Geochronology, geochemistry and tectonic significances of the Yamansubei pluton in eastern Tianshan, Northwest China

The Yamansubei granite pluton (YB) is situated in the Late paleozioic Qoltag orogenic belt, eastern Tianshan, Northwest China. Petrographically, the pluton is a K-feldspar granite, which is composed of quartz (25%similar to 40%), perthite (40%similar to 70%), plagioclase (10%similar to 25%, An=18 similar to 30) and biotite (2%similar to 5%). Zircon LA-ICP-MS U-Pb dating shows that the YB pluton intruded at 227. 9 +/- 0. 47Ma of Middle Triassic. Geochemically, the pluton is characterized by high silicon (SiO2 = 74. 27%similar to 75. 99%), alkali (ALK =7. 64%similar to 8. 29%), potassium (K2O = 4. 37%similar to 4. 79%) and metaluminous, whereas low titanium, calcium, iron and magnesium, which attributes to high K calc-alkaline granite. The pluton is also rich in LILE (K, Rb, Cs etc.), HFSE (Th, U, Zr, Hf etc.) and depleted in Ba, Sr, Nb, Ta and Y. Chondrite-normalised REE distribution pattern for the YB pluton displays right skewed shapes with slightly negative Eu anomalies (delta Eu =0. 48 similar to 0. 86), indicating fractionation of LREE, and fractionation between LREE and HREE. Zircon in-situ Hf isotopic composition analysis yields the epsilon(Hf)(t) and t(DM2) values of the YB pluton varying + 8. 60 similar to+ 11. 31 and 538 similar to 711 Ma, respectively. Integrated studies in petrography, geochemistry and Hf isotope and regional tectonic evolution indicate that the YB pluton resulted from mantle magma underpalting induced partial melting of the Neoproterozoic new-born lower crust. After comprehensive study on previous contributions, this paper suggests that the geodynamic source for Indosinian magmatism in eastern Tianshan could attribute to the influence of the Paleo-Tethys ocean tectonic regime.