Program > Browse abstracts by speaker > Erdmann Saskia

Earth's primitive mantle-derived magmas are variably H2O-rich, reflecting their production in variable geodynamic settings and deep global volatile recycling. Primitive magmas formed in arc settings are H2O-rich, but a key ongoing debate is how H2O-rich these magmas are. Are they typically moderately hydrous (~4 wt% H2O), or are they highly hydrous (≥8 wt% H2O)? Melt inclusions commonly indicate maximum melt-H2O contents of ~4 wt%, but they may have lost their record of the most primitive, highest melt-H2O concentrations. Mineral assemblages and mineral-melt compositions, in contrast, commonly suggest ultra-hydrous near-liquidus crystallization conditions, but accurate and widely applicable mineral-melt hygrometers for primitive arc magmas are lacking.

Calcium partitioning between olivine-melt is sensitive to melt-H2O concentration and thus a potentially powerful tool for tracking early, near-liquidus melt-H2O concentrations of primitive arc magmas. A provisional olivine-melt hygrometer based on Ca partitioning exists (Gavrilenko et al. 2016), but the uncertainty of the hygrometer is large (±1.4-1.8 wt% H2O) and the calibration data can be improved. We will present a new, experimentally calibrated olivine-melt Ca partitioning hygrometer for primitive arc magmas, for which olivine-melt Ca concentrations have been determined by LA-ICP-MS. Preliminary calibration data and published olivine-melt inclusion compositions from Grenada, Lesser Antilles, suggest that olivine-melt Ca partitioning records systematically higher melt-H2O concentrations than the measured H2O concentrations of glassy melt inclusions uncorrected for volatile loss. Olivine-melt hygrometry may thus indeed be powerful in tracking the earliest, undegassed melt-H2O concentrations and become a key tool in search of H2O-rich arc melts.