Displays

Despite more than a century of investigation, the relationship between basement rocks throughout the Svalbard Archipelago is still a mystery. Though these rocks display similar geochronological ages, they show significantly different metamorphic grades and structures. Thus far, Svalbard was believed to be composed of three terranes of rocks formed hundreds–thousands of kilometers apart and accreted in the mid-Paleozoic during the Caledonian and Ellesmerian orogenies.

New evidence from seismic, gravimetric, aeromagnetic, seismological, bathymetric, and field data show that these terranes might have already been juxtaposed in the late Neoproterozoic. Notably, the data show that at least three–four, crustal-scale, WNW–ESE-striking fault systems segment Spitsbergen and merge with Timanian thrusts in the northern Barents Sea and northwestern Russia. These thrusts were reactivated as and/or overprinted by sinistral-reverse oblique-slip faults and partly folded during the Caledonian Orogeny and Eurekan tectonic event, and reactivated as and/or overprinted by sinistral-normal faults during Devonian–Mississippian extensional collapse of the Caledonides, thus offsetting N–S-trending Caledonian grain and post-Caledonian basins, and explaining the juxtaposition of basement rocks with seemingly different origin.

The presence of Timanian faults explains basement heterogeneities throughout the Svalbard Archipelago, strain partitioning during the Caledonian Orogeny and Eurekan tectonic event and, thus, the western vergence of early Cenozoic folds in Devonian rocks in central–northern Spitsbergen (previously ascribed to the Late Devonian Ellesmerian Orogeny) and the arch shape of the early Cenozoic West Spitsbergen Fold-and-Thrust Belt in Brøggerhalvøya, the distribution of Mississippian rocks and Early Cretaceous intrusions along a WNW–ESE-trending axis in central Spitsbergen, the transport of Svalbard in the Cenozoic from next to Greenland to its present position (c. 400 km southwards), the strike and location of transform faults and oceanic core complexes and gas leakage along the Vestnesa Ridge west of Spitsbergen, the continental nature and NW–SE strike of basement fabrics in the Hovgård Ridge between Greenland and Svalbard, and the occurrence of recent (< 100 years old) earthquakes in Storfjorden and Heer Land in eastern Svalbard.

Further implications of this work are that the tectonic plates constituting present-day Arctic regions (Laurentia and Baltica) have retained their current geometry for the past 600 Ma, that the Timanian Orogeny extended from northwestern Russia to Svalbard, Greenland and, potentially, Arctic Canada, that the De Geer Zone does not exist, that the Billefjorden Fault Zone (Svalbard) and the Great Glen Fault (Scotland) were not part of the same fault complex, and that the Harder Fjord Fault Zone (northern Greenland) possibly initiated (or was reactivated) as a Timanian thrust.

How to cite: Koehl, J.-B.: Impact of Timanian thrusts on the Phanerozoic tectonic history of Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2170, https://doi.org/10.5194/egusphere-egu2020-2170, 2020.

The Svalbard’s Southwestern Basement Province in contrary to the Northwestern and Eastern Basement Provinces is commonly correlated with the Pearya Terrane or Timanides and bears a complicated internal structure. Here, we present new data from Oscar II Land supporting the model of Svalbard’s Basement being divided into the Laurentia and Barentsia plates in the late-Caledonian period.

In Oscar II Land the enigmatic Müllerneset Formation is tectonically juxtaposed against the remaining greenschist facies metamorphosed basement. It consists of Mesoproterozoic to Neoproterozoic metapelites and metapsammites that experienced a polymetamorphic history. The progressive amphibolite facies event M1 of unknown age reached the pressure-temperatures conditions of 5-7 kbar at 500-560 °C. The subsequent greenschist facies overprint (M2) is associated with mylonitization strongly pronounced across the whole Müllerneset Formation. Mylonitic foliation S2 dips steeply to the SW and it is associated with a stretching lineation dipping moderately-to-shallowly to the SE. In the western part of the unit, monazite is growing within the S2 foliation and related shear bands mainly replacing allanite. Th-U-total Pb dating of homogenous monazite population yielded a weighted average age of 410 ± 7 Ma with MSWD = 0.26 and p = 0.997. In the western part, where mylonitic foliation is less prevalent, monazite growths within M1 porphyroblasts and within the S2 foliation. Th-U-total Pb dating revealed an array of ages between 480 – 280 Ma with no correlation of chemical or structural features allowing divisions into subgroups.

