Constraints of middle-late Permian granites in Eastern Inner Mongolia on the final subduction of the Paleo Asian Ocean

The Xilinhot region, located in the eastern segment of the Xingmeng orogenic belt, represents a key area for investigating the evolutionary history of the Paleo-Asian Ocean due to its close association with Late Paleozoic subduction–accretion processes. However, significant controversy remains regarding the final timing of the Paleo-Asian Ocean’s evolution and closure, resulting in divergent interpretations of the Permian tectonic setting in this region, including models of subduction, post-collisional extension, and intraplate stretching. In this study, we conducted an integrated analysis of zircon U-Pb geochronology, whole-rock geochemistry, and zircon Hf isotopes of the Narendle granodiorite to constrain its petrogenesis and tectonic setting. Combined with regional Late Paleozoic to Early Mesozoic magmatic records, our results refine the tectono-magmatic evolution of the Xilinhot area and provide critical geological constraints on the closure timing of the Paleo-Asian Ocean. The Narendle granodiorite yields weighted mean zircon U-Pb ages of 266.7 ± 1.8 Ma and 255.2 ± 2.0 Ma, indicating magmatic emplacement during the Middle-Late Permian. Geochemically, the granodiorite is high-K calc-alkaline and meta-aluminous, enriched in Rb, Th, and U, and depleted in Nb, Ta, and Ti, consistent with arc-related magmatism in a subduction setting. Zircon Hf isotopic compositions show positive εHf(t) values (+ 8.5 to + 11.4) and young two-stage model ages (tDM2 = 561–748 Ma), suggesting derivation from partial melting of juvenile ferromagnesian lower crust. Integrating regional ophiolitic remnants, bimodal volcanic rocks, back-arc basalts, stratigraphic data, and the Late Permian zircon U-Pb age of the Narendle granitoid in this study, we infer that the Paleo-Asian Ocean remained in a subduction regime during the Middle-Late Permian, with the minimum age of this subduction constrained to 255 Ma. The Paleo-Asian Ocean ultimately closed between 255 Ma and 250 Ma.