An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070267

Data on the absolute value of the geomagnetic field intensity at the beginning of the Cretaceous Normal Superchron (C34n) was obtained from basalts of Hooker Island of the Franz Josef Land archipelago (FJL). These basalts are considered as one of the manifestations of the High Arctic Large Igneous Province. The record of the ancient geomagnetic field in the studied Early Cretaceous basalts was preserved well due to the presence of pseudo-single domain grains of primary magmatic titanomagnetite. The paleointensity, obtained by the Thellier–Coe method, satisfies the generally accepted reliability criteria, taking into consideration other necessary evidence. This information indicates that 125 Ma, during the formation of the FJL traps, the intensity of the geomagnetic field was four times lower than today. Our estimates show that the mean value of the virtual dipole moment was 1.7 × 1022 Am2. These results support the views about the low paleointensity at the Barremian–Aptian boundary and indicate a correlation between the intensity of the geomagnetic field, the frequency of reversals, and the formation of mantle plumes.

Using 3D numerical modeling, we analyze the formation of postcollisional granitoids of the Kara orogen in Northern Taimyr under conditions of elevated heat flow due to the orogen’s breakup prior to its mantle plume episode (280–250 Ma). The initial geometry of the model area, the boundary conditions and physical properties for the crust and the mantle have been selected to reflect the structure of the crust in the junction zone of the Kara, Central Taimyr, and Siberian blocks. Comparing 2D and 3D modeling results with identical parameters and physical properties defined by the Rayleigh number shows that 3D modeling yields a more realistic and correct description of relevant magmatic processes. At the base of the modeled Earth crust an area of melting at a depth of 46–50 km appears, possibly with slight input of mantle component, which induces magma uplift and the formation of closely spaced granitoid intrusions. Plutons with diameters 10–20 km were emplaced at depths 14–8 km during 15 million years, which is close to the actual geological position and timing of postcollisional stocks of the Kara orogen.

We present a tectonothermal model showing the evolution of magmatism during the late Paleozoic postcollisional (pre-plume) development stage of the Kara orogen in northern Taimyr, Central Arctic. The model is based on new and published structural, petrologic, geochemical and geochronological data, as well as thermophysical parameters obtained for the Kara orogen that includes large amounts of syncollisional and postcollisional granites that formed due to the collision of the Kara microcontinent and the Siberian craton. Based on geological, geochemical and U–Th–Pb isotope data, the granites have been divided into syncollisional and postcollisional intrusions formed at 315–282 and 264–248 Ma respectively. Our previously published tectonothermal model [1] concerned the syncollisional formation stage of the Kara orogen at 315–282 Ma, during which the emplacement of anatectic granites took place. In this new study, we focus on the evolution of postcollisional magmatism in the orogen at the Permian–Triassic boundary. The existence of multiple bodies of allochthonous granitoids aged 265–248 Ma in the Kara orogen that predate the extensive eruption of the Siberian traps ( 250 Ma) motivates us to reconstruct the thermal state and melting mechanisms of the crust on the “pre-plume” stage. To solve this problem, numerical modeling of the thermal, tectonic, and magmatic evolution of the Kara orogen’s crust is used alongside geochemical and isotope data that reflects the magmatic sources of the granitoids.

We consider the evolution of A-type granite magmatism in the Cryogenian period during a tectonic transition of the Yenisei Ridge from its postcollisional state to the early development stages of an active continental margin. New geochronological and geochemical data are reported for A-type granites of two intrusions – the Strelka pluton belonging to the postcollisional Glushikha complex (752–718 Ma) and the Yagodka pluton of the Tatarka complex that formed on the active continental margin (711–629 Ma). New U–Pb and Ar/Ar geochronological data for these intrusions indicate that the time intervals for these two complexes overlap, showing the unbroken evolution of A-type magmatism during the tectonic transformation of the region.

