The Evolution Of Carboniferous—Triassic Basin In Tuolai River On The Northern Margin Of Center Qilian Block

The research area is located in the northeastern margin of Qinghai-tibet plateau, which is located between the North Qilian orogenic belt and the north margin of Middle Qilian micro landmass. The research area in the Carboniferous-Triassic Stratum mainly integrated conformity between the departments and series, and the sedimentary formation is given priority to a shallow sea—marine-terrigenous—continental stable construction facies. The analytical methods include the zircon U-Pb chronology of structural layer sandstone detritals and the Dickinson triangular diagram of the sandstone compositions systematacially. It has important theoretical significance to the restraint the sedimentary tectonic setting in this period and to restore the nature, sedimentary model and palaeogeographic features of the superimposed basin in the suture zone. And it is alse significant to discuss the tectonic evolution relationship both the tarim and qaidam basin.This paper is separately U-Pb dating for the samples from the southern margin of the North Qilian in late Permian, the northern rim of the Middle Qilian in late Permian and late Triassic. They have the similar age composition and can generally divided into five age groups—2600-2200 Ma, 1900-1300 Ma, 900-800 Ma, 500-400 Ma, 290-250 Ma. Two age groups of 2600-2200 Ma and 1900-1300 Ma include 95 zircons derived from the qilian crystalline basement. The age group of 900-800 Ma include 11 zircons likely derived from the gneissic monzonitic granite rock and the surrounding rocks in south mountain of tuolai. The age group of 500-400 Ma include 37 zircons, which come from the magmatic and metamorphic rocks formed in the orogenic period from the North Qilian orogenic belt and the Middle Qilian active continental margin. The age group of 290-250 Ma include 46 zircons derived from the ancient qilian orogenic belt.The research using the sandstone Dickison triangle illustration in Carboniferous and Triassic formations shows that the sample points in the Yanghugou group of the carboniferous and Jianghe group of the Triassic with high content of quartz fall into the orogenic belt; the sample points of the Daxigou, Hongquan and Zhongshigong group of Permian fall into the cutting arc area and the circular boundary orogenic belt;the sample points of the Xiahuancang and Jianghe group of the early Triassic fall into the circulation orogenic belt; the sample points of the atasi and galede group of the Triassic fall into cutting arc, these two strata with high feldspar content may be related that the provenance of plutonic intrusive rocks have risen to the surface as the material source of sandstone.Finally, the depositional palaeogeographic evolution of this area during the CarboniferousTriassic is overlap from south to north in the late carboniferous, and to the period of PermianTriassic is retreat to the south, the water level is gradually deepen at the end of the Permian.The sedimentary process of the Triassic show a shallow sea-coastal-delta-swamp facies continuously.