HR: 0830h
AN: S21E-0362    [PDF]
TI: Viscosity of silica-rich water at high pressure and temperature
AU: * Panero, W R
EM: wpanero@umich.edu
AF: Department of Geological Sciences, University of Michigan, 425 E University, Ann Arbor, MI 48109 United States
AU: Davis, M K
EM: mkdavis@umich.edu
AF: Department of Geological Sciences, University of Michigan, 425 E University, Ann Arbor, MI 48109 United States
AU: Boyd, O
EM: Oliver.Boyd@colorado.edu
AF: Department of Geological Sciences, University of Colorado at Boulder, 2200 Colorado Ave., Boulder, CO 80309-0399 United States
AU: Stixrude, L P
EM: stixrude@umich.edu
AF: Department of Geological Sciences, University of Michigan, 425 E University, Ann Arbor, MI 48109 United States
AB: Water released from subducting slabs into the mantle wedge due to pressure-induced dehydration reactions will contain small amounts of dissolved oxides. These fluids are ultimately responsible for magma generation above the slab resulting in arc volcanism. The viscosity of this super-critical fluid will affect the rate of mass transport into the overlying mantle. Small particles ($\sim$1 micron) in a fluid exhibit Brownian motion. The slope of the mean square displacement versus time is inversely proportional to the fluid viscosity. Three minutes of videotape data, digitized at 7 pixels per micron, allows for viscosity measurements with a precision of 0.5 log units for fluids with viscosities between 1 and 10$^{-5}$ Pa-s. Particles observed in the hydrothermal diamond anvil cell can then provide constraints on viscosities for transparent fluids at high pressures (up to 5 GPa) and temperatures (up to 1300 K), a range ideal for the study of fluids released from a subducting slab. Observed Brownian motion of tracer particles in silica-saturated water shows that 4 wt% dissolved silica (saturation at 1 GPa and 950 K) has the effect of increasing the fluid viscosity relative to that of pure water by a factor of 1000. Fluids released at 100 km through dehydration reactions contain up to 8 wt% silica. Pressure and concentration induced interconnectivity of silica tetrahedra in the fluid should further increase the viscosity of the fluid. Therefore, a continuum of behavior between fluid and melt is expected in the metasomatized mantle wedge despite the supercritical nature of the water.
DE: 3924 High-pressure behavior
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3994 Instruments and techniques
DE: 5139 Transport properties
DE: 8160 Rheology--general
SC: Seismology [S]
MN: 2003 Fall Meeting