Upper mantle seismic anisotropy beneath the western and central North China Craton

Abstract

We estimate over 2,000 shear wave splitting parameters from 84 teleseismic earthquakes recorded at 465 temporary broadband stations distributed over the western and central North China Craton to constrain lithospheric deformation and mantle flow. In the interior of the Ordos Block, the W-E trending fast polarization directions with small delay times are indicative of stable terrane, where a thick Archean cratonic keel has been imaged. The dominant W-E fast orientations with relatively large delay times observed in southern Trans-North China Orogen show a systematic directional deviation of ~30° from the absolute plate motion (APM) direction and are explained by a combined effect of APM-induced mantle fabric and a mantle flow around the southeast edges of the Ordos Block. The prominent rift-orthogonal fast orientations beneath rifts to the northern Ordos Block imply the existence of active mantle flow. Also, it is inferred that a mantle plume is responsible for generating the parabolic fast direction pattern beneath the Datong Volcano.