Geophysical investigation of deep crustal structure of the Siberian Platform region

Abstract

A sparse network of regional profiles developed in Siberia using deep seismic sounding methods (DSS) does not allow a valid three dimensional model of Siberian deep crustal structure to be constructed. To create such a model, interpretation methods of available geophysical and geological data are suggested. These are based on modelling of geological objects using potential fields. Information on DSS key profiles is considered to be key data.The results of such interpretation are shown in the crustal thickness map and in that of crystalline basement, as well as on a deep geological-geophysical profile across the West Siberian Plate and Siberian Platform. The crustal thickness in Siberia varies from 30 to 55 km. It is on average 4?6 km thicker on the Siberian Platform than the West Siberian Plate. The least crustal thickness of 30 to 33 km appears to be beneath regions with maximum thickness of Mesozoic deposits. Modern and Early Mesozoic rift zones are characterized by decreased crustal thickness of 36?39 km. Ancient shields of the Siberian Platform and adjacent folded mountain units are up to 45?55 km thick.The geometry of the top of crystalline basement in the young West Siberian Plate is sharply different from that of the ancient Siberian Platform. Within the West Siberian Plate structural features with 5 to 11 km of relief dominate, while on the Siberian Platform the structural relief varies from 2?3 to 14 km.The peculiarities of deep crustal structure have greatly influenced the formation and distribution of sedimentary units. The constructed section shows the depths and thicknesses of the Riphean, Vendian?Silurian, Devonian?Middle Triassic and Mesozoic?Cenozoic megacomplexes, most promising for oil and gas in Siberia. Data obtained on the deep structure of Siberian Platform regions are thus of great practical importance. They can be used to predict areas of petroleum potential and determine optimal trends of further oil and gas exploration by geophysical methods.