Chronostratigraphy And Tectonic Features Of The Dengshan Group In The Northeast Jiangxi Province In China

The tectonic position of the Dengshan group in the northeast jiangxi province is bounded by the jiangshao fault and the northeast jiangxi fault,and is located in the huaiyu region.The study of geological age,the position of the stratigraphic columns and the tectonic setting of the Dengshan group have long existed in various viewpoints,and the previous researches on the group lack of integrity.In recent years,the acquisition of high quality age data and geochemical data has prompted the academic community to further study the Dengshan group from a new perspective..The Dengshan group is adjacent to the ophiolite belt of the northeast of jiangxi province,and the north is in contact with the Wannian group that growing a large number of the magmatic arc volcanic rocks.The structure of the Dengshan group is very special,which is of great scientific significance for the study of the jiangnan orogenic belt.Therefore,in order to find out the relationship between time and space of the Dengshan group,we combination with predecessors' research data and research results,using stratigraphy,geochronology and geochemistry method to consider its characteristics of prototype basin and obtain the following main conclusions and innovations:1)Obtain Gaoshan formation at the bottom of the Dengshan groupbottom tuff zircon SHRIMP U-Pb age of 855.5Ma±5.2Ma.Bazhukeng formation is constrationed by the zircon SHRIMP U-Pb age with the oldest depositional age of 824.9±9.9Ma.The zircon SHRIMP U-Pb age of bimodal volcanic rock in the Yejia formation is798.8±7.8Ma.Determine the age of the Dengshan group at 855.5±8.2?798.8±7.8Ma.2)To optimize the stratigraphic sequence of the Neoproterozoic strata in Jiangxi province.Gaoshan formation and Xikou group,Shuangqiaoshan group,Wannian group and Luojiamen formation are the same stratum.Bazhukeng formation and Pingshui group,Changkeng formation and Hongchicun formation are the same stratum.Yejia formation and Jingtan formation are the same stratum.3)According to the sedimentology and geochemical analysis,Gaoshan formation and Bazhukeng formation are formed in fore arc basin.According to the result of sandstone matrix,Dengshan group and Wannian arc are arc-basin system.The tectonic setting of the Yejia group is the late stage of the collision orogenesis.The Hf isotope characteristics show that the materials of the Gaoshan formation and the Bazhukeng formation originated from the ancient crust,while the Yejia formation originated from the neogenetic crust or the depleted mantle.During the magmatic rise,some materials of the crust were mixed.Through summarizing the researching results of other geologists on the eastern park of Jiangnan Orogenic Belt,the geochronology date and geochemistry date attained by this thesis,the tectonic evolution pattern between 850 Ma and 770 Ma of the eastern of Jiangnan Orogenic Belt was built.