Opening of the South China Sea and Upwelling of the Hainan Plume

Abstract

AbstractOpening of the South China Sea and upwelling of the Hainan Plume are among the most challenging issues related to the tectonic evolution of East Asia. However, when and how the Hainan Plume affected the opening of the South China Sea remains unclear. Here we investigate the geochemical and isotopic features of the ~25 Ma mid‐ocean ridge basalt (MORB) in the Kenting Mélange, southern Taiwan, ~16 Ma MORB drilled by the IODP Expedition 349, and ~9 Ma ocean island basalt‐type dredged seamount basalt. The ~25 Ma MORBs reveal a less metasomatic depleted MORB mantle‐like source. In contrast, the Miocene samples record progressive mantle enrichment and possibly signal the contribution of the Hainan Plume. We speculate that MORBs of the South China Sea which could have recorded plume‐ridge source mixing perhaps appear since ~23.8 Ma. On the contrary, the Paleocene‐Eocene ocean island basalt‐type intraplate volcanism of the South China continental margin is correlated to decompression melting of a passively upwelling fertile asthenosphere due to continental rifting.