Understanding subduction initiation and mantle plume dynamics is central to plate-tectonic evolution but remains poorly constrained in ancient orogens. The tectonic evolution of the North Tianshan paleo-ocean basin, a key segment of the Paleo-Asian Ocean of the Altaids, has long been debated owing to the scarcity of diagnostic ophiolitic records. Here we present a systematic study of the Bayingou ophiolite that identifies two temporally and genetically distinct magmatic suites: a forearc-type ophiolitic assemblage (cumulate gabbro, gabbro, and plagiogranite; Group 1) and plume-related seamount basalts (Group 2). Zircon U-Pb geochronology indicates that Group 1 cumulate gabbro crystallized in the middle Cambrian (ca. 505 Ma), whereas Group 1 gabbro and plagiogranite record Early Carboniferous magmatism (ca. 345−330 Ma), implying episodic forearc magmatic activity. Group 1 rocks display major and trace element patterns and depleted Sr-Nd-Hf isotopic compositions comparable to those of typical Izu−Bonin−Mariana forearc basalts, while their Pb isotopes overlap Pacific mid-oceanic-ridge basalt (MORB) and Paleo-Asian MORB-type ophiolites, indicating derivation from a Pacific-type low-Th/U depleted mantle. Thermobarometric modeling suggests shallow (<8 kbar) and high-temperature (∼1156 °C) decompression melting of upwelling asthenosphere, consistent with extension-induced asthenospheric ascent in forearc settings. In contrast, Group 2 basalts are enriched in Nb, Ta, Ti, and light rare earth elements [(La/Yb)N = 4.6−6.6] and exhibit a pronounced DUPAL anomaly (first documented by Dupré and Allègre, 1983), indicating an enriched, plume-related deep-mantle source analogous to global hotspots (e.g., Hawaii, USA, North Pacific Ocean, and St. Helena, South Atlantic Ocean). Integrating these results with regional geology, we infer early Cambrian forearc development linked to subduction initiation, followed by sustained intra-oceanic subduction beneath the Yili−Central Tianshan block from the Early Carboniferous (ca. 345−265 Ma), accompanied by supra-subduction zone−type ophiolite formation. Widespread plume-related seamount volcanism produced composite oceanic lithosphere that later accreted into the orogenic complex. This study provides crucial constraints on forearc magmatism and plume activity, serving as a vital analogue for tectonic evolution in ancient orogenic systems.