Age, Genesis and Geological Significance of Granodiorite in the Lajiepu Mining Area, Western Gangdese Metallogenic Belt, South Tibet

The Lajiepu mining area is located in the western section of the southern margin of the Gangdese metallogenic belt. Understanding the formation mechanism of the Paleogene granite here is crucial for discussing the genesis and tectonic background of arc magmatic rocks in the Angren area, also on the southern margin of Gangdese. This study employs zircon U–Pb dating, Hf isotopes, rock geochemistry, and Sr–Nd–Pb isotope analyses of granodiorite samples from the mining area. The results show that LA-ICP-MS zircon U–Pb dating yields a weighted average age of 50.10 ± 0.51 Ma, placing the emplacement of these intrusive rocks in the Early Eocene. Geochemical data classify the pluton as high-potassium calc-alkaline, with A/CNK values between 0.94 and 1.02, indicating it is an I-type granite. The rock is enriched in large ion lithophile elements (LILE) such as Rb and Ba and depleted in high field strength elements (HFSE) like P, Nb, and Ti. Light rare earth elements (LREE) are enriched, while heavy rare earth elements (HREE) show no significant differentiation, and moderate negative Eu anomalies (δEu = 0.65–0.76) are present. The εHf(t) values of the pluton’s zircon range from 3.03 to 7.09, with two-stage model ages (TDM2) between 676 and 932 Ma. The initial (87Sr/86Sr)i values range from 0.705637 to 0.705732, and the εNd(t) values range from –0.38 to –0.28, with two-stage Nd model ages (TDM2) between 883 and 890 Ma. These findings suggest a magma source region with characteristics of both mantle-derived and crust-mantle mixed sources. Additionally, lead isotope data further support a crust-mantle mixed source within the orogenic belt. Combining the regional geological background, the formation of the rock mass is related to the partial melting of the newly formed lower crust caused by the upwelling of the mantle source material of the Neo-Tethys oceanic crust after the Indo-Asian continental collision. The material source of granodiorite includes crust source and mantle source. At this time, it may still be in the early stages of the Indo-Asian continental collision.