Palaeocurrent Direction And Detrital Zircon Provenance Of Triassic Bayan Har Group In Songpan-ganzi Basin

The Songpan-Ganzi Basin is located in the southwestern part of China.It is adjacent to the East Kunlun orogenic belt and the Qinling-Dabie orogenic belt on the northen.And to the east,the Longmenshan thust nappe structural belt is between the basin and Yangtze plate.On the southern of the basin is link to the Qiangtang block by Jinshajiang suture belt.The basin is like a huge inverted triangle,which contains a huge thick Triassic sedimentary.The analysis of the sediment source has always been the focus of scholars' debate in recent years.This paper analyzes the strata of Bayan Har mountain group from the paleocurrent and the U-Pb age of detrital zircon.The paleocurrent information of this paper is based on the combination of field collection and previous data.After processing,two paleo flow patterns are obtained.Through the analysis of the paleocurrent data,we found that the northern part of the basin mainly exists the paleo flow of North West,north-east to the south West and south east.And the northeastern part of the basin has the paleo flow of north East to south west.In the south of the basin,near the Yidun arc,the paleocurrent is mainly south,the south east to the north and the north west.It is also found that there is a converging phenomenon of paleo currents within the basin.The center of convergence is in the Huashixia-Yushu area.It is considered that the area is relatively low in Triassic,and it is also considered as a sedimentary center in the basin.In addition,two sets of samples were tested,and 214 data points were tested for U-Pb dating.The data show that most zircon Th/U>0.3 are magmatic zircon.The sample 20110808 has four age groups: 200-320 Ma,380-550 Ma,700-1000 Ma,1700-2000 Ma.And the sample 20120801 also has four age groups: 214-330 Ma,390-520 Ma,1700-2000 Ma,2400-2600 Ma.Through comparative analysis,the zircon from the 200-330 Ma and 380-550 Ma ages comes from the eastern Kunlun orogenic belt and the Qinling orogenic belt.The zircon from the 700-1000 Ma age section mainly comes from the Qinling orogenic belt and the Dabie orogenic belt,and the zircon from two ages of 1700-2000 Ma and 2400-2600 Ma mainly comes from the North China plate.There is no zircon from Yangtze plate has been found.Therefore,this paper thinks that the mainly source areas of the Songpan-Ganzi basin are the East Kunlun orogenic belt,the Qinling orogenic belt,the Dabie orogenic belt and the North China plate.In addition,during the 237-206 ma period,the Yidun arc had relatively intense magmatic activity,which may have provided some clastic materials for the southern part of the basin.Based on the detrital zircon data and the previous research data collected by the authors,this paper uses the accumulated zircon age probability curves summarized by Australian scholar Cawood,and finds that the structural background of the SongpanGanzi Basin is dominated by the collision environment.