Dating results indicating an early Caledonian signal should be attributed to the progressive M1 event. Uniform monazite age of 410 ± 7 Ma in the western part represents the timing of the M2 greenschist facies overprint. Younger ages obtained in the eastern part suggest fluid related disturbance of Th-U-Pb system during late Caledonian, Ellesmerian and Eurekan events. The timing of monazite growth during the M2 event is identical with the 410 ± 2 Ma ⁴⁰Ar/³⁹Ar cooling age reported by Dallmeyer (1989). Geochronological evidence combined with structural observations suggests that the Müllerneset Formation in the Early Devonian was tectonically exhumed on the NW-SE trending left-lateral strike- to oblique-slip shear zone. Similarly oriented tectonic zones within the Southwestern Basement Province, in the Berzeliuseggene unit and the Vimsodden-Kosibapasset Shear Zone are also of similar age. This set of anastomosing shear zones is roughly parallel to the proposed orientation of the suture between Barentsia and Laurentia (Gudlaugsson et al. 1998). The documented Early Devonian sinistral displacement may mark the western boundary of the Barentsia microplate laterally extruded during the final Caledonian collision in a style similar to present day Anatolian Plate escape.

This work is funded by NCN research project no. 2015/17/B/ST10/03114, AGH statutory funds 16.16.140.315 and RCN Arctic Field Grant no. 282546.

Dallmeyer, R. D. (1989). Partial thermal resetting of ⁴⁰Ar/³⁹Ar mineral ages in western Spitsbergen, Svalbard: possible evidence for Tertiary metamorphism. Geological Magazine, 126(5), 587-593.

Gudlaugsson, S. T., Faleide, J. I., Johansen, S. E., & Breivik, A. J. (1998). Late Palaeozoic structural development of the south-western Barents Sea. Marine and Petroleum Geology, 15(1), 73-102.

How to cite: Ziemniak, G., Majka, J., Manecki, M., Walczak, K., Jeanneret, P., Mazur, S., and Kośmińska, K.: Early Devonian sinistral strike-slip in the Caledonian basement of Oscar II Land advocates for escape tectonics as a major mechanism for Svalbard terranes assembly, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1044, https://doi.org/10.5194/egusphere-egu2020-1044, 2020.

Release of greenhouse gasses is of major concern when it comes to climate change. Large amount of those gases are released through faults and fractures at the ocean floor, forming pockmarks at the surface. Understanding the formation of pockmarks and the fracture - fault network underlying them, is thus of first importance to apprehend the dynamics of gas seepages. We suggest that such fractures are closely related to the regional stress field and thus control by the combination of large scale tectonic processes, sedimentation - erosion mechanism and reactivation of inherited structures in the underlying basement.

The present study focus on the calculation of the regional stress field along Vestnesa ridge, a key location for methane seepage and pockmarks study. This area is located in a tectonically active region, boarded in the west by the Atlantic ridge and two major transform faults. In addition, deglaciation since the last glacial maximum (LGM), has induced a rebound of the lithosphere which also affects the stress field of the area including Fennoscandia, Svalbard and Greenland. However, it is difficult to estimate the effect of post-glacial rebound on the regional stress field, especially in a zone where the stress is mostly dominated by the effect of the Atlantic ridge push. To assess this problem, we built a time-dependent mechanical model of an elastic crust and viscoelastic mantle underlying the area of interest. We apply an ice cover on the surface of the model that varies according to the time-dependent ice-thickness model of Patton et al., 2016; 2017. The model runs for 50 000 yrs which includes 1) a glaciation phase till the last glacial maximum (LGM) at about -16000 yrs and 2), a deglaciation phase from the last LGM up to present time.

Preliminary results show that the amplitude of the stress change resulting from glacial adjustment, can be of the order of -2 MPa to 2 MPa along Vestnesa ridge. Moreover, the orientation of the maximum horizontal stress (σH) is modified according to the geometry and evolution of the ice cover, just as to the topography of the region affected by the lithospheric adjustment.

How to cite: Vachon, R., Schmidt, P., Lund, B., Patton, H., Beaussier, S., Plaza-Faverola, A., and Hubbard, A.: Regional stress field computation along the West Svalbard margin (Vestnesa ridge): Effect of the glacial isostatic adjustment., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19927, https://doi.org/10.5194/egusphere-egu2020-19927, 2020.

