Petrogenesis and Tectonic Setting of the Late Permian Granitoid in the East Kunlun Orogenic Belt, NW China: Constraints from Petrology, Geochemistry and Zircon U-Pb-Lu-Hf Isotopes

Permian magmatic rocks are extensively distributed in the East Kunlun Orogenic Belt (EKOB), yet controversies persist regarding the petrogenesis of granitoid and the tectonic evolution of the Buqingshan-A’nyemaqing Ocean (BAO), a Paleo-Tethys oceanic branch. This study addresses these debates through petrological analyses, whole-rock geochemistry, and zircon U-Pb-Lu-Hf isotopic investigations of newly identified granitoids in the EKOB. The monzogranite (MG) and quartz porphyry (QP) yield weighted mean ages of 254.7 ± 1.1 Ma and 254.3 ± 1.1 Ma, respectively. Geochemically, the MG shows metaluminous to weakly peraluminous low-K calc-alkaline I-type granites, characterized by high SiO2, low K2O, MgO, FeOT contents, and marked enrichment in light rare earth elements (LREEs), but depletion in Eu, Ba, Sr, P and Ti anomalies. In contrast, the QP exhibits peraluminous high-K calc-alkaline I-type affinities, displaying high SiO2 but low Na2O and P2O5 contents. It is enriched in LREEs and Rb but displays negative Nb, Sr, P, and Ti anomalies. Zircon εHf(t) values range from −1.6 to 2.6 (MG) and −4.4 to 1.5 (QP). We suggest the MG and QP are derived from the partial melting of the juvenile mafic lower crust, and the MG has undergone highly fractional crystallization. Synthesis of multiscale geological evidence allows us to delineate a five-stage tectonic evolution for the BAO in the EKOB: (1) oceanic basin initiation prior to ca. 345 Ma; (2) incipient northward subduction commencing at ca. 278 Ma; (3) slab roll-back stage (263–240 Ma); (4) syn-collisional compression (240–230 Ma); and (5) post-collisional extension (230–195 Ma).