The Late Paleozoic bimodal volcanic rocks located on the southern margin of the Junggar Basin are mainly composed of basalts and dacite porphyries. Zircon LA-ICP-MS U-Pb ages of 298±2 Ma and 297~304 Ma could be interpreted as the formation epochs of the basalts and dacite porphyries, respectively. Most of dacite-porphyries are characterized by high SiO₂, Al₂O₃ and Na₂O, obvious enrichment of large ion lithophile elements (e.g., Th) and LREE, and strong depletion of high field strength elements (e.g., Nb, Ta and Ti) relative to the primitive mantle. The basalts are characterized by obvious enrichment of Th, LREE, Zr and Hf and depletion of Nb, Ta and Ti relative to the primitive mantle. All the two types of rocks exhibit high εNd(t) (+6.5~+11 and +7.5~+8.4, respectively) and low (⁸⁷Sr/⁸⁶Sr)_t (0.705 and 0.704, respectively), suggesting that they probably originated from a more depleted mantle. With a comprehensive consideration of field geology, petrology, geochemistry and whole rock Sr-Nd isotopes, it is concluded that basalts and dacite-porphyries might have originated from the same parental magma. The basalts were probably derived from partial melting of depleted mantle and experienced a certain degree of crustal contamination, while the dacite-porphyries were generated by partial melting of a juvenile crustal component. Combined with regional investigation, the authors hold that the Eastern Tianshan region at least began its post-collisional extension in the Late Permian (about 298 Ma). During this period, its tectonic framework began to transfer from compression to extension.