GEOLOGICAL STRUCTURE OF THE FOUNDATION OF THE PRIURAL PART OF THE WEST SIBERIAN OIL- AND GAS- BEARING MEGABASIN. K.S. Ivanov, Yu.N. Fedorov, Yu.V. Erokhin, V.S. Ponomarev

The results of studies are presented, as a result of which a significant amount of new geological data on the basement of the Ural part of the West Siberian megabasin was obtained. Based on a comprehensive geological and geophysical analysis, geological maps of the pre-Jurassic basement in the west of Western Siberia (Shaimsky region) (scale 1 : 200,000, with generalization up to a scale of 1 : 500,000) and the basement of the junction area of the Subpolar Urals and the West Siberian megabasin (North-Sosvinsky district) (scale 1 : 500,000), and the Triassic North Sosva graben was mapped for the first time. It is shown that it is made up of three formations: basalt (lower Tapsu subformation), basalt-terrigenous (upper Tapsu subformation), and upper terrigenous (Nerokhskaya suite).

In the Shaim region, ophiolites and other mafic-ultramafic complexes, which are fragments of the earth's crust of the oceanic type, were studied. Two complexes of granitoids have also been identified, differing in petrologic-geochemical, mineralogical and geochronological features. It has been established that the metamorphic rock complexes in the territory of the pre-Jurassic basement of the Shaim region, transformed as a result of the greenschist facies of metamorphism, were composed mainly of sedimentary Late and Middle Devonian rocks (358–395 Ma). Metamorphic transformations of rocks occurred in the Early Permian (280–300 Ma), at the same time, intrusions of acidic and intermediate composition intruded into sedimentary and other sequences. The stages of tectonic activity of Western Siberia are identified, which are quite well synchronized with the largest stages of tectonic restructuring of other regions of the Earth (the Urals, etc.)