Seamount volcanism associated with Earth’s basal mantle structures

While seafloor spreading and subduction explain much of the volcanic activity in Earth’s oceans, magmatism occurring within tectonic plate interiors requires a deeper mantle explanation. Various types of oceanic intraplate volcanism, including oceanic plateaus and hotspot-associated seamount chains, have been attributed to plumes rising from the margins of two continent-sized structures termed large low-shear-velocity provinces (LLSVPs) in the lowermost mantle beneath Africa and the Pacific Ocean. Here we analyse seamount catalogues and show that seamount volcanism is more voluminous on seafloor that has passed above a LLSVP. We find that this volcanic enhancement is evident above both LLSVPs, but is greater above the Pacific one and has declined since the mid-Cretaceous. We suggest that weak plumes rising from both LLSVPs interact with oceanic lithosphere to promote seamount volcanism. This process may be enhanced for the Pacific because of elevated mantle temperature, transition zone hydration and/or convective vigour in the Pacific hemisphere. Our findings provide additional support for the hypothesis that plumes carrying heat from the LLSVPs are responsible for most oceanic intraplate volcanism, including dispersed seamounts. This deep mantle connection means that seamount volcanism is sensitive to, and thus may constrain, the time-dependent dynamics of Earth’s deepest mantle.