Structural deformation features and dynamic mechanism of Neoproterozoic strata in Zhanggongshan area, northern margin of the Jiangnan Orogen

Abstract：Zhanggongshan area is located in the junction zone between Anhui Province and Jiangxi Province. The flysch formation, consisting mainly of continental margin epimetamorphic fine clastic rocks and subordinately of volcanic rocks, is widely distributed in the area. A mass of high precise isotopic dating shows that the epimetamorphic strata might have been formed in Neoproterozoic between 820 Ma and 840 Ma. On the basis of a systematic field investigation, 5 stages of fold deformation were recognized through the analysis of the strata. F1 is the outcrop scale rootless intrafolial fold shaped in tight congruous fold and recumbent fold with original bedding (S0) as he deformation face; F2 is nearly EW-trending open inclined fold and congruous fold with early structural foliation as the deformation face; F3 is the tight congruous fold or inclined fold related to large scale thrust nappe; F4 belongs to penetrative asymmetrical tight shear fold group related to heat uplift of Yanshanian granitic magmas; F5 is a plunging vertical fold distributed near the regional brittle shear strike-slip faults zone. These folds correspond to different tectonic cycles respectively. This paper emphatically describes the geometry, superposition pattern, deformation order and kinematic characteristics of fold deformation, and analyzes the deformation mechanism and geocontinental dynamics.