Electromagnetic evidence for volatile‐rich upwelling beneath the society hotspot, French Polynesia

We have conducted a seafloor magnetotelluric survey that images, for the first time, three‐dimensional electrical conductivity structure in the upper mantle beneath the Society hotspot. A striking feature in our model is a high‐conductivity anomaly a few hundred kilometers in diameter, which is continuous from the lowest part of the upper mantle to a depth of approximately 50 km below sea level. Using theoretical and experimental results from mineral physics, we interpret the high‐conductivity anomaly as evidence of the melt fraction up to 2.2 vol.%, which is robust regardless of assumed temperature, and the existence of carbonated silicate melt beneath the hotspot. Our results suggest that the Society hotspot is a pathway for ascending volatiles from the deeper part of the upper mantle to the surface. Key Points Three‐dimensional high electrical conductivity anomaly is imaged in the upper mantle beneath the Society hotspot The anomaly can be explained by the presence of upwelling of volatile‐rich and partially molten material A pathway for ascending volatiles from the deeper part of the upper mantle has formed the Society hotspot