Retreat and advance subduction processes in the Yamansu-Central Tianshan arc (NW China): insights into the long-lasting accretionary orogenesis and final closure of the Palaeo-Asian Ocean in the southern Altaids

Subduction processes of Eastern Tianshan are crucial to understanding the mechanism of the orogenic evolution of the southern Altaids. To identify whether the tectonic setting of the Late Carboniferous or later was continuous subduction, we present a systematic study on Late Carboniferous magmatic rocks exposed continuously in time and space in the Weiya area, which were mainly derived from crustal materials with involvement of mantle-derived materials in a subduction-related setting. Our newly discovered 319 Ma A-type granites imply an extensional environment; 306 Ma diorites were derived from thickened crust. Combined with published data, we propose that rollback of the southward-subducted North Tianshan oceanic plate induced subduction retreating and tectonic extension in the Yamansu-Central Tianshan arc from 324 to 318 Ma. It was followed by advancing subduction from 315 to 301 Ma, during which the crust of the arc was thickened, and much more crustal material was involved in subduction-related magmatism. In the Early Permian, the arc was in an extensional environment followed by a change in the movement direction of the subducting plate, rather than in a post-orogenic setting. The final closure of the North Tianshan Ocean was likely completed in the Middle Triassic.