S, Torsvik T et al (2014) 4D Arctic: a glimpse into the structure and evolution of the Arctic in the light of new geophysical maps, plate tectonics and tomographic models. Oslo Surv Geoph Open Access 35:1095–1122 10. Gaina C, Nikishin F, Petrov E (2015) Ultraslow spreading, ridge relocation and compressional events in the East Arctic region: a link to the Eurekan orogeny? Arktos A 16:11 11. Glebovsky V, Kaminsky V, Minakov A et al (2006) Formation of the Eurasia Basin in the Arctic Ocean as inferred from geohistorical analysis of the anomalous magnetic field. Geotectonics 40:263–281 12. Gradstein F, Ogg J, Schmitz M, Ogg G (2012) The geologic timescale 2012. Elsevier, 1139 p 13. Jakobsson M, Mayer L, Coakley B et al (2012) The international bathymetric chart of the Arctic Ocean (IBCAO) ver. 3.0. Geophysics 3.0. Geoph Res Lett 39:6 14. Jokat W, Lehmann P, Damaske D, Nelson J (2016) Magnetic signature of North-East Greenland, the Morris Jesup Rise, the Yermak Plateau, the central Fram Strait: Constraints for the rift/drift history between Greenland and Svalbard since the Eocene. Tectonophysics 691:98–109 15. Langinen A, Lebedeva-Ivanova N, Gee D, Zamansky Y (2009) Correlations between the Lomonosov Ridge, Marvin Spur and adjacent basins of the Arctic Ocean based on seismic data. Tectonophysics 472:309–322 16. Lutz R, Franke D, Berglar K et al (2018) Evidence for mantle exhumation since the early evolution of the slow spreading Gakkel Ridge, Arctic Ocean. J Geodyn Geodyn 118:154–165 17. Nikishin A, Gaina C, Petrov E et al (2018) Eurasia Basin and Gakkel Ridge, Arctic Ocean: crustal asymmetry, ultraslow spreading and continental rifting revealed by new seismic data. Tectonophysics 746:64–82 18. Nikishin A, Petrov E, Malyshev N,. Ershova V (2017) Rift systems of the Russian eastern arctic shelf and arctic deep water basins: link between geological history and geodynamics. Geodyn Tecton 8:11–43 19. Ocean as inferred from geohistorical analysis of the anomalous magnetic field. Geotectonics 40:263–281 20. Pease V, Drachev S, Stephenson R, Zhang X (2014) Arctic lithosphere—a review. Tectonophysics 628:1–25 21. Schreider AA, Brekhovskikh AL, Sazhneva AE, Galindo-Zaldivar J, Klyuev MS, Rakitin IY (2023) Geochronology of the Eurasian basin floor. In: Chaplina T (ed) Processes in GeoMedia, Springer geology, vol VI. Springer, Cham, pp 431–440 22. Sclater J, Abbot D, Thiede J (1977) Paleobathymetry and sediments of the Indian ocean. In: Indian ocean geology and biostratigraphy. A.G.U. Meeting, pp 25–59 23. Weigelt E, Jokat W (2001) Peculiarities of roughness and thickness of oceanic crust in the Eurasian basin, Arctic Ocean. Geophys J Int 145:505–516 24. Schreider AA (2001) Geomagnetic studies of the Indian Ocean. Nauka, 319 p 25. Schreider AA (1994) Inversions of the earth’s magnetic field and changes in the natural environment. Phys Earth 9:97–101 26. Schreider AA (1998) Magnetic chronology of the ocean floor. Phys Earth 11:61–75

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27. Schreider AA (1988) On the principles of axes of linear palaeo-magnetic anomalies of the ocean. Theses of reports of VIII all-union school of marine geology, vol 2. Izvo IOAN, p 109 28. Klyuev M, Schreider A, Rakitin I (2023) Technical means for underwater archaeology. Earth and environmental sciences library. Springer, Cham, 95 p, 117 Il. ISBN 978-3-031-27501-2 29. Klyuev M, Schreider A, Zverev A (2023) Shelf fluvial paleo structures: seabed seismic acoustic view. Earth and environmental sciences library. Springer, Cham, 79 p, 70 Ill. ISBN: 978-3031-27519-7 30. Chernykh AA, Krylov AA (2010) History of sedimentogenesis in the Amundsen basin in the light of geophysical data and ACEX drilling materials (IODP-302). VNIIOkeangeologiya 210:56–66 31. Schreider AA (2004) Linear magnetic anomalies of the Arctic Ocean. Oceanology 44(5):768– 777 32. www.topex.ucsd.edu/html/mar_topo.html (2023) 33. Amante S, Eakins B (2009) ETOPO1 1 arc-minute global relief model: procedures, data sources and analysis. In: NOAA technical memorandum 2009. NESDIS NGDC-24, 19 p 34. Ivanov VA, Pokazeev KVV, Schreider AA (2008) Fundamentals of oceanology. SPb., Lan, 575 p 35. Ivanov VA, Pokazeev KVV, Schreider AA (2022) Fundamentals of oceanology. SPb., Lan, 578 p 36. Trukhin VI, Pokazeev KV, Kunitsyn VE Schreider AA (2004) Fundamentals of environmental geophysics. SPb., Lan, 384 p 37. Schreider AA, Sazhneva AE, Klyuev MS, Brekhovskikh AL, Rakitin IY, Zuev OA (2019a) Bottom kinematics of the subgreenland region of the Eurasian basin. Oceanology 59(2):282– 291 38. Schreider AA, Sazhneva AE, Klyuev MS, Brekhovskikh AL (2019b) Kinematic model of the development of the areas east of the mid-oceanic Gakkel Ridge in the Eurasian basin of the Arctic Ocean. Oceanology 59(1):143–152 39. Schreider AA, Brekhovskikh AL, Sazhneva AE, Klyuev MS, Galindo-Zaldivar H, Rakitin IY (2022) Kinematics of the Eurasian basin floor. Prots Geos 30(1):1504–1511 40. Schreider AA, Brekhovskikh AL, Sazhneva AE, Klyuev MS, Galindo-Zaldivar H, Rakitin IY (2021) Geochronology of the Eurasian basin floor. Prots Geos 29(3):1297–1305 41. Schreider AA (2023) Evolution of the oceanic crust parameters of the Nansen basin of the Eurasian basin in the Cenozoic. Prots Geos 35(1):1920–1924 42. Schreider AA, Brekhovskikh AL, Sazhneva AE, Klyuev MS (2023) Evolution of the oceanic crust parameters of the Amundsen basin of the Eurasian basin in the Cajonozoic. Prots Geos 35(1):1955–1960 43. Brozena J, Childers V, Lawver L et al (2003) New aerogeophysical study of the Eurasian basin and Lomonosov Ridge implications for basin development. Geology 31:825–828 44. Coakley BJ, Cochran JR (1998) Gravity evidence of very thin crust at the Gakkel Ridge (Arctic Ocean). Earth Planet Sci Lett 162:81–95

Chapter 6

Evolution of Oceanic Crustal Parameters of the Amundsen Basin in the Cenozoic

6.1 Introduction Geological and geophysical studies of the Eurasian Arctic basin floor have been carried out by the world scientific community for many years in the context of restoring the evolution of the Arctic Ocean as part of the world economic system of our planet. The accumulated volume of bathymetric materials indicates that the bottom relief of the Eurasian basin, divided by the mid-Arctic Gakkel Ridge into two elongated deep-water basins, has considerable diversity [1–13]. The morphological structures of the Amundsen Basin (Figs. 2.1 and 4.1), located between the Gakkel Ridge with oceanic crust and the continental Lomonosov Ridge, are characterised by a large range of bottom relief depths from hundreds to thousands of metres. Significant efforts are made by the world scientific community for systematic aeromagnetic studies of the linear magnetic anomalies of the Amundsen Basin. The most modern version of their distribution is presented in Fig. 6.1 [5]. At the same time, intensive, first of all ship-based, geological and geophysical studies allowed obtaining important data not only on the relief and geochronology of the bottom, but also on the parameters of sedimentation and acoustic basement, the surface of which is identified with the upper boundary of the oceanic lithosphere underlying the sedimentary layer. Such data are collected mainly by labour-intensive and expensive seismic methods [14–21]. The geographical location of the most reliable data obtained using modern navigation systems is shown in Fig. 6.1, which is essentially the result of one of the first attempts to systematise the research materials by modifications of the multichannel seismic profiling method in the Amundsen Basin.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0_6

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Fig. 6.1 Bottom chronology in the Amundsen basin according to [5] and the position of seismic sounding points where data on the bottom depth, sediment thickness and depth of the acoustic basement were obtained (based on the data of [9, 14–19, 21–23, 23–26]). Numbers 2a, 5, 6, 13, 18, 20, 24, 25, 26 denote the ends of the chron ends of palaeo-magnetic anomalies C2An.3n, C5n.2n, C6n, C13n, C18n.2n, C20n, C24n.3n, C25n, C26n, respectively. Modified

6.2 Research Results Comparison of the observed and theoretical magnetic anomalies in the model of the ocean floor expansion allowed us to identify the C1–C26n chrons in the Eurasian basin using the most modern version [27] of the geochronological scale from [4, 5]. In the Amundsen Basin (Fig. 6.1), the chrons correspond to the position of the ends of the oldest blocks of positive polarity in the model of the inversion magnetically active layer in accordance with the generally accepted principle of separation [28]. According to the scale of linear magnetic anomalies [27], the age of such ends of the oldest blocks is 3.596 Ma for palaeo-anomaly C2An.3n, C5n.2n–11.056 Ma, C6n– 19.722 Ma, C13n–33.705 Ma, C18n.2n–40.145 Ma, C20n–43.432 Ma, C24n.3n– 53.983 Ma, C25n–57.656 Ma, C26n–59.237 Ma. In Fig. 6.1 of this paper, the above chron ends have been labelled as 2a, 5, 6, 13, 18, 18, 20, 24, 25, 26, respectively, in order to simplify the labelling. The dots on the map show the location of seismic survey sites where the bottom depth, sediment thickness and seismic basement depth were determined simultaneously according to the materials of the works referenced in the text to Fig. 6.1. In the same figure, the modern spreading axis of the Mid-Arctic Ridge is represented by a dotted line in accordance with [5, 16]. More than 70% of the points analysed in this study are located at a distance of more than 200 km from the modern spreading axis within the oceanic crust with a bottom depth of more than 3 km (Fig. 6.2) and an age of more than 30 Ma (Fig. 6.3). Figures 6.2 and 6.3 show that the spreading regime gradually changed in the interval of 20–30 Ma. This situation may be related to the restructuring of its regime, which resulted in an abrupt change in the direction of bottom expansion in conjunction with a change in the character of depth of the consolidated basement surface. These data provide independent information on the peculiarities of the evolution of the Eurasian basin lithosphere development and changes in the volumes of incoming material of the new oceanic crust on the spreading axes, supporting the conclusions of [29].

6.2 Research Results

63

Fig. 6.2 Bottom depth as a function of crustal age in the Amundsen Basin according to the data of the works referenced in Fig. 6.1

Fig. 6.3 Distance of seismic sounding points from the modern spreading axis as a function of crustal age in the Amundsen basin based on seismic results of the studies referenced in Fig. 6.1

The practice of analysing the measurement results indicates that finding an approximating function with the reliability coefficient R2 > 0.7 (e.g., [16]) can be attributed to good results. The standard deviation of point values from the curve of the graph of the approximating function changes most with increasing degree of the approximating polynomial when moving from linear to quadratic approximation. The transition to approximating polynomials of higher degrees only complicates the shape of the curve, although it does not change the character of the distribution of analysed points depending on the age of the lithosphere. In this connection, in order to demonstrate the general behaviour of changes in the sedimentary thickness and depth of

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the acoustic basement surface in time, the present work gave preference to plots of polynomials of the second degree. At the same time, no significant variations in the thicknesses of accumulated sediments depending on age (Fig. 6.4) are noted, which is probably related to a certain uniformity of feeding provinces in relation to the sediment supply rates along the continental margin of Siberia and the Lomonosov Ridge. Such variations are undoubtedly related to the heterogeneity of the distribution of feeding provinces and sedimentary material inflow rates into them along the continental margin of Siberia. This is also indicated by a very low reliability coefficient R2 = 0.44 (Fig. 6.4). The plots of sediment thickness distribution (Fig. 6.4) and the depth of the acoustic basement surface of the oceanic crust (Fig. 6.5) show polynomial approximations with equations and values of approximation reliability R2. The closer the value of R2 is to 1, the more accurately the selected function approximates the used measurement data.

Fig. 6.4 Variations of sediment thickness at seismic survey points in the Amundsen basin based on the data of the works referenced in Fig. 6.1

Fig. 6.5 Depth of the acoustic basement surface in the Amundsen basin at the seismic survey points referenced in Fig. 6.1

References

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This circumstance is emphasised by the degree of close connection between the synchrony of the synchronous ducking of the acoustic basement surface and the accumulating sediment thicknesses. The surface of the acoustic basement (Fig. 6.5) generally deepens from values of about 4 km at a lithosphere age of about 8 Ma to values of about 7 km at an age of more than 50 Ma. This result confirms the planetary regularity of the deepening of the bottom surface and oceanic crust in time [30, 31] and for the first time specifies their behaviour for the case of the Amundsen Basin. The obtained calculation results are based on the joint study of the seafloor geochronology based on paleomagnetic anomalies and the integrated geological and geophysical study of seismic results. They supplement the information on the kinematics of the Eurasian basin floor obtained in [5].

