Siberian Superplumes: Did They Really Exist?

Siberian traps can be regarded as a unique natural object because of their structure, composition and voluminous lava shields, which are rarely found in other LIPs. As is known, Perm-Triassic traps of the Western Siberian Plate (WSP) and Siberian Platform (SP) are due to multi-level magma sources and are of a certain geochemical and petrochemical zoning (Sharma 1997; Reichow et al 2005). In Russian geodynamic and petrogenetic literature of the last decade, the formation of Mesosoic granitoids of Central Asia and Siberian Platform is explained due to the influence of 'superplumes' on the continental lithosphere. However, no details are given concerning the mechanism for this. This work is a generalization of a series of numerical experiments using a quantitative model for the intraplate mantle-crust magma system, where all the conditions for the melting zones of the convecting upper mantle, interacting with the multi-layered lithosphere were taken into account. For this we used a modified version of MAiX 2D convection codes for a complex 7-phase diagram (Perepechko, 2003). The three-layered structure for the profile of melting materials has been taken into account (Sharapov et al, 2006). Both the depth and the horizontal dimensions of melting zones, as well as their detailed structure and evolution can be computed using the convection codes. The results of our modeling showed that the idea of the existence of 'superplumes' explaining SP and WSP trap magmatism is disputable; both systems rather seem to be independent and have different features for multilevel melting zones development. The virtual voluminous magma shields coextensive with what we find in reality can be obtained due to a series of scattered hotspots. For the scheme of trap formation development, two-level melting zones with tholeiites in the metasomated lithosphere appear virtually over hotspots. Sometimes over hotspots, the appearance of two successive melting cycles is possible. This work was supported by the Russian Ministry for Science and Education (Grant DSP.2.1.1.702) and by RFBR Grant # 07-05-00685.