Geochronology and Geochemistry of the Wulanwuzhuer Intermediate–Felsic Intrusion from Qimantag Area, East Kunlun Mountains: Implications for Regional Tectonic Evolution

A vast suite of intermediate–felsic intrusive rocks, the Wulanwuzhuer intrusion, which intrude the Jinshuikou Group in the Qimantag area of the Eastern Kunlun Mountains, Qinghai Province, has an unclear formation age and petrogenesis. In this paper, we discuss their formation time, petrogenesis, and tectonic background. Based on detailed field geological surveys, this paper presents zircon U-Pb isotope chronology and petrogeochemistry to identify the genesis of rocks, determine the intrusion age, and explore their tectonic significance. The Wulanwuzhuer rocks are composed of fine-grained granodiorite, gneissic biotite granite and potassic granite. Zircon LA-ICP-MS U-Pb dating of zircon yields an age of 475 ± 2 Ma for the gneissic biotite granite. This indicates a Caledonian formation age, contrasting with the previously assumed Hercynian age. The Wulanwuzhuer rocks show SiO2 contents that vary from 62% to 74%, K2O varies from 4.0% to 5.2%, K2O/Na2O varies from 1.41 to 6.29, and A/CNK varies from 0.79 to 1.26. The rocks are weakly peraluminous to metaluminous and belong to the shoshonitic series. These geochemical signatures suggest that the formation of the Wulanwuzhuer rocks was predominantly influenced by subduction-related processes, including metasomatism by fluids derived from the subducted oceanic slab. Contributions from an enriched mantle source, as indicated by LILE and LREE enrichment, also played a role. Combined with the age and tectonic evolution, it is concluded that these rocks were formed at an island arc-type active continental margin, which is a response of the Proto-Tethys oceanic crust subducting beneath the Qaidam massif from south to north along the vicinity of modern Kunzhong Fault in the Early Caledonian.