P Wave Anisotropic Tomography of the SE Tibetan Plateau: Evidence for the Crustal and Upper-Mantle Deformations

The upper crust in the SE Tibetan Plateau is rotating around the eastern Himalayan syntax clockwise, and the western margin of the Yangtze Craton has been involved in the active tectonics. However, it is still unclear whether and how the deep crust and upper mantle respond to the plateau expansion. In this study we present a high-resolution three-dimensional model of P wave velocity tomography and azimuthal anisotropy in the crust and uppermost mantle beneath the SE Tibetan Plateau determined using traveltime data recorded by a dense seismic network. Widespread low-velocity zones are revealed around a high-velocity body in the deep crust and uppermost mantle beneath the southwest Yangtze Craton, where fast-velocity directions of the azimuthal anisotropy are mostly parallel to the contour lines of the surface topography and the Moho depth along the plateau margin. These results indicate that gravitational potential plays an important role in the crustal and uppermost-mantle deformations in the SE Tibetan Plateau. Meanwhile, the shallow crust may drop down to the deep crust and drive the ductile deep-crustal material to intrude into the adjacent regions. The extruded crust is trapped in a deep-crustal corner and obstructed by the surrounding strong blocks. The trapped crustal material may rise up, causing significant uplift and high heat flow at the surface.