West Siberian Basin subsidence promoted by the Siberian LIP magmatism

Geodynamic origin of the world’s largest intracontinental West Siberian Basin (WSB) remains enigmatic, although its subsidence history is well established by borehole data. The basement includes a complex mixture of various tectonic terranes and suspected microcontinents, amalgamated during the Pangea supercontinent assembly, which places the WSB within the Tethyan realm. While rifting is unanimously recognized as the mechanism of the WSB formation, lithosphere stretching was too small to explain the basin subsidence, and thermal subsidence associated with the emplacement of the Siberian traps at ca. 250 Ma, when the WSB subsidence has started, has long been proposed as critical subsidence factor.

Here we present results of 3D tesseroid gravity modeling for the WSB lithospheric mantle, constrained by available detailed geological and borehole data on the sedimentary structure, geophysical data on seismic velocity structure of the WSB crust, and thermal structure, including lithosphere thickness. Our results show large regional variations in density structure of the lithospheric mantle below tectonically heterogeneous WSB basement. We discuss the results in terms of paleotectonics, trap magmatism and various subsidence mechanisms, and attribute the long-lasting basin subsidence to the presence of a large high-density eclogitic body below the major WSB rift system, associated with the Siberian LIP magmatism.