THE TECTONIC EVOLUTION OF WEST SIBERIA - AN ATTEMPT AT A GEOPHYSICAL ANALYSIS

An interpretation of the tectonic evolution of West Siberia is presented, based on new high-precision geophysical data, corroborated, wherever possible, with key geological data. The basement of the West Siberian Basin is a heterogeneous and multi-aged mosaic containing five types of tectonic unit: (1) convergent systems, i.e. extinct island arcs and marginal seas or continental margin arcs; (2) microcontinents; (3) relict ocean basins; (4) rifts; (5) aborted oceans. The basement developed in two distinct stages under different tectonic regimes. (1) During the Late Precambrian and the whole of the Paleozoic, subduction of the Paleo-Asiatic and Uralian oceans produced new continental crust that was gradually accreted to the margins of the European, Siberian and Kazakhstan continents. Initially separated by great distances, these continents converged and by Early Mesozoic time formed the Laurasian part of Pangea. However, collision was incomplete, and in the central part of West Siberia, small relict basins containing Paleozoic ocean crust were preserved. (2) For a limited period during the Early Mesozoic, a second tectonic regime operated. The newly formed West Siberian basement began to disintegrate as a result of rifting, which progressed to sea-floor spreading in the Obsky paleo-ocean and the Yenisei-Khatanga Trough. The structures generated under these earlier regimes controlled the subsequent passive evolution of West Siberia during Mesozoic and Cenozoic time.