In this paper, the diabase from the Akbastao ophiolitic mélange in West Junggar was taken as the research target. A detail field geological survey, LA- ICP- MS zircon U- Pb isotopic dating and geochemical analysis were carried out to shed light on its petrogenesis, petrogenic age and tectonic setting and provide new data support for understanding the tectonic evolution of West Junggar. The geochemical characteristics show that the diabase is characterized by high SiO2 (51. 15%~54. 34%), Na2O (4. 95%~6. 36%), TiO2 (1. 79%~2. 08%), and low MgO (3. 90%~5. 15%), K2O (0. 13%~0. 80%), and Na2O>K2O. The total REEs of 117. 52×10-6 to 143. 12×10-6, LREE/HREE ratios of 1. 79 to 2. 04, and (La/Yb)N ratios of 1. 04 to 1. 22 displays unapparent differentiation between LREE and HREE with an average δEu of 0. 93. The diabase is enriched in LILEs (K, Rb, Sr) and strongly depleted in high HFSEs (Th, Nb, Ti), showing the similar characteristics of both N- MORB and IAT. 176Hf/177Hf values of zircons from diabase range from 0. 282783 to 0. 282993 with an average value of 0. 282926 and εHf(t) values range from +8. 0 to +15. 2 with the average value +12. 8. The geochemical characteristic study of the diabase implies that the source area of the diabase was the product of 25%~30% partial melting of the depleted mantle spinel lherzolite metasomatized with subduction fluid. Meanwhile, the magma underwent some extent of crystallization differentiation during its evolution. The zircon U- Pb geochronology study shows that the diabase from the Akbastao ophiolitic mélange formed at 357. 6±2. 4 Ma (n=24, MSWD=5. 3), suggesting the Early Carboniferous in age. This dating age also verifies that the evolution of the oceanic basin in the West Jungger area continued to the Early Carboniferous, and provides evidence for extinction time of the Late Paleozoic residual oceanic basin in West Junggar. Combined with regional geological background and diagenetic age, it can be concluded that the Akbastao ophiolitic mélange formed in the back- arc basin which was associated with the subduction in the Early Carboniferous.