Petrogenesis and Tectonic Significance of the Late Paleozoic Granites from the Western Tianshan, Xinjiang

The Western Tianshan Orogen is located in the southwestern Central Asian Orogenic Belt (CAOB). The widespread magmatic rocks provide a critical window for investigating regional tectonic-metallogenic dynamics. To address controversies regarding the petrogenesis, tectonic setting of granitoids, and the closure timing of the North Tianshan Ocean in the Western Tianshan region, this study focuses on the Late Paleozoic granitoids (Guozigou, Halegati, Jinghe, and Nalati plutons) located along the northern margin of the Yili Block, through integrating geochronological, whole-rock elemental, and Sr-Nd-Hf isotopic analyses. The studied plutons are predominantly composed of monzonitic granite and potash feldspar granite. Zircon LA-ICP-MS U-Pb dating reveals that these plutons were emplaced between (368.1±1.5) Ma (Late Devonian) and (301.9±2.8) Ma (Late Carboniferous). Combined with regional geochronological data, the magmatism in the northern Yili Block can be temporally subdivided into two stages, late Devonian to early Carboniferous and late Carboniferous. The studied granitoids exhibit high silica (SiO₂ = 66.62%~76.08%) and total alkali (K₂O+Na₂O=6.72%~8.85%) contents. In terms of rare earth elements, the studied samples show LREE-rich patterns with variable negative Eu anomalies (δEu = 0.30–0.97). The trace element patterns of the studied rocks are characterized by enrichment in Rb and Th and depletion in Nb, Ta, and Ti, comparable to those of continental arc granites. The late Devonian granitoid samples show slightly enriched radiogenic isotopic signatures, with negative ε_Nd(t) from -3.79 to -1.3 and ε_Hf(t) from +0.3 to +5.0, indicating magma sources dominated by ancient crustal materials with mantle-derived contributions. In contrast, the Late Carboniferous granitoids show more radiogenic ε_Nd(t) (+0.8 to +5.9) and ε_Hf(t) (+4.1 to +15.1) values, indicative of a juvenile lower crustal origin. Integrating previous studies, we propose that the 368–307 Ma granitoids are of I-type granite and were formed associated with the northward subduction of the Northern Tianshan Ocean beneath the Yili Block, whereas later A2-type potash feldspar granites and I-type monzonitic granites in the context of post-collisional lithospheric delamination initiated at ~305 Ma. Additionally, the Late Devonian-early Carboniferous to Late Carboniferous granitoids in the Borohoro region exhibit significant potential for Cu-Mo mineralization.