--> Abstract: Deep Structure of the West Siberian Plate and Zones of its Joint with North Kara Plate, by Nina Ivanova; #90177 (2013)

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Deep Structure of the West Siberian Plate and Zones of its Joint with North Kara Plate

Nina Ivanova

The West Siberian Plate is characterized by continental and thinned earth’s crust, with an average thickness of 38 – 40 km. The crustal thickness increases to 41 – 42 km within large fault zones of the thrust type in the north of the North Siberian Weir, in the zone where it joins to the North Kara Plate. This may indicate detachment of the earth’s crust. The crustal thickness is reduced to 30 – 35 km within graben-like structures as a result of rifting. The following four main tectono-stratigraphic units were distinguished in the section of the Earth’s crust: 1) the sedimentary cover; 2) Riphean–Palaeozoic folded complexes; 3) the upper crystalline crust (granite-gneissic metamorphic complexes of Archean-Proterozoic age); 4) the lower crust (the granulite-basic and basic complexes). The sedimentary cover of the epi – Hercynian West Siberian Plate (or Geosyneclise) is represented mostly by Mesozoic – Cenozoic terrigenous sediments with volcanic formations in the lower part of the cover. These sediments lie on folded Paleozoic rocks of the intermediate structural stage. By seismic data PZ sediments are folded extensively and eroded within uplifts. Several seismic reflecting horizons in the Palaeozoic sections highlight a large PZ basin in the south-eastern part of the Kara Shelf close to Taimyr Peninsula. Several grabens were recorded in the base of sedimentary cover. The largest of them is the Koltogorsko-Urengoy graben, which continues offshore. In the southern part of the Kara Shelf, the north-eastern outline of Pukhuchansko – Beloostrovskaya graben - rift system was clarified. It shows a significant destruction of the Earth Crust within the region. The system of the rift troughs starting in Western Siberia extends into the southern part of the Kara shelf pre-defining the formation of the Western Siberian Plate. Seismic and gravity/magnetic modeling made it possible to define the North Siberian Weir’s deep structure more precisely. A large faulted area of a thrust nature complicates the northern part of the North-Siberian Weir. There are graben-like structures filled by Proterozoic and Palaeozoic rocks, which were folded as a result of the Cimmerian tectogenesis. The magnetic-field pattern enables us to associate this area with the thrust zone within the Taymyr Orogen. Besides, it was determined that the North Siberian Weir can be associated with the north-eastern part of the Paikhoy-Novozemelskiy fold belt. Therefore, the North Siberian Weir is the northern limit of Western Siberia’s extended rifting system. Geophysical data suggest that joining the West Siberian and North Kara plates had a collision character and resulted in thrusting the North Kara Plate onto the West Siberian Plate, with the development of the North Siberian Weir. Deep structure; West Siberian Plate, Sedimentary cover, rifting

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013