Sediment Source Analysis Of The Second Member Of Xujiahe Formation In Northeast Sichuan Basin In Late Triassic

The Qinling Orogenic Belt is the climatic and geographical boundary between the north and south of China in central China,and also the boundary between the North China Plate and the Yangtze Plate.Its tectonic evolution is a very long and complicated process,and its structure and evolution deeply affect the area adjacent to it.The Sichuan Basin is located in the south of the Qinling Orogenic Belt.The development and evolution of the basin are inextricably linked to the Qinling Orogenic Belt.The Late Triassic was the main orogenic period of the Qinling orogenic belt.The Sichuan Basin,on the south side of the Qinling orogenic belt,also experienced a sedimentary facies transition in the northeast,from marine facies to coastal facies.The second member of the Xujiahe Formation is the first stable horizon that appeared in the Late Triassic,and its provenance can well reflect the tectonic events of the Qinling orogenic belt before the Late Triassic,the nature,characteristics,strength,uplift age and uplift speed of the orogen.Therefore,the study of the second member of the Xujiahe Formation is of great significance to the recovery of tectonic events in the Qinling orogenic belt.The thesis is based on the special fund funded by the China University of Geosciences(Beijing)Funding Project "Research on the Coupling Relationship between the Qinling Orogenic Belt and the Basin-Mountain of Northeast Sichuan and South Ordos Foreland Basin" and plate tectonic theory and continental dynamic exploration,taking mountain-basin unity and structural superimposed deformation as the main line of study.In order to explore the response of the second member of the Xujiahe Formation to tectonic events in the Qinling orogenic belt,the sedimentology characteristics and petrology,geochemistry and zircon age of clastic rock samples in five typical sections of the second member of Xujiahe Formation-: Wanyuan Shiguansi section,Tongjiang Nuoshuihetang Erping section,Wanyuan Gujunshan section,Xuanhan Qili section,Dazhu section-in northeastern Sichuan were studied.Through the research on the detrital particle characteristics,geochemical characteristics and zircon age of the second member of the Xujiahe Formation in the paper,combined with previous research and analysis,it is concluded that the source of the second member of the Xujiahe in the Northeast Sichuan Basin mainly comes from the southern Qinling Mountains.The belt,its clastic composition,chemical composition,zircon age,etc.have a good coupling relationship with the structural events of the Qinling orogenic belt.The study of the second member of the Xujiahe Formation can infer the approximate evolution of the Qinling orogenic belt:(1)The basement of the central part of the South Qinling Orogenic Belt was formed in Archean and was earlier than 3292.18Ma;(2)The southern Qinling plate was separated from the Yangtze plate during the Devonian period and merged with the northern Qinling subduction during the Carboniferous period.On the northern margin of the southern Qinling orogenic belt,sediment deposition continued from the Permian to the Early Triassic;(3)During the period of about 228-215 Ma,after the extinction of the Mianluo oceanic crust,the Yangtze plate and the South Qinling plate collided along the Mianlue suture zone in the mid-Triassic;(4)During the Mesoproterozoic and late Paleozoic,the Qinling orogenic belt was relatively stable in structure,and its uplift was relatively gentle,and the whole was relatively stable.