Arc-basin System And Tectonic Paleogeographic Configuration In Eastern Jiangnan Orogenic Belt

The early-middle Neoproterozoic(950?810 Ma)of the eastern Jiangnan Orogenic Belt has complex stratum structure.It outcrops a series of shallow metamorphic sedimentary-volcanic series,granitic pluton and two important ophiolitic mélange belts,which is crucial for understanding the tectonic evolution of whole Jiangnan Orogenic Belt and Precambrian geological evolution of south China.This paper is dedicated to find out the stratigraphic correlation and tectonic evolution pattern of the early-middle Neoproterozoic in eastern Jiangnan Orogenic Belt.In the framework of the isotope chronology,combine with tectonic stratigraphy,sedimentology,geochronology and rock geochemical methods,researched the age of stratigraphic and stratigraphic correlation,tectonic attribute,and tectonic paleogeographic pattern.The main conclusions and innovativeresults were listed as follows:We use LA-ICP-MS zircon U-Pb dating obtained the age of welded volcanic tuff from the Wannian Group in Dexing area is 843.8±5 Ma;LA-ICP-MS detrital zircon U-Pb dating obtained the youngest peak age of sandstone from the Chentangwu Formation,“Pingshui Group” in Pujiang County is 828±3.8 Ma;Zircon SHRIMP U-Pb dating of dacite volcanic from the Jingtan Formation is 815.1±7.1 Ma;Zircon SHRIMP U-Pb dating of intermediate-acidic welded volcanic tuff is 824±9 Ma from the Changkeng Formation in south Anhui Province.They are the mid-Neoproterozoic strata.Reshape the stratigraphic sequence of the Likou Group in southern Anhui Province,the Shuangqiaoshan Group in northwestern of Jiangxi Province and the Luojiamen Formation in the western Zhejiang Province.There is a set of thick mudstone in the lower of Niuwu Formation,Likou Group.This stratum may correlate with the Shangli Formation,Shuangqiaoshan Group and the Yangtianping Formation in Lushan area.Through the field investigation,we compared the above strata,and dated these strata age at 850?820 Ma,the middle Neoproterozoic.Based on these newly high-quality ages,combined with previous data,the isochronous stratigraphic correlations of the early-middle Neoproterozoic strata have been refined.And also,two set of the volcanic-sedimentary system are discovered and confirmed: the Shuangxiwu Group and the Wannian Group,“Pingshui Group”.This paper study the sedimentology and geochemical of the Wannian Group,the“Pingshui Group” in Pujiang County,the Likou Group,the Shuangqiaoshan Group,the Luojiamen Formation,the Jingtan Formation and the Changkeng Formation.The results show that the Wannian Group and the “Pingshui Group” are formed in volcanic arc;the Huansha Formation in the Likou Group are formed in back-arc basin;the lower of Niuwu Formation in the Likou Group are formed in marginal-sea basin;the upper of Niuwu Formation in the Likou Group are formed in peripheral foreland basin;the Kengkou Formation,Shatan Formation and Shangli Formation in the Shuangqiaoshan Group are formed in marginal-sea basin;the Yishan Formation in the Shuangqiaoshan Group are formed in peripheral foreland basin;the Luojiamen Formation are formed in marginal-sea basin;the Jingtan Formation and the Changkeng Formation are formed in closed marginal-sea basin,the tectonic feature of Jingtan Formation is volcanic arc and the Changkeng Formation is its corresponding forearc basin.Through summarizing the studying results of other geologists on the Jiangnan Orogenic Belt,the latest high precise isotope geochronology data and tectonic attribute attained by this thesis,the early-middle Neoproterozoic system tectonic paleogeographic configuration and tectonic evolution pattern of the eastern segment of Jiangnan Orogenic Belt was built.