Paleogene rocks from Svalbard yield exceptionally high vitrinite reflectance values up to 4%. Even higher vitrinite reflectance data, along with high bitumen reflectance values, are found from Cretaceous to Paleogene rocks of the conjugated northeast Greenland margin. These rocks also contain coke. Since the distinct pattern of high thermal maturity affects both sides of the Fram Strait, it is interpreted to be caused by a heating event during a time when Greenland and Svalbard / Eurasia were still contiguous or close together. As heating overprints Paleogene sediments, we further assume that it postdates the Eocene Eurekan deformation and is related to subsequent (trans-)tensional movement leading to continental separation and eventually to the opening of the Fram Strait. The Fram Strait is the only deepwater connection of the Arctic Ocean with other oceans and is key for understanding the climatic, tectonic and paleo-oceanographic evolution of the Arctic realm. Timing and trigger mechanisms for mid- to late Miocene tectonic activity around the Fram Strait are still poorly constrained. For this study, we will test the following hypotheses using apatite fission track and apatite (U-Th-Sm)/He thermochronology: (i) Heating of the west and east side of the Fram Strait occurred simultaneously and was caused by incipient sea floor spreading in the Fram Strait; (ii) heating occurred during mid- to late Miocene in relation to uplift/exhumation and enhanced magmatic activity. Vitrinite reflectance data indicate temperatures high enough to reset low-temperature thermochronometers, thus our results will allow to date the thermal event and to investigate how it was temporarily and spatially connected to the separation of Greenland from Svalbard and thus to the opening of the northern North Atlantic Ocean and the Fram Strait. First Data will be presented.

How to cite: Meier, K., Jochmann, M., Blumenberg, M., Kus, J., Piepjohn, K., O'Sullivan, P., Monien, P., Kolb, V., Lisker, F., and Spiegel, C.: Thermal anomalies in Late Mesozoic to Cenozoic basin deposits: What can they tell us about the separation of Greenland from Svalbard?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18991, https://doi.org/10.5194/egusphere-egu2020-18991, 2020.

Cenozoic small-scale contractional structures are widespread in the Norwegian (west) and Russian (east) Barents Sea. While the exact dating of the deformation is unclear, it can only be inferred that the contraction is younger than the early Cretaceous. One likely contractional mechanism is related to Greenland plate kinematics at Paleogene times. We use a thin plate finite element modelling approach to compute stresses and deformation within the Norwegian Barents Sea in response to the Greenland-Eurasia relative motions at Paleogene times. The analytical solution for the 3-D folding of sediments above basement faults is used to assess possibilities for folding. Two existing Greenland plate kinematic models, differing slightly in the timing, magnitude and direction of motion, are tested. Results show that the Greenland plate’s general northward motion promotes growing anticlines in the Norwegian Barents shelf. Folding is more likely in the northern Norwegian Barents Sea than in the south. Folding is correlated with the Greenland plate kinematics through time: model M2 predicts a main phase of contraction at earliest Eocene while model M1 predicts contraction a bit later in the Eocene. Both models successfully explain folding above NW-SW Timanian trended faults in the southern Norwegian Barents Sea and above SSW-NNE Caledonian-trended faults in the north. We conclude that Paleogene Greenland plate kinematics are a likely candidate to explain contractional structures in the Norwegian Barents Sea.

How to cite: Gac, S., Minakov, A., Shephard, G. E., Faleide, J. I., and Planke, S.: Stress and deformation analysis in the Norwegian Barents Sea in relation to Paleogene transpression along the Greenland-Eurasia plate boundary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17894, https://doi.org/10.5194/egusphere-egu2020-17894, 2020.

The NE Atlantic is a tectonically complex region, also interesting in terms of georesources and therefore large areas are well covered by geophysical and geological data. In this work, we present a 3D lithospheric-scale structural and density model of the region including the eastern-most area of Greenland, the western coast of Norway, Iceland and Svalbard. It covers an area of 2000 km in longitude by 2500 km in latitude with a depth of 300 km and a resolution of 10 km. The model was developed by integrating different kinds of data and regional or global previous models, mainly of seismic origin, and constrained by gravity observations.

