A 3D model of the crustal structure of the region including the Chukchi Borderland with the adjacent ocean and Chukchi‒Alaska Shelf has been compiled and calculated. A specific feature of the crustal structure consists of three-sided isolation of the Chukchi Borderland and a transitional zone from the south connecting the Chukchi Borderland with the Chukchi‒Alaska Shelf. The connection between the Chukchi Borderland and Wrangel Rise of the Chukchi Shelf is traced through the North Chukchi Rise located between the North Chukchi Trough and the Hanna Trough. Clockwise rotation of the Chukchi Borderland began in the Early Cretaceous, because basalts at the bottom of sedimentary strata sections along the eastern and southern boundaries of the Chukchi Basin have reversed magnetization: their outpouring occurred before the beginning of the Cretaceous superchron, earlier than 121 Ma. Near the upper boundary of the Neocomian, there was a large-scale shear displacement of crustal blocks along the eastern boundary of the Chukchi Rise, which had a thrust pattern before that. The 3D model demonstrates that the Chukchi Borderland and Chukchi Basin are natural components of the continental margin, since they have a strong geological connection with the continental masses of the Chukchi Shelf.

In 2011‒2020 a significant number of seismic lines were carried out in the Eurasian Basin of the Arctic Ocean, which made it possible to study the structure of the junction zones of the Gakkel Ridge with the Nansen and Amundsen basins on a number of profiles. During 2019‒2020 15 sections of the Gakkel Ridge and its rift valley were studied using a sub-bottom profiler and seismo-acoustic profiling. New data on the relief of the basement, as well as the use of databases of bathymetry, gravity, and magnetic anomalies updated at VNIIOkeangeologia, made it possible to calculate the magnetization of the rocks of the Gakkel Ridge along a number of profiles crossing the ridge and to perform model calculations of the structure of the Earth’s crust using a complex of geological and geophysical data in the area of the southeastern termination of the ridge. The Gakkel Ridge is a structure that was isolated in the Early Oligocene (34 Ma)–Early Miocene (23 Ma) in the process of radical restructuring of the spreading kinematics in the existing ocean basins in the regions of the North Atlantic and the Arctic. The values of the calculated magnetization of the magnetic layer of the Earth’s crust show that this layer is partly composed of oceanic basalts, but mainly of deep-originated rocks, gabbro, and peridotites that were brought to the surface during detachment accompanying spreading. The Laptev Sea continuation of the rift valley of the Gakkel Ridge to the south of the caldera passes above many kilometers of sediments, at the base of which sedimentary rocks of Cretaceous and Late Jurassic age occur.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23050057

The Gramberg All-Russia Research Institute for Geology and Mineral Resources of the World Ocean (FSBI VNIIOkeangeologia) carries out a wide range of research in the fields of geology, engineering geology, geophysics, and geochemistry. The specialists of the institute perform studies using most-up-to-date equipment in several directions, including the study of the geology and mineral resources of the Arctic, Antarctic and the World Ocean. The geological and tectonic maps and atlases of the Eurasian sector of the Arctic shelf and adjacent deepwater zones of the Arctic Ocean have been compiled. This allow one to recognize the rift-related basins on the East Arctic shelf of Russia, and the conjunction areas of the Lomonosov, Gakkel, and Mendeleev oceanic ridges with the Eurasian continental margin. A comprehensive interpretation of geological and geophysical data has revealed features of the tectonics of the Amerasian Basin, which indicate that the evolution of the basin structures took place under conditions of continental rifting. One of the main scientific conclusions drawn at the preparation of the Submission of the Russian Federation in respect of the continental shelf boundary in the Arctic Ocean is the proof of the continental nature of the structures of the Central Arctic Rise Complex: the Lomonosov Ridge, Podvodnikov Basin, Alpha–Mendeleev Rise, Chukchi Basin, and Chukchi Borderland. This conclusion is confirmed by the characteristics of the main layers of the Earth’s crust in the above structures. A geodynamic model of the evolution of the Precambrian complexes of East Antarctica has been developed and the main tectonic provinces of Antarctica have been distinguished. A universal seismostratigraphic model of sedimentary basins has been developed for the marginal seas of East Antarctica. An important area of research in Antarctica was the study of the subglacial Lake Vostok. When studying the history of the formation of sulfide mineralization, it was found that the discharge of hydrothermal ore-bearing solutions most often occurs continuously, and only the intensity of the ore formation process changes with time. The possibility of formation of massive sulfide ore volumes additional to the main surface deposit due to metasomatic replacement of host igneous rocks has also been established.

