Thick Underplating and Buoyancy of the Bermuda Swell

Abstract Bermuda is an intraplate ocean swell that does not conform to traditional mantle plume theory. Unlike other prominent bathymetric swells, such as Hawaii, it lacks age‐progressive volcanism, a deeply rooted mantle plume, and modern volcanism. High‐frequency receiver‐function imaging of the shallow lithosphere beneath the Bermuda swell reveals two prominent interfaces interpreted as the fossil oceanic Moho and the bottom of an underplated layer. This underplated layer is ∼20 km thick, ∼2x greater than observations at many other intraplate ocean islands. Based on the topography of the Bermuda swell, this layer could be rock that is ∼50 kg/m 3 less dense than the lithospheric mantle it has replaced. We suggest that the Bermuda swell is supported by a ∼20 km thick layer of modified lithospheric mantle, not a hot thermal anomaly from a mantle plume.