Genesis of Intrusive Rocks in the Bairiqili Area: Constraints on the Closure Time of the Paleo-Tethys Ocean in the East Kunlun Orogen

To explore the tectonic evolution of the Bairiqili area in the East Kunlun Orogen, we conducted petrological, geochemical, and geochronological analyses of fine-grained quartz diorite, coarse-grained quartz diorite, and granite porphyry from the region. The results show that the weighted average ages of these rocks are 251.6 ± 1.2 Ma for fine-grained quartz diorite, 250.2 ± 0.6 Ma for coarse-grained quartz diorite, and 245.8 ± 0.9 Ma for granite porphyry, indicating formation during the Early and Middle Triassic periods. The coarse-grained quartz diorite is peraluminous, low in silicon, and high in iron. It belongs to the calc-alkaline series of magmatic rocks, enriched in large ion lithophile elements (Rb, K, Ba), and relatively depleted in high-field strength elements (P, Nb, Ti). The zircon ε_Hf(T) values for fine-grained quartz diorite range from –8.68 to –3.39, with two-stage model ages (T_DM2) between 1493 and 1828 Ma. The zircon ε_Hf(T) values for coarse-grained quartz diorite range from –9.46 to –2.88, with T_DM2 ages from 1459 to 1875 Ma, and for granite porphyry, the zircon ε_Hf(T) values range from –3.37 to –1.56, with T_DM2 ages from 1374 to 1488 Ma. These geochemical data suggest that the three plutons primarily derive from crust-mantle mixed sources. All plutons formed in a volcanic arc environment, related to arc magmatism driven by the northward subduction of the Paleo-Tethys oceanic crust. Regional data indicate that the Paleo-Tethys Ocean closed likely in the Middle Triassic.