—We report results of a detailed study of the paleomagnetic record in the sedimentary rocks of the Taseeva Group of the Yenisei Ridge in three typical sections in the lower courses of the Angara, Taseeva and Irkineeva rivers. Our results confirm that the geomagnetic field was in an anomalous state at the Precambrian–Phanerozoic boundary. It is well known that Ediacaran rocks in general have preserved several different paleomagnetic directions that do not conform to the geocentric axial dipole model. For example, Siberian sections display two equally valid groups of paleopoles that cause many debates over the geometry of the geomagnetic field and whether any of the components correspond to its dipole configuration. The paleomagnetic record we studied is unique in that the rocks of the Chistyakovka and Moshakovka formations have captured both these components, which is factual evidence of a synchronous existence of two sources. To explain these findings, we propose an original hypothesis in which the bipolar component that is widely present in the rocks and corresponds to the Madagascar group of paleomagnetic poles is associated to the field of the geocentric axial dipole. The less widespread monopolar component corresponding to the Australian–Antarctic group of poles is reflective of a stationary anomalous source. The recording of this source became possible due to the abrupt decrease in the strength of the virtual dipole moment that probably was at its lowest during the accumulation of the Chistyakovka and Moshakovka formations. The new paleomagnetic pole calculated for the bipolar component – 39.2°N, 61.1°E – plots on the apparent polar wander path for Siberia and can be considered a key determination for the age ~570 Ma.

The structural features of the continental shelf and oceanic basin of the Eastern Arctic as well as its tectonic history are particularly controversial. The New Siberian Islands (NSI) archipelago is one of the few territories accessible for direct geologic study in this region. The De Long Islands occupy the northernmost part of the NSI archipelago and are situated at the junction of the major tectonic units of the Eastern Arctic. This, coupled with the lack of geologic information caused by the remoteness of the islands, leads to many debates concerning the tectonic affinity and relations of the De Long Islands with adjacent units. Here we review the geology and paleomagnetism for Cambrian-Ordovician rocks of the De Long Islands. The similarity of benthic fauna groups of the De Long and adjacent Anjou basins to the Siberian Taimyr-Verkhoyansk margin indicates that the De Long unit was close to Siberia. However, some detrital zircon groups indicate their non-Siberia provenances. In this review, based on paleomagnetic evidence, we propose a global tectonic reconstruction showing interactions and drift kinematics of the NSI and the nearby Arctic terranes as well as the cratons Siberia, Laurentia and Baltica from 510 to 450 Ma. We propose the existence of a New Siberian - Chukotka - Alaska carbonate platform - a large epicontinental basin between Siberia and Laurentia with a biogeographic connection to the Verkhoyansk shelf of Siberia and potential detrital provenances from Chukotka - Alaska. The mostly transform tectonic boundaries surrounding the platform enabled its constituent terranes to drift independently while preserving conditions for unimpeded migration of Siberian benthic fauna but not for Siberia-derived zircons. Moreover, its De Long margin developed up to the Ordovician period in a suprasubductional setting and perhaps had a tectonic connection with the Mendeleev Rise.

Abstract The Northern West Siberian–South Kara Composite Tectono-Sedimentary Element (NWSSK CTSE) occupies over 1 million km 2 of the northern West Siberian Basin and the South Kara Basin. It formed as a result of the latest Permian–earliest Triassic crustal extension following thermal subsidence. The Early Triassic palaeorifts are buried under 10–12 km-thick post-rift Middle Triassic–Quaternary siliciclastic sediments. In the Tithonian–Early Berriasian period, a deep-water anoxic depression formed in the West Siberian Basin and accumulated the organic-rich carbonate-siliceous Bazhenov shales that are the main source of hydrocarbons. The West Siberian Basin, including the NWSSK CTSE, is one of the major petroleum provinces worldwide. Oil and gas deposits have been identified in Paleozoic carbonate basement rocks and Triassic, Jurassic and Cretaceous reservoirs. The main gas reserves are concentrated in the Lower Aptian–Cenomanian play. Significant gas and oil reserves are located in the Berriasian–lowest Aptian and Jurassic plays. The CTSE comprises 18–20% of the world's known gas reserves and provides approximately 90% of all Russian natural gas, which comprises 22% of global gas extraction. In this chapter we provide a summary of the CTSE geology and petroleum geology based on bulk results published mostly in the Russian literature.

