The reduced nature of the subducting slab has been used to explain the relatively poor endowment of economic porphyry copper deposits in Paleo-Tethyan arc systems. The presence of numerous porphyry Cu deposits in the southern Yidun terrane potentially challenges this model, because these deposits are thought to be the product of Paleo-Tethyan subduction. To investigate this, two representative deposits (i.e., Pulang and Songnuo porphyry Cu deposits) from the southern Yidun terrane have been studied. Zircon U-Pb ages of pre- and syn-mineral porphyries in Pulang are 221 +/- 2 Ma (MSWD = 0.89) and 215 +/- 2 Ma (MSWD = 1.50), respectively. Zircon and garnet U-Pb ages of the Songnuo syn-mineral porphyry are 217 +/- 2 Ma (MSWD = 1.15) and 223 +/- 5 Ma (MSWD = 0.97), respectively. The Pulang and Songnuo porphyries both have high whole-rock Sr/Y ratios with minor or no negative Eu anomalies, consistent with derivation from hydrous magmas that underwent minor early plagioclase crystallization but abundant amphibole fractionation. The two porphyry intrusions are characterized by high large-ion-lithophile elements (LILE: Th, U, Ba, Rb) abundances, and low concentrations of high-field-strength elements (HFSE: Nb, Ta, Ti, Zr, Hf). They have similar initial Sr isotope ratios from 0.7055 to 0.7073, epsilon(Nd) (t) values from - 4.3 to - 1.6 and zircon epsilon(Hf) (t) values of - 1.81 +/- 1.34 (n = 47) that are distinct from published results for the Permian-Early Triassic Paleo-Tethyan arc granitoids in the Sanjiang region but similar to the Neoproterozoic arc intrusions in the nearby western Yangtze craton. The Pulang and Songnuo porphyries have relatively high zircon Eu-N/Eu-N* ratios (0.59 +/- 0.04, n = 52) and calculated Delta log fO(2) (FMQ) values (1.61 +/- 0.23, n = 52), consistent with relatively oxidized magmas. This feature is similar to the published data for the Neoproterozoic arc intrusions (Eu-N/Eu-N* = 0.55 +/- 0.08; Delta log fO(2) (FMQ) = 2.14 +/- 0.60), but distinct from the published data for the reduced normal Paleo-Tethyan arc magmas (Eu-N/Eu-N* = 0.29 +/- 0.10; Delta log fO(2) (FMQ) = - 0.68 +/- 0.88). Given that the most recent tectonic reconstruction models suggest that the Paleo-Tethys Ocean closed before similar to 220 Ma, we propose that the Pulang and Songnuo porphyries Cu deposits were formed in a postsubduction setting from oxidized melts generated by reactivating the Neoproterozoic arc root, unrelated to Paleo-Tethyan subduction.