Petrogenesis of the Permian granitoids in the western Gonghe basin, NE Tibetan Plateau (China): Implications for the Late Paleozoic tectonic evolution of the Paleo-Tethys Ocean

The western Gonghe basin in the NE Tibetan Plateau, witnessed extensive magmatism during the Triassic, whereas only few magmatic flare-up events occurred during the Permian. Understanding the geodynamic setting of these magmatic pulses is important in the reconstruction of the Paleo-Tethys tectonic history. In this contribution, we present in-situ zircon UPb geochronological and LuHf isotopic data, as well as whole-rock major and trace elements data from monzogranite and syenogranite dyke in the western Gonghe region to constrain their petrogenesis and tectonic implications. Zircon UPb data show that the monzogranite (253–260 Ma) and syenogranite dyke (247-261 Ma) were formed during the Late Permian, rather than the Jurassic as presumed in previous studies. Mineralogical characteristics and geochemical affinities reveal that these rocks are high-K calc-alkaline, metaluminous to weakly peraluminous (ASI = 0.95–1.02), moderately-highly fractionated (DI = 81–95) I-type granites. The major and trace element characteristics (including Mg#, Ni, Cr, Zr/Hf, Nb/Ta, and Th/U contents), together with the zircon εHf(t) values (−5.90 to 1.22, TDMC = 845–1250 Ma) and 176Hf /177Hf ratios (0.282481 to 0.282674) suggest that the magmas were derived through partial melting of the Early Mesoproterozoic metagreywacke in the lower crust with minor juvenile crust addition. Extensive fractional crystallization of plagioclase and subordinate K-feldspar as well as apatite is inferred. Our findings in this study, in conjunction with those from previous studies, suggest that the magmatic flare-up event during the Late Permian in the western Gonghe area is related to local extension concomitant with the break-off of the subducting slab associated with the northward subduction of the Paleo-Tethys oceanic lithosphere.