Petrogenesis of the Helong Granites in Southern Jiangxi Province, China: Constraints from Geochemistry and In Situ Analyses of Zircon U-Pb-Hf Isotopes

The Jinzhuping and Changkeng granites are related to the Helong W-Sn ore field in southern Jiangxi Province, China. Three different phases can be found in the Jinzhuping pluton, and their LA-ICP-MS zircon U-Pb ages are 155.2 +/- 0.68 Ma, 154.0 +/- 0.56 Ma, and 153.4 +/- 0.99 Ma, respectively, indicating two types of granitic rocks. All granites in the Helong ore field have similar geochemical characteristics, they have high contents of SiO2 (73.99 wt.%-77.68 wt.%), and total alkali (7.56 wt.%-8.76 wt.%) and are weakly to strongly peraluminous. They are slightly enriched in HREE and depleted in Eu, Ba, Sr, P, and Ti. Zircon epsilon Hf(t) values of the Jinzhuping three granites are from -14.4 to -10.4, from -15.3 to -11.4, and from -18.1 to -10.5, and the Hf TDM model ages range from 1.83 to 2.06 Ga, from 1.89 to 2.14 Ga, and from 1.83 to 2.31 Ga, respectively. Whole-rock geochemistry and Hf isotope analysis indicate that the Helong granites experienced a high degree of differentiation and evolution derived by partial melting of the Late Paleoproterozoic crustal materials, and they formed in a backarc caused by low-angle subduction of the Paleopacific plate.