This project will use high-pressure and high-temperature laboratory experiments to simulate processes of magma formation. Researchers will study different electrical charges of iron in Earth’s mantle and how differing conditions affect key Earth processes. Examples include the production of volcanic gases, the concentration of critical minerals and ores, and the formation of diamonds. The team will then use the experimental results to develop a mathematical model and that model will be shared with other researchers to answer their own questions about how magmas form on Earth. The team will develop the U.S. STEM workforce by training students and researchers in cutting-edge laboratory and modeling techniques. Members of the public will be able to learn about this research through public programs. Outcomes of this project will aid in strengthening national economic prosperity and global competitiveness. The proposed project is a combined experimental, analytical, and modeling campaign with the major goal of determining the Fe3+/ΣFe of peridotites in magma source regions in Earth’s mantle by inverting measured Fe3+/ΣFe of basalts. They will test whether differences in source oxygen fugacity between mid-ocean ridges basalts (MORB) and oceanic island basalts (OIB) may be accounted for by the difference between melting in the spinel stability field (MORB) versus the garnet stability field (OIB). New experiments will produce liquids saturated in either a garnet peridotite or spinel peridotite residue. Fe2O3 in these phases will be analyzed by a combination of electron microprobe and X-ray absorption near-edge structure (XANES) analyses. Fe2O3 mineral/melt partition coefficients relevant to melting in the spinel and garnet stability fields will update an empirical model of mantle melting that will allow investigation of the oxygen fugacity of melting under a range of possible temperature regimes and source peridotite compositions. This open-source model will be avail