The Crustal Anisotropy of West Ordos Block and Its Geodynamic Implications

Abstract

Based on the teleseismic records of the dense broadband seismic array, the crustal anisotropy parameters of the west Ordos block and its adjacent regions were determined with P wave receiver functions. The results indicate that the dominant direction of the fast wave is NEE-SWW, N-S in Yingshan block and north Ordos block, N-S in the south Ordos block, and E-W in the Qinling–Dabie orogen belt. The fast wave direction of crustal anisotropy in the north Ordos block is distinctly different from that in the south Ordos block, both well related to the major geological events, such as the Paleoproterozoic continent-to-continent collision between the Ordos Block and the Yinshan Block, the collision between the Western Block and Eastern Block of the North China Craton and the material migration from the Tibetan plateau in Cenozoic. Our results indicate that the crustal anisotropy in the Ordos block preserves the traces of ancient tectonic movements. Combining the results of previous geophysical studies, we presented a crust-mantle interaction model to explain the geophysical observations. The most prominent features of the model are the horizontal eastward expansion of the mantle material in the southern Ordos and the vertical upwelling of the mantle material in the northern Ordos. The different modes of movement of the mantle material led to the deep contrasting structures of north and south Ordos, including the crustal anisotropy. The mantle upwelling also implies that the north Ordos block might be currently experiencing craton destruction.