Igneous rocks geochemistry, zircon U-Pb age and its geological significance in the central section of Xiemisitai area, Xinjiang

The igneous rocks, occurred in the central section of the Xiemisitai area in Xinjiang, are made of the andesite, dacite and rhyolite. Geochemical data indicate that the igneous rocks have a high-K calc-alkaline composition (K2O = 3. 42% similar to 9. 85%; Na2O =0.48% similar to -5.30%), and are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE) with a clear negative Nb, P and Ti anomaly. REE patterns show distinct enrichments in LREE relative to HREE. Lead isotope composition of the rocks span a narrow range (Pb-206/Pb-204 =18. 435 similar to 19. 409, (207)pb/Pb-204 = 15. 535 similar to 15. 602, Pb-208/Pb-204 = 38.361 similar to 39.213). The rocks also exhibit high initial epsilon(Nd)(t) (+ 4. 43 similar to + 6.65) ratios and low initial Sr-87/Sr-86 values (0.700953 similar to 0. 704435). Volcanic activity occurred at 422.5 +/- 1. 9Ma based on U-Pb (SIMS) analyses of zircons from the rhyolite. These data are consistent with a mature arc and suggest that the volcanic rocks were derived from the partial melting of multiple sources including oceanic crust and enriched mantle, with melts undergoing significant crystal fractionation and minor crustal assimilation during convergence between the paleo-Junggar ocean and the Xiemisitai mature arc in Late Silurian.