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Petrology, geochemistry, platinum group elements (PGEs: Os, Ir, Ru, Rh, Pt, and Pd), and Re‐Os isotope data of harzburgites and plagioclase lherzolites from the Shuanggou ophiolite (southwest China) are presented in this study, in order to determine whether ancient refertilization process can be preserved in ophiolitic plagioclase peridotites. The harzburgites in the Shuanggou ophiolite are divided into two groups: (1) the Group‐1 harzburgites have 187Os/188Os ratios (0.12297–0.12727) and PGE abundances similar to those of oceanic peridotites, thereby representing the convecting upper mantle; (2) the Group‐2 harzburgites have extremely low 187Os/188Os ratios (0.11307–0.11651) with considerable fractionation in iridium group PGEs (Os, Ir, and Ru), indicative of an ancient refractory mantle in the oceanic lithosphere. The plagioclase lherzolites were formed by melt impregnation of the Group‐2 harzburgites, according to the PGE compositions and the petrographic features. However, the large Os isotope difference between the lherzolites (187Os/188Os: 0.12470–0.12666) and the Group‐2 harzburgites indicates that the refertilization process took place much earlier than the exhumation of the mantle at 0.4 Ga. In addition, clinopyroxene composition suggests that the percolating melt is different from the Shuanggou diabases and typical mid‐ocean ridge basalts. This study therefore demonstrates that some plagioclase lherzolites possibly were not related to mantle exhumation beneath the spreading center but formed by much older melt impregnation processes in the mantle instead. Key Points: First platinum‐group element (PGE) and Re‐Os isotope results for peridotites of Paleo‐Tethys ophiolites in southwest ChinaAncient refractory mantle domains are preserved in the mantle peridotitesPlagioclase lherzolites were converted from the ancient refractory domains by refertilization much earlier than the seafloor spreading [ABSTRACT FROM AUTHOR]

Abstract: The late Permian Panzhihua syenitic stock in the Pan-Xi area, SW China, showing the typical association of mantle-derived mafic and alkaline rocks along with silicic units, is genetically related to the upwelling Emeishan plume head. This syenitic intrusion consists mainly of metaluminous syenite, metaluminous to peralkaline quartz syenite with subordinate syenite porphyry and alkali-feldspar granite. SHRIMP U–Pb zircon analysis reveal that the Panzhihua syenitic pluton was emplaced at 253.1±1.9 Ma, and is slightly younger than the crystallization age of the spatially associated gabbroic intrusion. These syenitic and granitic rocks have a distinctive A-type chemistry characterized by elevated high-field-strength elements (HFSE) contents and high Ga/Al ratios (3.95 to 6.79). Nb/Ta and Zr/Hf ratios of the syenitic and granitic rocks, gabbros and syenodiorites are similar to those typical of oceanic island basalt (OIB). These granitoids all have relatively low initial 87Sr/86Sr ratios (0.7037–0.7058), positive ε Nd(t) values (+2.4 to +3.5). The magmatic zircons from the syenites exhibit positive ε Hf(t) values between 5.9 and 10.4, which correspond to single-stage depleted mantle Hf model ages (T DM1) of 494 to 671 Ma. In contrast, the magmatic zircons from the syenite porphyries are characterized by positive ε Hf(t) values of 11.4 to 12.9 with younger T DM1 model ages of 382 to 449 Ma than those of the syenites. The positive ε Nd(t) and ε Hf(t) values of the Panzhihua syenitic intrusion indicate a significant contribution of plume-derived basaltic underplating to magma genesis. The similarity of the Nd isotopic compositions of the syenitic and granitic rocks, gabbros and syenodiorites suggests that their parental magmas were derived from a common reservoir. We propose that the Panzhihua syenitic intrusion was predominantly generated by the emplacement of two distinct syenitic melts from differentiation of newly underplated, mildly alkaline basaltic magmas ponded at depth, with incorporation of little Neoproterozoic lower crustal melts, and subsequent fractional crystallization of individual melts. It is therefore demonstrated that the growth of juvenile crust through mantle-derived underplating during the late Permian was significant in the inner zone of the Emeishan large igneous province. [Copyright &y& Elsevier]