Late Paleozoic post-collisional granitoids are widespread in West Junggar, as well as northern Xinjiang. As a representative of those intrusions, the Jietebutiao granite occurs in the southwestern margin of the West Junggar (northwest China), and is mainly composed of mid-coarse-grained monzogranite and syenogranite. In the present study, we report the results of high-precision zircon laser-ablation–inductively-coupled plasma mass–spectrometry U–Pb dating on the Jietebutiao granite for the first time, and yield weighted mean 206Pb/238U ages of 287 ± 9 Ma and 278 ± 3 Ma for monzogranite and syenogranite, respectively. The Jietebutiao granite has a pronounced A-type affinity; it is metaluminous to slightly peraluminous; has a high-K calc-alkaline composition; high concentrations of Na2O + K2O, varying from 6.8 to 8.5 wt%; high FeOt/MgO; 10 000Ga/Al ratios, a low CaO, MgO, and TiO2 content; enriched in some large ion lithophile elements (LILE, such as Rb and Th) and high field strength elements (HFSE, such as Zr, Hf, and Y); and depleted in Sr, Ba, and Ti. In addition, the granite has a relatively high rare earth element (REE) content (except for Eu), with significant negative Eu anomalies (Eu/Eu* = 0.01–0.72), and showing slight tetrad REE patterns and non-charge and radius controlled (CHARAC) trace element behavior. Petrographic, geochemical, and geochronological data suggest that the parental magma of Jietebutiao intrusions are of mixed origin, and are most probably formed by the interaction between the lower crust- and mantle-derived magmas in the Early Permian post-collisional tectonic setting. The basaltic magmas underplated and interacted with the lower crust that was dominated by deeply buried arc (and back-arc basin) series and the oceanic crust formed in the Paleozoic, and then triggered the partial melting of the juvenile lower crust, producing voluminous granitic melts and forming the Jietebutiao A2-type monzogranites, with the lithospheric mantle progressively thinning and rifting to form A1-type granites, such as syenogranites, in the Jietebutiao pluton. This further proves the important contribution of Late Paleozoic granitic magmatism in terms of vertical crustal growth in northern Xinjiang.