Features of Deep Structure of the North West-Siberian Plate in Connection with Riftogenic Processes
Nina Ivanova, Igor Belyaev, and Yulia Kolesnikova
Geological-geophysical, Federal State Unitary Science-industrial Company of Marine Geological Prospecting Works "SEVMORGEO", St. Petersburg, Russia.
The area under consideration is covering the southern part of the Kara Shelf, Ob-Taz, Gydan - Yuratsk shallow waters, and coastal parts of the Yamal, Yavai and Gydan peninsulas. From 2001 Sevmorgeo is conducting the seismic investigations in the Kara Shelf and adjacent bays. The area under consideration is located in the northern part of the epi - Hercynian West - Siberian Plate (or Geosyneclise). The following units were identified in the sedimentary cover: Upper Paleozoic (?)- Lower Triassic (rift or tafrogenous), Middle-Upper Triassic and plate’s units: Jurassic, Cretaceous - Paleogene and Paleogene - Quaternary. Based on the data of the integrated seismic and gravimetric - magnetic modeling, Pre-Mesozoic folding complexes, granite - gneissic layer of upper consolidated crust (crystalline AR - PR basement) and granulite - basite layer are distinguished. The Earth crust thickness reduction to 31.0-34.0 km was identified within the graben - shaped troughs. In the depression area of the North-Seyakhinskaya basin and East - Gydan Megatrough, the “basalt window” is identified. Positive forms of the consolidated crystalline basement are fixed under all grabens. It illustrates the saturation of the crystalline basement with basic rocks in the form of intrusions of the gabro - diabase types, dolerites and etc. The overlying Paleozoic folding unit (possibly with the Riphean sediments at the base) is varying in thickness from 0-5.0 km in the troughs to 8.0-13.0 km within the uplifts. The system of the rift structures was traced, including the northern fragments of the Koltogorsko-Urengoy graben and its north-western continuation - the Yavai graben. Within the Ob Bay, complicated South - Ob, Middle - Ob, North - Ob graben-like structures were revealed. 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 started in Western Siberia extended into the southern part of the Kara shelf predefining the formation of the Western Siberian Plate. Large uplifts were identified, formed, as a rule, on the outer flanks of the rift troughs.
AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia