Coexistence of Hainan Plume and Stagnant Slab in the Mantle Transition Zone beneath the South China Sea Spreading Ridge: Constraints from Volcanic Glasses and Seismic Tomography

Abstract The influence of Hainan mantle plume and subducting recycled oceanic crust beneath the spreading ridge South China Sea (SCS) have been widely proposed recently, but still controversial ambiguous. Here, we present seismic tomographic evidence, new major trace element, Pb isotopic compositions volcanic glasses from one International Ocean Drilling Program drill core (Site U1434) in SCS ridge. are relatively enriched alkalis light rare earth elements (LREEs) depleted heavy REEs (HREEs), exhibit slightly positive anomalies Nb, Ta, Zr, Hf as well a Nb relative to La Th, show high 207Pb/206Pb 208Pb/206Pb ratios, suggesting ocean island basalt- (OIB-) type 2- (EM2-) geochemical features likely related plume. These consistent with those late Cenozoic rocks surrounding areas associated plume, providing SCS. primary-melt indicate that source involved 18.5% eclogite (dense, stagnant subducted slab) 46.1% garnet pyroxenite (produced by reaction between peridotite melt crust). existence slab is further supported geophysical evidence recent three-dimensional P-wave model.