Numerous late Paleozoic granitic intrusions occur in the West Junggar region, however, the petrogenesis of these granites and their tectonic setting remain subjects of debate. In this study, we present new petrology, geochemistry and zircon Hf- O isotopic compositions of the quartz monzonite found in the Aerjiati mountain, located in the northern Western Junggar. Our objective is to elucidate the origin and tectonic setting of these granites and explore their relationship with juvenile crustal growth. Zircon U- Pb dating of two samples indicates that these quartz monzonite formed during the late Carboniferous, with ages of 301.8±1.4 Ma and 303.7±3.1 Ma. These samples contain hornblende and are characterized by high Si (SiO2=67.8%~68.9%), Al (K2O+Na2O=9.36%~9.89%) contents, but low A/CNK ratios (0.96~1.00), Ga/Al (2.27~2.34) and Rb/Sr (0.35~0.50) contents, consistent with the geochemical features of I- type granites. They are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depleted in high field strength elements (HFSEs)(e.g., Nb, Ta, Ti), with negative Eu (δEu=0.72~0.85), akin to typical subduction- related island arc magmas. These I- type granites exhibit high and positive εHf(t) values and young tDM2 (604~392 Ma). Their δ18O (5.73‰~6.51‰) values are slightly higher than those of the mantle. They also display high Zr contents and zircon saturation temperatures (Tzr=854~895℃), implying that they originated from partial melting of juvenile lower crust in a high temperature geological setting. Previous studies have indicated the presence of high temperature I- and A- type granites and adakitic dikes in the northern West Junggar. Combined with previous findings, we propose that these high- temperature rock associations were likely generated by ridge subduction and the formation of a slab window. The ridge subduction led to the upwelling of hot asthenospheric mantle, triggering partial melting of the juvenile lower crust formation of I- and A- type granites. Most of the lower crust was formed in the early Paleozoic, suggesting a significant contribution of juvenile crustal growth during the Phanerozoic in the West Junggar.