Seismic imaging of the crust and upper mantle beneath the North China Craton

Abstract

We determined three-dimensional (3D) P-wave velocity structure down to 600 km depth beneath the North China Craton using 149,054 arrival times from 7940 local and regional earthquakes, and 193,085 data from 12,657 teleseismic events, which were recorded by 585 seismic stations in our study region. Our tomographic images show some new features. Prominent low-velocity (low-V) and high-velocity (high-V) anomalies are imaged beneath the North China Basin, Trans-North China Orogen, and the cratonic Ordos Block. A lithospheric root of over 250 km thick is imaged clearly beneath the Ordos block. A high-V anomaly which may represent the subducting Pacific slab is imaged in the mantle transition zone beneath the eastern edge of the study area. A few other high-V zones are also imaged in the deep portion of the upper mantle, which may reflect the stagnant Pacific slab and detached Archaean continental lithosphere. Two prominent low-V anomalies are imaged beneath the North China Basin, which may reflect asthenospheric upwelling associated with the deep subduction of the Farallon and Pacific plates since late Mesozoic. We consider that the lithospheric thinning of the eastern part of the North China Craton was caused by the long-term replacement, metamorphism, and chemical and thermal erosion of the ancient lithosphere by the hot asthenosphere.