Focused Mantle Upwelling Beneath the Southeastern Asian Basalt Province Revealed by Seismic Surface Wave Tomography

Following the termination of seafloor spreading in the South China Sea (SCS) basin, abundant intraplate volcanism widely spreads in the Indochina block, SCS basin, and Leiqiong area, forming the Southeastern Asian Basalt Province (SABP). The geodynamic origin of the SABP has long been enigmatic and debated. Here, we present a high-resolution 3-D upper mantle S-wave velocity model in the region by conducting earthquake-based surface wave tomography with seismic data collected across Southeast Asia. The resultant images depict a plume-like structure beneath the central area of the SABP, characterized by a continuous, sub-vertical low-velocity column in the upper mantle. Our new findings, combined with previous geochemical and geodynamic evidence, suggest that the extensive post-spreading intraplate volcanism within the SABP is likely induced by this focused mantle upwelling, which could be further traced down to the core-mantle boundary as inferred by existing global velocity models. The well-known Southeastern Asian Basalt Province (SABP), which covers an extensive area of the South China Sea (SCS) and surroundings, is characterized by voluminous volcanism after the cessation of seafloor spreading in the SCS basin. However, the geodynamic mechanism responsible for the formation of the SABP remains debated and not well understood. In this study, we build a high-resolution 3-D seismic velocity model in the region utilizing multiple sources of seismic data collected throughout Southeast Asia. We find a distinct plume-shaped low-velocity anomaly in the upper mantle beneath the central region of the SABP. Combining with previous geochemical and geodynamic research results, we interpret that the abundant intraplate volcanism within the SABP may be contributed by the underlying focused mantle upwelling. This mantle upwelling, as evidenced in previous global seismic velocity models, could be further traced down to the core-mantle boundary (similar to 2,900 km below the Earth's surface). Our tomographic images provide valuable insights into the origin and mantle dynamics related to the young intraplate volcanism that occurred in Southeast Asia. A high-resolution 3-D upper mantle S-wave velocity model surrounding the South China Sea is constructedA continuous, low-velocity column is imaged beneath the central region of the Southeastern Asian Basalt ProvinceThe post-spreading intraplate volcanism within the Southeastern Asian Basalt Province is likely induced by the focused mantle upwelling