We propose a geodynamic model capable of explaining the formation of structural features of the Earth’s crust in the Amerasian Basin. The model relates the evolution of the crust of the Alpha-Mendeleev Rise and the Podvodnikov Basin in the Cretaceous to the dynamics of an isometric convective cell in the upper mantle, which can be interpreted as an upper mantle plume. The presented results of numerical modeling confirm the applicability of the presented approach for explaining the geodynamic evolution of the continental crust of the Alpha-Mendeleev Rise and the surrounding basins of the Amerasian Basin in the Cretaceous.

A 3D model of the Earth’s crust for the continental margin of the Laptev Sea and the adjacent part of the Eurasian Basin was developed using the latest seismic and gravity data. The thickness of the consolidated part of the Earth’s crust in the study area is estimated at 7–11 km, which corresponds to a highly extended continental or oceanic crust. The formation of the basement and sedimentation in this area most likely began in the Late Jurassic. The southeastern part of the Eurasian Basin is separated from the rest of the basin by a dextral shear zone, the displacement along which during the Paleogene was more than 100 km.

— The Chukchi Borderland is a tectonic unit of the eastern part of the Arctic continental margin of Eurasia that is part of the complex of the Central Arctic rises, along with the Lomonosov Ridge, the Alpha‒Mendeleev Rise, the Podvodnikov, Chukchi and Mendeleev basins. The study provides data on the structure of the Chukchi Borderland and the surrounding geological structures, morphology and geology, uses bathymetric materials, seismic materials from CDP and deep seismic survey, sampling and drilling data. A review of materials on the study region was carried out. The latest results of geomorphological analysis of bathymetric data and 3D modeling of the Earth’s crust of the study region using geophysical data are presented. To explain the identified features of the morphology and deep structure of the Chukchi Borderland, a tectonic model is proposed that explains the deep mechanisms of its formation and adjacent structures, as well as a structural-tectonic scheme of the Arctic Alaska–Chukotka microplate, which presents the morphological and geological connection of the Chukchi Borderland with the continental shelf.

A vast area of up to five million square kilometers is located in the Pacific Ocean to the east of Australia. The Earth’s crust up to 10–23 km thick is submerged here to a depth of 1–4 km. This contrasts with the surrounding Southwest Pacific where the crust is submerged up to 5–6 km and has a thickness of 7 km, which is more typical for oceans. As is known from dredging and deep-sea drilling, Zealandia is composed of the continental crust. For a long time, it was close to the sea level and then it subsided into the depths. The same thickness, water depths, and subsidence history are found for some domains in the Central Arctic, Lomonosov Ridge, Podvodnikov Basin, and Mendeleev Ridge. The continental nature of the crust has been proven here by drilling and is suggested by the results of study of the sea floor bedrock. Deep basins of the Central Arctic and Zealandia were formed without intense crustal stretching. Its origin can be explained by the increase in density of gabbroids in the lower crust due to prograde metamorphism.

The western part of the large Amerasia Basin in the Arctic Ocean comprises the smaller basins of Podvodnikov and Makarov. Judging by the sedimentary structure and the crustal subsidence history, both basins were developed on the continental crust despite their 3-4 km water depths. By the early Miocene, prior to the rapid formation of the basins, the crustal surface had been close to the sea level for a long time. Lithospheric stretching had a minor input to the subsidence, which was rather driven mainly by the prograde metamorphism of gabbro in the lower crust and its transformation into denser eclogite. The mechanism of subsidence associated with the metamorphic transformation from gabbro to eclogite implies that high-velocity eclogite belongs to the lower continental crust metamorphosed under the effect of mantle fluids. This idea undermines the seismic and gravity basin models that commonly attribute mafic eclogite to the sub-Moho lithospheric mantle on the basis of P-wave velocities similar to those in peridotite and interprets the crust beneath the Podvodnikov and Makarov basins as thin continental and oceanic crustal types, respectively.

КОНТИНЕНТАЛЬНАЯ КОРА В ЗАПАДНОЙ ЧАСТИ АМЕРАЗИЙСКОГО БАССЕЙНА. МЕХАНИЗМЫ ПОГРУЖЕНИЯАртюшков Е. В., Смирнов О

The purpose of this work was to study the seismic attributes of the Podvodnikov Basin basement. It was found that these attributes, first of all, P-wave velocities of 5.9–6.2 km/s, the ratio VP/VS = 1.71, and the diffraction nature of the reflections from the basement indicate that the basin has a continental origin and that its tectonic development began at the pre-oceanic stage of evolution of the Arctic.

