Crust and upper mantle structures of the North China Craton from Eikonal tomography and shear velocity inversion

Abstract

Using the vertical component seismograms of 1583 events recorded by 1712 broadband stations in the SeisDmc and the ChinArray projects, Rayleigh wave phase velocities at 20–160 s periods of the North China Craton were estimated through Eikonal tomography. Phase velocities at 8–50 s periods and group velocities at 10–140 s periods from previous studies were included as an augmentation of our Rayleigh wave velocities dataset. The dispersion curves for phase and group velocities were inverted together for a 3-D Vs model. Our model demonstrates remarkable variations in crustal thicknesses and upper mantle velocities from the west to the east, indicating different evolutionary processes since the Cenozoic rejuvenation. Significant lateral inhomogeneities in the Trans-North China Orogen suggest that the lithosphere under the central segment is less modified during the Phanerozoic than that below the rest portions. The low velocities in the upper mantle below Datong volcanoes may originate from a hot upwelling of asthenospheric materials associated with a rifting process under the northeast margin of Ordos. Our model supports the inference that the southern and northern parts of the Weihe-Shanxi Rift System are experiencing different rifting mechanisms. The southern part experienced a long history of extension and complicated rifting processes triggered by the early uplift of the Tibetan plateau. The opening of the northern segment is a combined effect of ongoing asthenospheric upwelling and the anticlockwise rotation of the Ordos block.