6.3 Conclusion The first systematic study of published seismic data, which provide information on the bottom topography, sediment thickness and acoustic basement surface in combination with modern data on the age of the oceanic crust in the Amundsen Basin at the seismic sounding point, was carried out. The integrated geological and geophysical characterisation allows us to clarify the parameters of the kinematics of the basin development in the Cenozoic known in the literature. Calculations show that the thicknesses of sedimentary rocks within the crust with the age of more than 35 million years experience significant variations ranging from hundreds of metres to 3–5 km. This is undoubtedly due to the heterogeneity of the distribution of feeding provinces and sedimentary material flow rates along the continental margin of Siberia. At the same time, the surface of the acoustic basement generally deepens from values of about 4 km at a lithosphere age of about 8 million years to values of about 7 km at an age of more than 50 million years. This result confirms the general pattern of deepening of the bottom surface and oceanic crust in time known in the literature and specifies them for the case of the Amundsen Basin.

References 1. Ivanov VA, Pokazeev KVV, Schreider AA (2022) Fundamentals of oceanology. SPb., Lan, 576 p 2. Trukhin VI, Pokazeev KV, Kunitsyn VE, Schreider AA (2004) Fundamentals of environmental geophysics. SPb., Lan, 384 p 3. Khain VE (2001) Tectonics of continents and oceans. Scientific World, 606 p 4. Schreider AA (2004) Linear magnetic anomalies of the Arctic Ocean. Oceanology 44(5):768– 777 5. Schreider AA, Brekhovskikh AL, Sazhneva AE, Klyuev MS, Galindo-Zaldivar H, Rakitin IY (2021) Geochronology of the Eurasian basin floor. Prots Geos 29(3):1297–1305

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6. Schreider AA, Sazhneva AE, Klyuev MS, Brekhovskikh AL, Rakitin IY, Zuev OA (2019a) Bottom kinematics of the subgreenland region of the Eurasian basin. Oceanology 59(2):282– 291 7. Schreider AA, Sazhneva AE, Klyuev MS, Brekhovskikh AL (2019b) Kinematic model of the development of areas east of the mid-oceanic Gakkel Ridge in the Eurasian basin of the Arctic Ocean. Oceanology 59(1):143–152 8. Brozena J, Childers V, Lawver L et al (2003) New aerogeophysical study of the Eurasian Basin and Lomonosov Ridge implications for basin development. Geology 31:825–828 9. Dossing A, Hansena T, Olesen A (2014) Gravity inversion predicts the nature of the Amundsen basin and its continental borderlands near Greenland. Earth Planet Sci Lett 408:132–145 10. Dossing A, Hopper J, Olesen A (2013) New aero-gravity results from the Arctic: linking the latest Cretaceous-early Cenozoic plate kinematics of the North Atlantic and Arctic Ocean. Geochem Geophys Geosyst 14:22 11. Gaina C, Medvedev S, Torsvik T et al (2014) 4D Arctic: a glimpse into the structure and evolution of the Arctic in the light of new geophysical maps, plate tectonics and tomographic models. Oslo Surv Geoph Open Access 35:1095–1122 12. Gaina C, Nikishin F, Petrov E (2015) Ultraslow spreading, ridge relocation and compressional events in the East Arctic region: a link to the Eurekan orogeny? Arktos A 16:11 13. Jakobsson M, Mayer L, Coakley B et al (2012) The international bathymetric chart of the Arctic Ocean (IBCAO) ver. 3.0. Geophysics 3.0. Geoph Res Lett 39:6 14. Rekant PV, Petrov OV, Kashubin SN et al (2015) History of the sedimentary cover formation in the deep-water part of the Arctic basin according to the data of seismic studies of the MOU-OGT. Reg Geol Metall 64:11–30 15. Chernykh AA, Krylov AA (2010) History of sedimentogenesis in the Amundsen basin in the light of geophysical data and ACEX drilling materials (IODP-302). VNIIOkeangeologiya 210:56–66 16. Schreider AA (2023) Evolution of the oceanic crust parameters of the Nansen basin of the Eurasian basin in the Cajonozoic. Prots Geos 31:1297–1305 17. Engen O, Gjengedal L, Faleide J et al (2009) Seismic stratigraphy and sediment thickness of the Nansen basin, Arctic Ocean. Geoph J Int 176:805–821 18. Jokat W, Lehmann P, Damaske D, Nelson J (2016) Magnetic signature of North-East Greenland, the Morris Jesup Rise, the Yermak Plateau, the central fram strait: constraints for the rift/drift history between Greenland and Svalbard since the Eocene. Tectonophysics 691:98–109 19. Lutz R, Franke D, Berglar K et al (2018) Evidence for mantle exhumation since the early evolution of the slow spreading Gakkel Ridge, Arctic Ocean. J Geodyn Geodyn 118:154–165 20. Nikishin A, Gaina CC, Petrov E et al (2018) Eurasia Basin and Gakkel Ridge, Arctic Ocean: crustal asymmetry, ultraslow spreading and continental rifting revealed by new seismic data. Tectonophysics 746:64–82 21. Weigelt E, Jokat W (2001) Peculiarities of roughness and thickness of oceanic crust in the Eurasian basin, Arctic Ocean. Geophys J Int 145:505–516 22. Berglar K, Franke D, Lutz R et al (2016) Initial opening of the Eurasian Basin, Arctic Ocean. Front Earth Sci 4A:91, 14 23. Ehlers B, Jokat W (2009) Subsidence and crustal roughness of ultra-slow spreading ridges in the northern North Atlantic and the Arctic Ocean. Geophys J Int 177:451–462 24. Langinen A, Lebedeva-Ivanova N, Gee D, Zamansky Y (2009) Correlations between the Lomonosov Ridge, Marvin Spur and adjacent basins of the Arctic Ocean based on seismic data. Tectonophysics 472:309–3222 25. Nikishin A, Petrov E, Malyshev N, Ershova V (2017) Rift systems of the Russian eastern arctic shelf and arctic deep water basins: link between geological history and geodynamics. Geodyn Tecton 8:11–43 26. Pease V, Drachev S, Stephenson R, Zhang X (2014) Arctic lithosphere—a review. Tectonophysics 628:1–25 27. Gradstein F, Ogg J, Schmitz M, Ogg G (2012) The geological timescale 2012. Elsevier, 1139 p

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28. Schreider AA (1988) On the principles of axes of linear palaeo-magnetic anomalies of the ocean. Theses of reports of the 111th all-union school of marine geology, vol 2. Izvo IOAN, p 109 29. Schreider AA, Brekhovskikh AL, Sazhneva AE, Klyuev MS, Galindo-Zaldivar H, Rakitin IY (2022) Kinematics of the Eurasian basin floor. Proc Geos 30(1):1504–1511 30. Schreider AA (2001) Geomagnetic studies of the Indian Ocean. Nauka, 319 p 31. Sclater J, Abbot D, Thiede J (1977) Paleobathymetry and sediments of the Indian ocean. In: Indian ocean geology and biostratigraphy. A.G.U. Meeting, pp 25–59

Chapter 7

Evolution of Oceanic Crustal Parameters of the Nansen Basin in the Cenozoic

7.1 Introduction Geological and geophysical studies of the Eurasian Arctic basin floor have been carried out by the world scientific community for many years in the context of restoring the evolution of the Arctic Ocean as part of the world economic system of our planet. In the middle of the last century, on the initiative of the Arctic Scientific Committee, an international digital model of the Arctic Ocean floor topography (The international bathymetric chart of the Arctic Ocean—IBCAO) was created [1]. The constantly updated modern version of the bathymetric chart of the bottom relief, reconstructed on the basis of mainly altimetric data, IBCAO V3.0 has a resolution often better than 0.5 × 0.5 km. The accumulated volume of bathymetric materials indicates that the bottom relief of the Eurasian basin, divided by the mid-ocean ridge of Gakkel into two elongated deep-water Amundsen and Nansen basins (Figs. 2. 1 and 4.1), has considerable diversity [2–13]. The Nansen Basin is adjacent to the Russian continental margin and its morphostructures are characterised by a wide range of bottom relief depths from hundreds to thousands of metres. Along with the study of the bottom topography, considerable efforts are made for systematic aeromagnetic studies of the linear magnetic anomalies of the basin, the most modern version of which is presented in Fig. 7.1 [6]. At the same time, intensive, primarily ship-based, geological and geophysical studies have provided important data not only on the bottom topography, but also on sedimentation parameters and the underlying acoustic basement, the surface of which is identified with the upper boundary of the oceanic lithosphere underlying the sedimentary layer. Such data are mainly collected by seismic methods, which are labour-intensive and expensive to implement, and are therefore in the early stages of the accumulation process. The geographic location of the most reliable data obtained using modern seismometry and navigation systems is shown in Fig. 7.1, which is essentially the result of one of the first attempts to systematise the research materials by modifications of the multichannel seismic profiling method in the Nansen Basin. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0_7

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7 Evolution of Oceanic Crustal Parameters of the Nansen Basin …

Fig. 7.1 Bottom chronology in the Nansen basin (according to [6]) and seismic sounding points where data on bottom depth, sediment thickness, and acoustic basement depth were obtained (based on [10, 14–24]). Modified

7.2 Research Results Comparison of the observed and theoretical magnetic anomalies in the model of the ocean floor expansion allowed us to identify the C1–C26n chrons in the Eurasian basin using the most modern version of the geochronological scale from [5, 6, 25]. In the Nansen Basin (Fig. 7.1), the chron lines correspond to the oldest ends of the blocks of positive polarity [26] in the model of the inversion magnetically active layer C2An.3n (3.596 Ma), C5n.2n (11.056 Ma), C6n (19.722 Ma), C13n (33.705 Ma), C18n.2n (40.145 Ma), C20n (43.432 Ma), C24n.3n (53.983 Ma), C25n (57.656 Ma), C26n (59.237 Ma). In order to simplify the captions in Fig. 7.1, they have been labelled as 2a, 5, 6, 13, 18, 20, 24, 25, 26, respectively. In the figure, the modern spreading axis of the mid-Arctic ridge is represented by a dashed line. The dots show the location of seismic survey sites where the bottom depth, sediment thickness, and seismic basement depth were determined simultaneously (according to [10, 14–21, 23, 24]). More than 80% of the points analysed in this paper are located between 200 and 450 km from the modern spreading axis within oceanic crust with bottom depths greater than 3 km (Fig. 7.2) and ages greater than 40 Ma (Fig. 7.3). The plots of sediment thickness distribution (Fig. 7.4) and the depth of the acoustic basement surface of the oceanic crust (Fig. 7.5) show polynomial approximations with equations and values of approximation reliability R2. The closer the value of R2 is to 1, the more accurately the selected function approximates the used measurement data. The practice [27] of measurement results processing shows that good results include finding an approximating function with the reliability coefficient R2 > 0.7 (at the same time, a very reliable approximation result is achieved at R2 > 0.8). Estimates show that the standard deviation of point values from the curve of the graph of the approximating function with increasing degree of the approximating polynomial changes to the greatest extent in the transition from linear to quadratic

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Fig. 7.2 Distance of seismic sounding points from the modern spreading axis in the Nansen basin

Fig. 7.3 Bottom depth in the Nansen basin according to the data of the works referenced in Fig. 7.1

Fig. 7.4 Sediment thickness variations at seismic survey points in the Nansen basin

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Fig. 7.5 Depth of the acoustic basement surface in the Nansen basin at seismic survey points

approximation. The transition to approximating polynomials of higher degrees only complicates the shape of the curve, but does not change the character of the behaviour of the analysed points depending on the age of the lithosphere. Therefore, in order to demonstrate the general behaviour of changes in sediment thickness and depth of the acoustic basement surface in time, the present work gave preference to plots of polynomials of the second degree. Such variations are undoubtedly related to the heterogeneity of the distribution of feeding provinces and sedimentary material inflow rates into them along the continental margin of Siberia. This is also indicated by a very low reliability coefficient R2 = 0.44. The surface of the acoustic basement (Fig. 7.5) generally deepens from values of about 4 km at a lithosphere age of about 8 Ma to values of about 7 km at an age of more than 50 Ma. This result confirms the planetary regularity of the deepening of the bottom surface and oceanic crust in time [27, 28] and for the first time specifies their behaviour in the case of the Nansen Basin. Changes in the pattern of basement burial starting from an age of about 25 Ma are outlined. At the same time, the reliability coefficient R2 = 0.49 of the approximating function remains very low, which is probably due to the relatively small (about 30 analysed points) amount of material available so far for the Nansen Basin. The obtained calculation results are based on the joint study of the seafloor geochronology based on paleo-magnetic anomalies and the integrated geological and geophysical study of the seismic results. They supplement the data on the kinematics of the Eurasian basin floor obtained in [6].

7.3 Conclusion The first systematic study of published seismic data, which provide information on the bottom topography, sediment thickness and acoustic basement surface in combination with modern data on the age of the oceanic crust in the Nansen Basin at the seismic sounding point, has been carried out. The integrated geological and geophysical characterisation allows us to clarify the parameters of the kinematics of

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the basin development in the Cenozoic known in the literature. Calculations show that the thicknesses of sedimentary rocks within the crust with the age of more than 35 million years experience significant variations ranging from hundreds of metres to 3–5 km. This is undoubtedly related to the heterogeneity of the distribution of feeding provinces and sedimentary material flow rates along the continental margin of Siberia. Changes in the character of the basement burial starting from the age of about 25 Ma are outlined. The surface of the acoustic basement generally deepens from values of about 4 km at a lithospheric age of about 8 Ma to values of about 7 km at an age of more than 50 Ma. This result confirms the general pattern of deepening of the bottom surface and oceanic crust in time known in the literature and specifies them for the case of the Nansen Basin.

