Early Mesozoic intracontinental orogeny and stress transmission in South China: evidence from Triassic peraluminous granites

The Early Mesozoic tectonic and magmatic events in South China are considered to represent intracontinental orogeny, although the mechanism and geodynamic setting remain debated. Here we report zircon U–Pb geochronology, Hf isotopes and whole-rock geochemistry from four granitic plutons in the Nanling and Yunkai domains. The zircon data define seven groups of weighted mean ²⁰⁶Pb/²³⁸U ages as 218 ± 2, 222 ± 4, 225 ± 3, 227 ±3, 221 ± 3 and 231 ± 3 Ma, representing the magmatic crystallization ages. These intrusions are characterized by a peraluminous nature, with high A/CNK values (>1.1), negative Eu, Ba, Sr, Nb and Ti anomalies, and enrichment in LREE, Rb, Th, U and Pb. Zircon grains from all the samples show variably negative ε_Hf(t) values (–3.8 to –18.6) with two-stage Hf model ages clustered in the range 1.4–2.5 Ga. Our data indicate that the Early Mesozoic granitic magmas were generated by the partial melting of crustal rocks with insignificant input of mantle materials. In conjunction with other geological evidence, we suggest that Triassic intracontinental deformation was triggered by far-field stress propagation from the plate boundary of South China.