Volatiles in Basaltic Glasses from Loihi Seamount, Hawaii: Evidence for a Relatively Dry Plume Component

New H ₂ O, CO ₂ and S concentration data for basaltic glasses from Loihi seamount, Hawaii, allow us to model degassing, assimilation, and the distribution of major volatiles within and around the Hawaiian plume. Degassing and assimilation have affected CO ₂ and Cl but not H ₂ O concentrations in most Loihi glasses. Water concentrations relative to similarly incompatible elements in Hawaiian submarine magmas are depleted (Loihi), equivalent (Kilauea, North Arch, Kauai–Oahu), or enriched (South Arch). H ₂ O/Ce ratios are uncorrelated with major element composition or extent or depth of melting, but are related to position relative to the Hawaiian plume and mantle source region composition, consistent with a zoned plume model. In front of the plume core, overlying mantle is metasomatized by hydrous partial melts derived from the Hawaiian plume. Downstream from the plume core, lavas tap a depleted source region with H ₂ O/Ce similar to enriched Pacific mid-ocean ridge basalt. Within the plume core, mantle components, thought to represent subducted oceanic lithosphere, have water enrichments equivalent to (KEA) or less than (KOO) that of Ce. Lower H ₂ O/Ce in the KOO component may reflect efficient dehydration of the subducting oceanic crust and sediments during recycling into the deep mantle.