Geochronology, petrogenesis and tectonic significance of Dahongliutan pluton in Western Kunlun orogenic belt, NW China

Abstract

The Dahongliutan granitic pluton, in the eastern part of the West Kunlun orogenic belt, provides significant insights for studying the tectonic evolution of West Kunlun. This paper presents a systematic study of LA-ICP-MS zircon U-Pb age, major and trace elements, Sr-Nd-Hf isotopes, and the first detailed Li isotope analysis of the Dahongliutan pluton. LA-ICP-MS zircon U-Pb dating shows that the Dahongliutan granites were emplaced in the Late Triassic ((213±2.1) Ma). Geochemical data show relatively high SiO2 contents (68.45 wt%–73.62 wt%) and aluminum saturation index (A/CNK=1.11–1.21) indicates peraluminous high-K calc-alkaline granite. The Dahongliutan granites are relatively high in light rare earth elements (LREE) and large ion lithophile elements (LILEs) (e.g., Rb, K, Th), and relatively depleted in high field strength elements (HFSEs) (e.g., Nb, Ta, P, Ti). The eNd(t) values range from −8.71 to −4.73, and (87Sr/86Sr)i=0.7087–0.71574. Zircons from the pluton yield 176Hf/177Hf values of 0.2826181 to 0.2827683, and eHf(t) values are around 0; the two-stage Hf model ages range from 0.974 to 1.307 Ga. The δ7Li values are 0.76‰–3.25‰, with an average of 2.53‰. Isotopic compositions of the pluton suggest a mixed trend between the partial melting of the Middle Proterozoic ancient crustal material and a juvenile mantle-derived material. This study infers that the Dahongliutan rock mass is formed in the post-collisional extension environment, when the collision between South Kunlun and the Tianshuihai terranes results in the closure of the Palaeo-Tethys. The mantle-derived magma results in partial melting of the lower crust.