We present a tectonothermal model for the late Paleozoic syncollisional formation stage of the Kara orogen in northern Taimyr in the Central Arctic. The model is based on new and published structural, petrological, geochemical, and geochronological data, as well as thermophysical properties obtained for the Kara orogen. The latter hosts a significant volume of granites formed as a result of the collision between the Kara microcontinent and the Siberian craton. Based on geological, geochemical, and U–Th–Pb isotope data, the granites were differentiated into syncollisional and postcollisional intrusions that were emplaced in the intervals 315–282 and 264–248 Ma, respectively. The presented tectonothermal model covers only the syncollisional formation stage of the Kara orogen, during which anatectic granites formed. The 2D models help to reconstruct the main tectonothermal processes of the syncollisional stage of formation of this structure, taking into account the local peculiarities of the thermal state of the Earth’s crust in the region. The model shows the mechanisms of increase in the lower crust temperature necessary for the formation of syncollisional anatectic granites. The estimates obtained from the model constrain the time interval between collision/tectonic stacking and the granite formation. The modeling also showed the general regularities typical for orogens on syncollisional stages.

Tectonic and geodynamic models of the formation of the Amerasian Basin are discussed. The Arctic margins of the Chukchi region and Northern Alaska have much in common in their Late Jurassic–Early Cretaceous tectonic evolution: (1) Both have a Neoproterozoic basement and a complexly deformed sedimentary cover, with the stage of Elsmere deformations recorded in their tectonic history; (2) the South Anyui and Angayucham ocean basins have a common geologic history from the beginning of formation in the late Paleozoic to the closure at the end of the Early Cretaceous, which allows us to consider them branches of the single Proto-Arctic Ocean, the northern margin of which was passive and the southern margin was active; (3) the dipping of the oceanic and, then, continental lithosphere took place in subduction zones southerly; (4) the collision of the passive and active margins of both basins occurred at the end of the Early Cretaceous and ended in Hauterivian–Barremian time; (5) the collision resulted in thrust–fold structures of northern vergence in the Chukchi fold belt and in the orogen of the Brooks Ridge. A subduction-convective geodynamic model of the formation of the Amerasian Basin is proposed, which is based on seismic-tomography data on the existence of a circulation of matter in the upper mantle beneath the Arctic and East Asia in a horizontally elongated convective cell with a length of several thousand kilometers. This circulation involves the subducted Pacific lithosphere, the material of which moves along the bottom of the upper mantle from the subduction zone toward the continent, forming the lower branch of the cell, and the closing upper branch of the cell forms a reverse flow of matter beneath the lithosphere toward the subduction zone, which is the driving force determining the surface kinematics of crustal blocks and the deformation of the lithosphere. The viscous dragging of the Amerasian lithosphere by the horizontal flow of the upper mantle matter toward the Pacific leads to the separation of the system of blocks of Alaska and the Chukchi region from the Canadian Arctic margin. The resulting scattered deformations can cause a different-scale thinning of the continental crust with the formation of a region of Central Arctic elevation and troughs or with a breakup of the continental crust with subsequent rifting and spreading in the Canadian Basin.