Processing of data from regional geophysical surveys completed in the northern Barents Sea has provided updates to gravity and magnetic databases, structural maps of seismic interfaces, and positions of anomaly sources, which made a basis for 3D density and magnetic models of the crust. The new geological and geophysical results placed constraints on the boundaries between basement blocks formed in different settings and on the contours of deposition zones of different ages in the northeastern Barents Sea. The estimated thicknesses of sedimentary sequences that formed within certain time spans record the deposition history of the region. There is a 20-50 km wide deep suture between two basins of Mesozoic and Paleozoic ages in the eastern part of the region, where pre-Late Triassic reflectors have no clear correlation. The suture slopes eastward at a low angle and corresponds to a paleothrust according to seismic and modeling data. In the basement model, the suture is approximated by a zone of low magnetization and density, which is common to active fault systems. The discovery of the suture has important geological and exploration implications. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Based on obtained data, the paper considers the structure of the sedimentary cover and basement in the continent–ocean transition zone. We analyze the structure of modern tectonic activity zones in the Laptev Sea and structurally similar zones in the Novosibirsk Trough and the De Long Massif. Three sedimentary Anisin–Laptev, Amundsen, and West Laptev basins separated by basement uplifts are distinguished in sedimentary cover. The Anisin–Laptev Basin is separated from the West Laptev Basin by the North Laptev Horst and from the Amundsen Basin by an uplift stretching from the Lomonosov Ridge and covered by the Neogene–Quaternary deposits. The modern tectonic activity zone, marked by a rift valley and earthquakes, stretches across the continental slope from the Gakkel Ridge above a sedimentary rock sequence possessing many-kilometers thickness. The zone reached its present-day position in the Pliocene. Near the shelf boundary, the zone bifurcates, with one branch departing into the West Laptev Basin, and the other branch departing into grabens that developed to the west of New Siberian Islands forming the Laptev microplate.

Summary A large amount of data on the structure of the sedimentary cover in the Eurasian Basin was obtained during the Russian seismic expeditions in 2011, 2012, and 2014. These data allow to analyze the zoning of the Eurasian Basin structure. A number of the reliably traceable linear magnetic anomalies are fewer in the direction from west to east. Eastward from 75° E, there is a clear asymmetry of the potential fields anomalies about to the modern spreading axis, located in the rift valley of the Gakkel Ridge. The observed pattern of magnetic anomalies can be explained by the spreading axis jump in the eastern part of the basin in the Miocene. On a large area in the Eurasian Basin, linear magnetic anomalies are questionable. Joint interpretation of magnetic, gravity, and new seismic data provided opportunity to outline in the Eurasian Basin: Gakkel Ridge area (up to magnetic anomaly 5, ∼10–12 ma), area formed from the Early Oligocene (borders near anomaly 13), area formed from the Early Eocene (borders near anomaly 24), and extensive area of the Mesozoic oceanic basement. The geodynamic model of the Eurasian Basin structure formation should be designed based on the new seismic data.

The time seismic reflection sections obtained in Podvodnikov basin (Central Arctic) during expedition «Shelf-2011» were interpreted. The tectonic zoning of Podvodnikov basin and adjacent structures was carried out with the use of lineamental analysis of bathymetric, anomalous gravitational and magnetic maps. The distribution of riftogenic structures is shown within the whole Podvodnikov basin. The thickness of riftogenic complexes reaches 5 km.

Characteristic features of deep structure and composition of Ural (UFB) and Paikhoy-Novaya-Zemlia (PNZFB) fold belts, which were investigated with the use of results of geological and geophysical investigations along reference geophysical profiles (geotransects) are considered. In the structure of Uralian deep sections typical elements of collisional orogen are distinguished: deformed margin of submerged plate, suture zone and deformed margin of override plate. Participation in the process of the Late Paleozoic collision more than "Baltic". "Kazakhstan" plates, but micro plates of continental type lead to complication of typical model of collision orogen due to inclusion into the UFB deep structure additional blocks and suture zones. PNZFB zonality is not typical for classical collision orogens. Fold-thrust belt on the "Svalbard" plate margin is modeled in its deep section. Intensity of the fold-thrust deformations decreases to relict oceanic basin, which is modeled in the basement of the South-Kara sedimentary depression.

The time seismic reflection sections obtained in Podvodnikov basin (Central Arctic) during expedition "Shelf-2011" were interpreted. The tectonic zoning of Podvodnikov basin and adjacent structures was carried out with the use of lineamental analysis of bathymetric, anomalous gravitational and magnetic maps. The distribution of riftogenic structures is shown within the whole Podvodnikov basin. The thickness of riftogenic complexes reaches 5 km.

Characteristic features of deep structure and petrophysical parameters of intraplate structures (hot spots, intracontinental rifts, inrtraplate basins and passive continental margins) are considered. Examples of the structures of Barents-Kara region and Eurasian continent north margin are presented.