The volcanic rocks in Junggar Basin are mainly basaltic and andesitic rocks, and subordinately dacite and rhyolite. Most of the rocks exhibit slight enrichment of LREE and somewhat low HFSE abundances relative to the LIFE. Such features are commonly regarded as characteristics of subduction-related magmatism. The rocks in the three regions have positive εNd(0) and relatively low (87Sr/86Sr)i, suggesting that the basement volcanic rocks were generated in the depleted mantle wedge that had been enriched in incompatible elements by subduction without old continental contamination. In addition, Nd single-stage model ages vary from 400 Ma to 700 Ma. The single-stage model age indicates that the subducted sedimentary rocks are younger than 700 Ma. The isotopic and trace element geochemical characteristics of basaltic volcanic rocks imply that these regions should belong to different arc accretionary systems. On such a basis, it can be inferred that the basement volcanics formed in the environment of arc accretion and the juvenile materials added to the crust through the arc volcanism, which constituted the most important mechanism at that time, and that the basement of Junggar Basin was presumably assembled by the three different arc accretion terrains which belonged to Middle Asian Kazakstan, Tarim, and Siberia Plate respectively.