Evidence for a deep mantle source for EM and HIMU domains from integrated geochemical and geophysical constraints

Abstract

Subduction of oceanic and continental crust (and associated sediments) into the mantle over geologic time generates mantle domains with geochemically distinct signatures, referred to as HIMU (high “μ”, where μ=238U/204Pb) and EM (enriched mantle) domains. Identification of EM and HIMU geochemical signatures in hotspot lavas provides evidence that subducted crustal materials are recycled into the source of hotspots. It remains uncertain where these materials are located in the mantle, and a key question is whether upwelling mantle plumes are required to transport mantle domains with EM and HIMU signatures to the shallow mantle beneath hotspots. Therefore, this study evaluates relationships between extreme EM and HIMU compositions at oceanic hotspots and the presence (or absence) of seismically-constrained mantle plumes beneath the hotspots. We draw on three existing plume catalogs based on global seismic shear-wave velocity models, and these plume catalogs indicate the presence or absence of a plume beneath each of 42 oceanic hotspots. From each hotspot, we select a lava with the highest 206Pb/204Pb composition and one with the lowest 143Nd/144Nd composition.We show that hotspots associated with seismically defined plumes show a greater likelihood of hosting lavas with either extreme EM (143Nd/144Nd ≤ 0.512630) or extreme HIMU (206Pb/204Pb ≥ 20.0) compositions than hotspots not associated with plumes, but HIMU hotspots show a stronger association with plumes than EM hotspots. The significance of the relationship between plumes and extreme geochemical signatures at hotspots improves if extreme EM and HIMU compositions are considered together instead of separately: hotspots sourced by mantle plumes are even more likely to exhibit extreme EM or extreme HIMU signatures than hotspots not sourced by plumes. The significance tests also show that hotspots with extreme EM or HIMU compositions are more likely to be associated with mantle plumes than hotspots that lack extreme geochemical signatures. A relationship between seismically detected deep mantle plumes and the presence of extreme EM or HIMU compositions at hotspots provides evidence for a deep mantle source for these geochemical domains.