Mesozoic deformations of the Dabashan in the southern Qinling orogen,central China

摘要

The Dabashan, a curved tectonic belt in the southern Qinling orogen, was formed as a result of the collision of the Qinling micro-plate and the Yangtze plate in the Late Triassic. This study shows that the Dabashan experienced multistage structural deformations. Two main deformational episodes are recognized, (1) foreland folding and thrusting due to the Late Triassic collision and (2) structural superposition during the Late Jurassic to Early Cretaceous. The northern Dabashan is typified by imbricate thrust sheets, whereas the southern Dabashan is characterized by occurrence of widespread superimposed folds. The early fold axis is orientated almost due north or NE-SW. The folding propagated southward and south-westward into the Sichuan basin from the Chengkou-Fangxian fault, which separates the southern from the northern Dabashan belts. It is concluded that the southern and northern Dabashan were two distinct domains, at least in early Mesozoic. This interpretation is important for understanding the tectonic evolution of the Qinling orogen and the collisional process of the North and South China plates.