The West Siberian Sedimentary Basin. Highly Heterogeneous Crustal Subsidence: A Result of Metamorphism Catalyzed by an Influx of Mantle Fluids

Most researchers relate the formation of large continental sedimentary basins to strong lithospheric stretching (rifting). The formation of the world’s largest West Siberian Basin is explained by post-rift crustal subsidence after the Permian–Triassic rifting. This subsidence is typically described with a classical pure shear model. The analysis of seismic profiles of a total length of 2500 km showed that this model is inapplicable to the West Siberian Basin. The rate of post-rift crustal subsidence should rapidly and smoothly decrease with time. In the West Siberian Basin, the most rapid subsidence occurred, however, in the Jurassic and Cretaceous, when the post-rift subsidence should almost have been completed, rather than in the Triassic just after the suggested stretching. Moreover, the crustal subsidence in the Mesozoic and Cenozoic was very complex and highly heterogeneous both in time and in space. Far from active plate boundaries, this subsidence with an accumulation of up to 6–7 km of sediments could have been caused only by significant contraction of crustal rocks as a result of prograde metamorphism, which was catalyzed by an influx of surface-active mantle fluids into the crust. The high heterogeneity of subsidence indicates the temporal and, possibly, compositional heterogeneity of this fluid influx.