Late Carboniferous–Early Permian granitoids are widespread in the Tianshan area and their tectonic setting is controversially discussed. Our research presents fresh whole-rock geochemical and Pb isotopic data, along with zircon U-Pb ages and Hf isotopic data for representative monzonitic and granitic intrusions in the Kumishi area. The aim is to decipher their magma sources and illuminate their geodynamic evolution. Zircon U-Pb dating results reveal that biotite monzonites in the Central Tianshan Belt were emplaced at 312.7 ± 2.9 Ma, while the quartz-monzonites and syenogranites in the South Tianshan Belt were formed at 284.5 ± 2.4 Ma and 283.4 ± 3.9 Ma, respectively. The biotite monzonites generally exhibit metaluminous and high-K calc-alkaline characteristics. They have a positive ε_Hf(t) value (+4.9–+14.1), and are enriched in LREEs and LILEs but depleted in HREEs and HFSEs. These characteristics indicate that they were derived from a mixed magma source of the lower crust and the input of components derived from the mantle wedge above the subduction zone. The quartz-monzonites and syenogranites are high-K calc-alkaline to shoshonitic I-type granites, with ε_Hf(t) values of +14.9–+15.5 and +6.6–+14.9, respectively. They are enriched in LREEs but depleted in HFSEs (e.g., Nb, Ta, and Ti), displaying relatively flat HREE patterns and negative Eu anomalies. The genesis of these rocks is attributed to a partial melting of the lower crust in which mantle-derived magmas participated, which was triggered by an upwelling asthenosphere in a post-collisional extensional geodynamic setting. These granitoids, together with regional analysis of other magmatism in the study area, suggest that the Kumishi area has experienced an evolution from subduction to post-collision from the Late Carboniferous to the Early Permian, which constrains the local closure of the Paleo-Asian Ocean.

Subduction of the South Tianshan Ocean caused widespread Devonian magmatism, lithospheric deformation, and thinning along the south margin of the Central Tianshan Belt. However, the details of this subduction process remain elusive. This study presents comprehensive data on Devonian granitoids from the Kumishi area, including whole-rock geochemical data, Sr-Nb-Pb isotopic compositions, zircon U-Pb ages, and zircon Hf isotopic data. Dioritic porphyrites, medium–fine-grained monzogranites, and coarse–medium-grained monzogranites were emplaced at 397 ± 2 Ma, 397 ± 3 Ma, and 395 ± 3 Ma, respectively. The dioritic porphyrites have relatively high Sr contents, low heavy rare earth element (HREE) and Y contents, and high Sr/Y ratios, which are characteristics of adakites. High Al and Na₂O contents suggest that the rocks formed through partial melting of subducted oceanic crust. The monzogranites display I-type and subduction-related arc affinities, sourced from a mixed magma of crustal materials and mantle wedge components. The granodiorites were emplaced at 373 ± 3 Ma, and also exhibit pronounced I-type and subduction-related arc affinities. Combined with previous data, our results demonstrate that the studied area of Devonian magmatism records the entire spatiotemporal evolution of subduction of the South Tianshan Ocean slab, from initial shallowing of the subduction angle to flat-slab subduction, followed by final slab rollback.