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

Abstract

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.