We report results of paleomagnetic studies of mafic dikes and sills from the Tas-Yuryakh magmatic complex on the Olenek uplift in the northeast of the Siberian platform. The paleomagnetic record in the rocks corresponds to an episode of anomalous state of the geomagnetic field that persisted from the Ediacaran period (~580 Ma and younger) to the end of the Fortunian age. Paleointensity measurements indicate an extremely low value of the virtual dipole moment during this time. This presumably caused a disruption of the normal Geocentric Axial Dipole model, so much so that the world magnetic anomalies made a substantial contribution. We propose that the Antarctic anomaly influenced the magnetization of the Siberian craton rocks during this period of very low dipole moment. The high latitudes corresponding to the observed paleopole do not correspond to the actual paleogeography of Siberia and can be used for paleoreconstructions only after adjusting for this anomaly. The true position of the Olenek uplift at the Precambrian–Paleozoic boundary was close to 30° S above the southeastern periphery of the African (Tuzo) mantle hot field.

Data on the petrographic–geochemical and U–Th–Pb geochronological studies of granitoids of the Bukeschensky and Samyrsky massifs of small intrusions complex of the western part of the Yana–Kolyma gold belt are reported. The granitoids intruded terrigenous rocks of the Kular–Nera and Polousniy–Debin terranes and the Verkhoyansk fold and thrust belt. According to the U–Pb geochronological data obtained on zircons (SIMS SHRIMP-II), the granitoids were formed in the Early Cretaceous, in the interval of 144.5–143 Ma. Their geochemical characteristics are similar to the associated Late Jurassic (151–145 Ma) dikes of various composition of the Nera–Bokhapcha complex. The granitoids could have been formed from a mixed source with the participation of mantle (OIB- and E-MORB-type), subduction, or crustal components. The intrusion into the Early Cretaceous granitoids probably contributed to the final processes of migration and localization of gold in the Yana–Kolyma belt. Systems of tectonic faults of different orders, such as longitudinal (northwestern), Adycha–Taryn and others, and faults transverse to them (northeastern), also played in favor of this process.

The special issue is focused on the problems of tectonics, paleogeography, geodynamic evolution, and mineral resources of the continental margins of the Russian Arctic. This topic is relevant, since the knowledge of the geologic structure of the Arctic Ocean and its formation and evolution can solve many global problems of geology and important regional problems, including the formation of oil- and gas-bearing sedimentary basins as well as prospecting for, and development of, diamonds and deposits of nonferrous, noble, rare-earth, and other minerals. In previous issues of Russian Geology and Geophysics, considerable attention was paid to the geology and oil and gas potential of the Arctic. In this special issue, emphasis is placed on the tectonics, stratigraphy, paleogeography, and petrology of the Arctic continental margins of Russia, the development of tectonic and geodynamic models for key structures, and diamond content and metallogeny of Arctic zones of the Siberian Platform, Chukotka, and the Kola Peninsula.

The Yenisei–Khatanga Composite Tectono-Sedimentary Element (CTSE) is located between the Siberian Craton and the Taimyr–Severnaya Zemlya Fold and Thrust Belt. The total thickness of the Mesoproterozoic–Cenozoic sediments of the Yenisei–Khatanga CTSE reaches 20–25 km, and they are divided into four tectono-sedimentary elements (TSEs): (i) Mesoproterozoic–early Carboniferous Siberian Craton continental margin; (ii) middle Carboniferous–Permian synorogenic Taimyr foreland basin; (iii) late Permian–Early Triassic synrift; and (iv) Triassic–Early Paleocene post-rift. The last one is the most important in terms of its petroleum potential and is the most drilled part of the CTSE. Its thickness accounts for half of the total thickness of the Yenisei–Khatanga CTSE. The margins of the post-rift TSE and the inner system of inversion swells and adjacent troughs and depressions were shaped by three tectonic events: (i) Middle Triassic uplift of South Taimyr; (ii) the Late Jurassic–Early Cretaceous Verkhoyansk Orogeny; and (iii) Late Cenozoic uplift. These processes led to more intense migration of hydrocarbons, the trap formation and their infill with hydrocarbons. Triassic, Jurassic and Lower Cretaceous source rocks are mostly gas-prone; and of the 20 discovered fields in Jurassic and Cretaceous plays, 17 are gas or mixed-type fields.