The developed model includes the topography, bathymetry and ice thickness obtained from global compilations models. The thickness distribution of sediments was incorporated based on detailed mapping of most areas covered by the model. The structure of the crystalline crust, differentiating between the oceanic and continental areas, is based on seismic information and previous regional models, cross-checked by additional seismic profiles available in the region. The model also includes high velocity/density lower crustal bodies defined by a previous compilation at the Norwegian and Greenland margins and by the analysis of deep seismic profiles in the case of the Iceland area.

We assigned constant densities to each layer following seismic velocities and literature-suggested values for every lithology. Due to the active tectonic setting of the area and its consequent elevated temperature and thus low density, the portion of mantle included in the model is the only layer with variable density. To obtain the mentioned density variation, we evaluated different seismic tomographic data for the area and converted them into temperatures. To mitigate the poor reliability of the tomographic models at shallow depths and also taking into account that the effect of the temperature in the uppermost mantle is especially important near mid oceanic ridges, we evaluated the thermal effect of this area by running a thermal model. Therefore, we calculated 3D distribution of temperatures for the whole portion of the mantle included in the model to obtain the reduction in density that these temperatures would cause considering the thermal expansivity of mantle rocks. 

The gravity response of the model was calculated and compared to the gravity observations using the 3D interactive software IGMAS+. The developed model includes the latest data and information of the area and, at the same time, reasonably fits the measured gravity anomalies. Comparison of the first-pass 3D gravity model to the observed gravity data detected some residual anomalies that require further differentiation of crustal densities. The new 3D lithosphere-scale model allows us to analyze the structural configuration of the area and interpret its tectonic implications. It also forms the base for thermal and mechanical models to obtain the 3D distribution of physical variables and predict the rheological and dynamic behavior of the wider NE Atlantic region.

How to cite: Gomez Dacal, M. L., Faleide, J. I., Abdelmalak, M., Scheck-Wenderoth, M., Anikiev, D., and Meeßen, C.: 3D lithospheric structure and density of the NE Atlantic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18271, https://doi.org/10.5194/egusphere-egu2020-18271, 2020.

The North Slope of Alaska has experienced a complex tectonic and geodynamic history. Although regional paleogeographic reconstructions for the North Slope of Alaska have been interpreted from the geological record, a process-based understanding of the source-to-sink system accounting for both the landscape and sedimentary basin evolution of the region has not been undertaken. Additionally, the interaction of the complex tectonic and climatic forces and their influence on the development of sedimentary basins is not well understood. 

We investigate the influence of tectonics (including deep mantle flow), eustasy and isostasy (including flexure) on the source to sink system on the North Slope to better understand its evolution since the Jurassic.

We use a quantitative forward modelling approach with the open-source surface evolution code Badlands () which incorporate time-dependent dynamic topography estimates from mantle convection models linking plate motions and mantle flow. We present a new method to implement 3D tectonic displacements (including dynamic topography) in landscape evolution models.  

The models capture the North Slope’s complex tectonic history and reproduce the sediment depositional trends as observed from the sedimentological record. The spatial variation in dynamic topography through time results in tilting of the basin which influenced sediment routing directions. Sea-level fluctuations significantly slow the depositional system, trapping more sediment in the proximal basin. Cross-sections of the modelled deposition are used to more closely analyse the shelf margin evolution. They reveal that the models reproduce the large-scale stratal geometries observed from the seismic record, as well as the shelf margin trajectory shifts since the Jurassic. This study demonstrates the importance of linking deep Earth processes to landscape evolution models to gain a better understanding of the long-term evolution of sedimentary basins.

How to cite: Clinton-Gray, C., Zahirovic, S., Mallard, C., Salles, T., and Garrad, D.: Example of the interplay of Tectonics, Eustasy and Surface Processes on the North Slope of Alaska Since the Jurassic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20674, https://doi.org/10.5194/egusphere-egu2020-20674, 2020.

