Characteristics of the Dabashan fold-thrust nappe structure at the southern margin of the Qinling

The huge Dabashan thrust nappe structure on the southern margin of the Qinling orogenic belt mainly formed by long-continued combined action of Late Triassic plate subduction and collisional orogeny of the Qinling orogenic belt and intracontinental orogeny since the Meso-Cenozoic. Detailed field and laboratory studies indicate that the Dabashan fold-thrust nappe structure may be divided into the northern Dabashan thrust nappe structure and the southern Dabashan thrust nappe structure with the Bashan arc-shaped thrust fault as the boundary. The former consists from north to south of the Ankang-Wudang nappe, Ziyang-Pingli nappe, Gaoqiao-Zhenping nappe and Gaotan nappe. The southern Dabashan thrust nappe structure is subdivided into the foreland thrust fold belt in the north and foreland fold belt in the south with the Zhenba-Yangriwan fault as the boundary. The northern Dabashan thrust nappe structure mainly resulted from overlapping and modification of the Indosinian collisional orogeny and Yanshanian intracontinental thrusting, while the southern Dabashan thrust nappe structure is the product of Yanshanian progressive deformation. The northern zone is characterized by intense folding and thrusting, while the southern zone by folding. The folds are tight and complex in the north and become gentle thin-skin structure southward progressively. The thrusts propagated southward in terms of the time sequence.