The magmatic emplacement age, petrogenesis, and tectonic evolution of the Gangdese magmatic arc are of great significance for revealing the subduction of the Neo-Tethys Ocean, the collision of the Indian and Asian continents, and the characteristics of mineralization. Combined with field geological work, a systematic U-Pb chronology and geochemical study of the Lajiepu granite pluton in the Xiongba area, western Gangdese, has been carried out. Zircon U-Pb dating yielded emplacement ages of 46.7 ± 1.2 46.7±1.2 Ma for biotite monzogranite and 10.89 ± 0.11 10.89±0.11 Ma for monzogranite porphyry, corresponding to the Neo-Tethyan subduction stage and the India-Eurasia post-collisional extension, respectively. Geochemical characteristics show that the Eocene rock mass is a high-K cal-alkaline I-type granite, which was derived from partial melting of basic crust metasomatized by subduction fluid. The Miocene intrusion belongs to alkali-calcite A-type granite, which was formed by melting of thickened lower crust and mixed with mantle-derived materials. Tectonic discrimination indicates the Eocene granite formed during the main Indian-Asian collision induced by Tethyan oceanic plate subduction, while the Miocene granite was related to post-collisional crustal extension. The metallogenic characteristics show that the Sr/Y ratio (14.6–54.5), oxygen fugacity ( log ? ? ? 2 = ? 15.95 ～ ? 9.63 ) (logf O 2 ? ? =?15.95～?9.63) and water content of the two types of rock masses are low, which are significantly different from those of the ore-forming rock masses of the Zhunuo porphyry copper deposit in the adjacent area. Therefore, the magmatic activity in Lajiepu records the tectonic transition of the Gangdese belt. Although the Eocene intrusion has relatively high oxygen fugacity, its ore-forming conditions remain inadequate. Subsequent prospecting and exploration should focus on Miocene rock masses characterized by high oxygen fugacity ( log ? ? ? 2 = ? 14.3 (logf O 2 ? ? =?14.3 to ? 7.9 ?7.9, avg. ? 11.7 ?11.7), high water content, and high Sr/Y ratios (avg. 76.3 76.3), similar to those in the Zhunuo deposit.