Based on new seismic survey, offshore drilling and geological structure of the adjacent onshore a new model of geological evolution of sedimentary basins of the East-Siberian and Chukchi seas since the Mesozoic has been constructed. The main stages of their tectonic history are highlighted: 1) forming of the foreland basin in Jurassic – Early Creatceous time; 2) synrift extension in Aptian-Albian time; 3) start of postrift subsidence in Later Cretaceous; 4) uplift and deformations at the turn of Cretaceous and Paleogene, start of forming of the thick (up to 4-6 km) clinoform complex; 5) episode of synrift extension in Middle-Later Eocene, forming of the system of multiple low-amplitude normal faults; 6) inversion deformations in Oligocene-Miocene; 7) relatively calm tectonic conditions in Neogene-Quaternary time. Boundaries of the interpreted seismic complexes corresponding to these stages has been extended to the entire Amerasia basin with regards to the ages of magnetic anomalies in the Gakkel Ridge and sea-bottom sampling on the Mendeleev Rise. Volcanic areas of the De Long Islands and the North Wrangel High has been traced on the seismic profiles toward Mendeleev Rise and Podvodnikov Basin and dated as ±125 Ma. According to the seismic interpretation, the age of the Podvodnikov and Toll basins is not older than Aptian. The reported study was funded by RFBR and NSFB, project number 18-05-70011, 18-05-00495 and 18-35-00133.

How to cite: Startseva, K. and Nikishin, A.: Seismic stratigraphy of the East-Siberian and Chukchi seas as a key to the Amerasia Basin stratigraphy end evolution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1707, https://doi.org/10.5194/egusphere-egu2020-1707, 2020.

The growing interest of geoscientists to the Eastern Arctic shelf is caused one of the most important problems of the present time – the creation of a tectonic model for assessing the hydrocarbon potential of the Eastern Arctic basins. In this time, over the past decade, the study of the East Siberian sea seismic lines have increased. Now, we operated a new seismic data, the interpretation of which gives the key to understanding the structure of the East Siberian continental margin.

This paper presents an analysis of the tectonic structure and geological history of the shelf of the East Siberian continental margin based on the interpretation of seismic lines in conjunction with geological information.

The modern ideas of the East Arctic rift tectonic evolution and formation of sedimentary basins over the entire East Siberian shelf resulted from the large-scale tectonic and magmatism events took place and the intense rifting or stretching phase widespread the entire shelf in the Albian-Aptian.

The East Siberian basin includes the main structural elements, formed in a postcollisional destructive stage of development – the New Siberian rift, the De Long uplift, the Zhokhov Foredeep basin, the Melville trough, the Baranov rise, the Pegtymel trough, the Shelagskoe rise.

The New Siberian rift is located between the elevations of the New Siberian Islands and the archipelago De Long. Rift extends in a southeast direction from the East-Anisin Trough deflection to the Islands of Faddeev Island and New Siberia Islands. The New Siberian rift is a bright negative structural element and clearly stands out on the maps of the anomalous magnetic and gravitational fields, contrasting with the positive anomalies of surrounding rises and ridges.

De Long Plateau is a large positive structure. The uplift boundaries and internal structure are clearly visible in the gravitational and magnetic fields. The magnetic anomaly expressed in the De long, it is a typical for the areas of development of volcanogenic formations and basalts trap magmatism.

The East Siberian Rift System located from the northwestern part of the De long Plateau to the eastern part of the North Chukchi basin. System includes the Melville trough in the southern part of the East Siberian Sea. The reflector packages on seismic lines in the De Long Plateau and The East Siberian Rift System indicate that continental rifting occurred over the mantle plum.

The length of the Melville trough is a 350-370 km; with a width of 100-150 km. Trough is the symmetrical deflection consists of two narrow rifts separated by a rise.

The eastern branch of the rift system of the Melville trough joins the Baranov rise. The Baranov rise has a block structure with the geometry of which is similar to the block structure of the De-Long Plateau.

The Dremkhed trough is a deep rift structure transitional between the East Siberian and North Chukchi basins, the thickness of the sedimentary cover in central part of section is 7000 ms.

The study was funded by RFBR project - 18-05-70011.

How to cite: Zhukov, N., Nikishin, A., and Petrov, E.: Rift systems of the East Siberian basin, Arctic region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8551, https://doi.org/10.5194/egusphere-egu2020-8551, 2020.

