Plate Movement and Crustal Evolution of The Jiangnan Proterozoic Mobile Belt, SOUTHEAST CHINA

It is still in argument, whether the plates existed and their movement controlled the tectonics of earth crust during Proterozoic time. In this paper the authors present an example of the middle-late Proterozoic plate movement and the result thereof discolsed in Southeast China. The Jiangnan Proterozoic mobile belt is located in the vast areas from the Kuaiji Mountains and the Longmen Mountains in east Zhejiang Province, through the border mountains of Zhejian, Anhui and Jiangxi Provinces, the Poyang Lake in north Jiangxi Province and the Dongting Lake regions in north Hunan Province, and the Xuefeng Mountains in west Hunan Province, to the Jiuwandashan Mountains in north Guangxi Zhuang Autonomous Region, roughly corresponding to the Chiangnania of Huan (1945), structurally in the conjunction between the Yangzi platform and Southeast China, where the Caledonian foldbelt forms a striking arcuate tectonic zone. Since the 1970s the present authors have devoted themselves to making a research on rock types, sedimentary formations, and tectonic evolution of the Jiangnan Proterozoic region in terms of the plate tectonic concept, and they suggest that the Southeast China oceanic plate subducted toward the Yangzi continental plate during Proterozoic time, and the Jiangnan Proterozoic trench-arc-back arc basin system was originated. This tectonic system experienced the Dong'anian, the Laokedongian, and the Xuefengian orogenies. In the light of analysis of the sedimentation and tectonic setting of the Sibao Group, the oldest exposed strata in the study area, it is revealed that the border region between the Yangzi continental crust and the Southeast China ancient oceanic crust was a passive continental margin during the early stages of the Dong'anian tectonic cycle. In the course of the Dong'anian cycle, the subduction of the Southeast China oceanic plate against the Yangzi continental plate took place, and consequently an embryo of the Jiangnan Proterozoic trench-arc-back arc basin system appeared. In the Xuefengian cycle, the Southeast China oceanic plate subducted toward the Yangzi continental plate inherently or newly in different parts of the island arc. The Xuefengian orogeny swept across all strata of trench-arc-back arc basin system of the Dong'anian and the Xuefengian cycles, producing a huge anticlinorium belt and giving rise to a regional metamorphism of the greenschist facies. Finally, huge granitic batholiths were emplaced, and a granitic and gneissic layer representing a continental crust of the Jiangnan Proterozoic mobile belt was formed.