Abstract: This paper has studied the geochemical data including major and trace elements and Sr-Nd isotopes of the volcanics from Qi’eshan Group occurred in east Tianshan，Xinjiang，NW China. The results indicate that the volcanics belong to calc-alkaline series with SiO₂ content of 47.75%-57.78% and A1₂O₃ content of 17.92%-19.88%. MgO changes from 3.96% to 6.46%，and Mg^# changes from 52.16 to 58.20. The chondrite-normalized REE patterns show that the volcanics are enriched in LREE but depleted in HREE，with intense fractionation between LREE and HREE. The primitive mantle-normalized spider diagrams are characterized by LILE enrichment and HFSE depletion. Isotopic geochemistry shows that values of I_Sr（ t）range from 0.702 386 to 0.704 264 and ε_Nd（t）from 5.61 to 8.66. Based on our geochemical study，the volcanics may derive from the long term depleted mantle，and also contain materials both from mid-ocean ridge and volcanic arc，indicating that they were most plausibly formed by mixing between the asthenospheric mantle-derived and metasomatized lithosphere mantle derived melts（or fluids）. The matrix of volcanics previously formed in different stages and tectonic units represent mélanges of materials both frommid-ocean ridge and volcanic arc，which were cumulated along long and narrow belt after amalgamation of different plates. Combining with previous studies，we suggest the formation of volcanics from Qi’eshan Group was related to northward subduction of southern Paleo-Asian oceanic crust，which would be well constraint for Paleozoic tectonic evolution of southern Paleo-Asian Ocean.

Key words: volcanic rocks, geochemistry, Nd-Sr isotopes, Qi’eshan Group