Analysis of structural deformation in the North Dabashan thrust belt, South Qinling, central China

摘要

The North Dabashan thrust belt, which is located in South Qinling, is bounded by the Ankang fault on the north and the Chengkou-Fangxian fault on the south. The North Dabashan thrust belt experienced multiple stages of structural deformation that were controlled by three palaeostress fields. The first structural event (Middle Triassic) involved NNW-SSE shortening and resulted in the formation of numerous dextral strike-slip structures along the entire Chengkou-Fangxian fault zone and within the North Dabashan thrust belt, which suggests that the South China Block moved to the NW and was obliquely subducted under the North China Block. The second structural event (Late Triassic-Early Jurassic) involved NE-SW shortening that formed NW-SE-trending structures in the North Dabashan thrust belt. The third structural event (Late Jurassic-Early Cretaceous) involved ENE-WSW or nearly E-W shortening and resulted in additional thrusting of the North Dabashan thrust belt to the WSW and formation of the WSW-convex Chengkou-Fangxian fault zone, which has an oroclinal shape. Owing to the pinning of the Hannan massif and Shennongjia massif culminations, numerous sinistral strike-slip structures developed along the eastern Chengkou-Fangxian fault zone and were superimposed over the early dextral strike-slip structures.