Tectonic Environment of the Metamorphosed Basement in the Jiangnan Orogen and Its Evolutional Features

There are many different ideas about the forming and evolution of the metamorphosed basement of the "Jiangnan Orogen". This paper tries again to discuss its tectonic types and evolution features, based on regional stratigraphic correlation, volcanic—sedimentary assemblages, tectono-deformation, a large amount of isotopic dating in recent years, the distribution of magmatic rocks and analysis of tectonic environments of muscovite-peraluminous granite (MPG) and cordierite-peraluminous granodiorite (CPG). The writers consider that the "Jiangnan Orogen" can not correlated with the 1100~950 Ma "Grenvillian Orogen" in the formation of the metamorphosed basement and its tectonic evolution. It was the deposits of the continental margin of different blocks (e.g. Yangtze Block and Cathysia Block) after Rodinia Super continent was broken up. They underwent 820~780 Ma "regional" Jinningian movement and reformed the Middle and Late Neoproterozoic continental margin of the Yangtze Oldland. The feature of the "Jinningian Orogen" are as follows: (1) in evolution, it had a strong collision in early stage; then extrusion deformation—relaxation and extension formed different rift basins or rift clastic—volcanic deposits; finally re-collision. (2) In region, it was bounded by shear faults of Hunan—Jiangxi provinces and Poyang Lake—Ganjiang River. The metamorphosed basement of the "Jiangnan Orogen" was formed by three different tectonic environments; a collision of continent to continent of the passive continent margin was formed in the western part (Hunan, Guizhou and Guangxi) and the middle part (northwestern Jiangxi). However, the difference between them in extrusion and extension led to the different tectonic forms. The tectonic environments from active continental island arc and back-arc basins to oceanic-continental subduction collision are the features of the eastern part (Jiangxi, Anhui and Zhejiang Province).