An evolving tectonic environment of Early to Middle Permian granitic plutons in the Barkol area, East Junggar: insights from integrated zircon U–Pb ages, geochemistry, and Nd–Sr–Hf isotopes

Located in the central part of the Central Asian Orogenic Belt, East Junggar represents one of the most important sites of juvenile crustal growth during the Phanerozoic. However, the mechanism of juvenile crustal growth during the Permian remains controversial. The Daheishan granites in the eastern segment of East Junggar are dated at ~292 Ma (Early Permian) and 269 Ma–267 Ma (Middle Permian). The Early Permian granites are coarse-grained with very high SiO2 (76.64 wt%–80.02 wt%), Al2O3 (10.72 wt%–12.96 wt%), and K2O/Na2O (1.27‒2.14), and low TiO2 (0.12 wt%–0.18 wt%), CaO (0.27 wt%–0.90 wt%), Mg# (25–32), and Sr/Yb (16–25). The Middle Permian granites are medium‒fine-grained with relatively high SiO2 (71.84 wt%–76.26 wt%), Al2O3 (11.26 wt%–13.00 wt%), and K2O/Na2O (0.53–1.54), and low TiO2 (0.17 wt%–0.21 wt%), CaO (0.37 wt%–3.20 wt%), Mg# (33–43), and Sr/Yb (5–9). These Permian granites display slightly positive whole-rock εNd(t) (+0.77 to + 1.04) and highly positive zircon εHf(t) (+7.3 to + 8.7) values, and low Ga/Al (2.04–2.55 2O5 (0.02%–0.05%