LA-ICP-MS zircon U-Pb dating, geochemistry and tectonic implications of the Neoproterozoic Xiaoxigong granite at Dunhuang block, northeastern Tarim, NW China

摘要

We present new zircon U-Pb ages, Hf isotopes, and whole-rock geochemistry of the Xiaoxigong granite pluton in the Dunhuang block, northeastern Tarim Craton. LA-ICPMS zircon U-Pb dating yields a weighted mean Pb-206/U-238 age of 841.3 +/- 8.1 Ma (MSWD = 4.4), interpreted as the emplacement age of the Xiaoxigong granite. Zircons have epsilon Hf(t) values ranging from +4.53 to +8.63 and TDM2 model ages from 1.16 to 1.38 Ga. Geochemical characteristics show that the granite belongs to the shoshonite series and has weakly peraluminous-metaluminous features. It is enriched in Si, K, Na, Rb, Th and REE, and has elevated Ga/Al ratios and high (Zr + Nb + Ce + Y) abundance, and is depleted in Mg, Ca, Mn, Ba, Sr, P and Ti. The REE composition shows significant negative Eu anomalies (Eu/Eu* = 0.18-0.31) and low (La/Yb)(N) (4.54-7.33). It is typical aluminous A-type granite. The geochemical and Hf isotopic signatures suggest that the Neoproterozoic Xiaoxigong granite was generated by partial melting of crustal rocks during the the post-orogenic period.