Origin and tectonic significance of Eocene sodic lamprophyres in the Southern Qiangtang Orogen, Tibet

[Display omitted] •The Eocene Gumu sodic lamprophyres (GSLs) are identified in the Southern Qiangtang Orogen.•The GSLs belong to the sodic alkaline series with OIB-like affinity.•The GSLs are likely originated from asthenosphere mantle modified by slab fluids.•The GSLs were generated during the upwelling of asthenosphere triggered by delamination of the lithosphere. Sodic lamprophyres have important implications on crust-mantle interactions and tectonic evolutionary processes. This study presents detailed mineralogical and geochemical dataset to elucidate the origin of the sodic lamprophyres in the Gumu area and geodynamic implications for the Southern Qiangtang Orogen. The Gumu sodic lamprophyres (GSLs)with a zircon 206Pb/238U age of 42 Ma are primarily composed of amphibole (45%-57%), plagioclase (20%-30%) and clinopyroxene (10%). They exhibit sodic alkaline series affinity with high Na2O content (3.65 wt% on average) and Na2O/K2O ratio (2.26 on average). The GSLs show OIB-like geochemistry, including enrichment in LREEs and LILEs, positive zircon εHf(t) (+1.16 to + 7.39), slightly higher εNd(t) (−0.38 to + 0.9), and lower initial 87Sr/86Sr (0.70522 to 0.70589) values), and they were likely derived by the partial melting of an asthenosphere mantle source previously modified by slab fluids under spinel-garnet facies at about 1,321 °C-1,399 °C and 2.1–2.7 GPa. Integrating published regional contemporaneous mafic–intermediate rocks from the Qiangtang Orogen and this study, we propose that the GSLs formed in an intracontinental setting during asthenosphere upwelling triggered by delamination of the lithosphere. The GSLs provide new perspective for reconstructing the Eocene tectonomagmatic process in the Southern Qiangtang Orogen.