Structure of lithospheric mantle and its implications for the evolution of major basins in China

Seismic P_n waves sample the top of the upper mantle right beneath the Moho. Because P_n velocity varies with changes in temperature and material composition and P_n anisotropy may indicate the history of mantle deformation, P_n velocity and anisotropy have become an important tool to probe lithospheric structure. The lithosphere mantle P_n velocities of China are characterized by a mosaic of very fast and very slow anomalies, mirroring the heterogeneity of geology at surface. The major basins in the west (Tarim, Junggar, Tuha, Qaidam, and Sichuan basins) have high Pn velocities and small P anisotropy, which suggests that the lithosphere of these basins is cold and strong with little deformation. A large area of North China shows prominent low P_n velocities beneath the Archean basement. Our observations are consistent with rifting, lithospheric thinning, and mantle upwelling in the region. The P_n anisotropy is consistent with a dextral simple shear in the NNE direction in the lithosphere mantle during the last (and ongoing) major deformation period. The locations of gold ore deposits in North China and oil deposits in North China and Songliao basins correlate remarkably well with low P_n velocities of the region, suggesting the metallogenesis and oil formation of the region may be closely related to magma and thermal activity in lithospheric mantle and crust-mantle interaction since Mesozoic and Cenozoic.