East-West Asymmetry of the Deep Lithosphere beneath Northern Tibet Revealed by a 3D Gravity Inversion

The Tibetan Plateau, produced by collision between the Indian and Asian plates in Cenozoic, shows an asymmetric surface topography in the east-west direction, but the mechanism of lithospheric deformation controlling the uplift of plateau is still unclear. This study proposes a new lithospheric density model obtained in a 3D gravity inversion constrained by a tomography model converted to density variations. The results show that there is a significant change in the density structure of the upper mantle in the east-west direction beneath the vicinity of the Jinsha suture (34–35°N). Taking 89°E as the dividing line, the western region shows the obvious low-density anomaly, which may be caused by removal of lower lithosphere and upwelling of asthenosphere material. In contrast, the eastern part shows a high-density anomaly dipping to the south, which may reflect the subduction of the Asian lithospheric mantle beneath Tibet. In summary, the deformation of the deep lithosphere beneath northern Tibet is asymmetric in the east-west direction, in which lithospheric root loss and intracontinental subduction may play important roles in the west and east, respectively.