Zircon U-Pb geochronology, geochemical and Sr-Nd-Hf isotopic compositions of the Triassic granite and diorite dikes from the Wulonggou mining area in the Eastern Kunlun Orogen, NW China: Petrogenesis and tectonic implications

The Wulonggou mining area in the Eastern Kunlun Orogen of NW China is characterized by extensive granitoid magmatism, ductile faulting, and skam-type Cu-Pb-Zn and orogenic gold mineralizations. The Balugou granite dike, which hosts skarn-type Cu-Pb-Zn mineralizations, is located in northeast Wulonggou, whereas the Huanglonggou diorite dike, which is cut by the Huanglonggou gold veins, is located in the central part of the area. This study investigated the major and trace-element compositions, zircon U-Pb dates, and Sr-Nd-Hf isotopic compositions of these rocks. Three Balugou granite dike samples yielded an average zircon U-Pb age of similar to 244 Ma (Anisian), and two Huanglonggou diorite dike samples yielded an average zircon U-Pb age of similar to 215 Ma (Norian). Therefore, the skarn-type mineralizations in the Wulonggou area formed during the early Anisian (similar to 244 Ma), and the orogenic gold mineralizations formed after similar to 215 Ma. The Anisian Balugou granite dike is metaluminous to slightly peraluminous and has high alkali contents of 7.19-9.57 wt.%, high Zr + Nb + Ce + Y contents, high Fe2O3T/MgO ratios, and high Rb/Nb and Y/Nb ratios, which suggest an A-type affinity. The Norian Huanglonggou diorite dike is metaluminous and has high Al2O3 contents (15.61-16.40 wt.%), high Mg# values (0.49-0.54), relatively high Sr contents (370-507 ppm), high Sr/Y ratios, high (La/Yb)(N) ratios, and low HREE and Y contents, which suggest an adakite-like high-Mg diorite. The Anisian granite dike has initial Sr-87/Sr-86 (I-sr) ratios of 0.707289 to 0.708981, epsilon(Nd)(t) values of -3.6 to -3.1, and zircon epsilon(Hf)(t) values of -3.9 to +1.3. The Norian diorite dike has initial Sr-87/Sr-86 (I-sr) ratios of 0.709166 to 0.709529, epsilon(Nd)(t) values of -5.7 to -5.1, and zircon epsilon(Hf)(t) values of -4.9 to -1.0. The Sr-Nd-Hf isotopic data suggest that the Anisian granite dike was likely derived from partial melting of dominantly Mesoproterozoic mafic lower crust, whereas the Norian diorite dike was likely derived from partial melting of mantle peridotite that was metasomatized by the addition of Mesoproterozoic subducted sediment-derived melts. We propose that the Anisian granite dike was emplaced in a post-collision environment after the closure of the Proto-Tethys in a subduction setting associated with the northward subduction of the Paleo-Tethys oceanic plate, whereas the Norian diorite dike was emplaced during the subduction of the Paleo-Tethys oceanic plate. (C) 2014 Elsevier B.V. All rights reserved.