Southeastward extrusion of the Tibetan Plateau limited by the strong Emeishan large igneous province from earthquake surface wave tomography

Abstract

Active deformation is ongoing in the southeastern margin of the Tibetan Plateau due to the collision of the Indian and Eurasian continents. While large-scale motion of the surface occurs, the nature of deformation at depth remains unresolved. We construct new lithospheric seismic anisotropic (radially and azimuthally) and shear-wave velocity models using fundamental-mode Rayleigh- and Love-wave phase velocity at periods of 20–100 s obtained from the ChinArray experiment to constrain the deformation style of the crust and upper mantle in the southeastern margin of the Tibetan Plateau. The results show that the uppermost mantle (Moho-90 km) underneath the Tibetan Plateau and northwestern part of the western Yangtze block are characterized with NE-SW oriented azimuthal anisotropy, prominent slow velocity and negative radial anisotropy (V_SH < V_SV). We interpret that this seismic pattern reflects the southeastward extrusion of the Tibetan uppermost mantle that may thermally erode the northwestern edge and result in the vertically coherent fabric due to the barriers of the left strong Emeishan large igneous province (i.e., south of the western Yangtze block) dominated by the high shear wave velocities. Low velocity anomaly, N-S trending azimuthal anisotropy, and negative radial anisotropy in the uppermost mantle beneath the eastern Yangtze block are most probably associated with vertical migration of hot mantle material from the lithosphere delamination and/or a branch of the Hainan plume.