Petrogenesis of Early Devonian granodiorite in the Xiaobaishitou W–(Mo) ore district of East Tianshan, Northwest China, and tectonic implications: U–Pb geochronological, geochemical, and Sr–Nd isotopic evidence

Abstract

The Palaeozoic intrusions of East Tianshan, China, are important for understanding the tectonic evolution of the Central Asian Orogenic Belt. We investigated one such Devonian granodiorite, located in the Xiaobaishitou W–(Mo) ore district of the Central Tianshan Block, to constrain its petrogenesis and geodynamic setting. Laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) zircon U–Pb dating indicates that the granodiorite emplaced at 407 Ma and can be classified as an I‐type granite based on its mineralogy and whole‐rock geochemistry. The granodiorite also exhibits moderate Mg# values, high MgO, Ni, and CaO contents, depleted Ti and Nb concentrations, and negative εNd(t) values (−8.32 to −3.73), indicating a magma derived from the mantle but contaminated with ancient crustal rock. Mineral chemistry, saturation thermometry, and whole‐rock Fe2O3/FeO ratios indicate crystallisation temperatures of 654–822°C, pressures of 1.8–2.1 kbar, and oxygen fugacity of ≤NNO for the granodiorite stock. We compare granodiorite geochemical data to those from other recent studies of Palaeozoic intrusive rocks in East Tianshan and infer that the formation of the Early Devonian granodiorite in the East Tianshan was due to a south‐dipping subduction of the Kanggur Ocean plate toward the Central Tianshan Block.