References 1. Jakobsson M, Mayer L, Coakley B et al (2012) The international bathymetric chart of the Arctic Ocean (IBCAO) ver. 3.0. Geophysics 3.0. Geoph Res Lett 39:6 2. Ivanov VA, Pokazeev KVV, Schreider AA (2022) Fundamentals of oceanology. SPb., Lan, 576 p 3. Trukhin VI, Pokazeev KV, Kunitsyn VE, Schreider AA (2004) Fundamentals of environmental geophysics. SPb., Lan, 384 p 4. Khain VE (2001) Tectonics of continents and oceans. Scientific World, 606 p 5. Schreider AA (2004) Linear magnetic anomalies of the Arctic Ocean. Oceanology 44(5):768– 777 6. Schreider AA, Brekhovskikh AL, Sazhneva AE, Klyuev MS, Galindo-Zaldivar H, Rakitin IY (2021) Geochronology of the Eurasian basin floor. Prots Geos 29(3):1297–1305 7. Schreider AA, Sazhneva AE, Klyuev MS, Brekhovskikh AL, Rakitin IY, Zuev OA (2019a) Bottom kinematics of the subgreenland region of the Eurasian basin. Oceanology 59(2):282– 291 8. Schreider AA, Sazhneva AE, Klyuev MS, Brekhovskikh AL (2019b) Kinematic model of the development of areas east of the mid-oceanic Gakkel Ridge in the Eurasian basin of the Arctic Ocean. Oceanology 59(1):143–152 9. Brozena J, Childers V, Lawver L et al (2003) New aerogeophysical study of the Eurasian basin and Lomonosov Ridge implications for basin development. Geology 31:825–828 10. Dossing A, Hansena T, Olesen A (2014) Gravity inversion predicts the nature of the Amundsen basin and its continental borderlands near Greenland. Earth Planet Sci Lett 408:132–145 11. Dossing A, Hopper J, Olesen A (2013) New aero-gravity results from the Arctic: linking the latest Cretaceous-early Cenozoic plate kinematics of the North Atlantic and Arctic Ocean. Geochem Geophys Geosyst 14:22 12. Gaina C, Medvedev S, Torsvik T et al (2014) 4D Arctic: a glimpse into the structure and evolution of the Arctic in the light of new geophysical maps, plate tectonics and tomographic models. Oslo Surv Geoph Open Access 35:1095–1122 13. Gaina C, Nikishin F, Petrov E (2015) Ultraslow spreading, ridge relocation and compressional events in the East Arctic region: a link to the Eurekan orogeny? Arktos A 16:11 14. Rekant PV, Petrov OV, Kashubin SN et al (2015) History of the sedimentary cover formation in the deep-water part of the Arctic basin according to the data of seismic studies of the MOU-OGT. Reg Geol Metall 64:11–30 15. Chernykh AA, Krylov AA (2010) History of sedimentogenesis in the Amundsen basin in the light of geophysical data and ACEX drilling materials (IODP-302). VNIIOkeangeologiya 210:56–66

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16. Berglar K, Franke D, Lutz R et al (2016) Initial opening of the Eurasian basin, Arcticocean. Front Earth Sci 4A:91, 14 17. Ehlers B, Jokat W (2009) Subsidence and crustal roughness of ultra-slow spreading ridges in the northern North Atlantic and the Arctic Ocean. Geophys J Int 177:451–462 18. Engen O, Gjengedal L, Faleide J et al (2009) Seismic stratigraphy and sediment thickness of the Nansen basin, Arctic Ocean. Geoph J Int 176:805–821 19. Jokat W, Lehmann P, Damaske D, Nelson J (2016) Magnetic signature of North-East Greenland, the Morris Jesup Rise, the Yermak Plateau, the central fram strait: constraints for the rift/drift history between Greenland and Svalbard since the Eocene. Tectonophysics 691:98–109 20. Langinen A, Lebedeva-Ivanova N, Gee D, Zamansky Y (2009) Correlations between the Lomonosov Ridge, Marvin Spur and adjacent basins of the Arctic Ocean based on seismic data. Tectonophysics 472:309–322 21. Lutz R, Franke D, Berglar K et al (2018) Evidence for mantle exhumation since the early evolution of the slow spreading Gakkel Ridge, Arctic Ocean. J Geodyn Geodyn 118:154–165 22. Nikishin A, Gaina CC, Petrov E et al (2018) Eurasia Basin and Gakkel Ridge, Arctic Ocean: crustal asymmetry, ultraslow spreading and continental rifting revealed by new seismic data. Tectonophysics 746:64–82 23. Nikishin A, Petrov E, Malyshev N, Ershova V (2017) Rift systems of the Russian eastern arctic shelf and arctic deep water basins: link between geological history and geodynamics. Geodyn Tecton 8:11–43 24. Pease V, Drachev S, Stephenson R, Zhang X (2014) Arctic lithosphere—a review. Tectonophysics 628:1–25 25. Gradstein F, Ogg J, Schmitz M, Ogg G (2012) The geological timescale 2012. Elsevier, 1139 p 26. Schreider AA (1988) On the principles of axes of linear palaeo-magnetic anomalies of the ocean. In: Theses of reports of VIII all-union school of marine geology, vol 2. Izvo IOAN, p 109 27. Schreider AA (2001) Geomagnetic studies of the Indian Ocean. Nauka, 319 p 28. Sclater J, Abbot D, Thiede J (2001) Paleobathymetry and sediments of the Indian ocean. In: Indian ocean geology and biostratigraphy. A.G.U. Meeting, pp 25–59; Weigelt E, Jokat W (2001) Peculiarities of roughness and thickness of oceanic crust in the Eurasian basin, Arctic Ocean. Geophys J Int 145:505–516

Chapter 8

Kinematics of the Polar Area of Lomonosov Ridge Bottom in Arctic

8.1 Introduction In the sub-polar region of the Lomonosov Ridge in the range between 88° and 89°N the Intra Basin [1, 2] is located. Depths of which exceeds 2.6 km and has flat bottom and dimensions of 100 × 30 km. The position of the Lomonosov ridge crest is at depth of about 1.5 km. The origin of the Intra Basin and its role in the evolution of the polar region of the Arctic Ocean has been discussed in many studies [1–6]. In these studies, the origin of the Intra Basin is associated with the deformation of the Lomonosov Ridge that occurred in the pre-Cenozoic era as a result of the gravitational slippage of one wing of the ridge along the other, stretching and splitting of the ridge as a piece of continental crust from the Barents Sea shelf, etc. Available data on sedimentary structure obtained as a result of analysis of seismic sounding, of magnetic and gravitational fields, of bottom relief by the international database IBCAO [8] can be used to restore the peculiarities of evolution of the polar region of the Arctic Ocean (at the same time it is flagged that bathymetry in the IBCAO project framework is a subject to prognosis and continuous refinement), which is the goal of the presented study.

8.2 Research Methodology A computer method was proposed in [7] for the best isobaths combination on the example of the Atlantic Ocean. The alignment was done by trial and error method, by minimizing the angular misalignment measured along the Euler latitudes. The technique illustrates the principle of the best match, which helps to restore the primary continuity of any contours, including isochronous, isobaths, isohypses, etc. Here this technique [7] is applied for the first time for overlapping slope zones of the Intra Basin in the sub-polar region of the Lomonosov Ridge. Calculations of the Euler © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0_8

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poles and angles of rotation are performed using original computer programs of the Laboratory of Geophysics and Tectonics of the World Ocean Floor of the P. P. Shirshov Institute of Oceanology of RAS. Complex geological and geophysical interpretation of data from international banks of digital and analogue information IBCAO [8] on bathymetry, magnetometry, distribution of gravity, seismic data on sedimentary rock power and structure of the crust is the basis for creating a new geodynamic model of the Lomonosov Ridge subpolar region evolution. As a result, for the first time the evolution of the Intra Basin bottom and adjacent areas of the Lomonosov Ridge has been restored quantitatively. The trough is stretched along the axis of the ridge and is surrounded by elevations with peaks at depth of about 1.5 km (Fig. 8.1). The slopes of the Intra Basin from the side of the Amerasian and Eurasian basins are rather steep and have a slope of up to 10°–20°. On profiles J-K (Cavalla7) and G-H (HB 9801), sub-latitudinally crossing the Lomonosov Ridge, in the area of the Intra Basin (Figs. 8.1 and 8.2) according to [1] there is a minimum of gravity field in the Fai reduction. Its relative amplitude does not exceed 80 mGal. Absolute values above the depression are—50 mGal, and above the adjacent areas with the continental crust of the Lomonosov Ridge from the side of Makarov and Amundsen Basins the values are 30–50 mGal (Fig. 8.2). There are 8 aeromagnetic profiles known in the area of the Intra Basin (Fig. 8.3) [9]. The decrease of the anomalous magnetic field with amplitude about hundred nT is associated with the central part and sides of the trough. It has rather complex

Fig. 8.1 Bathymetry of the Intra basin (isobaths in hundreds of meters). In accordance with data [7, 8, 10 with changes] the position of the main profiles of seismic (thick lines 38–44) and gravimetric F-E, L-M (NP-28) (dashed lines) measurements are shown, as well as profiles of anomalous values in Fai reduction along the profiles of G-H, J-K. The points of hydro-acoustic probing SB 86, SB 92 and SB 93 by sonobuoy are marked with dashes. Letter designations with dashes correspond to end-points of profiles shown in Figs. 8.2, 8.4 and 8.5. Modified

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Fig. 8.2 Bottom relief (dashed line) and anomalous values of gravity field in milliGals (solid line) at sections A–A' and B–B' of I-K and L-Z profiles (shown in Fig. 8.1), modified

configuration and, in our opinion, does not possess any signs of a linear magnetic anomaly born in the process of bottom spreading. Estimation modelling suggests the sources of the anomalous field to be related to tectonic heterogeneities in the crystal foundation of the sides and bottom of the trough. Six seismic profiles (lines 39–44) of the HOTRAX project are acquired and processed together with data from the ACEX project (Arctic Coring Expedition, IODP, Leg 302) [5]. In this case line 40 (Fig. 8.1) is the closest to the extraction points of geological samples of the ACEX drilling project and is characterized by high quality of seismic recording. Comparison of seismic signals and drilling geological data shows (Fig. 8.4) that among the fixed seismic layers (units 1–4) the most near-surface of them has the power of about 0.15 km with the velocity of longitudinal seismic waves up to 1.7 km/s. At the same time, the underlying reflector “D”

Fig. 8.3 Profiles of the anomalous magnetic field along the aeromagnetic observation lines according to data [9, 11], modified. Isobaths are in hundreds of meters. The scale in nanotesla (nT) is given

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Fig. 8.4 Longitudinal seismic wave velocities in the region of multichannel seismic profiling point SB 86 (modified by [5]). Position of line 40 and points of profiling are shown in Fig. 8.1. Vertical axis represents time of double run of seismic signal in seconds

(Fig. 8.4) correlates with hiatus, which reflects a break in sediment accumulation, dated to the interval of 16–44 mln years [5]. Seismically more transparent layers with velocities of 1.8 km/s underlie further. This layers are most likely composed of muddy rocks observed when sampling columns according to ACEX drilling project. A pack of Cenozoic sedimentary deposits of more than 0.7 km in thickness with velocities close to 2.2 km/s is located on boards and inside Intra Basin. The reflector ‘A’ in Fig. 8.4 corresponds to the boundary between Cenozoic and Mesozoic sediments [5]. Seismic records in the peripheral part of line 39 illustrate the most complete crosssection of the Cenozoic sediments (Fig. 8.5). The slope of sediment deposits recorded at line 39 for Middle and Late—Cenozoic deposits allows to assume [5], that the sedimentaion was mostly filled from the North-West on the West, in the Siberian part of the trough. Data interpretation along line 39 [5] serves for expansion of sedimentary layer structure vision in the sub-pole region of the Lomonosov Ridge known along line 40 and allows detecting a number of inter-layers (units 1–5). Unit 1 is represented by silt with thickness up to 0.5 km and age less than 16 mln years. Below its thickened silts are of lower depth (unit 2), and the underlying reflector correlates with hiatus reflecting a break in sedimentation process. Estimation calculations show that unit 3 is composed of highly compacted silt and loams with thickness of about one

Fig. 8.5 Sedimentary layers Y1–Y5 (numbers in parentheses indicate millions of years) and estimated geochronological interpretation along line 39 between points G–G' (Fig. 8.1) at the Eurasian slope of the Intra basin (modified by [5, 11])

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kilometer and age 44–50 mln years. Unit 4 is composed of clay (?) material with the age of 50–70 mln years. Unit 5 is represented by consolidated (?) sedimentary rocks with thickness of more than one kilometer and age of more than 70 mln years. The pattern of seismic recording suggests the presence of even more ancient sediments, underlying unit 5. Earlier sediments of varying thickness (from 0.5 to 1.5 km) with velocities of 2.6–3.9 km/s are characterized by moderate deformations. Seismic lines on the ridge heights show an acoustic foundation at a depth of about 3 km, and the position of reflecting horizons in the trough, usually parallel to the bottom surface, shows depth of 4.5 km. This fact and the presence of layers [5] with higher velocities (about 4–5 km/s) suggest, as mentioned above, the presence of well consolidated even older sediments, with possible ages of up to 110 mln years or even older. Our estimates and data from [1, 9, 12–14] do not allow to identify with certainty the material underlying the trough sediments as fragments of the oceanic crust.

8.3 Paleo-Geodynamic Calculation Results The analysis of the geomorphology of the Intra Basin bottom allows to highlight a number of bathymetric features that can be interpreted within the framework of the lithospheric plate tectonics concept. The most important are the similarity of the isobaths patterns on opposite slopes of the trough (Fig. 8.6a). The maximum similarity has the isobaths of 1.8 km for about forty kilometers (Fig. 8.6b). The junction of conjugate isobaths is registered for more than 40 km and can be described by the Euler Pole of finite rotation at a point with coordinates 82.43° N, 166.14° W. The angle of rotation was 14.15° ± 3.2°. The point alignment error was 1.2 ± 0.7 km (9 values). As a result, for Intra Basin the position of axis of split zone is restored and mutual position of sides of the depression is reconstructed (Fig. 8.7a). Also the profile of the bottom before the split along D–D1 line is obtained.

