Water is essential to a wide range of geological processes occurring on Earth. The cycling of water, for example, governs the flux of heat and mass between the lithosphere and hydrosphere. To better understand the water cycle in the Earth?s interior, however, it is important to constrain the distribution of chemical components such as hydrogen and deuterium (hydrogen with an added neutron ? ?heavy hydrogen?) that constitute the water dissolved in volcanic glasses and minerals. The concentration of deuterium- and hydrogen-rich molecules in these phases likely constrain the observed differences on the hydrogen-deuterium composition between mantle and oceanic H2O reservoir, as well as the subduction zone contributions to the mantle-water cycle. These differences in the abundance of hydrogen/deuterium between water reservoirs implies that cycling of water in the mantle is not extensive or that hydrogen and deuterium react differently at high temperatures when dissolved in minerals, melts and fluids. Experimental results will, thus, shed light on the fate of water that resides deep in the Earth?s interior and promote our current understanding of planetary evolution and formation.
In this study, we will investigate the relationship between deuterium/hydrogen partitioning and speciation of C-O-H volatiles in silicate melts and fluids at pressures and temperatures reflecting lower crust and upper mantle conditions. We will study the relative distribution of H-D isotopologues of methane, hydrogen, and water dissolved in melts and coexisting fluids in-situ by Raman and infrared spectroscopy in a series of hydrothermal diamond-anvil cell experiments at high temperature and pressure. These experiments will be complemented by the use of 1H/2H Nuclear Magnetic Resonance and TC/EA-Isotope Mass Ratio Spectrometry on quenched melts. Experimental results will help us constrain isotope exchange reactions as function of elemental speciation and partitioning between melts, crystalline phases and aqueous solutions. The novel use of vibrational spectroscopy for in-situ and real-time measurement of isotope molecules can be expanded to other applications including mineral physics, geochemistry and energy-related research. An undergraduate student will participate during a 10-week internship program established in the second and third year of the project. This research will also support the M.Sc. thesis of a graduate student from the George Mason University.
