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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).

Arc-arc amalgamation occurs during the evolution of composite orogens at convergent plate margins and plays a critical role in controlling accretionary patterns and processes. The eastern Junggar terrane in the southern Central Asian Orogenic Belt underwent a long-lived subduction-accretion process in the Paleozoic, but whether and how the Yemaquan and Dananhu-Harlik arcs were amalgamated remain debatable. A systematic U-Pb-Hf-O isotopic study was conducted on zircons from Silurian granitic rocks in the Yemaquan arc. The U-Pb dating results suggest that these rocks were emplaced at 433-422 Ma and inherited abundant 536-435 Ma zircons representing a predominant magmatic episode in the Yemaquan arc. Their positive εHf(t) values and young Hf model ages indicate that the Yemaquan arc is dominated by juvenile basement with significant crustal growth during the Neoproterozoic to early Paleozoic. The variations in zircon Eu/Eu*, εHf(t), and δ18O values reveal that the Yemaquan arc experienced remarkable crustal thickening and remobilization at ca. 450 Ma, similar to the northern Dananhu-Harlik arc, and this was followed by extension that initiated at ca. 420 Ma. These features support the amalgamation of these two arcs occurring ca. 450-420 Ma. Integrated with regional data, we correlated this amalgamation event in the eastern Junggar terrane with the orogenic event in the Chinese Altai terrane, and we propose a middle Paleozoic tectonic evolution model in the eastern Junggar-Altai area from arc assembly to dispersal in association with a transition in accretionary mode. This scenario probably took place as a response to plate reorganization during the breakup of the northern margin of Gondwana. [ABSTRACT FROM AUTHOR]