Fig. 8.6 Intra Basin bottom on the Lomonosov Ridge: a bathymetry (hundreds of meters deep) of according to data [8, 11] and the position of the end-points of conjugate isobaths 1.8 km 1–2 on the Southern and 11–21 on the Northern slopes of the trough, as well as the direction (arrows) of the closure points, b junction of conjugate isobaths 1.8 km Southern (solid line) and Northern (dashed) slopes of the trough, location of points is shown in Fig. 8.6a. Modified

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Fig. 8.7 Slopes of the Intra basin: a paleo-geodynamic reconstruction of oncoming slope closure, location of points is shown in Fig. 8.6a, black bold line shows the restored position of the rift axis, isobaths in hundreds of meters; b cut of the primary relief of the bottom before the breakup of fragments of the Lomonosov Ridge along the D–D' line, which is shown in Fig. 8.7a, the point indicates the exit of the rift axis to the bottom surface. Modified

As the crust of the Lomonosov Ridge is continental and, according to the results of the above mentioned geological and geophysical studies, there are no obvious signs of oceanic crust fragments under the Intra Basin, the crust underlying the depression should also have continental origin. Thus, the process of destruction has not led to the splitting of the continental lithosphere in the area of the Intra Basin and the formation of the Oceanic crust. The above calculations also allow restoring the peculiarities of mutual position of the primary relief of the trough bottom that existed before the split (Fig. 8.7b) and marking the exit of the split axis to the bottom. These results seem to be very important in restoration of parameters of the stress state of the crust at the Lomonosov Ridge breakup from the periphery of the Eurasian continent.

8.4 Conclusion Thus, the computer technique for the best isobath alignment [7, 15] is first applied to the case of isobath alignment in the Intra Basin at the Lomonosov Ridge sub-polar region of the Arctic Ocean. Numerous studies of the connectivity of different parts of different and homonymous isobaths have shown that the most suitable for the purposes of paleo-geodynamic analysis are parts of isobaths in the range of 1.6– 2.2 km, which correspond to the steepest slope section with the lowest sediments thickness. Therefore isobate areas of 1.8 km are identified on the counter slopes of the Intra Basin to show good connection with each other. For these sections, Euler’s finite poles are calculated and the rotation angles are determined, the axis of the split zone is restored in the crust of the Intra Basin, and the features of the paleo-relief of the bottom are presented. No clear evidence of oceanic crust fragments in the trough is found.

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The reconstructions made possible to restore paleo-bathymetry in the sub-polar area of the Lomonosov Ridge and to estimate the age of the bottom split in the Intra Basin as possibly reaching 100 mln years or even more. The conclusions obtained do not contradict the results [10]. The results of the studies seem undoubtedly important in the face of the discussion of justifying issues for the position of the Russian continental shelf in the Arctic Ocean outer limit.

References 1. Cochran J, Edwards M, Coakley B (2006) Morphology and structure of the Lomonosov ridge, Arctic Ocean. Geochem Geophys Geosys 7(Q05019):26. https://doi.org/10.1029/200 5GC001114 2. Bjork G, Jakobsson M, Rudels B et al (2007) Bathymetry and deep-water exchange across the central Lomonosov ridge at 88–89° N. Deep-Sea Res 54:1197–1208 3. Backman J, Moran A et al (2006) Proceeding IODP. 302. Integrated Ocean Drilling Program Management International, Inc., Edinburgh. https://doi.org/10.2204/iodp.proc.302.2006 4. Jakobsson M, Macnab R et al (2008) An improved bathymetric portrayal of the Arctic Ocean: implications for ocean modeling and geological, geophysical and oceanographic analyses. 35:L07602. https://doi.org/10.1029/2008GL033520 5. Lebedeva-Ivanova N (2010) Geophysical studies bearing on the origin of the Arctic basin. Uppsala University Press, Uppsala, p 79 6. Truhin VI, Pokazeev KV, Kunicyn VE, Schreider AA (2004) Osnovy ekologicheskoi geofiziki. St.-Petersburg, Lan, p 384 (in Russian) 7. Bullard E, Everett J, Smith A (1965) The fit of continents around Atlantic. symphosium on continental drift. Phil Trans Roy Soc London 258A:41–51 8. IBCAO (2020). www.ngdc.noaa.gov/mgg/bathymetry/arctic/ 9. Brozena JM, Childers VA, Lawver LA, Gahagan LM, Forsberg R, Faleide JI, Eldholm O (2003) New aerogeophysical study of the Eurasia basin and Lomonosov ridge: implications for basin development. Geology 31(9):825–828 10. Artjushkov EV, Poselov VA (2009) Kontinental’naja kora v glubokovodnyh vpadinah na severovostoke Rossijskogo sektora Arktiki. Geologija poljarnyh oblastej Zemli Mat XLII Tektonich soveshh 1:24–27 (in Russian) 11. Schreider AA, Brehovskih AL, Sazhneva AE, Kluev MS, Rakitin IY, Galindo-Zaldivar J, Evsenko EI, Greenberg OV (2020) Kinematics of the bottom of the appearance area of the lomonosov ridge in the arctic. Process GeoMedia. 3(25):823–828 (in Russian) 12. Langinen A, Lebedeva-Ivanova N, Gee D, Zamansky Y (2009) Correlations between the Lomonosov ridge, Marvin Spur and adjacent basins of the Arctic Ocean based on seismic data. Tectonophysics 472:309–322 13. Langinen AE, Gee DG, Lebedeva-Ivanova NN, Zamansky YY (2006) Velocity structure and correlation of the sedimentary cover on the Lomonosov ridge and in the Amerasian basin, Arctic Ocean. In: Scott RA, Thurston DK (eds) Proceeding fourth international conference on Arctic margins, OCS Study MMS, 179–188 14. Jokat W, Uenzelmann-Neben G, Kristoffersen Y, Rasmussen T (1992) ARCTIC’91: Lomonosov ridge—a double sided continental margin. Geology 20:887–890 15. AlA S et al (2016) Bottom kinematics near the Svalbard region of the Eurasian basin. Okeanol. 56(5):791–803 (in Russian)

Chapter 9

Kinematic Model of the Arlis Spur Breakaway from the Lomonosov Ridge in the Arctic Ocean

9.1 Introduction The Makarov Basin is stretched along the Amerasian footwall of the Lomonosov Ridge, which is an outlier of the Barents-Kara paleo-edge of the continent. The basin narrows towards the Siberian shelf (Fig. 9.1). It is separated from the adjacent Podvodnikov Basin by a low Arlis sill, up to 2.5 km deep [1]. In this area, the cartographic materials of many articles highlight an unnamed spur (spur), which is adjacent to the Geophysicists’ spur or, possibly, even a part of it, as it is indicated in the domestic application to the UN on shelf delineation, or the Oden Spur [2, 3]. In this connection, for convenience of presentation of the material in this paper, this spur of the Lomonosov Ridge will be called Arlis Spur. The questions of the origin of the Central Arctic structures play a key role in the problem of elucidating the nature of the circumpolar region of the Arctic Ocean as a whole. In this connection, it is important to reconstruct the peculiarities of the Barents-Kara palaeo-edge of the continent, the fragments of which include the Arlis Spur and adjacent seabed areas. Deep-water drilling and special geophysical works (seismic, aeromagnetic, etc.) aimed at reconstruction of the geochronology and geodynamics of the bottom in the area of these objects have not been carried out directly within the territory indicated in Fig. 9.1. At the same time, the available data on the bottom topography of the international database IBCAO 1 can be used for detailed reconstruction of the connection between Arlis Spur and a fragment of the periphery of the Mendeleev Ridge and the Lomonosov Ridge, which is the task of this study.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0_9

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Fig. 9.1 General features of the bottom bathymetry of the eastern part of the Makarov Basin according to IBCAO data [6]. The position of the end points of the conjugate isobaths is shown: 1–2 on the northern slope of the Lomonosov ridge (2.5 km), 11–21 on the northern slope of the Arlis Spur (2.7 km), 3–4 on the southern slope of the Arlis Spur (2.1 km), 31–41 on the periphery of the Mendeleev ridge (2.6 km). The arrows connect the ends of the conjugate isobaths and show the direction of their closure. Modified

9.2 Peculiarities of Research Methodology In [4], a computer-based technique was proposed for the best matching of any contours using isobaths as an example. The matching was done by trial and error, by minimizing the angular discrepancy measured along Eulerian latitudes. The technique illustrated the principle that best fit can be performed for any contours that are determined or assumed to have once formed a single contour. By realizing the principle of best fit, it is possible to achieve reconnection and restoration of primary continuity of any contours, including isochrones, isobaths, isohypses, etc., and to restore the primary continuity of any contours. In the present work, the above methodology is applied for the first time to the case of isobath matching in the east of the Makarov Basin of the Arctic Ocean. Numerous tests of the alignment of different sections of different and homonymous isobaths have shown that the most suitable for the purposes of palaeo-geodynamic analysis were the sections of the isobath in the interval of 2.1–2.9 km, which correspond to the steepest part of the slope and, according to data on the character of the sedimentary strata [2, 5–10], have a low thickness of sediments. Note that the calculations of Euler poles and rotation angles were made using original programmes of the Laboratory of Geophysics and Tectonics of the World Ocean Floor of the Shirshov Institute of Oceanology of the Russian Academy of Sciences. The principles of the calculations are described in [3, 4].

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9.3 Research Results At the position of the Eulerian pole of finite rotation at the point with coordinates 84.51°N, 156.59° W, it is possible to obtain for more than 50 km (Sects. 9.1 and 9.2 in Figs. 9.1 and 9.2a) the alignment of the 2.5 km isobath in the lower part of the slope of the Lomonosov Ridge and the 2.7 km isobath of the Arlis Spur at the eastern periphery of the Makarov Basin. The rotation angle was 24.15° ± 3.2°. The point alignment error was 7.9 ± 3 km (9 values). With the position of the Eulerian pole of final rotation at 87.50° N, 146.12° W, it is possible to get a very good alignment of the 2.1 km isobath in the lower part of the Arlis Spur slope and the 2.6 km isobath of the unnamed spur of the Mendeleev Ridge north of 84° for more than 70 km (Sects. 9.3 and 9.4 in Figs. 9.1 and 9.2b). The rotation angle was 30.7° ± 1.9°. The point alignment error was 7.5 ± 4 km (9 values). The result of the reconstruction is the reconstruction of the axes of the rejection zones of the peripheral areas of the Lomonosov and Mendeleev Ranges (brown lines in Fig. 9.3) in the Arlis Spur region. Since the crust of the Lomonosov Ridge is continental, the rejected peripheral areas should also have continental crust. The above calculations also allow us to reconstruct the features of the primary bottom relief that existed prior to the detachment of the peripheral fragments from the Lomonosov Ridge. The data of palaeo-bathymetric profiles indicate that these peripheral fragments exceed the main body of the ridge by 0.4–0.6 km. Fig. 9.2 Junction of the opposite slopes: a Lomonosov ridge (2.5 km isobath—solid line) and Arlis Spur (2.7 km isobath—dotted line), b Arlis Spur (2.1 km isobath—solid line) and the peripheral part of the Mendeleev ridge spur (2.6 km isobath—dotted line). The position of points 1–4 is shown in Fig. 9.1

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Fig. 9.3 Reconstruction of the intersection of the counter slopes of the Lomonosov ridge, Arlis Spur and peripheral areas of the Mendeleev ridge. Points 1–4 are the same as in Fig. 9.1. Paleo-isobaths (marks in red) of Arlis Spur and the Mendeleev ridge fragment are brought to the modern bathymetry of the Lomonosov ridge. The reconstructed breakaway axes of these fragments are shown in brown colour. Section A–A1—position of the bottom palaeo-relief profile (Fig. 9.4)

Fig. 9.4 Profile along the line A–A1 (see Fig. 9.3) of the primary bottom relief before the breakup of the Arlis Spur and a fragment of the Mendeleev ridge from the Lomonosov ridge. The points of isobath junction are shown. Depths along the profile for Arlis Spur and for the fragment of the Mendeleev ridge are given to the values of modern depths of the Lomonosov ridge

An important circumstance of the reconstruction is the difference in depth of up to 0.6 km between the jointed isobaths. The latter circumstance most likely reflects the fact of different-scale sliding along the fault plane and thus different-scale burial during the detachment of the peripheral regions of continental crust from the main body of the Lomonosov Ridge (Fig. 9.5) in accordance with the modification [11] of B. Wernicke’s scheme [12].

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Fig. 9.5 Model of sliding along the Arlis Spur (II) and a fragment of the Mendeleev ridge (III) relative to the Lomonosov ridge (I) in accordance with the modification [11] of B. Wernicke’s scheme [12]. 1—faults, 2—rocks of landsliding blocks of continental crust, 3—direction of their displacements

9.4 Conclusion Thus, the computer methodology for the best isobath matching [4] was first applied to the case of isobath matching in the eastern region of the Makarov Basin of the Arctic Ocean. Numerous tests of the connectivity of different sections of different and homonymous isobaths have shown that the most suitable for the purposes of palaeogeodynamic analysis were the sections of isobaths in the interval of 2.1–2.9 km, which correspond to the steepest part of the slope with the lowest sediment thickness. In this connection, the sections of isobaths on the counter slopes of the bottom structures in the Makarov Basin, which are well connected with each other, were identified. The final Euler poles were calculated for these areas and a palaeo-reconstruction of the bottom relief was made. As a result of the reconstruction, it is possible to reconstruct the axes of the rejection zones of the peripheral areas of the Lomonosov Ridge. Since the crust of the Lomonosov Ridge is continental, the rejected peripheral areas should also have continental crust. The reconstructions made it possible to reconstruct fragments of the continental crust spreading areas in the near-pole region, as well as palaeo-bathymetry within their limits. This conclusion is consistent with the results of [13–15]. The most important result of this work is the independent confirmation of the connection between the Arlis Spur and a fragment of the periphery of the Mendeleev Ridge and the Lomonosov Ridge and the conclusion about their continental nature. The results of the work are important in the light of the discussion of the issues of substantiating the position of the outer boundary of the Russian continental shelf in the Arctic Ocean.

