Yanshanian fold-thrust tectonics and dynamics in the Middle-Lower Yangtze River area, China
长江中下游燕山期逆冲推覆构造及成因机制

The Middle-Lower Yangtze River area is one of famous copper, iron and polymetallic ore metallogenic belts in China. In this paper, the Middle-Lower Yangtze River area is divided into the five tectonic units: the North China Block, the Dabie Orogenic Belt, the Yangtze Block, the Cathaysia Block, the Middle-Lower Yangtze River Foreland Belt. Furthermore, the Middle-Lower Yangtze River Foreland Belt is subdividied into three subunits: the Baokang-Wuhan-Susong-Chaohu Fold-and-thrust Belt, the Daye-Huaining-Wuhu Mesozoic Depression, the Tongshan-Ruichang-Ningguo Fold-and-thrust Belt. In the Early Yanshanian, the Wuhan-Susong-Chaohu Fold-and-thrust Belt north of the Yangtze River underwent the SE-directed thrusting; while the Ruichang-Ningguo Fold-and-thrust Belt south of the Yangtze River experienced the NW-directed thrusting. South of the Yueyang-Puji-Xianning-Yangxin, the fold styles from north to south varies from chevron anticlines to chevron synclines, and the imbricate thrust faults to the south are more developed. The Jiuling-Mufushan Basement and the basements of the Cretaceous red basins developed many high-angle thrust faults and chevron synclines. The Proterozoic metamorphic rocks are involved in this thrusting, showing a typical thick-skinned structure. In the north of the Yangtze River, the closed asymmetric folds are mostly developed in the Indosinian. The Early Yanshanian thrusting modified the pre-exsiting structures. The deep and shallow structures north of the Yangtze River are coupling. However, the deep and shallow structures south of the Yangtze River are decoupling. The architecture of the upper and lower crust looks like "fish-spur" over the Middle-Lower Yangtze River. These deep structures should be the residual effect of the Indosinian subduction of the Yangtze Block to the North China Block. In the Middle-Lower Yangtze River, the south-directed thrusting should be related to the slow extrusion of the UHP metamorphic rocks in the Dabie Orogenic Belt. However, the northwest-directed thrusting may be related with the Middle Jurassic subduction of the Paleo-Pacific Plate to the Asian Continent.