The report focuses on the strata of the Mendeleev Rise and adjacent Podvodnikov Basin, Makarov Basin, Toll Basin, and North Chukchi Basin together with Lomonosov Ridge and Chukchi Plateau. Eleven 2-D seismic profiles with a total length of 7540 km were interpreted. The uplifts within the study area are represented by asymmetric raised blocks of the crust with strongly rugged by half-graben structures. We found semi-continuous, from moderate to bright high-amplitude gently dipping reflectors similar to SDRs inside some half-grabens. The SDRs complexes distribute only in half-grabens. A few wedges with several kilometers thick can be distinguished here. The lower boundary of SDRs does not clearly trace. The relationship with underlying complexes is uncertain.  SDRs top is bright enough and interpreted as an angular unconformity, that is progressively onlapped by overlying sediments. Top of SDRs probably coincides with rift-postrift boundary age of 110-100 Ma.  We traced the distribution and direction of SDRs and made a map. SDRs dip from the central axis of Mendeleev Ridge in opposite directions – toward to Toll and Podvodnikov basins. In the central part of Podvodnikov and Toll basins are recognized small raised blocks of continental crust to which anti-directional SDRs converge. The nature of this rises can be explained by tectonic uplift. Thus, SDRs complexes dip symmetrically in two directions from the Mendeleev Rise. Two-directional SDRs also occur in conjugate Podvodnikov and Toll basins. They dip from the Mendeleev Rise and from the Lomonosov Terrace and the Chukchi Plateau, respectively. The SDRs occur on the hyperextension continental crust complex and accompany magmatism on volcanic passive margin (VPM). We propose that the Mendeleev Rise was formed as two-directional VPM, and the Lomonosov Terrace and the Chukchi Plateau also was formed as one-directional VPM. The Mendeleev Rise was formed simultaneously with Podvodnikov, Toll and North Chukchi basins ca. 125-100 Ma because of extensional tectonics. We also assume that the Makarov Basin (with obvious half-graben structures) could form simultaneously with the Nautilus Basin. This work was supported by RFBR grants (18-05-70011 and 18-05-00495).

How to cite: Rodina, E., Nikishin, A., Startseva, K., and Petrov, E.: Seaward Dipping Reflectors Sequences (SDRs) mapping in the field of the Mendeleev Rise, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4912, https://doi.org/10.5194/egusphere-egu2020-4912, 2020.

The Kucherov Terrace is a prominent flat platform lies on a depth about 1200 meters below sea level between shelf area of the Chukchi Sea and deep-water area of Podvodnikov Basin and Mendeleev Rise. Due to location between main tectonic features of the East Arctic basin this territory carries some important insights to the tectonic history of the Arctic. By available seismic data and regional seismic correlation, we outlined series of the key moments of the geological history and estimated ancient geomorphological features of the territory.   

Based on our interpretation we suppose main rifting event took place on the territory in Aptian-Albian ages. After the rifting stage thermal subsidence lead to increasing of water depth and infilling of the basin by sediments from the Siberia territory. Two main stages of sedimentary history of the area were identified: Late Cretacerous-Paleocene and Eocene-Recent.    

By presence of obvious clinoform sequences in a sedimentary cover of the Kucherov terrace, we interpret the terrace itself as submerged ancient shelf was formed not later than end of Paleocene. Using clinoform geometry we calculated paleodepth of the Podvodnikov and Toll basins as around 800-1000 meters below sea level in Paleocene. At the same time adjacent to the shelf area seamounts of the Mendeleev Rise already existed in this time and played a role of a natural barrier to the prograding shallow-marine clastic wedges.  By shelf-edge position of a clinoform sets we estimated mean subsidence rates as 15-22 meters/myr in an area with preceding sediment loading less than 3 km.  The obtained estimates can be used as good constraints during further subsidence modelling.

During Eocene-Recent stage existence of flat platform led to a peculiar pattern of a sedimentation in a Chukchi shelf. Shallow-marine circumstances led to a very fast descending profile with less or absence of basin-floor fans. Formation of the mass wasting deposits starts in this area only in the Miocene unlike adjacent territories.

The study was funded by RFBR ‐ projects № 18-05-70011 and 18-05-00495.

How to cite: Freiman, S. and Nikishin, A.: Geological history and tectonic implication of the Kucherov Terrace (East Siberian Arctic shelf). , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8206, https://doi.org/10.5194/egusphere-egu2020-8206, 2020.

