The structure of H2O-saturated silicate melts, coexisting silicate-saturated aqueous solutions, and supercritical silicate liquids in the system Na2O center dot 4SiO(2)-H2O has been characterized with the sample at high temperature and pressure in a hydrothermal diamond anvil cell (HDAC). Structural information was obtained with confocal microRaman and with FTIR microscopy. Fluids and melts were examined along pressure-temperature trajectories defined by the isochores of H2O at nominal densities, rho(fluid), (from EOS of pure H2O) of 0.90 and 0.78 g/cm(3). With rho(fluid) = 0.78 g/cm(3), water-saturated melt and silicate-saturated aqueous fluid coexist to the highest temperature (800 degrees C) and pressure (677 MPa), whereas with rho(fluid) = 0.90 g/cm(3), a homogeneous single-phase liquid phase exists through the temperature and pressure range (25-800 degrees C, 0.1-1033 MPa). Less than 5 vol% quartz precipitates near 650 degrees C in both experimental series, thus driving Na/Si-ratios of melt + fluid phase assemblages to higher values than that of the Na2O center dot 4SiO(2) starting material.

Solubility and solution mechanism(s) of reduced (N+H)- and H-containing N-O-H volatile components in Na2O-SiO2 composition melts in equilibrium with NH3+H-2+N-2 and H2O+H-2 fluid and H- and N-isotope concentrations ill these melts were determined experimentally at 1.5 GPa and 1400 degrees C as a function of hydrogen fugacity,fa, and melt polymerization (composition), NBO/Si (NBO/Si = 0.4-1.18). This NBO/Si-range is similar to that between dacite and olivine tholeiite melt (NBO/Si similar to 0.4-1). The f(H2) was controlled between that of the iron-wftstite + H2O [logf(H2)(IW) similar to 3.42 (bar)] and that of the magnetite-hematite + H2O [logf(H2)(MH) similar to-0.91 (bar)] buffer.

The structure of H2O-saturated silicate melts and of silicate-saturated aqueous solutions, as well as that of supercritical silicate-rich aqueous liquids, has been characterized in-situ while the sample was at high temperature (to 800 degrees C) and pressure (up to 796 MPa). Structural information was obtained with confocal microRaman and with FTIR spectroscopy. Two Albearing glasses compositionally along the join Na2O center dot 4SiO(2)-Na2O center dot 4(NaAl)O-2-H2O (5 and 10 mol% Al2O3, denoted NA5 and NA10) were used as starting materials. Fluids and melts were examined along pressure-temperature trajectories of isochores of H2O at nominal densities (from PVT properties of pure H2O) of 0.85 g/cm3 (NA10 experiments) and 0.86 g/cm(3) (NA5 experiments) with the aluminosilicate + H2O sample contained in an externally-heated, Ir-gasketed hydrothermal diamond anvil cell.

The structure of silicate melts in the system Na2O center dot 4SiO(2) saturated with reduced C-O-H volatile components and of coexisting silicate-saturated C-O-H solutions has been determined in a hydrothermal diamond anvil cell (HDAC) by using confocal microRaman and FTIR spectroscopy as structural probes. The experiments were conducted in-situ with the melt and fluid at high temperature (up to 800 degrees C) and pressure (up to 1435 MPa). Redox conditions in the HDAC were controlled with the reaction, Mo + H2O = MoO2 + H-2, which is slightly more reducing than the Fe + H2O = FeO + H-2 buffer at 800 degrees C and less.

The effect of dissolved silica on the PVT properties of H2O and structure of silica-saturated aqueous fluids in equilibrium with quartz in the SiO2-H2O system has been determined in situ with the materials at temperature (up to 800 degrees C) and pressure (up to 1350 MPa) in a constant-volume hydrothennal diamond anvil cell. Pressure was measured with the Raman shift of C-13 synthetic diamond and was also calculated from the PVT properties of pure H2O. The two sets of pressures thus obtained differ by <= 50 MPa at T < 500 degrees C. At higher temperatures (and pressures), the pressure difference increases and reaches about 350 MPa at 800 degrees C.