The Geza arc is an important part of the Yidun arc belt and porphyry metallogenic zone in the Sanjiang region, Southwestern China. In this paper, we report on new laser-ablation inductively coupled plasma–mass spectroscopy zircon U–Pb age and bulk geochemical and Hf isotopic data of the Tongchanggou granodioritic porphyries from the Geza arc. The results indicate that these intrusions were emplaced in the Late Cretaceous (87.6 ± 0.6–83.6 ± 1.1 Ma). The intrusive rocks have SiO2, Al2O3, and K2O + Na2O contents of 62.51–72.86, 11.43–16.30, and 5.32–7.81 wt%, respectively, similar to those of high-K calc-alkaline rock. They are enriched in large-ion lithophile elements (e.g., K, U, Th, Rb, Ba, and Sr) and light rare-earth elements (LREE (light rare-earth elements)/HREE (heavy rare-earth elements) = 16.96–24.78), but depleted in high-field-strength elements (e.g., Nb, Ta, P, and Ti) and HREE, with a slightly negative Eu anomaly (δEu = 0.72–0.89). The intrusions show uniformly negative eHf (t) values between − 9.55 and − 3.49. These elemental geochemical and Hf isotopic data indicate that the Tongchanggou porphyries were mainly derived from partial melting of the delaminated lower crust in an extensional setting at the post-collisional stage. The collision-induced upwelling of the lithospheric mantle led to the partial melting of the crust and formed the potassium-rich and Mo-bearing parental magma. Magma rising and intruding along the deep faults eventually resulted in the Late Cretaceous tectonic–magmatic and Mo-polymetallic mineralization in Geza area.