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References 1. Khain VE (2001) Tectonics of continents and oceans. Nauch. Mir, Moscow, 606 p 2. Evangelatos J, Mosher D (2016) Seismic stratigraphy, structure and morphology of Makarov basin and surrounding regions: tectonic implications. Mar Geol 374:1–13 3. Le Pichon L, Franchot J, Bonin J (1997) Plate tectonics. Mir, 288 p 4. Bullard E, Everett J, Smith A (1965) The fit of continents around Atlantic/symposium on continental drift. Philos Trans Roy Soc Lond Ser A Math Phys Sci Lond 258A:41–51 5. Cochran J, Edwards M, Coakley B (2006) Morphology and structure of the Lomonosov ridge, Arctic Ocean. Geochem Geophys Geosyst 7:Q05019 6. Langinen A, Lebedeva-Ivanova N, Gee D, Zamansky Y (2009) Correlations between the Lomonosov ridge, Marvin Spur and adjacent basins of the Arctic Ocean based on seismic data. Tectonophysics 472:309–322 7. Bruvoll V, Kristoffersen Y, Coakley B et al (2012) The nature of the acoustic basement on Mendeleev and northwestern Alpha ridges, Arctic Ocean. Tectonophysics 514–517:123–145 8. Poselov VA, Butsenko VVV, Kaminsky VD, Sakulina TS (2012) Mendeleev rise (Arctic Ocean) as a geological continuation of the continental margin of Eastern Siberia. Dokl Acad Sci 443(2):232–235 9. Poselov VA, Avetisov GP, Butsenko VV et al (2012) Lomonosov ridge as a natural continuation of the Eurasian continental margin into the Arctic basin. Geol Geophys 53(12):1662–1680 10. Bogoyavlensky IV, Borukaev GCC, Sidorenko SA, Polyakova ID (2017) Central Arctic region of the Arctic Ocean: seismic stratigraphy and prerequisites for oil and gas bearing. Arctic Ecol Econ 4(28):98–107. https://doi.org/10.25283/2223-4594-2017-4-98-107 11. Schreider AA (2011) Formation of the deep-water basin of the Black Sea. Nauch. Mir, Moscow, 216 p 12. Wernike B (1985) Uniform sense normal simple shear of the continental lithosphere. Can J Earth Sci 22:108–125 13. Lebedeva-Ivanova N, Zamansky Y, Langinen A, Sorokin Y (2006) Seismic profiling across the Mendeleev ridge at 82° N: evidence of continental crust. Geophys J Int 165:527–544 14. Artyushkov EVV, Poselov VA (2009) Continental crust in the deep-water troughs in the northeast Russian sector of the Arctic. Geol Earth’s Polar Reg Proc XLII Tectonic Meeting 1:24–27 15. Kazmin YB, Lobkovsky LI, Kononov MV (2014) Geodynamic model of the Amerasian Arctic basin development (to substantiate the affiliation of the Lomonosov ridge, Mendeleev Rise and Podvodnikov basin to the Russian continental margin. Arctic Ecol Econ 4(16):14–27

Chapter 10

Kinematic Model of Development of Eastern Areas of the Gakkel Mid-Ocean Ridge in the Eurasian Basin of the Arctic Ocean

10.1 Introduction An important direction in Arctic research is the study of the paleo-geodynamics of the Arctic Ocean [1]. The tectonic development of the Arctic Ocean has been and remains widely discussed in the literature [2–12]. Study of the Eurasian Basin is particularly important, because it hosts the MidArctic Ridge, the only modern active ridge in the Arctic Ocean. The eastern areas of the Eurasian Basin and its Laptev Sea closure include a number of basins and uplifts (Fig. 10.1). The Nansen Basin is located between the spreading axis of the Mid-Arctic Ridge and the Eurasian shelf. The Amundsen Basin (also known as the Fram Basin [13] and the Polar Abyssal Plain [14]) is located between the Lomonosov Ridge and the axis of the Mid-Arctic Ridge. The Laptev Sea (called the Nordenskjold Sea until 1935) is geographically located between the north coast of Siberia in the south, the Taimyr Peninsula, the Severnyaya Zemlya Islands in the west, and the New Siberian Islands in the east. The International Hydrographic Organization [15] defines the northern border of the Laptev Sea along the line connecting the northern tips of Komsomolets and Kotelny islands. At the same time, according to IBCAO [16], the northern border of the sea (between Komsomolets and Kotelny islands) passes through the intersection point of the northern tip of Kridny Island with the edge of the continental shelf (Cape Anysia) (79° N, 139° E). In either case, the western Laptev Sea includes part of the Amundsen and Nansen basins, as well as the Laptev Sea closure of the Mid-Arctic Range separating them. Geological–geophysical study of the Laptev Sea segment of the Mid-Arctic Ridge plays an important role in reconstructing the geodynamic development of the eastern Eurasian Basin. Therefore, studies by the international scientific community in the past 50 years have made it possible to obtain information on the morphology of the seafloor relief, sedimentary cover, and anomalous potential fields in the Laptev Sea and adjacent areas. However, it should be noted that the ice cover of the Arctic Ocean, including the Laptev Sea, hinders collection of data on the geological structure © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0_10

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Fig. 10.1 Bathymetry of floor of Laptev Sea part of Eurasian basin based on data of [27]. Isobath in hundreds of meters. I, Lomonosov ridge; II, Amundsen basin; III, Nansen basin; IV, Eurasian continental margin. Position of end points of conjugate isobaths is shown: (1–2), on Eurasian margin; (1' –2' ) on Lomonosov ridge. Straight lines, aligned points in areas of Eurasian margin (2 km isobath) and Lomonosov ridge (2.5 km isobath). N.P., North Pole. Modified

of the seafloor. There is uncertain whether the geological samples taken aboard research vessels are not products of ice rafting. The ice conditions severely limit the possibilities to obtain data from deep-water drilling. Under these conditions, comprehensive analysis of the available geological–geophysical data make it possible to answer a number of important questions about the developmental stages of the eastern segment of the Mid-Arctic Ridge, which is the focus of this work.

10.2 Geological Research A comprehensive geological–geophysical study of the areas of the Gakkel Ridge yielded important information about its crustal structure and paleo-geodynamics. The free-air anomalous gravity field [17] is characterized by the presence of positive anomalies with an absolute value of up to 50–150 mgL, related to elevations on the seafloor. Negative anomalies with an absolute value of up to –80 mgL are associated with bottom basins well known in the literature. An anomalous Bouguer gravity field was calculated based on the IBACO seafloor topography database and free-air gravity values for an intermediate layer density of 2.85 g/cm3 [17]. Its distribution is characterized by the presence of positive anomalies with an absolute value up to 240 mgL, associated with bottom basins. Negative

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anomalies with an absolute value of up to – 70 mgL are associated with islands and continental shelves. Conversion of seismic wave velocities into density characteristics reveals [18] that sedimentary rocks with longitudinal seismic wave velocities of 1.9–2.2 km/s have densities of 1.92–2 g/cm3 . Rocks with velocities of 3.1–3.2 km/s are characterized by densities of 2.25 g/cm3 . Rocks with velocities of 4.3–5.2 km/s are characterized by densities of 2.62 g/cm3 . Rocks with velocities of 5.43–5.84 km/s are characterized by densities of 2.65 g/cm3 . Rocks with velocities of 6.24–6.58 km/s are characterized by densities of 2.73–2.75 g/cm3 . The densities of upper mantle material were taken as 3.3 g/cm3 in calculations. Taking into account the indicated density characteristics of the lithosphere in the comprehensive interpretation of the Bouguer gravity field [17–20], it was possible to construct a series of crustal profiles. According to these [21, 22], in the central part of the Amundsen basin, at depths of 4.1–4.2 km, for lithosphere with an age of 43–50 Ma, the heat f lux values are 73–127 MW/m2 , averaging 102 ± 12 MW/m2 based on eight values. These measurement data indicate an increased heat f lux in comparison to its mean oceanic values, which are close to 50 MW/m2 . The latter may reflect the remoteness of the studied areas of the Amundsen Basin, which are 100–200 km from the modern active spreading axis of the Mid-Arctic ridge. The tectonic activity of the floor of the Laptev Sea closure of the Mid-Arctic Ridge manifests itself as seismicity in the ridge’s axial zone, where shallow focal earthquakes have been observed with magnitudes of 4–5 and source depths not exceeding 35 km (data [23, 24]). Based on seismic data, the structure of the Mid-Arctic Ridge is traced to the east between 128° and 131° E and 77.5° N, where it is sharply broken by the Khatanga Fault [25]. Beneath the Mid-Arctic Ridge, gravity calculations give a crustal thickness approximately 1.5 smaller than that observed under other mid-ocean ridges. Evidence of recent volcanic activity within its margins have also been obtained [26].

10.3 Structure of the Crust The successive bedding of sediments along seismo-acoustic profiles does not yet have a consistent nomenclature. However, the available materials have allowed us to compile a new map of the total thickness of bedding (Fig. 10.1) based on integration of all available cartographic (including specialized) results of studies of the sedimentary cover in the Eurasian Basin [5, 18, 22, 28–39]. According to this new map, the sediment thickness near the foot of the Gakkel Ridge is around 1 km or less, while in the Amundsen Basin in the direction of the Lomonosov Ridge, it does not exceed 2 km. The isopachous strike mainly inherits the geomorphological configuration of the basin. It is important to note that in the Nansen Basin in the direction of the shelf, the sediment thickness also increases to 3 km or more. The bottom of the sediment layer in the Laptev Sea region of the Eurasian Basin is characterized by an irregular topography with individual forms having relative

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amplitudes of many hundreds of meters. Seismic studies using reflected waves and wide-angle seismic profiling indicate that the acoustic basement underlying the sediments is characterized by the presence of numerous faults, along which some of its blocks have moved relative to others (e.g., [18, 35]). The basement is broken to a high degree [32] and has a complex internal structure [22] with reflectors mainly in the depth range of 4–9 s of two-way travel time. The longitudinal seismic wave velocities in the surface parts of the basement are close to 5.2 km/s. In areas where continental crust has developed, the reflectors pertain to a granite layer with seismic velocities close to 6.2 km/s. In areas where ocean-type crust has developed, the velocities at comparable depths in the crust are close to 7 km/s and correspond to a basalt layer. The available materials have allowed us to create a new map diagram of the total thickness of the crust (Fig. 10.2) based on the integration of all available cartographic (including specialized) research results of continental and oceanic crustal layers in the Eurasian Basin [18, 22, 30, 31, 33, 35, 40–50]. Analysis of this new map shows that oceanic crust with a thickness of 5–10 km underlies morpho-structures of the MidArctic Ridge in an area with a lithospheric age of no more than 30 Ma. Meanwhile, crust with a thickness of about 20 km pertains to the transition zone from oceanic to continental crust and is replaced by continental crust with a thickness of 25 km or more. Aeromagnetic observations [51–63] have yielded information on anomalies in the Laptev Sea region of the Eurasian Basin. According to this information, the MidArctic Ridge, including the spreading axis zone, is characterized by small-amplitude linear magnetic anomalies (less than 500 nT) with a wavelength of up to 30 km. The axial magnetic anomaly reaches 2000 nT only in the west of the ridge and becomes substantially smaller in amplitude in almost all other areas [64]. Comparison of the observed and theoretical magnetic anomalies in the seaf loor spreading model [12, 62, 63]. made it possible to identify paleo-magnetic anomalies C1–C25 (Fig. 10.3).

Fig. 10.2 Compilation diagrams of crustal thickness (a) and sediment layer (b) according to data of [18, 22, 30, 31, 33, 35, 40, 50]. Isopachous lines in km. N.P., North Pole. Modified

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All authors claim that the horizontal displacements of paleo-magnetic anomalies and bottom structures do not exceed 10–30 km with respect to each other. Figures in different studies showing the transform faults do not coincide in position and strike. The directions of the faults are 70° [51], 45° [25], 30° [65], or even 120° [66]. Figure 10.4 shows the most modern version of the seafloor chronology of the Laptev Sea segment of the Eurasian Basin encompassing the Mid-Arctic Ridge and adjacent Amundsen and Nansen basins.

Fig. 10.3 a Plots of anomalous magnetic field along aeromagnetic survey profiles at foot of Lomonosov ridge after [67]. Thick lines, chrons C18–C25 reconstructed in this study. b Theoretical paleo-anomalies in model of inverted magneto-active layer and example of identification of paleo-anomalies along profile A–B using geochronological scale [68]. Modified

Fig. 10.4 Linear magnetic anomalies C1(speckles)–C25 (segments of curves) in eastern part of Eurasian basin according to data of [12, 51–55, 61–63, 76] and Fig. 10.3. Isobaths in hundreds of meters after [27]. Modified

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Its most important difference from earlier diagrams is the present study’s detection of paleo-anomaly C25 in the eastern Amundsen Basin, based on materials from [67], which established a correlation between observed and theoretical magnetic anomalies in the seaf loor spreading model in the direction of the spreading axis. The most modern version of the scale of paleo-magnetic anomalies [68], in development of [69], was used to calculate theoretical magnetic anomalies and identify paleomagnetic ones according to the modeling results [12]. Comparison of the spatial position of anomaly C25 with the position of the continental–oceanic crust boundary from [70] (taking into account research data [25, 65, 66]) shows that the boundary is located on the periphery of chron C25r (57.656– 58.959 Ma). Since the boundary marks the transition from continental crust to crust generated by spreading, the onset of the formation of oceanic crust in the Laptev Sea segment can be dated to about 59 Ma ago. The boundary itself is spatially close to the position of the 2.0–2.5 km isobath from the circumpolar region to 79° N. Seafloor spreading occurs orthogonally to the strike of the axial zone of the ridge. Kinematic calculations show that in the paleo-anomaly interval C25–C13, seaf loor spreading occurred at rates of about 0.9–1.2 cm/year. At the same time, the buildup of new oceanic crust in the Amundsen Basin proceeded more intensively than in the Nansen; in the paleo-anomaly interval younger than C13, the rates did not exceed 0.6 cm/yr with an overall decrease in seafloor spreading rates to the east. This tremendously complicates reliable interpretation of specific paleo-magnetic anomalies and makes it necessary to identify trains of anomalies (e.g., C4–C5, C17–C19, etc.).

