The Middle Triassic Turbidite From The Lannigou Gold Ore Deposits: Implications For Sediment Provenance And Tectonic Process

Lannigou gold mining area is located in the north of the Nanpanjiang basin,and the thick of the turbidite in the basin has became the geological research object,but the problems of the turbidites’ provenance and sedimentary tectonic background have been controversial,this study selectes Lannigou area and the southwest of the tail region called Weiruo as the research object,through a lot of field research,the sedimentary and structural characteristics of turbidite are studied in detail;Based on the previous research results of basin palaeo-current,the source direction is roughly determined by bouguer gravity anomaly.Through elemental geochemical analysis and isotopic dating,the provenance and sedimentary tectonic background of the second and third member turbidite of the middle Triassic xuman formation in the study area were comprehensively analyzed,and the following research results were obtained:(1)The sedimentary structures of the second and third member of the Xuman Formation of the middle Triassic in the study area are rich and diverse,mainly manifested as incomplete bauma series.The sedimentary structures are mainly summarized as bedding structure,layer structure and wrap-around structure.(2)Integrated regional geology and gravity data of Nanpanjiang basin,the terrain of the basin is high in the south,low in the north,high in the southeast,low in the northwest and high in the southeast.The anomaly area is divided into two parts with the boundary of Ceheng-Lannigou.There are differences in the gradient changes of gravity anomalies.The basement of the middle Triassic basin in Nanpanjiang basin is high in the east and low in the west,and high in the south and low in the north,and combined with the results of paleo-current researches,it can be roughly concluded that the thick middle Triassic turbidite series fillings in the study area come from the southwest or the south of the basin(3)In the analysis of provenance,the activity level of the main elements in judging the weathering degree of the source area is relatively low,and all of them indicate medium weathering degree.The test results of trace and rare earth elements show that the main parent rocks of turbidite in the study area are felsic or acidic volcanic rocks in the upper crust;Most of the collected samples belong to the magmatic crystallization zircon.The U-Pb ages spectrum of detrital zircons indicate that the turbidite fillings in the second and third member of the middle Triassic Xuman Formation in the study area mainly came from the Song Ma suture belt along the southwest margin of the Nanpanjiang basin,the ailaoshan-babu ocean tectonic belt including the north of the Vietnam block,and the Yunkai block in the southeast of the basin including the Qinfang fold belt.(4)Elemental geochemical results show that the turbidite deposits in the study area are involved in island arc and the sedimentary tectonic environment of turbidite in the study area is continental island arc environment.