Demise of the Siberian Plume: Paleogeographic and Paleotectonic Reconstruction from the Prevolcanic and Volcanic Record, North-Central Siberia

Abstract

The Siberian flood basalts are underlain almost everywhere by terrigenous, coal-bearing sedimentary rocks of the Tungusskaya Series, which is Middle Carboniferous to Late Permian in age and commonly ranges in thickness from 100-150 m to 1400 m. Systematic studies of paleogeographic and paleotectonic conditions during Tungusskaya Series accumulation indicate that its deposition was accompanied by well-balanced subsidence throughout the area occupied by well-developed flood-basalt sequences. The surrounding territories, which experienced denudation and fed this accumulation, subsequently experienced little or no flood-basalt activity. Pronounced inheritance is observed in the evolution of the areas of accumulation and denudation, with no reorganization in the Late Permian that can be ascribed to the influence of a mantle plume. Moderate erosion (from tens to several hundreds of meters), with some local uplifts and local, complex folding, have been observed at the sedimentary/volcanic interface, but these uplifts can hardly be considered to be related to a plume head. The flood-basalt eruptions themselves were accompanied by significant, commensurate subsidence, likely caused by the draining of intermediate magmatic chambers. Low relief was preserved during the entire volcanic episode. Because surficial uplift in response to thermal expansion is a necessary consequence of the existence of anomalously hot, plume-related material in the upper mantle, the geologic record shows conclusively that Siberian flood-basalt volcanism was not plume related. Rather, we consider this extensive volcanism to represent convective partial melting released by lithospheric shear and reiated, local extension.