Closing history of the southern Tianshan oceanic basin, western China: an oblique collisional orogeny

Abstract

The Tianshan (Tien Shan) Range is an important Paleozoic collisional orogenic belt and the key to understand the central Asia tectonic evolution. This paper integrates our research results with the existing Chinese and international literature on sedimentology, geochemistry, isotopic geochronology, paleontonology and paleomagnetism of the Tianshan and Tarim regions to propose that the oblique collision may have played an important role in the late Paleozoic closing of the southern Tianshan oceanic basin. As a result of the Sinian (latest Proterozoic, younger than 800 Ma) continental extension and rifting process, the Tarim and Yili blocks separated from their parent continent in the Late Cambrian–Ordovician. The southern Tianshan oceanic crusts between the two blocks subducted northward beneath the southern margin of the Yili block in the Silurian. During the Devonian–Early Carboniferous, the Tarim block rapidly drifted to the north and rotated about 46° clockwise. This process induced the collision of the Yili micro-continent with the eastern segment (present geographical position) of the Tarim continent in the Late Devonian, and the southern Tianshan oceanic crust evolved to be a west-facing remnant oceanic basin. During the Late Carboniferous–Early Permian, the Tarim block, located within an almost constant latitude range, rotated about 26° clockwise with respect to the Yili micro-continent, which ultimately closed the remnant oceanic basin in a `scissors-like' manner from east to west and completed the Tarim–Yili collision. Subsequent A-type subduction of the Tarim continental crust and lithosphere-scale sinistral shearing generated a magmatic arc on the southern margin of the Tarim–Yili suture zone. The Late Permian–Early Triassic clastics deposited in a peripheral foreland basin developed above the arc.