Geochemical Characteristics and Tectonic Significance of the Late Devonian Volcanics in Wushentara Area, Xinjiang

Located in the middle of the South Tianshan orogenic belt, Late Devonian volcanics of WuShitala area occurred in the middle and lower section of Pochengzi Formation and is mainly composed of a set of acidic volcanics and neutral volcanics-sedimentary rocks, including dacite porphyry, rhyolite porphyry and a small amount of andesite. The volcanic rocks are distributed in a NW trend. The geochemical characteristics show that the Pochengzi Formation volcanics belong to the Calc-alkaline quasi-aluminium to peraluminous series, enriched in LREE and relatively depleted in HREE, and with weak Eu (an average of 0.68) negative anomaly; There is an obvious enrichment in large ion lithophile elements (such as K, Rb, Th), a relative deficit in high field strength elements, as well as obvious negative Ba, Nb, Ta, P, Ti anomalies. Furthermore, the ratio of Th/Ta is higher (9.04-14.37) but the value of Ta/Yb is lower (0.27-0.69), signifying that it has the characteristics of continental marginal island arc volcanic rocks. Ratio of ⁸⁷Sr/⁸⁶Sr from 0.71314 to 0.72507 is relatively higher, reflecting crustal material contamination in magma evolution. According to the tectonic evolution characteristics of the South Tianshan orogenic belt, the characteristics of volcanics in Pochengzi Formation suggest that they were probably formed in an active continental margin environment.