Energy and mass transfer processes in the Earth and terrestrial planets involve melting and crystallization of rock-forming materials at high temperature and pressure. These processes control materials recycling near convergent plate boundaries, govern lithosphere destruction and formation throughout the Earth’s history, are responsible for volcanic and seismic hazards, and impact on distribution and availability of economic and energy resources in the Earth. Characterization of these processes requires understanding of structure and property relations among silicate melts and water-rich fluids under pressure, temperature, and redox conditions relevant to the mantle and the crust of the Earth.To this end, the central focus of current research and will remain so in the future. This portion of the research program can be divided into the following subsections:

• Structure of silicate-COH components in and partitioning between melt and fluid with to advance modeling of transport properties and behavior of fluids and melts in the Earth and terrestrial planets
• Equation-of-state and structure of COH fluids and solvent characteristics, at high temperature and pressure.
• Characterization of stable isotope intramolecular partitioning (mostly D/H) and partitioning between minerals, melts, and fluids. COH
• Fluid structural speciation and isotopologues in hydrothermal environments

The structural behavior of volatiles in silicate-C-O-H melts and fluids aids in characterization of element partitioning and as well as isotope fractionation (e. g., D/H recycling) in subduction zones. Vibrational spectroscopy (infrared and Raman) was employed for structural characterization of melts and fluids and for determination of hydrogen isotope partitioning within and between haploandesitic melts and fluids in alkali aluminosilicate–C-O-H systems. Mass spectrometer and nuclear magnetic resonance spectroscopy of quenched samples add further to the arsenal of tools forthis purpose.

In silicate-COH systems at high pressure and temperature under oxidizing conditions, melt and fluid comprise CO2, CO3-groups, HCO3-groups, H2O, and silicate components. The abundance ratios, CO3/CO2 and CO3/HCO3, decreases with increasing temperature and pressure with ∆H-values for the exchange equilibria between -15 and -25 kJ/mol. The abundance ratio, CO3/silicate, also decreases with increasing temperature and pressure. Hydrogen isotope exchange within coexisting fluids and melts yields ∆H-values near 14 and 34 kJ/mol, respectively, which results in ∆H=-25 kJ/mol for D/H exchange between coexisting fluid and melt. Lack of spectroscopic resolution precluded determination of D/H behavior in the bicarbonate (HCO3) species. Under reducing conditions (near that to the iron-wustite oxygen fugacity buffer), melt and fluid comprise molecular CH4, CH3-groups, H2, OH-groups, and H2O. Hydrogen isotope exchange within fluids and melts yields ∆H near -5 and -1 kJ/mol, respectively with a ∆H-value for D/H exchange between coexisting fluid and melt of -4kJ/mol. The D/H exchange between CH4 and CD4 species results in ∆H near 40 kJ/mol, whereas the ∆H-value –s near -4 kJ/mol under oxidizing conditions where ∆H-values average near -6 kJ/mol for D/H exchange between hydrous melt and silicate-saturated aqueous fluid.

Condensed-phase isotope effects are inferred to play a key role on the evolution of H/D isotopologues, likely induced by differences in the solubility of the isotopic molecules driven by the excess energy/entropy developed during mixing of nonpolar species in the H2O/D2O structure. Our experiments show that isotope fractionation effects need to account for the presence of condensed matter (e.g. melts, magmatic fluids), even at conditions at which theoretical models suggest minimal (or nonexistent) isotope exchange, but comparable to those within the Earth’s crust.

Nitrogen and carbon solubility in NH- and CH-saturated melts on the order of 1 wt% with positive correlation of solubility in melts with pressure, temperature, hydrogen fugacity, and melt polymerization. Under reducing conditions, near that of the iron-wüstite buffer, carbon dissolves in melts to form CH3 groups attached to Si and triple-bonded to C. Nitrogen forms NH-bearing complexes, possibly NH4+. There is evidence for 13C/12C isotope fractionation at or above 20 ‰ between C dissolved in silicate and CO2 gas at magmatic temperatures.

The silicate speciation in fluids at high temperature and pressure reflects total silicate solubility because of positive correlation between solubility and speciation (structure) of silicate components. For example, the silica solubility in equilibrium with quartz/coesite reaches >5 mol/kg near 5 GPa and 900˚C with polymerized silicate species, SiO4, Si2O7, and SiO3 in the fluid. In equilibrium with enstatite and forsterite, the silicate solubility is ~ 50% less and only SiO4 and Si2O7 species exist in the fluids. Those variables affect D/H isotope ratios. For example, the fluid/melt partition coefficients for hydrogen, KH, varies by ~40% as a function of variable silicate speciation in fluids in the 500˚800 ˚C/0.51 GPa temperature and pressure range. The hydrogen fluid/melt partition coefficient exceeds that of deuterium. Their temperature-dependence also differs so that for the exchange equilibrium of D and H between coexisting water-saturated melt and silicate-saturated aqueous fluid, the ΔH is between 4 and 6 kJ/mol. This difference is because in the more silicate-rich fluids (higher proportion of polymerized silicate species), the abundance ratio, OD/OH, is higher in the more polymerized silicate species in the fluid. As a result, increasing pressure, which leads to increasingly polymerization of silicate, will cause the D/H ratio of the fluid will increase. This also means that D/H fractionation between aqueous fluid and condensed silicate increases with increasing pressure.

These preliminary experimental data may have profound implications for core-formation, the Earth’s evolution, volatile budget, and degassing processes. To provide the needed experimental data to provide the information necessary to characterize these processes, we determine melt structure of binary metal oxide-silica and ternary metal oxide-alumina-silica systems with expansions to more complex chemical systems (including Fe-bearing) as needed. These properties are determined as a function of composition, pressure, temperature, and hydrogen fugacity. The compositional variables will be metal cation type, metal/silicon ratio, and Al/(Al+Si). Structural studies are conducted via Raman, Mössbauer, and FTIR spectroscopy with quenched materials and in-situ with the samples at high pressure and high temperature. Chemical and isotopic analyses of melts and coexisting gas are conducted with the electron microprobe, gas chromatographic, and mass spectroscopic methods