Upper mantle anisotropy and deformation beneath the western Mongolian Plateau revealed by SKS splitting

Abstract

The Mongolian Plateau, as an important geological unit of the Central Asian Orogenic Belt, has experienced extensive deformations in multiple periods since the Proterozoic. In this study, we measured SKS splitting from 114 portable stations to reveal the complicated deformation of the upper mantle under western Mongolia. The predominant NW-SE-oriented fast polarization directions (FPDs) are consistent with lithospheric deformation and asthenospheric flow to the first order. However, the FPDs of the stations close to the Siberian Craton are more parallel to the cratonic margin than those departing from the craton. It indicates that the shape of the rigid Siberian Craton may determine the extent of the present lithospheric deformation and cause the deflection of the asthenospheric flow. Large SKS splitting delay times are distributed in the Hovsgol rift and Gobi-Altai range, implying superimposed past and present lithospheric anisotropy, and the asthenospheric anisotropy as well under the Hovsgol rift. Small delay times in the Hangai Dome indicate the asthenospheric upwelling which causes the uplift of the dome.