Anisotropic Tomography and Dynamics of the Big Mantle Wedge

Abstract

We determine high-resolution 3-D tomographic images of P-wave isotropic velocity, radial anisotropy and azimuthal anisotropy beneath NE Asia down to 800 km depth. Our results show negative radial anisotropy (i.e., Vhorizontal < Vvertical) in the asthenosphere of the big mantle wedge (BMW), which may reflect mineral alignment caused by vertical flow in the asthenosphere. Across the Tanlu fault zone (TLF), the western and eastern parts of the BMW exhibit high and low P-wave velocities, respectively. Combining our tomographic results with surface geological features, we speculate that convection in the BMW includes upwelling asthenosphere beneath the Japan Sea and the Korean Peninsula and downwelling asthenosphere beneath the Songliao and North China basins. The downwelling asthenosphere beneath the two basins is associated with diminishing volcanism and anomalous tectonic subsidence since ∼110 Ma. The great TLF is an important boundary for the BMW structure and dynamics.