Lithospheric deformation in Mongolia revealed by anisotropic Rayleigh wave tomography: Implications for the mechanism of intracontinental orogeny

Abstract

The Mongolian Plateau is situated in the eastern part of the Central Asian Orogenic Belt that was formed during the Paleozoic era. In the Cenozoic era, the plateau has been reactivated, leading to significant topographic uplift, volcanism, and seismic activity. Several destructive earthquakes, ranging from magnitudes 6 to 8, have occurred in the 20th century. But the mechanism of these neotectonics remains unclear. To better understand these processes, we determined S wave velocity and azimuthal anisotropy in the crust and upper mantle under Mongolia using Rayleigh wave dispersion curves. Our findings indicate that the lithosphere is dominated by NW-SE fast velocity directions (FVDs). However, we observed different patterns in two specific regions. The lithospheric anisotropy under the Hangay Dome is weak, suggesting that it is accompanied by significant mantle upwelling under the dome. On the other hand, the FVDs in the Gobi Desert exhibit a circular pattern that wraps around the Ordos Block, which may have been caused by past and present deformation imposed on the stable block. These results offer new insights into the lithospheric deformation and dynamics of the Mongolian Plateau.