Late Triassic zircon U-Pb ages and Sr-Nd-Hf isotopes of Darongshan granites in southeastern Guangxi and their geological implications

The petrogenesis and geodynamic processes of the Darongshan granite have been a subject of much controversy. In this paper, the authors report U-Pb ages and Sr-Nd-Hf isotopes for the Darongshan granite in southeastern Guangxi. LA-ICP-MS U-Pb zircon analysis yielded ²⁰⁶Pb/²³⁸U weighted mean age of 253.6±2.1Ma, 256.4±1.8Ma and 256.8±2.8Ma for three granite samples respectively, indicating that these granites are of Late Permian origin rather than the Early-Middle Triassic origin. They have relatively high ε_Nd(t) values (-9.18~-13.4) and younger Nd model ages (t_DM^c=1.55~1.84Ga), which are consistent with ε_Hf(t) values (-5.5~-6.7) and Hf model ages (T_DM2=1.64~1.71Ga), suggesting an lower crustal source mixed with the Paleo-Mesoproterozoic materials. Combined with previous studies, the authors hold that the Darongshan granitic magmatism might have been related to anatexis of the lower crust due to the subduction/collision between Indosinian block and South China plate during the Hercynian to Indosinian period.