Newly discovered Devonian volcanic rocks occur on north margin of the Yili Plate, western Tianshan, including rhyolite, dacite and a small amount of andesite. The geochemical characteristics indicate that the rocks may be partial melting of the upper crust, with the source composed of plagioclase and hornblende, also show their affinity with the continental margin arc, this is consistent with the Early Carboniferous island arc setting in the western Tianshan. That is to say, the Junggar Ocean southward subducted to the Yili-Central Tianshan Plate in the Late Devonian-Early Carboniferous Period, forming island arc magmatic belt in northern margin of the Yili Plate.