Hydrogen isotopic evidence for a core component in Baffin Island lavas

Abstract

The nature of chemical exchange between Earth’s core and mantle is fundamental to understanding their evolution. Tungsten-182 and helium-3 anomalies in volcanic rocks from deeply sourced mantle plumes have been attributed to core-mantle exchange. Hydrogen (H) is potentially abundant in the core. Therefore, H may also be a sensitive tracer of core-mantle exchange. We measured ²H/¹H ratios (reported as δD) in olivine-hosted basaltic melt inclusions from a Baffin Island lava to test whether mantle plumes contain H from the core. The average δD value (−144 ± 24 per mil) is lower than some estimates for the average depleted upper mantle (δD ≈ −60 ± 20 per mil). The low δD composition likely derives from isotopic diffusion or H leakage from the core, not isotopic fractionation during magmatism or crustal contamination. Over geologic time, core-mantle exchange of H may have overprinted the isotopic composition of mantle plume source regions and much of the upper mantle.