We report interpretations of regional seismic lines and new data of analyses of rocks from Alpha-Mendeleev Rise. A new magmatic province is documented at the bottom of the North Chukchi Basin. Seismic data demonstrate synrift basalt sequences (half-grabens with bright reflectors) and a number of intrusions. The seismic stratigraphic age of the magmatism is ca. 125-100 Ma. Seismic data show evidence of magmatism in the area of De Long High. Basalts have isotopic ages on De Long islands of ca. 130-105 Ma. A huge magmatic province exists in the Barents Sea. Seismic data show a basalt province to the SE from Franz Josef Land. The two-way travel time of the basalt unit is 100 ms. The age of the basalts is ca. 125 Ma from correlation with borehole data. The area is enriched by intrusions of the same age. Similar magmatic provinces are known on Svalbard and the Canadian Archipelago. We recognize half-grabens and/or SDR complexes along the Mendeleev Rise. The dip of SDRs is toward the Podvodnikov and Toll basins. The Mendeleev Rise has an axial line which separates differently dipping SDRs. Half-grabens are filled with clastic rocks and basalts with ages ca. 127-110 Ma (Skolotnev et al. in preparation, and our correlations with seismic data). The Podvodnikov and Toll basins have SDR complexes also. The dipping of the SDRs is toward the axial lines of these basins, and the lines are parallel to the Mendeleev Rise axial line. We propose that intraplate, ca. 125 Ma basalt magmatism started between the Eurasian continent (including the Lomonosov and Alpha-Mendeleev terranes) and the Canada Basin (which formed before 125 Ma). This was followed by concentration of rifting and magmatism along Alpha-Mendeleev Rise and the adjacent Podvodnikov, Nautilus and Toll basins. These processes were aborted at ca. 100 Ma as a result of plate kinematic reorganization. Additional intraplate magmatism took place at 90-80 Ma. We propose that Alpha-Mendeleev Rise is a Eurasian aborted double-sided volcanic passive continental margin with stretched and hyper-extended continental crust intruded by basalts. This work was supported by RFBR grants (18-05-70011 and 18-05-00495).

How to cite: Nikishin, A., Cloetingh, S., Foulger, G., Freiman, S., Malyshev, N., Petrov, E., Startseva, K., Rodina, E., and Verzhbitsky, V.: Alpha-Mendeleev Rise is a Eurasian aborted volcanic passive continental margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4695, https://doi.org/10.5194/egusphere-egu2020-4695, 2020.

Base on thorough interpretation of Russian seismic reflection data the sedimentary architecture of Amundsen and Nansen basins was studied. Accordingly, we infer four development stages of the Eurasian Basin (EB) sedimentary system, caused by tectonic evolution of the region.

Continental break-up stage I ~120-56 MA leads to formation of 120-130 km wide synrift basins both in the Eastern Amundsen and in the Western Nansen basins. Both basins were floored by extremely extended continental crust. Therefore, the hypothesized continent-ocean boundary (COB) should be placed at the seaward edges of synrift portions of Amundsen and Nansen basins, roughly along the magnetic anomaly #20.

Spreading stage II (56-34 MA) was characterized by seafloor spreading in the EB as low as 8 mm/year, which was accompanied by expansion of the Amundsen and Nansen sedimentary basins up to their current sizes. The successive expansion of the sedimentary basins which is characteristic of the seafloor spreading basin, was revealed from the architecture of only this sequence, neither underlying nor overlapping. We propose the formation of a Gakkel Ridge rift valley and its infilling with thick sediments sequence during this stage.

Synoceanic stage III (34-~3 MA) was resulted in the accumulation of the undisturbed Oligocene-Quaternary sediment sequence all over the entire EB. If the non-tectonized architecture of this sequence indicates a calm tectonic regime for the most of the Oligocene-Miocene, the existence of the sediment veneer all over the entire EB proves that sedimentation basin and consequently the oceanic crust domain of modern size were already formed by the beginning of Oligocene.

Re-spreading stage IV (~3-0 MA) is characterized by the resumption of seafloor spreading in the Gakkel Ridge axial zone by propagation of the oceanic rift from Norwegian-Greenland basin toward the east.  

The proposed model of two-stage seafloor spreading in the EB allows us to explain most of the geological issues in this region and is of perfect relation to the known tectonic events along the Arctic periphery.

In particular: (1) thick sediments sequence in the Eastern and Central (e.g.  at 94°E by Rekant & Gusev, 2016)  Gakkel Ridge rift valley could be explained by the Eocene age of the rift valley, (2) recent spreading resumption could be considered as the cause of the unpredictable high both the hydrothermal activity and volcanism at the Western Gakkel Ridge, (3) the consolidated sand- and siltstones, dredged from the seamount scarp in the middle part of Amundsen Basin (Gaedicke et al., 2019), which thought to be fragments of Mesozoic continental crust, confirm the suggested COB position along magnetic anomaly No.20, (4) the eastward propagation of the ocean rifting along the Gakkel Ridge leads to apparent change of the accentuated high relief morphology of the Western Gakkel Ridge to a smoother ridge morphology of the Eastern Gakkel Ridge as well as to defocusing seismicity at the Eurasia Basin– Laptev Sea transition.

