Isotopic geochemistry, zircon U-Pb ages and Hf isotopes of A-type granites from the Xitian W-Sn deposit, SE China: Constraints on petrogenesis and tectonic significance

Zircon U-Pb geochronological, geochemical and petrological analyses have been carried out on the Xitian granite emplaced in the middle part of Shi-Hang zone, which is closely related to the economically important Xitian tungsten-tin deposit in Hunan Province, Southeast China. LA-ICP-MS zircon U-Pb dating of two representative samples yielded weighted means (206)pb/U-238 age of 151.7 +/- 1.2 Ma and 151.8 +/- 1.4 Ma. These granites are comprised mainly of K-feldspar, quartz, plagioclase, Fe-rich biotite and minor fluorite, and are characterized by enrichments in Rb, Th, REEs (total REE = 159-351 ppm), and HFSEs (e.g., Zr and Y) but depletions in Ba, Sr, P, Eu and Ti. They are metaluminous to weakly peraluminous and show a clear A-type granite geochemical signature with high SiO2 (73.44-78.45 wt.%), total alkalis (Na2O + K2O = 2.89-8.98 wt.%), Fe2O3*/MgO ratios and low P2O5, CaO, MgO and TiO2 contents. In-situ zircon Hf isotope analysis suggests their epsilon Hf(t) values ranging from -7.43 to -14.69. Sr-Nd isotope data show their epsilon(Nd)(t) values in the range of -9.2 to -7.3, with corresponding T-DM2 ages of 1.72-1.56 Ga. These characteristics indicate that the Xitian granite originated from partial melting of metamorphic basement rocks with a certain amount of mantle-derived materials. Combined with previous geochemical and isotopic data, it is derived that mantle-crust interaction was gradually enhanced from the early to late stages of magmatism. The ore-forming materials and fluids of the Xitian W-Sn deposit are mainly produced by the Early Yanshanian granitic magmatism, which is also responsible for the Late Jurassic (ca. 152 Ma) A-type granitic rocks that host the W-Sn polymetallic deposits distributed along the Shi-Hang zone, implying a significant Mesozoic extensional event in Southeast China likely caused by the subduction of the Paleo-Pacific plate. (C) 2015 Elsevier Ltd. All rights reserved.