Sedimentation Features,Provencan Analysis And Geological Significance Of Lower To Middle Triassic At Xinghai Area Of West Qinling

The study area is located in the east of the eastern Kunlun orogenic belt,sandwiched between the Nanshan fault in Qinghai and the ammaqing OPHIOLITIC MELANGE belt.The paper is based on the project of "1: 50 thousand regional geological and mineral resources survey in Taxiu trian area,Hainan",and selects the lower-middle Triassic of the study area with the guidance of the theory of plate tectonics and basin-mountain coupling,taking Longwuhe formation as the research object,discussing the sequence characteristics of sedimentarmy strata,features of sedimentary source,sedimentary environment,and further discussed the development of regional tectonic evolution process,which is great significance for the study of regional geology.Based on sedimentary petrology,detrital composition analysis,petrogeochemistry and zircon isotope chronology,The Longwuhe formation reflects the sedimentary characteristics of the inner turbidite fan of the continental slope.Combined with Unconformities,magmatic event,zircon U-Pb isotope chronolog and regional stratigraphic characteristics,it is concluded that the sedimentary epoch should be early-middle Triassic.According to the geochemical study of sandstone,samples of Longwuhe are consistent with the continental island arc environment,which shows the characteristics of near-source accumulation.It is indicated that these samples formed in the tectonic environment of the active continental margin,and the rock in the source area is mainly composed of medium acid arc magmatic rocks and ancient metamorphic basement.Through the Longwuhe group of zircon U-Pb isotope chronolog study,shows the mainly ages of samples are 1332-3702 Ma,611-1241 Ma,403-556 Ma,248-399 Ma,among them,248-399 Ma is the largest proportion of a group,the peak age is 297-267 Ma.In combination with regional geological data,he erosion and proximal sedimentary deposit in ancient eastern Kunlun and qaidam orogenic belt,provides main source of Longwuhe group,the eastern Kunlun and Qilian orogenic belt provides most of the content source,while the eastern Kunlun is the mainly source providing area.In combination with regional tectono-magmatic evolution events and data obtained from this paper,this area has experienced: early paleoproterozoic-neoproterozoic basement formation stage,early Paleozoic tethys ocean evolution stage,late Paleozoic-early Mesozoic ancient tethys ocean evolution and compound orogenic stage,including the ancient tethys ocean expansion phase and ocean basin subduction cut and Liu Liu collision orogenic stage,Mesozoic intracontinental tectonic evolution stage.