P wave radial anisotropy tomography of the upper mantle beneath the North China Craton

Abstract

AbstractWe present the first P wave radial anisotropy tomography of the crust and upper mantle beneath the North China Craton (NCC), determined using a large number of high‐quality arrival‐time data of local earthquakes and teleseismic events. Our results show a prominent high‐velocity (high‐V) anomaly down to ∼250 km depth beneath the Ordos block, a high‐V anomaly in the mantle transition zone beneath the eastern NCC, and a low‐velocity (low‐V) anomaly down to ∼300 km depth beneath the Trans‐North China Orogen (TNCO). The Ordos block exhibits significant negative radial anisotropy (i.e., vertical Vp > horizontal Vp), suggesting that its cratonic lithosphere has kept the frozen‐in anisotropy formed by vertical growth via high‐degree melting mantle plume in the early Earth. Prominent low‐V anomalies with positive radial anisotropy (i.e., horizontal Vp > vertical Vp) exist beneath the Qilian and Qaidam blocks down to ∼400 km depth, suggesting that the horizontal material flow resulting from the Tibetan Plateau is blocked by the Ordos thick lithosphere. Beneath the eastern NCC, high‐V anomalies with negative radial anisotropy exist in the upper mantle, possibly reflecting sinking remains of the Archean cratonic lithosphere. A high‐V anomaly with positive radial anisotropy is revealed in the mantle transition zone under the eastern NCC, which reflects the stagnant Pacific slab.