Quaternary deformation at the southeastern margin of the Ordos Block, North China: Inferred from structural analysis of basin-bounding faults

Abstract

The southeastern margin of the Ordos Block (SEMOB) is located at the juncture of the North China Block, the Ordos Block, and the Qinling Orogen. A series of faulted basins has developed in this area since the Cenozoic. The latest focal mechanism solution and stress field analyses indicate that the SEMOB is located at the adjacent regions of present different stress field, although the structural activity and internal mechanisms of this changing remain unclear. In this paper we describe the results of a study into the fault systems and Quaternary deformation between the Linfen and Weihe basins on the SEMOB. Based on the deformation sequences, kinematic analyses and activity timing, we found that the strain field in SEMOB underwent three evolutionary stages during the Quaternary: NW–SE extension in the early Pleistocene, NE–SW extension in the middle Pleistocene, and ca. N–S oblique extension from the late Pleistocene to the Holocene. This evolution of the strain field affected both the geomorphic patterns and the activity of paleo-earthquake events along the SEMOB during the Quaternary. Quaternary extensional deformation in the upper crust along the SEMOB possibly resulted from crust-mantle decoupling, which may be related to eastward expansion of the Tibetan Plateau and subduction of the Pacific and Philippine Sea plates.