10.4 Calculation of the Splitting Parameters This study is the first to use the Bullard method [71] to align slopes in the region of the Laptev Sea closure of the Mid-Arctic Ridge in the Eurasian Basin of the Arctic Ocean. Numerous tests for the adjacency of different areas of the same and different isobaths showed that the most suitable for the aims of paleo-geodynamic analysis were areas within the 0.9–1.2 km isobaths. The slope in this depth interval is the steepest (the mean angle of the surface of the slope exceeds 5°) and, based on the information of [72] on the character of subsidence of the sediment sequence, it has the smallest sediment thickness (or even none at all). The Euler poles and angles of rotation were calculated with proprietary software of the Laboratory of Geophysics and Tectonics of the Floor of the World Ocean, Shirshov Institute of Oceanology, Russian Academy of Sciences (IO RAS), incorporated into Global Mapper software [73, 74]; the calculation principles are explained in [3, 74, 75]. In the analyzed area, the depth of the seaf loor reaches 3 km (the area between conjugate points 1, 2 and 11, 21 in Fig. 10.1). Whereas the formation of the sedimentary basin, in accordance with the Wernicke scheme [77], is related to sliding of blocks of continental crust of the Lomonosov Ridge at the periphery of the Eurasian continental slope, the numerous tests for the adjacency of different areas of the same

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and different isobaths showed that areas within the 1.8–2.7 km isobaths are the most suitable for paleo-geodynamic analysis. According to the estimates for the position of the Euler pole of finite rotation at the point with coordinates 69.18° N, 138.53° E, it is possible north of 80° for an extent of more than 600 km to obtain quite good alignment of the 2.0 km isobath in the lower part of the Eurasian slope (the area between points 1 and 2 in Fig. 10.1) and the 2.5 km isobath on the Lomonosov Ridge (the area between points 1' and 2' ) (Fig. 10.5). The angle of rotation was 16.9° ± 0.3°. Here, the standard deviation at the calculated alignment points was ± 21 km (nine alignment points). The pole is spatially confined to the domain of existence of the previously known Cenozoic finite poles of opening of the Eurasian Basin, which were compiled in [70]. Paleogeodynamic calculations of the Euler pole and angle of rotation made it possible for the first time to estimate the paleo-geodynamic parameters of opening of the Laptev Sea segment of the Eurasian Basin. Thus, as a result of the calculations, a refined kinematic model of development of the eastern regions of the Eurasian Basin of the Arctic Ocean has been created, and the axis of the zone of splitting of peripheral continental fragments of the Lomonosov Ridge (thick line in Fig. 10.6a) from the Siberian continental shelf was reconstructed. An important circumstance of the reconstruction is identification of the difference in depth of adjacent isobaths down to 500 m. Based on this reconstruction and by introducing corrections to the sliding of the above-mentioned fragments, it is possible to reconstruct the primary paleo-bathymetry of the seaf loor before these sliding fragments separated (Fig. 10.6a, b). It is clear from these figures that, for the case of the studied water area, the initially adjacent areas of the Lomonosov Ridge and the surface of the Eurasian shelf were close in height. Fig. 10.5 Alignment of conjugate isobaths of Eurasian continental margin (2 km isobath, solid line) and Lomonosov ridge (2.5 km isobath, dotted line). Numbers of points (1) and (2) same as in Fig. 10.1. Modified

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Fig. 10.6 a Paleo-geodynamic and paleo-bathymetric reconstruction (see text) of eastern areas of Eurasian Basin of Arctic Ocean. Position of splitting axis is shown (thick curve). b Seafloor bathymetry profile along line A–B before splitting of fragment of Lomonosov ridge from Eurasian continental margin and paleo-isobath alignment point. Numbers of points (1) and (2) same as in Fig. 10.1. Modified

10.5 Conclusions Thus, as a result of our research, we have reconstructed the main paleo-geodynamic events and created a refined kinematic model of development of the eastern areas of the Eurasian Basin of the Arctic Ocean and its Laptev Sea closure. Before the onset of extension, the Eurasian shelf and the Lomonosov Ridge were part of the continental Eurasian Arctic margin. Over time, extension on the shelf became rifting, which transformed into spreading during chrons C25r–C26n (57.656–59.237 Ma ago). The spreading axis prograded eastward into the shelf zone and sheared the Lomonosov Ridge in a “scissors” fashion. Its eastern part did not lose its structural-tectonic similarity to the Eurasian shelf. Based on a comprehensive geological–geophysical analysis of the anomalous magnetic field, continental rifting around 59 Ma ago ultimately separated the Lomonosov Ridge from the Eurasian continental margin. Our calculations allowed us to reconstruct the configuration of the splitting zone axis of the Lomonosov Ridge. The Euler poles and angles of rotation describing the splitting kinematics were determined. The splitting marked the opening of the Laptev Sea segment of the Eurasian Basin, accompanied by the formation of linear magnetic anomalies on the spreading axis of the Mid-Arctic Ridge, beginning from chron C25o. Over time, the spreading axis prograded eastward, expanding the space of the oceanic crust toward the Siberian shelf. The spreading rates in the paleo-anomaly interval C25–C18 were about 1.2 cm/year, and from chron C13, they decreased to 0.6 cm/year. In conjunction with these events, a complex rift system formed on the Laptev Sea shelf, which most likely was related to the Mid-Arctic Ridge, although the latter was separated from it by the Khatanga Fault [12, 25, 65]. The development of these shelf structures continues today, as evidenced by their contemporary seismic activity. The

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southern margin of the spreading axes in the Laptev Sea is 77.5° N. A very important task for subsequent research is to substantiate and reliably search for a continental rift structure genetically related to the continental continuation of the Mid-Arctic Ridge.

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21. Okay N, Crane K (1993) Thermal rejuvenation of the Ermak Plateau. Mar Geophys Res 15:243– 263 22. Urlaub M, Schmidt-Aursch M, Jokat W, Kaul N (2009) Gravity crustal models and heat flow measurements for the Eurasia basin, Arctic Ocean. Mar Geophys Res 30:277–292 23. Avetisov GP (2009) Arctic seismological studies of the All-Russia Scientific Research Institute for Geology and Mineral Resources of the ocean: history, achievements, and prospects. Probl Arkt Antarkt 2:27–41 24. USGS Earthquake Hazards Program (2017). https://earthquake.usgs.gov/ 25. Sekretov S (2002) Structure and tectonic evolution of the south Eurasia basin, Arctic Ocean. Tectonophysics 351:193–243 26. Edwards M, Kurras G, Tolstoy M et al (2001) Evidence of recent volcanic activity on the ultraslow spreading Gakkel ridge. Nature 409:808–811 27. International Bathymetric Chart of the Arctic Ocean (IBCAO) (2017). http://www.topex.ucsd. edu/html/mar_topo.html 28. Verba VV, Kim BI, Kharitonova LY (2001) New data on the structure and thickness of sedimentary cover in the Eurasian basin. Dokl Earth Sci 381:906–910 29. Kim BI, Glezer ZI (2007) Sedimentary cover of the Lomonosov ridge: stratigraphy, structure, deposition history, and ages of seismic facies units. Stratigr Geol Correl 15:401–420 30. Poselov VA, Avetisov GP, Butsenko VV et al (2012) The Lomonosov ridge as a natural extension of the Eurasian continental margin into the Arctic basin. Russ Geol Geophys 53:1276–1290 31. Poselov VA, Zholondz SM, Trukhalev AI et al (2012) Power map of sedimentary cover of the Arctic Ocean. Tr. Vseross. Nauchno-Issled. Inst. Geol. Miner. Resur. Mirovogo Okeana im. I.S. Granberga, vol 223, no 8. Gramberg All-Russia Scientific Research Institute for Geology and Mineral Resources of the Ocean, St. Petersburg, pp 8–14 32. Chernykh AA, Krylov AA (2010) The history of sedimentogenesis in the Amundsen basin in terms of geophysical data and drilling materials ACEX (IODP-302). In: Geological and geophysical characteristics of lithosphere of the Arctic region, Tr. Vseross. Nauchno-Issled. Inst. Geol. Miner. Resur. Mirovogo Okeana im. I.S. Granberga, no 7. Gramberg All-Russia Scientific Research Institute for Geology and Mineral Resources of the Ocean, St. Petersburg, pp 56–66 33. Alvey A, Gaina C, Kuszner N, Torsvik T (2008) Integrated crustal thickness mapping and plate reconstructions for the high Arctic. Earth Planet Sci Lett 274:310–321 34. Engen O, Gjengedal J, Faleide J et al (2009) Seismic stratigraphy and sediment thickness of the Nansen basin, Arctic Ocean. Geophys J Int 176:805–821 35. Grantz A, Hart P, Childers V (2011) Geology and tectonic development of the Amerasia and Canada basins, Arctic Ocean. In: Spencer AM et al (eds) Arctic petroleum geology, geological society memoirs no. 36. Geological Society, London, pp 771–799 36. Kristoffersen Y, Mikkelsen N (2006) On sediment deposition and nature of the plate boundary at the junction between the submarine Lomonosov ridge, Arctic Ocean and the continental margin of Arctic Canada/North Greenland. Mar Geol 225:265–278 37. Langinen A, Lebedeva-Ivanova N, Gee D, Zamansky Y (2009) Correlations between the Lomonosov Ridge, Marvin Spur and adjacent basins of the Arctic Ocean based on seismic data. Tectonophysics 472:309–322 38. Oakey G, Stephenson R (2008) Crustal structure of the Innuitian region of Arctic Canada and Greenland from gravity modeling: implications for the Palaeogene Eurekan orogeny. Geophys J Int 173:1039–1063 39. Ritzmann O, Jokat W, Czuba W et al (2004) A deep seismic transect from Hovgard ridge to northwestern Svalbard across the continental–ocean transition: a sheared margin study. Geophys J Int 157:683–702 40. Kashubin SN, Petrov OV, Androsov EA et al (2011) Power map of the circumpolar Arctic crust. Reg Geol Metallog 46:5–13 41. Shreider AA (2014) Model of the separation of the Marvin Spur from the Lomonosov ridge in the Arctic Ocean. Oceanology 54:490–496 (Engl. Transl.)

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42. Schreider AA, Lobkovsky LI, Schreider AA (2013) Kinematic model of the opening of the Canadian basin, Arctic Ocean. Oceanology 53:481–490 (Engl. Transl.) 43. Dore A, Lundin E, Kusznir N, Pascal C (2008) Potential mechanisms for the genesis of Cenozoic domal structures on the NE Atlantic margins. Spec. Publ.–Geol. Soc., London 306, 1–26 44. Dossing A, Hansena T, Olesen A (2014) Gravity inversion predicts the nature of the Amundsen basin and its continental borderlands near Greenland. Earth Planet Sci Lett 408:132–145 45. Gaina C, Medvedev S, Torsvik T et al (2014) 4D Arctic: a glimpse into the structure and evolution of the Arctic in the light of new geophysical maps, plate tectonics and tomographic models. Surv Geophys 35:1095–1122 46. Grantz A, Clark D, Phillips R, Srivastava S (1998) Phanerozoic stratigraphy of Northwind ridge, magnetic anomalies in the Canada basin, and the geometry and timing of rifting in the Amerasia basin, Arctic Ocean. Geol Soc Am Bull 110(6):801–820 47. Grantz A, May S, Taylor P, Lawver L (1990) Canada basin. In: Geology of North America, vol. L: the Arctic Ocean region. Geological Society of America, Boulder, pp 379–402 48. Hall J (1990) Chukchi borderland. In: Geology of North America, vol. L: the Arctic Ocean region. Geological Society of America, Boulder, pp 337–349 49. Harbert W, Frei L, Engebretson D (1990) Paleo-magnetic and plate—tectonic constraints on the evolution of the Alaskian-eastern Siberian Arctic. In: Geology of North America, vol. L: the Arctic Ocean region. Geological Society of America, Boulder, pp 567–592 50. Kashubin S, Petrov O, Androsov E et al (2014) Crustal thickness in the Circum Arctic. In: ICAM VI: proceedings of the international conference on Arctic margins, May 2011. Fairbanks, pp 1–17 51. Karasik AM (1981) Geohistorical analysis of abnormal magnetic field in conditions of slow expansion of the ocean bottom by example of Eurasian basin of the Arctic Ocean. In Magnetic abnormalities of the oceans and new global tectonics. Nauka, Moscow, pp 162–174 52. Brozena J, Childers V, Lawver L et al (2003) New aero-geophysical study of the Eurasian Basin and Lomonosov ridge implications for basin development. Geology 31:825–828 53. Coles R, Taylor P (1990) Magnetic anomalies. In: Geology of North America, vol L: the Arctic Ocean region. Geological Society of America, Boulder, pp 119–132 54. The KY, Ridge N (1982) Arctic Ocean: some geophysical observations of the rift valley at slow spreading rate. Tectonophysics 89:161–172 55. Kristoferson Y (1990) Eurasia basin. In: Geology of North America, vol. L: the Arctic Ocean region. Geological Society of America, Boulder, pp 365–378 56. Lawver L, Scotese C (1990) A review of tectonic models for the evolution of the Canada basin. In: Geology of North America, vol. L: the Arctic Ocean region. Geological Society of America, Boulder, pp 593– 618 57. Lebedeva-Ivanova N (2010) Ph.D. dissertation in geophysics. Uppsala University, Uppsala 58. Miller EL, Verzhbitsky VE (2009) Structural studies near Pevek, Russia: implications for formation of the East Siberian shelf and Makarov basin of the Arctic Ocean. Stephan Mueller Spec Publ Ser 4:223–241 59. Petrov O, Morozov A, Shokalsky S et al (2016) Crustal structure and tectonic model of the Arctic region. Earth Sci Rev 154:29–71 60. Sweeney JF, Weber JR, Blasco SM (1982) Continental ridges in the Arctic Ocean: lorex constraints. Tectonophysics 89:217–238 61. Taylor P, Kovacs L, Vogt P, Johnson G (1981) Detailed aeromagnetic investigation of the Arctic basin: 2. J Geophys Res Solid Earth 86:6323–6333 62. Vogt P, Taylor P, Kovacs L, Johnson G (1979) Detailed aeromagnetic investigation of the Arctic basin. J Geophys Res Solid Earth 84(3):1071–1089 63. Vogt P, Taylor P, Kovacs L, Johnson G (1982) The Canada basin—aeromagnetic constraints in structure and evolution. Tectonophysics 89:295–336 64. Feden R, Vogt P, Fleming H (1979) Magnetic and bathymetric evidence for the “Yermak hot spot” north-west of Svalbard in the Arctic basin. Earth Planet Sci Lett 44:18–38 65. Drachev S, Kaul N, Biliaev V (2003) Eurasia spreading basin to Laptev shelf transition: structural pattern and heat f low. Geophys J Int 152:688–698

