Petrogenesis and tectonic implications of Late Permian S-type granites in the South Kunlun Belt, northern Tibetan Plateau

Abstract

• Two-mica granites in south Kunlun are identified as S-type with ages of 260–257 Ma. • These S-type granites were derived by H 2 O-fluxed biotite melting of metagreywacke . • These S-type granites and their genesis indicate anatexis of an accretionary wedge. S-type granites are striking products of supracrustal reworking and can provide crucial constraints on the anatexis of accretionary wedges in an accretionary orogen. In this study, we present new zircon and monazite dating results, whole-rock geochemistry, and zircon Lu-Hf isotopic data for the two-mica granites in the Muztagh area of the South Kunlun Belt. Integrated dating results reveal that the two-mica granites crystallized at 260–257 Ma. These two-mica granites are characterized by the presence of muscovite and an aluminum saturation index of 1.04–1.13 typical for S-type granite affinity. They display enrichment in LREEs and LILEs, depletion in HFSEs, and weak negative to positive Eu anomalies. The high CaO/Na 2 O ratios and Sr contents, and low Rb contents, together with a comparison with experimental melting results suggest that the two-mica granites were derived through H 2 O-fluxed biotite melting of metagreywacke. The ε Hf (t) values for co-magmatic zircons display a wide range from −11.5 to +1.14, together with heterogeneous ε Hf (t) values (−10.1 to +6.72) for inherited cores implying a mixed source involving ancient sediments and juvenile volcanic materials. Accordingly, the protoliths of the two-mica granites were formed in the forearc setting, and the Late Permian two-mica granites were generated in the subduction environment related to the Paleo-Tethyan Ocean. Our results, along with the occurrence of the Early Paleozoic peraluminous granites in the South Kunlun Belt, suggest that the forearc accretionary complex in the E-KOB underwent multiple anatectic events during continuous subduction and accretion of the oceanic plate.