GEOCHEMISTRY OF VOLCANIC ROCKS OF THE LOWER PERMIAN WULANG FORMATION IN WULASITAI AREA,XINJIANG

The volcanic rock of Lower Permian Wulang formation,distributed in the Late Paleozoic Awulale rift of Ili-Yisaikehu micro-plate,Kazakhstan-Junggar plate,is the assemblage of continental volcanic rocks and detrital rocks.Intense volcanic activities in the area left thick volcanic accumulation up to 4000 m,which belongs to the middle and upper layers of Wulang formation.The volcanic rocks are dominated by alkali-basic rocks and acidic rocks,characterized by bimodal.Lithogeochemistry shows a tectonic environment of intraplate basalt and continental rift basalt,which is in accordance with its tectonic location.The trachybasalt in the top layer is dated as Early Permian,with 207Pb/206Pb isotopic age of the 285±30 Ma.It is suggested that the volcanic activities of the Late Paleozoic Awulale rift tended to end in Early Permian.Then continental molasse was cumulated in Late Permian,marking the start of stable developing period of intracontinental basin.