<p>The Chinese Altai, a key component of the Central Asian Orogenic Belt (CAOB), represents a significant Phanerozoic accretionary orogenic belt. The oceanic-continental subduction processes spanning the Cambrian to Carboniferous and subsequent intracontinental extension since the Triassic have been well documented in the Chinese Altai, the southwestern segment of the CAOB. Deciphering the petrogenetic evolution of this region during the Permian is thus crucial for advancing our understanding of its tectonic transitions. However, the Permian tectonic setting of the Chinese Altai remains contentious. To address this knowledge gap, this study presents new geochronological and geochemical data for the Jiangjunshan pluton in the southern Chinese Altai. Zircon U-Pb geochronology reveals that the gabbro and two-mica alkali feldspar granite—which collectively constitute the primary lithology of the Jiangjunshan pluton—were emplaced at ∼272 ± 3.5 and ∼272 ± 1.6 Ma, respectively. Geochemically, the gabbro exhibits pronounced light rare-earth element (LREE) depletion, low Nb/Yb (0.39–0.46) and Ti/V (23.7–25.3) ratios, and trace-element signatures akin to normal mid-ocean ridge basalts (N-MORB). However, its conspicuous Nb-Ta depletion parallels that of island arc basalts. Depleted Hf-Nd isotopic compositions (<i>ε</i>_Hf(<i>t</i>) = +0.60 to +4.63, <i>ε</i>_Nd(<i>t</i>) = +6.32 to +7.80) in the gabbro, coupled with negligible correlation between <i>ε</i>_Nd(<i>t</i>) and SiO₂ contents imply limited crustal assimilation during magma evolution. Petrological modeling, based on Sm/Yb and La concentrations, suggests the gabbroic melt derived from ∼8%–20% spinel lherzolte mantle melting. Analogously depleted Hf-Nd isotopes (<i>ε</i>_Hf(<i>t</i>) = +6.81 to +9.10, <i>ε</i>_Nd(<i>t</i>) = +0.79 to +1.45) in the granite, together with petrographic evidence lacking mafic-ultramafic xenoliths, point to a juvenile lower-crustal source. Integrating the gabbro’s N-MORB-like affinity with arc-specific features, regional ultrahigh-temperature metamorphism in southern Chinese Altai, and Permian tectonics, we propose a ridge-subduction regime as the likely petrogenetic setting for the Jiangjunshan magmas. During ridge subduction, upwelling of asthenospheric mantle beneath the ridge induced partial melting of the lithospheric mantle, giving rise to the parental magma of the Jiangjunshan gabbro. This mafic magma underplating subsequently heated the juvenile lower crust, triggering its partial melting and generating the parental magma of the two-mica alkali feldspar granite. Our model indicates that ridge-subduction-related magmatism persisted in the Chinese Altai until the Middle Permian, followed by a tectonic shift from oceanic-continental subduction to intracontinental extension.</p>