Volatiles in melt inclusions and osmium isotopes from Hawaiian lavas: investigating the relationship between CO2 and H2O contents with mantle source lithology

Variations in radiogenic isotopes (Pb, Sr, Nd, Hf, He, etc.) and magmatic volatiles (CO2 or H2O) in Hawaiian volcanoes reveal a range of important processes that occur from the source to surface (mantle source heterogeneity, extents of melting, magma transportation, mixing, and storage, and eruption style). Hawaiian lavas are thought to originate from partial melting of a heterogeneous plume source containing a mixture of peridotite and ancient recycled oceanic crust (pyroxenite or eclogite). These lavas display a considerable range in volatile abundances (e.g. <1 to >1000 ppm for Kilauea) that is generally attributed to magmatic degassing or mixing during ascent. However, the source region for Hawaiian volcanoes may also be heterogeneous with respect to volatile concentrations. The effect of shallow degassing makes it difficult to determine if there is a relationship between mantle source composition, lithology, and the volatile budget. We will present Os isotopic ratios and volatile contents for over 25 samples from six Hawaiian volcanoes (Koolau, Mauna Kea, Mauna Loa, Hualalai, Kilauea, and Loihi) to determine if pre-eruptive volatiles in shield-stage magmas correlate with the different Hawaiian components (i.e. 'Kea' or 'Loa') and lithologies (i.e. peridotite or pyroxenite) identified by radiogenic isotopes. Rapidly-cooled submarine glasses and tephras will be analyzed, as subaerial lavas cool too slowly to prevent diffusive loss of H2O from melt inclusions. Olivine-hosted melt inclusions or groundmass glasses from each eruption will be analyzed for a range of volatiles (CO2, H2O, S, Cl, F). Additionally, olivine separates from each of these samples will be analyzed for Os isotopes. This study assesses the role of mantle heterogeneity, degree of partial melting, magma transportation, and degassing, in controlling the primary melt volatile concentrations. Although volatile abundances in parental magmas are likely to be modified by variable extents of exsolution, crystallization, and magma mixing and storage, pre-eruptive melt volatile concentrations can estimated by studying melt inclusions. Os isotopic analyses for Hawaiian lavas are sparse (especially for Loihi), compared to more traditional isotopes (i.e. Pb, Sr, and Nd). The new Os isotopic data will help to decipher the lithologic components for Hawaiian volcanoes and elucidate the nature of melt volatile concentrations in the mantle source region.