Moho depth and crustal density structure in the Tibetan Plateau from gravity data modelling

Abstract

Although a large number of geophysical experiments have been performed in the Tibetan plateau and its surroundings, our knowledge and understanding of the uplift and deformation in the Tibetan Plateau caused by the India-Asia collision is still incomplete. Gravity method is inevitable and indispensable tool to investigate the evolution of the Tibetan Plateau due to the environmental complexity. In this study, images of the Moho depth and density disturbances in the Tibetan plateau are derived from the separated regional and local gravity anomalies, respectively. The results show that the Moho depth and density present distinct change from north to south in the central and western Tibetan Plateau, but both are relatively featureless in the eastern region. Moho depth sublinearly increases from the south to north and exceed 70 km at the Bangong-Nujiang suture, interpreted as the downward bending of the Tibetan crust due to the subductions of the Indian plate to the south and Asian plate to the north. The significant low density occurs in the middle and lower crust beneath Himalayas, suggesting the absence of the eclogites under the fast subducting effect of the cold Indian plate. In contrast, the high density may suggest the probable presence of eclogites underneath the Lhasa and Qiangtang terranes, where the mantle convection and thickened crust would provide environment of the high temperatures and pressures for eclogite formation. Low density presents underneath the Jinsha suture, indicating that the partial melting occurs due to the upwelling of asthenospheric material.