The formation of basalt by partial melting of the Earth's mantle is one of the most significant geodynamic processes on the planet. Despite decades of high-pressure experiments, few peridotite partial melting data in the 2.0-3.0 GPa pressure range exist. In order to enhance our knowledge of near-solidus mantle melting, a three-year study investigating the 2.0-3.0 GPa partial melting systematics of multiple peridotite compositions will be completed. Handpicked olivine, orthopyroxene, clinopyroxene, and spinel grains from two mantle xenoliths, of differing compositional fertility, will be mixed in varying proportions to create starting materials of varying bulk composition. These same starting materials were studied previously at 1.0 GPa. Experiments will be performed using the piston-cylinder apparatus utilizing a combination of the diamond aggregate and "micro-sandwich" techniques to eliminate the problem of quench modification of the glass. This will enable determination of low melt fraction glass and residual crystalline phase compositions, estimation of solidus temperatures over a range of pressures, and quantification of melt productivity and the stoichiometry of mantle melting reactions.
The resulting polybaric dataset will provide constraints on the processes resulting in the formation of basalts in the mid-ocean ridge environment, as well as other tectonic regimes where polybaric melting and peridotite-melt interaction occur. An integral component and broader impact of the project includes the direct involvement of undergraduate research students and completion of an experimental petrology laboratory at a primarily undergraduate institution. Teaching activities using the laboratory and project data will be developed and incorporated into the geology curriculum, thus benefiting a larger population of students long into the future.
