Crustal Subsidence in the West Siberian Sedimentary Basin Caused by Prograde Metamorphism-Induced Rock Contraction in the Lower Crust

Abstract

The history of the crustal subsidence in the Mesozoic and Cenozoic in the West Siberian Basin – the largest sedimentary basin in the world is considered. Most researchers associate its formation with post-rift crustal subsidence, which followed an episode of strong lithospheric stretching about 250 Ma ago at the Permian–Triassic transition. A characteristic feature of post-rift subsidence is a decrease in its rate in time. During the Mesozoic–Cenozoic history, the crustal subsidence rate in Western Siberia should have decreased by an order of magnitude. However, the analysis of long (700–900 km) seismic profiles in the north of Western Siberia and in the Southern Kara Sea shows that, on average, there has been an acceleration of the crustal subsidence since the beginning of the Mesozoic in these regions. Under such conditions, lithospheric stretching in them could be responsible for only a small fraction of the total crustal subsidence by 6–7 km. In Western Siberia, the crust is close to the isostatic equilibrium. Due to this, in the absence of strong stretching, the accumulation of thick sedimentary sequences in the basin could only have been caused by rock contraction in the lower crust due to prograde metamorphic reactions. To obtain the above results, we used some simple methods for the first time to analyze the structure of the sedimentary sequences in the West Siberian Basin. Detailed seismic profiles for many other deep basins on all the continents have been published. The methods of their interpretation implemented in the present paper can be easily applied to determine the role of lithospheric stretching in the formation of deep sedimentary basins on the global scale.