Origin of the Shiwu pluton in Barluk region, Xinjiang: Zircon U-Pb chronological, geochemical and Sr-Nd-Pb-Hf isotopic constraints

The Shiwu pluton in Barluk region, Xinjiang, is mainly composed of quartz diorite porphyry and quartz diorite. By combined studies of zircon U-Pb chronology, Hf isotope, whole rock geochemistry and Sr-Nd-Pb isotopes on this pluton, its petrogenesis, tectonic setting and metallogenic significance are discussed. LA-ICP-MS zircon U-Pb dating on the quartz diorite porphyry and quartz diorite yields their crystallization ages of 322. 1 ± 1. 5Ma and 322. 4 ± 1. 5Ma, respectively, indicating the pluton was formed in Late Carboniferous. The quartz diorite porphyry and quartz diorite of the Shiwu pluton have similar geochemical characteristics. They have Mg# ranging from 32. 4 to 57. 2. The REEs are obviously fractionated with (La/Yb)N = 2. 36 ∼ 6. 04 and weakly Eu anomaly. They are also enriched in LILE and depleted in Nb, Ta, P and Ti. Sr-Nd-Pb isotopic compositions indicate that Shiwu granite body is characterized by positive ϵNd(t)(+4. 61 ∼ + 7. 03), low ISr(0.7036 ∼ 0.7045) and relatively young model ages (tDM) ranging from 0.59Ga to 0.78Ga, (206Pb/204Pb), =18. 173∼18.450, (207Pb/204Pb), =15.542 ∼15.562 and (208 Pb/204 Pb)i =37.830∼38.036. The ϵHf(t) values and tDM2 model ages of zircon are + 4. 5 ∼ + 15. 3 and 0. 36 ∼ 0. 62Ga, respectively. Comprehensive geological, geochemical and chronological studies demonstrate that the Shiwu intrusive rocks may be formed in an island background during early subduction stage in Late Carboniferous, and are derived from partial melting of the juvenile crust, which may be generated by underplating of depleted basaltic magma (the upwelling of magma formed by the fluid metasomatic mantle wedge). The tectonic setting and evolution of Shiwu pluton are very important for copper mineralization, and therefore it is worth for further evaluation. © Yanshi Xuebao/Acta Petrologica Sinica. All rights reserved.