East-west asymmetry of the deep lithosphere beneath northern Tibet revealed by a 3D gravity inversion

The Tibetan Plateau, formed by the collision between the Indian and Asian plates during Cenozoic, exhibits asymmetric surface topography, crustal deformation, and magmatic activity since the Middle Miocene in the east-west direction. However, the mechanism controlling the uplift of plateau through lithospheric deformation remains unclear. This study proposes a new lithospheric density model obtained by a 3D gravity inversion constrained by a tomography model. The results reveal a significant east-west variation in the density structure of the lithospheric mantle beneath the vicinity of the Jinsha suture (34-35 degrees N). Taking 89 degrees E as the dividing line, the western region (83-89 degrees E), at depth below similar to 100 km, exhibits an obvious low-density anomaly (less than -0.1 g/cm(3)), which may be caused by the removal of lower lithosphere and upwelling of asthenosphere material. In contrast, the eastern part (89-95 degrees E), from Moho to depth of similar to 160 km, shows a high-density anomaly (similar to 0.05 g/cm(3)) 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 exhibits asymmetric features in the east-west direction. In the west, the loss of the lithospheric root may lead to rapid uplift of the plateau and volcanic activity. In the east, intracontinental subduction is accompanied by the activation of large strike-slip faults and the eastward extrusion of related terranes.