Late Carboniferous Closure of the South Central Tianshan Ocean and the Implications for the Final Assembly of Pangea: New Depositional and Geochronological constraints from an Upper Carboniferous–Permian Stratigraphic Boundary marking the marine-to-t

The assembly of Pangea was largely complete by the Late Triassic, but the collision timing between the southern Central Asian Orogenic Belt (CAOB) and the Karakum-Tarim and North China cratons—specifically the closure of the South Central Tianshan Ocean—remains debated. We addressed this by integrating sedimentological analysis and detrital zircon U–Pb geochronology of the Upper Carboniferous Kangkelin Formation in southern South Tianshan. The formation records a deepening-upward marine sequence transitioning to shallow, high-energy settings with increasing terrigenous input, indicating a tectonic shift from subsidence to uplift and deformation. Detrital zircon ages range from 2500 Ma to 300 Ma, with prominent peaks at 420–440 Ma and secondary peaks at 300–340 Ma, 790–930 Ma, and 1000–1200 Ma. Geochemical proxies suggest magmatic sources from subduction-related arcs at 390–490 Ma and 300–345 Ma. The youngest zircon population (∼300 Ma) constrains deposition into the earliest Permian, and Late Carboniferous zircons from the Yili–Central Tianshan arc directly date ocean closure. We propose that the upper Kangkelin Formation represents distal foreland deposits formed during Late Carboniferous continental collision, providing new constraints on ocean closure and continental accretion in the CAOB.