Brillouin Scattering Studies of Glasses, Melts, and Aqueous Fluids

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9305071 Bass A qualitative understanding of fluid migration in the Earth requires accurate values of viscoelastic properties and the compressibility of fluids. We propose an experimental and theoretical study of the elastic properties (compressibility), relaxational properties (attenuation, viscosity), and the equation of state of fluids of geological importance, in particular, silicate melts and supercritical aqueous solutions. Physical mechanisms of these properties and data reduction methodologies are largely the same for both groups of materials, as is the experimental data to be obtained for each. In this sense, it is natural and appropriate for silicate melts and aqueous solutions to be encompasses in a single study of geological fluids. Specifically, we will measure the compressibility and viscosity of silicate glasses and melts up to 1600oC using the Brillouin light scattering technique. Experiments will be done under both dry conditions and in the presence of H2O in order to investigate the effect of water on the high T viscosity and elasticity of melts. Similar measurement on aqueous fluids will be made at lower temperatures (T700oC) and at high pressures up to 10 GPa using an externally heated diamond anvil cell. These experiments will require a full analysis of the lineshape of the Brillouin spectra. Although the Brillouin technique yields directly high frequency, unrelaxed properties, a full analysis of the lineshapes allows the low frequency, relaxed properties of the fluids to be extracted from the measurements. We can therefore investigate the frequency dependence of the observed properties. In addition, for some of the systems investigated we will obtain data sufficiently high temperature that the relaxed properties ar obtained directly. Molecular dynamics (MD) computer simulations of the fluid properties will be used to identify specific atomic mechanisms with the features displayed in the light scattering spectra, and to extrapol ate the properties beyond the range of measurements. High frequency dielectric permittivity of aqueous fluids will also be obtained from the proposed optical measurements and compared with results of MD simulations over a wide range of frequencies. These studies will allow more quantitative models of fluid thermodynamic and transport properties and fluid-rock interactions to be constructed.