Volatiles in basaltic glasses from Loihi seamount, Hawaii: Evidence for a relatively dry plume component

New H2O, CO2 and S concentration dat for basaltic glasses from Loihi seamou nt, Hawaii, allow us to model degassing, assimilation, and the distribution of major volatiles within and around the Hawaiian plume. Degassing and ass imilation have affected CO2 and CI but not H2O concentrations in most Loihi glasses. Water concentrations relative to similarly incompatible elements in Hawaiian submarine magmas are depleted (Loihi), equivalent (Kilauea, Nor th Arch, Kauai-Oahy), or enriched (South Arch). H2O/Ce ratios are uncorrela ted with major element composition or extent or depth of melting but are re lated to position relative to the Hawaiian plume and mantle source region c omposition, consistent with a zoned plume model. In front of the plume core , overlying mantle is metasomatized by hydrous partial melts derived fr om the Hawaiian plume. Downstream from the plume core, lavas tap a depleted so urce region with H2O/Ce similar to enriched Pacific mid-ocean ridge basalt. Within the plume core, mantle components, thought to represent subducted o ceanic lithosphere, have water enrichments equivalent to (KEA) or less than (KOO) that of Ce. Lower H2O/Ce in the KOO component may reflect efficient dehydration of the subducting oceanic crust and sediments during recycling into the deep mantle.