Paleozoic tectonic evolution of the Tianshan Orogen, northwestern China

Abstract

The Chinese Tianshan orogenic belt which extends west-east for about 1500 km is one of the most important Paleozoic orogenic belts in central Asia. It includes parts of the Tarim, Yili-Central Tianshan and Junggar plates, which are microcontinental blocks with Precambrian basements and Meso-Cenozoic depositional covers. The Tarim plate is separated from the Yili-Central Tianshan plate by the Southern Central Tianshan suture (Early Carboniferous). Ophiolitic melanges and blueschists are widespread in this suture and are believed to be produced by the collision between a passive continental margin on the north side of the Tarim plate and an active continental margin on the south side of the Yili-Central Tianshan plate. The collision occurred at the end of Early Carboniferous. The Yili-Central Tianshan and the Junggar plates are separated by the Northern Central Tianshan suture, also considered as an Early Carboniferous collisional zone, along which the Middle Ordovician ophiolitic melanges, blueschists and Late Devonian-Early Carboniferous ophiolites are exposed. In early Paleozoic times, the subduction of the paleo-Junggar ocean took place in an active margin on the north side of the Yili-Central Tianshan plate along the Northern Central Tianshan suture. At the end of Early Carboniferous, the north side of the Yili-Central Tianshan plate collided with the North Tianshan Arc along this suture. The paleo-oceanic crust in the Tianshan and adjacent region was entirely consumed at the end of Early Carboniferous. Meanwhile, the Tarim, Yili-Central Tianshan and Junggar plates were accreted to Eurasia. Epicontinental sediments were then deposited throughout the Tianshan region during the Middle-Late Carboniferous times. In the Early Permian, Tianshan began to uplift with accompanying volcanic eruption and granitic intrusion. The uplift was accelerated in the Late Permian and continental molasse was extensively deposited.