Origin of the Late Permian gabbros and Middle Triassic granodiorites and their mafic microgranular enclaves from the Eastern Kunlun Orogen Belt: Implications for the subduction of the Palaeo‐Tethys Ocean and continent–continent collision

Abstract

The geodynamic evolution of the Eastern Kunlun Orogen Belt (EKOB) during the late Palaeozoic–Early Mesozoic remains controversial. Here, we present new zircon UPb, element geochemical, and SrNdHf isotopic data for the Kaerqueka gabbros, granodiorites, and their mafic microgranular enclaves (MMEs) in the Qiman Tahg area of Qinghai Province (QTQP), western EKOB, with a view to constrain their petrogenesis and tectonic setting. New LA–ICP–MS zircon UPb ages indicate that the Kaerqueka gabbro, granodiorite, and its MMEs were emplaced at 257 ± 2, 244 ± 1, and 245–244 Ma, respectively. Based on our new ages and published data, three major episodes of magmatism (ca. 263–249, 247–240, and 237–211 Ma) during the Late Permian–Triassic are recognized in the EKOB. The gabbros are characterized by low SiO2 concentrations and are potassic with high K2O contents and K2O/Na2O ratios. They are enriched in light rare earth elements (LREEs) and large‐ion lithophile elements (LILEs) and have (87Sr/86Sr)i of 0.70737–0.70851, εNd (t) of −2.8 to −2.7 and εHf (t) of +0.7 to +2.9, indicating that the gabbros were derived from an enriched lithospheric mantle which was affected by slab‐derived fluids or melts. The MMEs and host granodiorites are enriched in LREEs and depleted in high‐field‐strength elements and have (87Sr/86Sr)i of 0.71090–0.71129, εNd (t) of −6.58 to −5.21, and εHf (t) of −5.3 to −1.8. Indistinguishable crystallization age, trace element pattern and isotopic compositions between the MMEs and host granodiorites indicate that they are cogenetic and were dominantly originated from the partial melting of Mesoproterozoic juvenile mafic lower crust. Combined with our new results and published geological, geochronological, and geochemical data, we propose that the subduction of the Palaeo‐Tethyan Ocean lasted from Late Permian to Early Triassic, and that the onset of the collision mostly occurred during the Middle Triassic in the EKOB.