Zircon U–Pb ages, geochemical data, and Sr–Nd–Hf isotopic data are reported for the Paleocene Qulong high-Mg dioritic plutons (HMDPs) in southern Tibet of the India–Asia collision zone to investigate their source, petrogenesis, and tectonic setting. The Qulong HMDPs consist of diorite with a 206Pb/238U age of 63.45 ± 0.87 Ma and gabbro-diorite with a 206Pb/238U age of 63.8 ± 0.57 Ma. They are metaluminous calc-alkaline rocks and exhibit sanukitic HMD affinity with moderate SiO2 and TiO2 and high MgO (5.24–8.64 wt%) and Mg# (55.78–65.89). They exhibit large ion lithophile element and light rare earth element enrichment and Nb–Ta depletion, relatively low (Th/Nb)N ratios, and high (La/Sm)N, La/Ta, and La/Nb ratios, which are similar to oceanic island basalts derived from the subduction-related mantle source. In addition, relatively low initial 87Sr/86Sr ratios (0.7056–0.7062), positive εNd(t) (+2.23 to + 3.34), and εHf(t) (+4.55 to + 12.35) indicate the origin of the Qulong HMDPs to be the subduction-related lithospheric mantle which had been modified by the asthenosphere, and mixed with the sediment melt. This study suggests that the Qulong HMDPs are a product of the upwelling of the asthenosphere triggered by the slab roll-back of the subducting NeoTethys slab of the India–Asia collision at ca. 64 Ma.