The Rongna Cu-(Au) deposit is a recently discovered giant low-grade composite porphyry-high sulfidation epithennal system in the Duolong ore district of central Tibet. We present zircon U-Pb ages, bulk-rock geo-chemical and Sr-Nd isotope data, as well as zircon Hf-O isotope data to constrain the petrogenesis of the Rongna granodioritic porphyry, on which the ore system is centered. Secondary ion mass spectrometry (SIMS) zircon U-Pb data for two samples yielded ages of 118.7 +/- 0.9 Ma and 117.1 +/- 0.9 Ma, respectively. The granodioritic porphyry is of high-K talc-alkaline and magnetite-series affinity, with enrichment of light rare earth elements (LREEs) and large-ion lithophile elements (e.g., Rb, Pb, and K), and depletion of high-field strength elements (e.g., Ta, Nb, and Ti), typical of the geochemical signature of arc magmas. The Rongna granodioritic porphyry has initial Sr isotopic ratios of 0.7060-0.7099, and epsilon(Nd)(t) values of -5.7 to -1.7 with T-DM (Nd) of 983-1900 Ma. The zircons have relatively narrow Hf-O isotopic compositions (epsilon(Hf)(t) = + 3.30- + 6.43; 8180 = + 5.94- + 6.96 parts per thousand), indicating the involvement of old crustal materials. Our data suggest that the Rongna granodioritic porphyry likely evolved by fractional crystallization from a hybrid magma of mantle-derived mafic melts and lower crustal felsic melts during a period of magmatic flare-up following flat-slab subduction.