How to cite: Rekant, P. and Petrov, O.: New model of two-stage seafloor spreading in the Eurasian basin (Arctic Ocean); insights from the analysis of the sedimentary basin architecture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5527, https://doi.org/10.5194/egusphere-egu2020-5527, 2020.

The studied intrusions are located within the Northern Taimyr domain (southern part of the Kara terrane) on the northwestern coast of the Taimyr Peninsula and on several islands in Kara Sea. Intrusions cut the Lower Paleozoic metasedimentary rocks.

Late Permian – Early Triassic intrusions are represented by coarse- to medium-grained quartz-syenites and alkali-feldspar-granites. U-Pb dating of these granites yelled age of 253 Ma. Ar-Ar micas ages varies from 236 to 251 Ma. The granites are high- to medium acidic, high alkaline (alkali-calcic to alkalic), ferroan and magnesian, mainly peraluminous. Granites are characterized by relatively low initial ⁸⁷Sr/⁸⁶Sr ratio (0.7041) and slightly positive εNd(t) value (1.03).

Middle – Late Triassic intrusions are represented by coarse-grained granodiorites and granites. U-Pb zircon ages of these granites range from 228 to 238 Ma. Ar-Ar micas and amphibole ages varies from 206 to 235 Ma. They are acidic to low acidic, moderately alkaline (alkali-calcic, calc-alkalic), magnesian, peraluminous and metaluminous. Middle – Late Triassic granites are characterized by higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.7045-0.7060) and negative εNd(t) values (-5.47 to -0.80).

Late Permian – Early Triassic high alkalic predominantly ferroan granites are most likely related to A-type granites. Middle – Late Triassic moderate alkalic magnesian granites have transitional I/S-type character. Thus, Late Permian – Early Triassic granites likely form an outer rim of the Permo-Triassic Siberian plume. Middle – Late Triassic granites of Northern Taimyr were formed from different source with more significant crustal component contribution. Obtained data suggests two magmatic events throughout Early Mesozoic that affected Northern Taimyr.

This research was supported by RFBR project No. 19-35-90006

How to cite: Kurapov, M., Ershova, V., Khudoley, A., Makariev, A., and Makarieva, E.: Late Permian – Triassic Granitic Magmatism of western part of the Northern Taimyr: evidence for two magmatic events., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12752, https://doi.org/10.5194/egusphere-egu2020-12752, 2020.

In 2019, the compilation of the new Tectonic Map of the Arctic (Tectonic Map of the Arctic, 2019: eds. O. Petrov, M. Pubellier) was completed. The map was compiled under the international project Atlas of Geological Maps of the Circumpolar Arctic, 1:5M with the participation of representatives of all Arctic states under the auspices of the Commission for the Geological Map of the World at UNESCO. The new 1:5M Tectonic map of the Arctic is a GIS project, which provides a transition to three-dimensional geological mapping of the Arctic. The project includes the crustal and sedimentary cover thickness maps, the crustal types map, the tectonic zonality map of the basement, schematic  map of key igneous provinces of the Circum-Arctic region and the geological transect compiled taking into account the latest scientific geological and geophysical data accumulated in recent decades as a result of high-latitude expeditions and scientific programs to substantiate the extended continental shelf in the Arctic. The new Tectonic map of the Arctic proved the continental nature of the Central Arctic Uplifts as a natural geological extension of Eurasia. Close structural relationships of deep-water parts of the Central Arctic and the shallow continental shelf of Northern Eurasia are substantiated by geological and geophysical characteristics of the consolidated crust, the upper mantle and sedimentary cover, as well as the common parameters of the magnetic and gravitational potential fields.

How to cite: Petrov, O., Pubellier, M., Morozov, A., Kashubin, S., Shokalsky, S., and Pospelov, I.: New CGMW Tectonic Map of the Arctic , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8266, https://doi.org/10.5194/egusphere-egu2020-8266, 2020.