Deformation features of the mid-upper crust of the Dabie orogenic belt—a case study of the Indosinian-early Yanshanian tectonic deformation in the Zhangbaling area

Abstract： The Zhangbaling tectonic belt is a part of the Dabie orogenic belt and an outcrop area of the mid-upper crust of the belt. By using the combined tectonic and stratigraphic method to analyze the l∶50000 geological mapping data of the Zhangbaling area and make structural analysis of the typical cases, the following new ideas have been got： there is no boundary of strong tectonic movement between the Zhangbaling Group-complex (Pt2～3) and the Nanhuaan-Ordovician or strata above them, and as a component part of the Dabie orogenic belt, the group-complex underwent strong deformation； in the Indosinian-early Yanshanian there mainly occurred three phases of tectonic deformation, i.e. a series of WNW-and nearly E-W-trending tight congruous folds in the early stage, a ductile shear zone in the middle stage, and the mainly NNE-trending, broad folds accompanied by SE-vergent overthrusting in the late stage. The superimposition of the three phases of deformation formed the basic tectonic framework of the area. Folding and overthrusting (front sliding) took place in the mid-upper crust (include sedimentary cover) concomitantly with subduction of the Yangtze block beneath the North China block and their collision. The three phases of deformation represent a process of progressive deformation.