Updated Pn-wave anisotropic tomography and dynamics of the North China Craton

Abstract

We determine detailed Pn-wave anisotropic tomography of the uppermost mantle beneath the North China Craton (NCC) and its surrounding areas by inverting 84,771 manually-picked Pn-wave arrival times of 2864 local earthquakes recorded at 586 seismic stations. Our results reveal significant lateral heterogeneities in both Pn-wave velocity and anisotropy. A low-velocity (low-V) anomaly exists in the uppermost mantle north of the Ordos block, indicating that the lithosphere has been partially destroyed there, probably associated with the eastward extrusion due to the India-Asia collision and/or mantle upwelling caused by the northwestward deep subduction of the Pacific plate. Low-V anomalies appear in the central NCC, being affected by the westward deep subduction of the Pacific plate. High-velocity (high-V) anomalies with a roughly E-W fast propagation direction (FPD) exist on the eastern and western sides of the North China basin (NCB), which may be remnants of lithospheric mantle delamination due to the underplating of basaltic magma. A low-V anomaly with a nearly N-S FPD exists under the central NCB, reflecting compressional deformation there. In the middle segment of the Tanlu fault zone, a high-V anomaly exists to the west and a low-V anomaly appears to the east, whereas the pattern of velocity anomalies is opposite in the southern segment. These results suggest that the NCC destruction could be caused by combined effects of lithospheric delamination and thermal erosion.