The styles and dynamics of thrust in the south of the Middle-Lower Yangtze River area, China

The study on the tectonics in south of the Middle-Lower Yangtze River area has confirmed that there occurred one thrusting in the Early Yanshanian (J(1)-J(2)). The folds and faults are characterized by some transitions perpendicular to or parallel to strike of the structural belt. Perpendicular to the strike, the thrust motion senses records of the top-to-north thrusting, resulting in root belt, central belt and front belt from SE to NW. The thrust styles from the root belt to the front belt vary from thick-skinned tectonics to thin-skinned tectonics. The root belt develops a lot of imbricate thrust faults with steep-dipping angles, which converge to deep-seated regional detachment fault between the cover and the basement. However, in the central belt, faults styles mainly consist of imbricate or duplex thrusts with lower dip angles and the deep-seated regional detachment layer shallower than that of the root belt, including a Silurian-involved detachment. The thrust tectonics of the central belt has no remarkable asymmetry, developing a -like or "Omega" - like style of folds. In the front belt, there are a series of imbricate faults accompanying with abundant opposite-directed faults and overturned folds, and the major thrusting detachment lies in the weak layer of Silurian and Triassic. Parallel to the strike, the thrusting is different between in the Middle Yangtze River area and in the Lower Yangtze River area. In the central and front belts of the Middle Yangtze River area, Silurian to Triassic strata are involved in folding and faulting, while in the middle and front belt of the Lower Yangtze River area, abundant Sinian to Cambrian strata are mainly involved in thrusting. The front belt mainly develops some asymmetric overturned folds in the Middle Yangtze River area. However,, the corresponding tectonic zone in the Lower Yangtze River area develops -like and "Omega" -like of folds. In the Middle Yangtze River area, the fold styles display chevron synclines from the root to the front belt. While in the Lower Yangtze River area, the fold styles from the middle to the front belt are chevron anticlines rather than chevron synclines. In addition, the depths of thrusting detachment are obvious different between in the Middle Yangtze River area and in the Lower Yangtze River area As for the deformation dynamics, the thrusting of the Middle and Lower Yangtze River area in the Early Yanshanian is related with the subduction of Paleo-Pacific Plate to the East-Asian Continent. The differences of thrust styles may be a contribution of the differential J(3)-K-1 uplift processes resulting from the Ganjiang Strike-slip Fault. To the east of the Ganjiang Fault, the Lower Yangtze River area uplifted and eroded to result in denudation of deep-level thrust tectonics. While to the west of the Ganjiang Fault, the thrust tectonics remain original appearance of shallow-level structures. It shows that the Gangjiang Fault is a significant boundary. This model is consistent with a viewpoint that the East Asia area belongs to an Andeans-type continental margin during J(3)-K-1.