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66. Andieva ES (2008) Tectonic position and general structure of the Laptev Sea. Neftegaz Geol Teor Prakt 3:1–28 67. Russian Arctic Geotraverses, Tr. Vseross. Nauchno-Issled. Inst. Geol. Miner. Resur. Mirovogo Okeana im. I.S. Granberga, vol 220. Gramberg All-Russia Scientific Research Institute for Geology and Mineral Resources of the Ocean, St. Petersburg (2011) (in Russian) 68. Gradstein F, Ogg J, Schmitz M, Ogg G (2012) The geologic time scale 2012. Elsevier, Amsterdam 69. Schreider AA (1992) Magnetism of the ocean crust and linear paleo-magnetic anomalies. Fiz Zemli 6:59–70 70. Glebovsky VY, Kaminsky VD, Minakov AN, Merkur’ev SA, Childers VA, Brozena JM (2006) Formation of the Eurasia Basin in the Arctic Ocean as inferred from geohistorical analysis of the anomalous magnetic field. Geotectonics 40:263–281 71. Bullard E, Everett J, Smith A (1965) The fit of continents around Atlantic. Philos Trans R Soc A 258:41–51 72. Zhmur VV, Sapov DA, Nechaev ID et al (2002) Intensive gravitational flows in near-bottom ocean layer. Izv Ross Akad Nauk Ser Fiz 66:1721–1726 73. Shreider AA (2005) Opening of the deep-sea basin of the black sea. Okeanologiya 45:592–604 74. Shreider AA (2011) Development of the deepwater basin of the black sea. Nauchnyi Mir, Moscow (in Russian) 75. Zonenshain DD, Lomize MG, Ryabukhin AG (1990) Practical manual on geotectonics. Moscow State Univ, Moscow (in Russian) 76. Weber JR, Sweeney JR (1985) Reinterpretation of morphology and crustal structure in the central Arctic Ocean basin. J Geophys Res Solid Earth 90(131):663–677 77. Wernicke B (1981) Low-angle normal faults in the basin and range province: nappe tectonics in an extending orogen. Nature 291:645–648

Chapter 11

Seafloor Kinematics of the Near-Greenland Region of the Eurasian Basin

11.1 Introduction One of the most important directions in studying the Arctic is clarifying problems on the paleo-geodynamics of the Arctic Ocean [18]. Questions of the origin and tectonic development of the Arctic Ocean are debated in the literature to this day [2, 4, 9, 10, 12, 13, 16, 19, 26, 37, 40, 51, 52, 61–63, 67, 70]. A particular role is played by studies of the Eurasian Basin, which hosts the Arctic Ocean’s sole active Mid-Arctic Ridge, the main link of which is known in the literature as the Gakkel [7], Nansen [67], and Nansen–Gakkel [48] mid-ocean ridge. For brevity and convenience, in the present study, we will refer to it as the Gakkel mid-ocean ridge or the Mid-Arctic Ridge. The Eurasian Basin also includes a number of smaller basins and uplifts. The Nansen Basin is located between the spreading axis of the Mid-Arctic Ridge and the Eurasian shelf. The Sophia Basin is located between the Yermak Plateau and Spitsbergen. The Amundsen Basin (also known as the Fram Basin [48] and the Polar Abyssal Plain [39]) lies between the Lomonosov Ridge and the axis of the Mid-Arctic Ridge; this basin also hosts the Earth’s North Pole. The Lincoln Sea Basin lies between the Morris Jesup (also spelled Morris Jessup [48]) Rise and the Lomonosov Ridge. The Mid-Arctic Ridge separates the Morris Jesup Rise and the Yermak Plateau (Fig. 11.1). Geological and geophysical study of the near-Greenland region of the Eurasian Basin, including the areas of the Amundsen Basin, the Morris Jesup Rise, the Lincoln Sea Basin, and contiguous areas of the Lomonosov Ridge, plays an important role in reconstructing the initial stage of the Eurasian Basin’s formation. Studies by the international scientific community in the last 50 years has made it possible to obtain information on the morphology of the seafloor relief, the sedimentary cover, the crustal structure, and anomalous potential fields of the Lincoln Sea Basin and its contiguous areas. In addition, it should be noted that the ice cover of the Arctic Ocean, including the area near Greenland, hinders the collection of data on the geological © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0_11

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Fig. 11.1 Bathymetry of near-Greenland part of Eurasian Basin after data of [21]. Isobaths in hundreds of meters. The positions of endpoints of conjugate isobaths 1–2 of Morris Jesup Rise and 1' –2' of Yermak Plateau are shown; segments indicate lines of their alignment. Modified

structure of its seafloor. There is still doubt that the geological samples recovered by research vessels may be the products of ice drift. The ice conditions extremely limit the possibilities of obtaining deep-water drilling data. Therefore, comprehensive analysis of the available geological and geophysical data may answer a number of questions on the stages of its geological development, which is the aim of the present study. Note that this paper uses the most updated version of the geochronological scale [36] developed in [15].

11.2 Seafloor Morphology and Deep Water Drilling Data The near-Greenland area of the Amundsen Basin in the Eurasian Basin of the Arctic Ocean has no clearcut, geographically substantiated boundaries. This study considers it to be within the sector of 79°–90° N, 0°– 35° E. It was mentioned above that it hosts the Lincoln Sea (its basin), which is a marginal sea of the Arctic Ocean near the coasts of the islands of Ellesmere and Greenland. It occupies the northernmost position of all the Arctic seas and lies fully north of 80° N. It is bounded in the north by the conditional line between Cape Columbia (Ellesmere Island) and Cape Morris Jesup (Greenland); in the west and southwest, by the coast of Ellesmere Island; in the south, by the line between Cape Sheridan (Ellesmere Island) and Cape Bryant (Greenland); and in the southeast and south, by the Greenland coast. The seafloor

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depths (data of [21]) in the near-Greenland region of the Amundsen Basin exceed 3.5 km, whereas in the eastern Lincoln Sea, they do not surpass 2.5 km and gradually decrease to the west to 1 km or less. The mean width of the central part of the Lincoln Sea Basin is close to 150 km. The Morris Jesup Rise has mean surface depths of 1–2 km and a width of up to 100 km. In the polar region of the Lomonosov Ridge, the 2004 ACEX expedition drilled five boreholes (M0002A, M0003A, M0004A, M0004B, and M0004C), which exposed an Upper Cretaceous–Holocene section of the sedimentary sequence. Based on a study of cores from boreholes M0002A (87°52.2’ N, 139°19.1’ E) and M0004A (87°52’ N, 139°10’ E) (Fig. 11.2a), a combined section was compiled with a thickness of 428 m and four lithostratigraphic complexes were identified, U1–U4 [20, 55]. Palynological data provide evidence for a Campanian age (~80 Ma ago) for the oldest U4 deposits recovered by drilling [20]. The sediment material in the boreholes is represented by [8, 14, 20] brown, olive-colored, gray, and black silts, silty clays, and clayey silts with colorful interlayers and lenses of sand. The available microfossil data point to a subtropical climate that existed at the end of the Paleocene—beginning of the Eocene in the polar area of the present-day Lomonosov Ridge with an average annual surface-water temperature of ~ 20°C in the basin. For the first time, the drilling results [8, 14, 20] have yielded data on large-scale erosion in the polar area of the Lomonosov Ridge, which spanned the Maastrichtian– Early Paleocene, preceding Cenozoic sediment accumulation. In the combined sequence of the sedimentary cover on the Lomonosov Ridge, a hiatus was established at a depth of ~ 200 m within the subcomplex U1/6 (Middle Miocene–Middle Eocene), indicating missing deposits from this age interval in the stratigraphic sequence.

11.3 Anomalous Gravity Field The anomalous free-air gravity field [24, 25, 53, 54] is characterized by the presence of positive anomalies with an absolute value of up to 50–150 mgl, related to rises in the seafloor water area. Negative anomalies with an absolute value of up to – 80 mgl are related to seafloor basins, well known in the literature. The anomalous Bouguer gravity field was calculated from the IBACO seafloor relief database [21] and free-air gravity values with an intermediate layer density of 2.85 g/cm3 [54]. Its distribution is characterized by the presence of positive anomalies with an absolute value of up to 240 mgl, related to seafloor basins. Negative anomalies with an absolute value up to – 70 mgl are related to islands and continental shelves. Here, the Morris Jesup Rise and the Yermak Plateau are characterized mainly by a weakly anomalous field with absolute values of gravity close to zero (sometimes with local extrema of up to 50 mgl). According to [56, 65], in the central part of the Amundsen Basin, at depths of 4.1–4.2 km, for lithosphere with an age of 43–50 Ma, the heat flux values range from 73 to 127 mW/m2 , averaging 102 ± 12 mW/m2 based on eight values. The obtained

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Fig. 11.2 Positions of deep-water drilling points a after data of [20, 55]; compilation scheme of sediment thickness, b after data of [8, 11, 14, 19, 29, 38, 41, 49, 50, 57, 59, 61, 65] and thickness of Earth’s crust, c after data of [3, 19, 41, 45, 57, 59, 65]. Isopachous lines in km. Modified

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measurement data point to an increased heat f lux compared to its mean oceanic values, which are close to 50 mW/m2 . The latter may reflect the closeness of the studied areas of the Amundsen Basin, which are separated by 100–200 km from the present-day active spreading axis of the Mid-Arctic Ridge in the Eurasian Basin of the Arctic Ocean. The tectonic activity of the seafloor in the near-Greenland region of the Amundsen Basin is also manifested as part of its seismic activity. Shallow-focus earthquakes with magnitudes of 4–5 s and source depths not exceeding 25 km are known in the Lincoln Sea (data of [1, 71].

11.4 Structure of the Unconsolidated Crust In recent years, a certain number of studies have been conducted in the studied area employing point seismic sounding and continuous seismic profiling to investigate the sedimentary sequence and underlying layers of consolidated crust. The total length of the seismic profiles exceeds 6000 km. The present work is based on CDP materials along the drift lines of “North Pole” stations: NP-21 (1973), NP-24 (1978–1980), as well as on CDP profiles obtained by the R/V Polarstern in 1991 and 1998 and CDP profile 20,010,300 obtained by the Polarstern in 2001 [42–44]. These data have been synthesized in many aspects in [8, 14, 50]. Seismic stratigraphic study of the upper part of the crust on the Lomonosov Ridge has revealed sediments of several seismic complexes, the numbering and abbreviations of which differ based on the specifics of the studies. Different styles of sediment identification for the same areas have also been noted. Thus, in [8, 43], along CDP profile 91,090, the sediment layers nearest the surface (LR, Lomonosov Ridge) include [43] seismic complexes LR6 (0.08–0.1 km thick), LR5 (0.12–0.15 km thick), and LR4 (0.12 km thick). In [8], they are combined into the single seismic complex LR7 with P-wave velocities of 1.8–2.0 km/s. The L3 layer beneath them (0.11–0.15 km thick), with P-wave velocities of 2.2 km/s [43], is denoted as seismic complex LR6 in [8]. Below this lie seismic complexes LR5–LR4 [8], which combine sediment erosion material. Beneath these [43] are layers LR2 (0.55–0.83 km thick) and LR1 (0.84–1.65 km thick), with P-wave velocities of 4.0– 4.6 km/s and 4.7 –5.2 km/s, respectively. They are combined into seismic complex LR3–LR1 [8]. From this it is clear that the stratigraphic representation of sediments along the profile has no uniform nomenclature. In addition, the available material has made it possible to present a new map of the total thickness of the sedimentary layer (Fig. 11.2b) that integrates all available mapping (including profile) results of studying the sedimentary cover of the Eurasian Basin [8, 11, 14, 19, 29, 38, 41, 49, 50, 57, 59, 60, 65]. According to this new map, the sediment thickness near the foot of the Gakkel Ridge is around 1 km or less. In the polar area of the Amundsen Basin, it increases up to 3 km, whereas closer to the Lomonosov Ridge, it does not exceed 2 km. The trend of isopachous lines mainly follows the configuration of the basin. It is important to

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note that in the area of the Lincoln Sea, the sediment thickness increases and south of 85° N it reaches 9–12 km.

