S-Wave Velocity Structure of the Crust and Upper Mantle beneath the North China Craton Determined by Joint Inversion of Rayleigh-Wave Phase Velocity and Z/H Ratio

Abstract

Abstract The North China craton (NCC) is one of the oldest craton in the world. Since the Cenozoic, the NCC has undergone severe lithospheric thinning, accompanied by extensive crustal deformations and volcanic activities. To better understand the mechanisms of the crustal and lithospheric deformations and intraplate volcanisms, we construct a high-resolution 3D S-wave velocity model for the NCC by jointly inverting Rayleigh-wave phase velocity dispersion and Z/H ratio measurements. Across the NCC, our model reveals significant lateral variations. In the shallow crust, prominent low-velocity anomalies associated with thick sediments are resolved in the Bohai Bay basin, and the Ordos basin and its surrounding grabens. Meanwhile, our model also shows that sediments are thin or even missing in the southeast of the Ordos basin and other orogens in the study area. The sedimentary structures of the Bohai Bay basin and the surrounding grabens of the Ordos basin may be the superficial response to the subduction of the Pacific plate and the northeastward push of the Tibetan plateau, respectively. Under the Datong volcano, our model reveals an integrated low-velocity anomalies from the mid-to-lower crust to the mantle, which verifies that the Datong volcano has a deep origin. Besides, the low-velocity zone beneath the eastern NCC (ENCC) connects to the low-velocity anomalies under the Datong volcano in the upper mantle. Combining the previous studies, we further propose that the asthenospheric upwelling of the Datong volcano and the subduction of the Pacific plate may jointly contribute to the lithospheric thinning of the ENCC.