Permian ridge subduction-related magmatism in the Eastern Tianshan: Implications for the evolution of the southern Altaids

Abstract

Permian large-scale transcurrent tectonics and syn -kinematic ultramafic–felsic magmatism are prominent features in the Eastern Tianshan of the southern Altaids. However, the genetic relationship between coeval Ni Cu mineralized mafic-ultramafic intrusions and felsic intrusions, and the geodynamics of the region remains equivocal. To assess these topics and improve our understanding of this geologically complex and economically significant region, zircon Hf isotope and bulk-rock geochemical data from Permian granitoids along the Kanggur–Huangshan Shear Zone (KHSZ) in the Eastern Tianshan are determined and interpreted in the context of previous geochronological–geochemical data. The Kungurian Longdong (ca. 278 Ma) and Hongshi (ca. 273 Ma) granitoids are high-K, calc-alkaline, metaluminous to weakly peraluminous I-type granitoids, whereas the Capitanian Shuangchagoubei (ca. 262 Ma) granitoids are calc-alkaline, peraluminous, adakitic I-type granitoids. All of the granitoid samples are enriched in light rare earth elements and large ion lithophile elements (e.g., Rb, U, and K), and depleted in high field strength elements (e.g., Nb, Ta, and Ti), similar to arc magmas, indicating that subduction-related magmatism was still active in the late Permian. Taking into account the regional geology, and the presence of Permian high-temperature metamorphism, adakites, I-type granites, Alaskan-type Ni Cu sulfide and orogenic Au mineralization, and EW-trending N-MORB type gabbro and mélange along the KHSZ, we suggest that subduction of a spreading center during the Permian generated a slab window, allowing the upwelling of asthenospheric mantle. This permitted the generation and migration of mantle-derived magmas to shallower crustal levels along translithospheric faults (e.g., Kanggur and Yamansu faults), forming the mafic–ultramafic intrusions and associated Ni Cu sulfide deposits. The continuous migration of magma provided the necessary heat to induce partial melting of juvenile crust, generating the Permian high-K to calc-alkaline I-type granitoids. Ridge subduction-induced juvenile crustal reworking likely played a central role in the formation of the granitoids during the late Paleozoic accretionary orogenesis of the southern Altaids. • Subduction-related magmatism was active in the Eastern Tianshan in the late Permian. • Crustal growth and reworking processes must have occurred simultaneously in the Eastern Tianshan during the Permian. • Ridge subduction-induced juvenile crustal reworking likely played an important role in the formation of the granitoids in the southern Altaids.