Here we present reconstructions indicating the stationary position and paleogeography of the Iceland plume, as well as its direct connection to the Mesozoic–Cenozoic large igneous provinces of the northern Atlantic and the Arctic. The main evidence for the stationary position of the Iceland hotspot comes from paleomagnetic data for the trap formation of the Franz Josef Land archipelago. Our reconstructions show that the Barents Sea magmatic province included in these traps belongs to the trace of the Iceland plume and formed as part of the High Arctic Large Igneous Province during a single relatively brief event ca. 125 Ma. Older pulses of basaltic magmatism inferred previously for the Franz Josef Land archipelago for the Early and Middle Jurassic period do not have known analogs in adjacent territories of the present-day Arctic.

The Tectonic Map of the Arctic (TeMAr) that has been compiled under the International project Atlas of Geological maps of the Circumpolar Arctic in scale 1:5 M. The TeMAr working group coordinated by Russia (VSEGEI) includes leading scientists from Geological Surveys, universities and national Academies of Sciences of Denmark, Sweden, Norway, Russia, Canada, the USA, France, Germany and Great Britain. The Tectonic Map compilation activities were aimed at acquiring thorough understanding of deep-water geological formations of the Arctic and Norwegian-Greenland basins, shelves of the marginal seas and the adjacent continental onshore areas of the oceans. The Tectonic Map is supplemented with a set of geophysical maps, schematic maps and sections that illustrate the deep structure of the Earth's crust and upper mantle of the Circumpolar Arctic.

We present the first comprehensive data for the early Ediacaran stage of evolution of the western active continental margin of the Siberian Craton (Yenisei Ridge). U-Pb (SHRIMP-II SIMS) data for zircons from dikes of picrodolerites, quartz diorites, and leucocratic granites show that they were emplaced at 625 ± 5, 623 ± 8, and 626 ± 5 Ma, respectively, which indicates a narrow time window of Ediacaran magmatic events. The mafic tholeiitic rocks have OIB and E-MORB mantle components in their magmatic sources. Mineralogical and geochemical observations showed that the mantle-sourced mafic melts assimilated some crustal material, forming Th-enriched dikes of intermediate composition and K- and Rb-enriched felsic rocks. The possible geodynamic conditions for the formation of these early Ediacaran dikes are shown and a geodynamic model is presented for the development of the Yenisei Ridge orogen from the late Cryogenian to the late Ediacaran.

We present the first definition of paleointesity of the Earth’s magnetic field that were obtained in the Early Cretaceous igneous rocks from the Franz Josef Land archipelago (Hooker and Scott Kelty Islands). The age of magmatism was determined by U-Pb method as the Early Cretaceous, about 125 Ma. A mean paleomagnetic direction for these rocks was calculated as D=40.2 deg, I=75.5 deg, a95=2.1 deg, k=89.3, N=52. A corresponding paleomagnetic pole is now located at Plat=69.0 deg; Plon=180.3 deg, A95=3.7 deg. An assessment of the domain structure of ferrimagnets using the Day plot diagram shows that the carriers of the natural remanent magnetization are pseudo-single-domain grains of titanomagnetites with varying Ti-content. Magnetic remanence was unblocked in temperatures of 350-400 °C. Some samples are characterized by unblocking temperatures of 560 °C. The determinations of the absolute values of paleointensity were obtained by the Thellier-Coe method with the implementation of the procedure "check-points". The values of Banc vary within 8.4–16 µT, which is noticeably lower than the current magnetic field at the sampling point ≈55 µT. The corresponding VDMs of 1.13–2.25 × 1022 Am2, with the current value of VDM ≈8 × 1022 Am2. Numerous basalt flows are well studied by paleomagnetic and rockmagnetic methods, together with a large number of geochronological definitions, this makes basalts from the Franz Josef Land promising for obtaining new qualitative determinations of paleointensity in the Early Cretaceous time. This work was supported by the RSF (project no. 19-17-00091) and the RFBR (project nos. 18-35-00273, 18-05-70035).