The Agashen Obo volcanic rocks are developed in "Jiangzeer Kuduke" Formation in eastern Junggar, Xinjiang. The characteristics of major elements suggest that the rocks are basaltic andesites of calc-alkaline series, whose chondnte normalized REE patterns are of rightly-oblique type characterized by LREE enrichment and HREE depletion((La/Yb)N=4.69~8.19). Primitive-mantle normalized patterns show evident geochemical characteristics of depletion of (HFSE) Nb, Ta, Zr, Hf and relative enrichment of (LILE) Cs, Rb, Ba, Pb. These geochemical data and the correlation diagram indicate that the rocks had typical island arc features, the magma source was related to plate subduction and experienced certain degrees of crustal contamination, but without the mixture of subduction sedimentary melt. LA-ICP-MS zircon 206Pb/238U age of 388.0Ma±6.7Ma shows that the island arc environment lasted at least until late Middle Devonian, the oceanic crust might have represented the subduction of Aermantai ophiolite melange towards North Siberia, and the Agashen Obo volcanic rocks were probably generated from partial melting of the nunde wedge enlarged by rising upper subduction fluid. There existed subducted accretion product of Armantai ocean belt in Paleozoic period, which constituted part of continued southward accretion of the southern margin of the Siberia plate.%新疆东准噶尔阿尕什敖包地区火山岩出露于中泥盆统蕴都喀拉组.主量元素特征显示其为一套钙碱性玄武安山岩,在球粒陨石标准化REE配分曲线图上表现出轻稀土元素富集而重稀土元素相对亏损的右倾型特征((La/Yb)N=4.69～8.19,在微量元素蛛网图上具有明显的(HFSE)Nb、Ta、Zr、Hf亏损和(LILE)Cs、Rb、Ba、Pb相对富集的地球化学特征.地球化学数据及相关图解表明,其具有典型的岛弧火山岩性质,岩浆源区与板块的俯冲相关,经历了一定程度的地壳混染.用LA-ICP-MS法测得的锆石206Pb/238U年龄为388.0Ma±6.7Ma,可能代表了中泥盆世位于阿尔泰南缘志留纪陆缘岛弧南侧的一个新生岩浆岛弧.其岩浆形成应与阿尔曼太蛇绿混杂岩所代表的洋壳俯冲相关,同是古生代阿尔曼太洋盆俯冲增生的产物,属西伯利亚板块南缘持续向南增生的一部分.
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