Geochronological, geochemical and petrogenesis of Bieluagaxi granodioritic pluton in western Junggar

For a better understanding of the petrogenesis and tectonic environment of the acidic intrusive rocks in Western Junggar, a study is carried out on Bieluagaxi granodioritic pluton located in the Central part of West Junggar. Its petrogenesis, magma source, tectonics setting based on petrography, zircon LA-ICP-MS U-Pb ages, whole-rock major and trace elements, and Sr-Nd isotopic compositions are discussed in detail. LA-ICP-MS U-Pb zircon data of the granodiorite give weighted ages of 318.7±3.3 Ma. Bieluagaxi granodiorite is calc-alkaline suite with high MgO(Mg#=49-59), Ni and Cr contents. Bieluagaxi granodiorite is strongly enriched in large ion lithophile elements (LILEs, e.g. K, Rb, Sr and Ba), but it displays depletion of high field strength elements (HFSEs, e.g. Nb, Ta and Ti). In terms of Sr-Nd isotopic compositions, granodiorite has low initial 87Sr/86Sr ratios (0.704 297-0.704 399) and high positive εNd(t) (5.8-6.5). Therefore, we suggest that the early Late Carboniferous Bieluagaxi granodioritic pluton has been generated in a subduction setting, the mantle wedge began to partially melt due to the upward fluid from the dehydration of subducting oceanic slab, resulting in the asthenospheric mafic magma underplating the lower crust. Then, the lower juvenile basaltic crust derived from the depleted mantle underwent partial melting to generate the I type granites of the Bieluagaxi granodioritic pluton. ©, 2015, China University of Geosciences. All right reserved.