A late Carboniferous transition from subduction to collision: Tectono-sedimentary evidence from southern Junggar, NW China

The Carboniferous to Permian tectono-sedimentary evolution of the southern Junggar area brings new insights into understanding the subduction-collision processes in the northern Tianshan region. Integrating geophysics, geochemistry, and geochronology approaches, this study investigates the Carboniferous-Permian strata in the southern Junggar Basin. The results have revealed three distinct tectono-stratigraphic evolutionary stages, each marked by a distinctive volcano-sedimentary sequence. The Early Carboniferous strata suggest intense volcanic activities in the southern Junggar area. During the Late Carboniferous, the southern Junggar Basin was controlled by normal faulting in an extensional setting, receiving sedimentary inputs from the Junggar terrane. The Lower Permian, unconformably overlying the Upper Carboniferous, was shaped by an extensional regime and is comprised by volcano-clastic sequences that received detritus from the Yili-Central Tianshan block. These findings indicate that a Late Carboniferous forearc basin developed in the southern Junggar area, and it evolved into a post-collisional rift in the Early Permian. This period marked a dynamic shift from bidirectional subduction (rollback) to the detachment of the North Tianshan oceanic slab. We propose that the collision between the Yili-Central Tianshan block and the Junggar terrane, along with the closure of the North Tianshan Ocean, likely occurred in the Late Carboniferous (ca.306-303 Ma).