ZONE OF MAJOR PLATFORM FAULTS IN THE SOUTHERN U.S.S.R. AND CENTRAL ASIA

Abstract

As a result of deep drilling and complex geophysical investigations conducted on a large scale the existence of a deeply fractured graben zone has been established in the basement of a pre-Paleozoic and epi-Hercynian platform. This zone stretches from the northwest to southeast over a distance of more than 4,000 km. In the northwest it is traced through the pre-Paleozoic Russian platform and includes the Pripyat, the Dnieper-Donets depressions and the Donets basin Hercynian folding zone. In the Fore-Caucasian territory it passes along the Russian and the epi-Hercynian platforms boundary within the buried range forming an extension of the Donets Basin. Further on, within the territory of Central Asia it is traced in the Mangyshlak mountain structure and the Bukhara- Khiva fracture zone. The activity of this tectonic zone during the post-Cambrian was displayed at different times. There is observed, therefore, a gradual NW-SE rejuvenation of sedimentary deposits filling up a graben system associated with the tectonic zone: Devonian deposits - in the Dnieper- Donets and Pripyat depression; Middle and Upper Carboniferous deposits-in the Donets Basin and within the area of the buried range; Permian-Triassic deposits - in the Mangyshlak mountain structure; and Jurassic deposits - in the Bukhara-Khiva zone. This shows that the renewal of tectonic activity along ancient fractures first began in the western part of the platform most elevated during the Paleozoic. During the Hercynian stage of tectogenesis tectonic processes of different characters took place in separate links of the entire zone: platform development - in the Dnieper-Donets depression; geosynclinal - in the Donets Basin, the buried range in the Bukhara-Khiva zone; geosynclinal and intermediary stage of intermontane depressions - in the Mangyshlak mountain structure.—Auth. English summ.