The Collage Process of the Western End of the Carboniferous-Permian Bogda Intra-oceanic Arc in North Tianshan and the Yili-Central Tianshan Island Arc

The Central Asian Orogenic Belt (CAOB) experienced a complex accretionary history; however, the westward extension of the Bogda intra-oceanic arc in the North Tianshan has long remained uncertain. This study presents geochronological and geochemical analyses of granitic porphyry from the northern segment of the Duku Highway, together with U-Pb dating and Lu-Hf isotopic analyses of detrital zircons from sedimentary rocks. Our results confirm that the Bogda intra-oceanic arc extends westward to the northern Duku Highway area and provide new constraints on the timing of its amalgamation with the Yili-Central Tianshan island arc. Samples were collected along the Duku Highway and the Manas River in the North Tianshan, including seven sedimentary rocks and one granitic porphyry dike. Key results include the following: ① Detrital zircons from the northern of the North Tianshan Orogen exhibit a unimodal age distribution and depleted Hf isotopic compositions, indicative of an intra-oceanic arc setting; ② Detrital zircons from sedimentary rocks along the northern margin of the Yili-Central Tianshan island arc exhibit a multimodal age distribution, including Precambrian grains, and some grains display enriched Hf isotopic compositions, suggesting derivation from a crustal source containing ancient continental materials; ③ An arc-related A-type granitic porphyry dike dated at 303.3 ± 3 Ma occurs within the North Tianshan Orogen, possibly representing an extensional event in the intra-oceanic arc. ④ The intra-oceanic arc of the North Tianshan was amalgamated with the Yili-Central Tianshan island arc after the Late Permian and before the Early Triassic. This study demonstrates that a Carboniferous-Permian intra-oceanic arc existed in the North Tianshan, representing the western extension of the Bogda intra-oceanic arc, and its amalgamation with the Yili-Central Tianshan island arc occurred after the Late Permian and before the Early Triassic. These results provide critical evidence for understanding the multi-stage accretionary processes of the CAOB.