The P-wave velocity structure of the crust-mantle transition zone in the continent of China

The crust-mantle transition zone (CMTZ) is an important site for mass and energy exchange between the lower crust and the upper mantle. Several types of CMTZ show different P-wave velocity structures corresponding to different rock associations existing beneath the continent of China. (a) The CMTZ beneath the Tibet Plateau exhibits a grid-shaped seismic reflection characterized by random and reticular high and low seismic velocity lamellae. This seismic velocity structure (about 30 km in thickness) was inherited from crustal overthrust and overlapping during the Cenozoic collision between the Indian and Euro-Asian continents. The corresponding crustal movement is still very intense in this region. (b) The CMTZ underneath East China is usually composed of a thinner, strong positive velocity gradient layer. It suggests that the crust is still active in East China after significant lithospheric thinning and thermal accretion. (c) The CMTZ in the tectonic stable regions is characterized by a relatively sharp seismic discontinuity. Such a feature beneath the Ordos basin corresponds to weak crustal movement after a long period of isolation from thermo-tectonic overprinting.