West Siberian Sedimentary Basin. Highly Heterogeneous Subsidence of the Earth's Crust Caused by Metamorphism Catalyzed by the Influx of Mantle Fluids

Most researchers associate the formation of large sedimentary basins on the continents with strong stretching of the lithospheric layer - rifting. The formation of the world's largest West Siberian basin is explained by post-rift subsidence of the crust after rifting at the Permian-Triassic transition. Post-rift subsidence is commonly described using the classical pure shear model. Analysis of seismic profiles with a total length of 2.500 km showed that this model is not applicable to the West Siberian basin. The rate of post-rift subsidence of the crust should decrease rapidle and smoothly over time. In the West Siberian Basin, the most rapid subsidence occurred, however, not in the Triassic, immediately after the supposed stretching, but in the Jurassic and Cretaceous, when the post-rift subsidence should have been practically completed. Moreover, in the Mesozoic and Cenozoic, the subsidence of the crust was very complex, and it was highly heterogeneous both in time and area. Far from the active boundaries between the plates, such a subsidence with the accumulation of up to 6-7 km of sediments could only be caused by significant contraction of rocks in the Earth's crust as a result of prograde metamorphism, catalyzed by the influx of surface-active fluids from the mantle into the crust. The strong heterogeneity of the subsidence indicates that the influx of these fluids into the crust was also heterogeneous in time, space, and possibly composition.