Geochronology and genesis of Dongkengkou acid pluton in Wuyuan, Jiangxi Province

Dongkengkou acid pluton in northeast Jiangxi Province was selected as a study case to expound its petrography, chronology, zircon Hf isotopes and petrogeochemistry. The LA-ICP-MS zircon U-Pb dating of granite porphyry and granodiorite porphyry yields ages of (134.25±0.99)Ma and(132.6±1.3)Ma respectively, indicating that the Dongkengkou pluton was emplaced during the late Yanshanian. The main element geochemical characteristics of Donggangkou acidic pluton are basically the same. They are all high-k calc-alkaline granites with high SiO₂ content and aluminum saturation index A/CNK values less than 1.1, which belong to typical I-type granite. The pluton is enriched in large ion lithophile elements such as Rb, Th and U, depleted in high field strength elements such as Ti and P, and slightly depleted in Ba and Sr. The characteristics of rare earth elements in acidic rocks are consistent, but Eu deficit is not obvious. Combined with Hf isotopes, it is indicated that the magma of the pluton was formed by the partial melting of metamorphic sandstone from the lower crust. It has typical characteristics of adakite rocks with low Mg. It is inferred that the pluton was formed during the transformation from crust thickening due to collision and compression to crust thinning due to extension in the process of continent-continent collision. The tectonic environment is intracontinental orogen. The subduction of the Pacific plate to the South China Continent results in the back-arc multi-stage lithospheric extension.