Zircon U–Pb geochronology, Hf isotopes, and whole‐rock geochemistry of Hongshuihe Early to Middle Triassic quartz diorites and granites in the Eastern Kunlun Orogen, NW China: Implication for petrogenesis and geodynamics

Abstract

The Hongshuihe area of Eastern Kunlun Orogen is well‐known for the BIF‐type deposits. Some widespread intrusive rocks in the northern Hongshuihe area were previously thought to be emplaced in the Hercynian. This article presents LA‐ICP‐MS zircon U–Pb ages, with LA‐MC‐ICP‐MS in situ Hf isotopes and major and trace element data for quartz diorites and granites of the Hongshuihe pluton. Two samples from the Hongshuihe quartz diorite and granite yielded a weighted mean zircon U–Pb age of 244 ± 2 Ma (Anisian) and 246 ± 1 Ma (Olenekian), respectively. The Hongshuihe subalkaline quartz diorite is metaluminous with the alumina saturation index values of 0.93–1.00, and high SiO2 contents of 59.67–65.51 wt.%, low Y values of 11.1–16.7 ppm, and low HREE (Yb = 1.08–1.83 ppm) that collectively suggest high‐SiO2 adakite‐like rocks. The Hongshuihe granites have slightly high alkali contents of 7.04–8.12 wt.%, alumina saturation index values of 1.01–1.03, low (Zr + Nb + Ce + Y) contents of 315.30–455.50 ppm, and high Fe2O3T/MgO ratios of 4.03–5.16, indicating fractionated I‐type normal island arc magma. The zircon εHf(t) values from −4.0 to −1.1 for the Hongshuihe quartz diorite sample and values from −2.4 to +1.7 for the granite sample correspond to partial melting of Mesoproterozoic thickened lower crust and partial melting of juvenile mantle‐derived mafic lower crust, respectively. We conclude that during the Early–Middle Triassic, the Eastern Kunlun area underwent a tectonic setting of the northward subduction of the Palaeo‐Tethys oceanic slabs.