Abstract:

The adjacent area between Anhui and Jiangxi is located in the northern margin of the eastern section of Jiangnan orogenic belt, in which Shuangqiaoshan Group is widely distributed in a large-thickness and low-grade greenschist-facies metamorphic flysch formation which is given priority to with argillaceous-arenaceous metamorphosed fine clastic rocks and contains a small amount of volcanic rocks. Synthesizing analysis of rock assemblages and sedimentary structures shows that Shuangqiaoshan Group may be formed in a set of volcanic-terrigenous clastic rocks which can be divided into four stages of sedimentary facies about the bathyal-shelf margin slope, neritic shelf, shelf slope and shelf slope-shelf facies under tectonic background of continental margin island arc, indicating the shrinking-closing stage of the basin evolution during the period. The proximal source region and discontinuous incomplete Bouma sequence of Hengyong Formation and Anlelin Formation, mainly generated by turbidity current and few by sandy debris flow, respectively formed during the northward limited subduction process of the lithospheric fault block in South China with oceanic crustal sea areas, and after that under ocean-basin thinning regressive environment in Neoproterozoic. From the perspective of volcanism with sedimentation co-evolution on the relationship between the sedimentation and tectonic analysis, the volcanic activity resulted from oceanic crust subduction may be started from southwest of the study area. This study provides the important evidence for the geotectonic evolution of the Neoproterozoic in the adjacent area between Anhui and Jiangxi from the aspect of the sedimentary stratigraphy.

Key words: Jiangnan orogenic belt, Shuangqiaoshan Group, sedimentary sequence, sedimentary environment, Anhui, Jiangxi