11.5 Structure of the Acoustic Basement The sole of the sedimentary layer in the near-Greenland part of the Eurasian Basin is characterized by an irregular relief with a relative amplitude of individual forms of many hundreds of meters. Seismic studies using reflected waves and wide-angle seismic profiling indicate that the acoustic basement underlying the sediments is characterized by the presence of multiple faults, along which some of its blocks moved relative to others (e.g., [38, 41]). The basement is highly compartmentalized [14] with a complex internal structure [65] and reflectors, mainly in the depth interval of 4–9 s (two-way travel time). The available material make it possible to present a new map of the total thickness of the crust (Fig. 11.2c) that integrates all available mapping (including profile) results of studying the continental and oceanic crustal layers of the Eurasian Basin [3, 19, 38, 41, 45, 59, 65]. Analysis of this new map makes it possible to characterize the composition and geometry of crustal layers. In areas where continental crust has developed, the reflectors pertaining to the granite layer have seismic velocities close to 6.2 km/s. In areas where oceanic crust has developed, the velocities at comparable depths in the crust are close to 7 km/s and correspond to the basalt layer. It was possible to obtain a complete section of the crust at 5 seismic sounding points SB (30, 31, 39, 48, 50) [29, 54]. At these points, mantle rocks have P-wave velocities of 8.2 km/s. In spreading areas of oceanic crust, the sole of the crust lies at depths close to 10 km, while in spreading areas of continental crust, the sole lies deeper than 30 km.

11.6 Anomalous Magnetic Field Aeromagnetic observations [26, 63, 67] have made it possible to obtain fundamental information on the distribution of magnetic anomalies in the near-Greenland area of the Eurasian Basin. According to this information, the Mid-Arctic Ridge, including the axial spreading zone, is characterized by low-amplitude linear magnetic anomalies (less than 500 nT) with a wavelength of up to 30 km. The axial magnetic anomaly reaches 2000 nT only in the west of the ridge and becomes significantly low in amplitude in almost all other areas. Comparison of the observed and theoretical magnetic anomalies in the sea floor spreading model has made it possible to identify linear magnetic anomalies C1–C25, which are associated with spreading. In [47], paleo-magnetic anomalies were identified for the ridge, the behavior of which differs from that discussed in [7] by the absence of transform faults. Note that study [46] recorded a high-amplitude shift in the spreading axis in the vicinity of 60°

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E. The most ancient anomaly has the number C24 [68], C24A, or even C24B [66]. In addition, studies [16, 47] identified areas with paleo-anomaly C25. In the latter work, the paleo-anomalies themselves in the Nansen Basin were traced to a large area in the direction of Spitsbergen. Certain studies have observed the continental continuation of a number of linear magnetic anomalies. Thus, the linear anomalies from the Nansen Basin (e.g., a nameless paleo-anomaly from [68] or anomaly 20 from [31]) cross to the eastern part of the Yermak Plateau. Linear magnetic anomaly C13 in [39] and C20 in [31] from the Amundsen Basin cross to the Morris Jesup Rise. The magnetic field in the Lincoln Sea has been intensively studied in recent decades. In a number of works (e.g., [35, 46]), elongated magnetic anomalies have been distinguished on the continental slope and shelf of the sea; other studies show that south of 85.5° N, there are no paleo-magnetic anomalies [16, 28, 31, 57, 62]. There are studies (e.g., [31]) that compare the observed and theoretical anomalies in the seafloor spreading model for the magnetic field of the basin north of 85.5° N. Based on the comparison, polarity chrons C18y–C24Bo have been identified, and in [16, 22], even C25o. Similar studies that model paleo-magnetic anomalies southeast of the Morris Jesup Rise have made it possible to identify paleo-anomalies C1–C13. However, e.g., near the southeastern foot of the Morris Jesup Rise, linear magnetic anomaly C13 from [62, 68] coincides with paleo-anomalies C7 from [39]. All of the above indicates a lack of consistency in identifying linear magnetic anomalies and the polarity chrons responsible for them. Therefore, it should be noted that the electronic database compiled by the authors of this article contains data on an aeromagnetic survey in 1998–1999 carried out by the United States Naval Research Laboratory (NRL) for the western half of the Eurasian Basin, which were published in 2003 [22]. The authors employed the survey results of the LOMGRAV-09 project published in [27], as well as the results of studies under the NOGRAM-99, NOGRAM 99-HELI, and NOGRAM00 programs. These surveys were carried out at an average flight altitude of 600 m. Analysis of the data from these surveys along specific observational profiles does not confirm the presence of magnetic anomalies stretching tens of kilometers in the Lincoln Sea south of 85.5° N, nor does it allow us to reliably identify any linear magnetic anomalies associated with spreading in the Lincoln Sea or in the area of the Morris Jesup Rise. This, together with the results of seismic and gravimetric studies mentioned above, points to the continental nature of the lithosphere of the Morris Jesup Rise and Lincoln Sea south of 85° N. Figure 11.3 shows the magnetic chronology of the seafloor of the near-Greenland area of the Eurasian Basin, as well as observed and theoretical magnetic anomalies in the inversion magneto-active layer. In addition to the chrons known in the literature, the diagram in Fig. 11.3 includes the results of their refinement and partial reinterpretation in the region west of the Morris Jesup Rise. Calculations of the spreading rates indicate that in the chron interval C25p–C13o, seafloor spreading proceeded at rates of ~ 0.85–1.5 cm/year. In the chron interval younger than C13y, they decreased and the rate of opening does not exceed 0.8 cm/

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Fig. 11.3 a Age chrons of lithosphere; b theoretical paleo-anomalies in inversion magneto-active layer model and correlation of paleo-anomalies C13–C25 along profiles 74,036, 74,039, 74,045, and 74,046, positions of which are shown in inset (c). Compiled from data of [16, 22, 27, 29] using geological scale from [36]. Modified

11.8 Calculation of the Splitting Parameters

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year with an overall decrease in the spreading rates to the east. These circumstances hinder the reliable identification of specific paleo-anomalies (their magnitude seldom exceeds 50–100 nT) and requires the identification of trains of chrons and their related paleo-magnetic anomalies (e.g., C4–C5; C17–C18; etc.). Analysis of paleo-magnetic anomalies indicates that chron12o is the closest to the eastern slope of the Morris Jesup rise from the Amundsen Basin side. Chron15y approaches the northernmost cape of the rise (in both cases, the data of [22] were used).

11.7 Discussion The comprehensive interpretation of the geological and geophysical data indicates that the Morris Jesup Rise and the Yermak Plateau are a fragment that detached from the Eurasian continent during the formation of the Eurasian Basin [30, 33, 34, 42]. This was most likely preceded by significant stretching of the continental crust in the junction area of Spitsbergen and the Morris Jesup–Yermak plateau. In this context, the existence of spreading-related linear magnetic anomalies on the continental Morris Jesup–Yermak plateau seems impossible. Therefore, we were forced to refute the identification of paleo-magnetic anomalies within their margins presented, e.g., in [31, 67, 68]. Analysis of these data along the observational profiles from [22], as well as the profile from [27], does not allow us, following [22], to reliably identify any linear magnetic anomalies in the Lincoln Sea. These are our grounds for suggesting the first reconstruction of the fracturing involved in the breakup of the once unified Morris Jesup–Yermak continental plateau.

11.8 Calculation of the Splitting Parameters In the present work, the Bullard technique [23] is applied for the first time to align the continental slopes of the Yermak Plateau and the Morris Jesup Rise in the Eurasian Basin of the Arctic Ocean. Numerous tests for the compatibility of different areas of different and same-named isobaths have shown that the most suitable for the purposes of paleo-geodynamic analysis were isobath areas in the range of 1.9–2.2 km. The slope in this depth interval is the steepest (the mean angle of inclination of the slope surface exceeds 7°) and, based on the data of [5] on the character of subsidence of the sediment sequence, it has the smallest sediment thickness (or is even completely devoid of sediment). The Euler poles and angles of rotation were calculated with original software of the Laboratory of Geophysics and Tectonics of the Floor of the World Ocean, Shirshov Institute of Oceanology (IO RAS), incorporated into the Global Mapper

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Fig. 11.4 Alignment of conjugate segments of isobaths of Morris Jesup Rise (2.1 km isobath, dotted line) and Yermak Plateau (2.0 km isobath, solid line). Points 1–2 are same as in Fig. 11.1. Modified

program [17], the calculation principles of which are explained in [6]. For brevity, we call the isobath areas of opposite slopes conjugate. If the breakup of the once unified Morris Jesup–Yermak massif, in accordance with the Wernicke scheme [69], is related to slipping of the Morris Jesup block of continental crust along the periphery of the Yermak, then the numerous tests for the compatibility of different areas of different and same-named isobaths have shown that the most suitable for paleo-geodynamic analysis were isobath areas in the range of 1.8–2.3 km. According to the calculated estimates, for a Euler pole of finite rotation at a point with coordinates 73.36° N, 23.56° W, it is possible over an extent of more than 130 km to obtain (Fig. 11.4) quite good alignment of the 2.0 km isobath of the Yermak slope (the area between points 1–2 in Fig. 11.1) and the 2.1 km isobath of the Morris Jesup slope (the area between points 1’–2’ in Fig. 11.1). The angle of rotation was 8.1° ± 0.8°. Here, the standard deviation at the calculated alignment points was ± 7 km (seven alignment points). Thus, as a result of these calculations, we reconstructed the axis of the splitting zone of the once joined Morris Jesup–Yermak continental plateau (thick line in Fig. 11.5). An important element in the reconstruction is identification of differences of hundreds of meters in the depths of the aligned isobaths. Based on this reconstruction, by introducing corrections for slipping of the above-mentioned fragments, we can reconstruct the primary paleo-bathymetry of the seafloor before the splitting of these sliding fragments (Fig. 11.6). It is clear from these figures that the initially peripheral areas of the Morris Jesup plateau rose above the main surface of the Yermak shelf by no more than a hundred meters. Our parameters for the opening presented above make it possible to reconstruct the geometry of splitting between the Morris Jesup Rise and the Yermak Plateau, but they bear no information on the time thereof. Meanwhile, the data in Fig. 11.4 indicate that the oldest chron near the foot of the Morris Jesup Rise from the Yermak Plateau side has been dated as C12o. The chron at the foot of the Yermak Plateau also is known

11.8 Calculation of the Splitting Parameters

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Fig. 11.5 Paleo-geodynamic reconstruction of closing of opposite slopes of Morris Jesup Rise and Yermak Plateau based on conjugate isobaths and reconstructed paleo-bathymetry. Axis of splitting is shown (segment of thick curved line). Points 1–2 are same as in Fig. 11.1. Modified Fig. 11.6 Paleo-bathymetry profile along lines A' –A in Fig. 11.5 before breakup of unified Morris Jesup–Yermak continental plateau. Modified

to be similarly dated [16, 22]. At the same time, chron C15o has been observed in immediate proximity to the northernmost submarine cape of the Morris Jesup Rise. This suggests that breakup of the continental crust along our reconstructed splitting occurred in the chron interval C15o–C13y (35.294–33.705 Ma ago), and regular spreading commenced in the chron interval C12o–C13y (33.705–33.157 Ma ago) and has continued to the present. The Euler poles describing the regular spreading are concentrated in the range 63°–73° N, 129°–145° E (data of [4, 32, 58, 64]). Therefore, the breakup process of the once joined Morris Jessup–Yermak plateau continued for ~ 1.5 Ma, 35.3–33.7 Ma ago.

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11.9 Conclusions Thus, as a result of our research, we found that the lithosphere of the Lincoln Sea formed during stretching of the continental Greenland–Barents Sea shelf. Prior to stretching, the continental shallow-water Morris Jesup Rise and the Yermak Plateau were a single unit. During rifting of the shelf, this single continental plateau broke apart, initiating propagation of the Gakkel mid-ocean ridge south toward the Atlantic. The breakup process continued for ~ 1.5 Ma, 35.3–33.7 Ma ago. The emplacement of numerous mafic dikes in the rifting process could have caused the high amplitude magnetic anomalies on the single plateau. For the first time, the fracture geometry involved in the breakup of the continental crust has been reconstructed, the Euler poles and angles of rotation describing its kinematics have been determined, and the paleo-bathymetry on the flanks of the fracture have been reconstructed.

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Conclusion

In conclusion, we note that only some aspects of the palaeo-geodynamics of the Eurasian Arctic Ocean basin floor have been considered in this paper. In particular, the geochronology of the Eurasian basin floor was discussed, palaeomagnetic anomalies in the Laptev Sea were described, and kinematic models of the Eurasian basin floor development were developed, Polar part of the Lomonosov Ridge (including the Arlis Spur breakaway from the Lomonosov Ridge), the Gakkel Ridge, the near-Greenland bottom region, and models of the evolution of the axial zone of the Mid-Arctic Ridge and the oceanic crust of the Amundsen and Nansen Basins were proposed. Nevertheless, a number of important issues have been left out of this book, which will be the subject of further exposition. This book is dedicated to the upcoming anniversaries: the 300th anniversary of the Russian Academy of Sciences (RAS) in 2024 and the 80th anniversary of the founding of the P. P. Shirshov Institute of Oceanology of the RAS in 2026.

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 A. Schreider et al., Paleo-Geodynamics Peculiarities of the Arctic Ocean Eurasian Floor, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-54798-0

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