Seismic imaging of the Reunion mantle plume

Since the mantle plume concept was proposed, the plume morphology has been debated in the past decades regarding its size, shape and origin. Reunion Island has been considered as the surface manifestation of a plume rising from the lower mantle. However, there has been few direct evidence from the deep mantle supporting this hypothesis until recent passive seismic observations. Here we use P-wave travel-time data recorded at many portable seismic stations to image the deep structure beneath Reunion Island, aiming to reveal the plume morphology and find evidence for off-axis interaction between the Reunion plume and the central Indian ridge (CIR). Our 3-D tomographic results show a mushroom-shaped low-velocity anomaly with a broad head and a thin, nearly vertical tail down to at least 1000 km depth, which exhibits an archetype plume and indicates weak mantle wind under Reunion Island. In the upper mantle, a low-velocity channel connects the Reunion plume and CIR along the Rodrigues ridge, indicating plume-related thermal and material exchanges from the Reunion plume to CIR. Slight ponding occurs around 660 km depth, which may reflect density stratification resulting from a phase change at the 660-km discontinuity.