Late Paleozoic tectonic framework and evolution in the Jiabaishan area, Qoltag, eastern Tianshan Mountains, Northwest China

The study area experienced the whole process of evolution from the passive to active continental-margin trencharc-basin systems on the northern margin of the central Tianshan old land in the Early Cretaceous. The Aqishan-Yamansu island-arc belt occurred on a wide continental shelf sea in the Visean Stage. The island arc has a large antiform structure, the Yamansu fault belt is a main conduit for volcanic eruption, and the forearc basin was formed in an arc-trench gap. In the early Late Carboniferous, collapse due to spreading .in the back-arc area led to the formation of a synformal marginal basin. At the end of the Late Carboniferous, the Kanggur Ocean on the northern side closed in the form of arc-arc junction, accompanied by emplacement of granitic magma in the arc area. The early Lower Permian was a relaxation stage, when an overlapped downfaulted basin formed in the interarc area and on the southern margin of the back-arc area. In the Late Pennian, the right-lateral strike-shp motion swept the whole region. Finally, tight-lateral slip displacement took place between the large-scale orogenic belt and the block, thus giving rise to the initial basin-range framework as now.