Neotectonics around the Ordos Block, North China: A review and new insights

The multiphase intensive intra-continental deformation of the Eurasian continent in the Cenozoic caused by Indo-Asian and Pacific-Asian collisions has been studied extensively. However, its Cenozoic intra-continental deformation process and dynamics remains poorly constrained. The western North China Plate of the Eurasian continent is characteristic of the Cenozoic faulted basin system around Ordos Block, and is a critical region to determine this deformation process. Here, new structural data and fault kinematic analysis, coupled with new geochronological results, delineate a two-stage Cenozoic tectonic evolution in the region, providing new structural evidence to decipher the intra-continental deformation due to Indo-Asian and Pacific-Asian collisions. The first stage is characterized by the formation of faulted basins in the northwestern and southeastern margins of the Ordos Block, dominated by a pure-shear mechanism. This stage further comprises the NW-SE extension spanning the Eocene to Late Miocene (ca. 10.5 Ma), and the subsequent basin inversion triggered by the NW-SE compression during the Late Miocene (ca. 10.5-9.5 Ma). Its tectonism is associated mainly with the far-field effect of the northwestward subduction of the Pacific Plate. The second stage is characterized by the development of the Shanxi and Hetao Basins in the eastern and northern parts of the Ordos Block, respectively, and an intensive mountain-building process in the western part since the Late Miocene (ca. 9.5 Ma), which is connected with a simple-shear mechanism. This stage is furthermore divided into three alternating episodes of shortening and extension events. These resulted predominantly from far-field responses to the northeastward growth of the Tibetan Plateau and partially from the Pacific subduction.