Provenance Analysis Of Lower-Middle Triassic In Gonghe Basin, Qinghai

Researching in Gonghe Basin in the east of Qinghai, not only discovering the property of Gonghe Basin in Early-Middle Triassic period, but also can restore the paleogeography of the region, and has the very important meaning in researching the tectonic evolution of the basin and its periphery. This paper intends to use the method of provenance analysis on provenance researching in Gonghe Basin, and then combination of provenance to discover the nature of the basin based on formations characteristic properties of the Gonghe Basin. First, based on the literature and field study found the eastern and western basins Early-Middle Triassic sediments with different characteristics, sedimentary sequence is also similar to the formation of back-arc basin, which is also similar to the composition of volcanic rocks back-arc basin; and then, according to paleocurrent analysis to determine the provenance from the west, northeast and south; determining from Dickinson triangle graphically the provenance from recycled orogen and magmatic arc, with a back-arc basin sediments the same provenance; geochemical obtained source area tectonic rock are active continental margin and continental island arc volcanic displays its provenance and land-based sources; then again by Heavy Mineral analysis method to determine the provenance from three directions, including the East Kunlun, South Qilian, and Anyemaqen Mountains. Finally, according to the above results, the provenance of Gonghe Basin is mainly from Qilian in northeast, East Kunlun magmatic arc in west, and Anyemaqen Mountains in south(Anyemaqen Mountains already uplift in this period), in the period the East Kunlun is a volcanic period, the northeastern part of Qilian continental sediment supply to the basin area, and there was no any ocean around the basin. There was volcanic facies in the west and continental sedimentary in the east, and the location of paleogeographic was just between the volcanic arc and the shallow sea of orogenic belt, and then found it was typical sedimentary characteristic of back-arc basin according to research in filling sequence of sedimentary stratum, so we define the Gonghe Basin was a back-arc basin in the Early-Middle Triassic period.