Zircon U-Pb dating, geochemistry and Sr-Nd-Pb-Hf-O isotopes for the Nan'getan granodiorites and mafic microgranular enclaves in the East Kunlun Orogen: Record of closure of the Paleo-Tethys

The East Kunlun Orogen in the Northern Qinghai-Tibet Plateau is an ideal region to investigate the geodynamic processes of magmatism related to the closure of the Paleo-Tethys Ocean. Here, we report petrology, zircon U-Pb geochronology, whole-rock geochemistry and multiple isotope data from granodiorites and the associated dioritic enclaves in a dominant Nan'getan granitoid in the East Kunlun Orogen. Zircon U-Pb ages indicate that the host granodiorites and dioritic enclaves were synchronously emplaced at similar to 243 Ma. The granodiorites are medium- to high-K calc-alkaline, metaluminous (A/CNK = 0.93-0.98), with high Al2O3 content (15.28%-16.10%), MB# (47-49), very low Sr/Y ratios (127-217), high abundances of incompatible elements (Y = 3.87-8.36 ppm, Nb = 3.04-5.71 ppm, Th = 3.04-5.71 ppm), low (Sr-87/Sr-88)(i) (0.7050-0.7079), negative whole-rock epsilon(Nd)(t) (-8.2 to -5.8), ((206)pb/Pb-204)(243Ma) of 18.520 to 18.772, (Pb-207/Pb-204)(243Ma) of 15.611 to 15.650, (Pb-208/Pb-204)(243Ma) of 38.227 to 38.528, delta O-18(SMOW) = 6.8 parts per thousand-9.1 parts per thousand, epsilon(Hf)(t) of - 12 to + 2.4. The dioritic enclaves (SiO2 = 51.08%-56.29%) have Mg-# values of 48-51, with negative Eu anomalies (delta Eu = 0.59-0.79), low (Sr-87/Sr-86)(i) (0.7058-0.7080), negative whole-rock epsilon(Nd)(t) (-8.2 to -5.8) (Pb-206/Pb-204)(243Ma) of 18.376 to 18.809, (Pb-207/Pb-204)(243Ma) of 15.606 to 15.661, (Pb-208/Pb-204)(243Ma) of 38.244 to 38.540, delta O-18(SMOW) = 5.6 parts per thousand-10.0 parts per thousand, epsilon(Hf)(t) -3.5 to + 1.7. These isotopic features of arc-type rocks from the East Kunlun suggest that the parental magmas of the Nan'getan granodiorites and the dioritic enclaves originated from an enriched lithospheric mantle. The Nan'getan granitoids might have recorded the northward subduction of the Paleo-Tethys ocean lithosphere following the initial collision of the Bayan Har-Songpan Ganzi-East Kunlun terrane and the closure of the Paleo-Tethys Ocean at similar to 243 Ma. (C) 2015 Elsevier B.V. All rights reserved.