Viscosity of Water at High Pressures and High Temperatures
Jeffrey S. Pigott
The Ohio State University School of Earth Sciences Columbus, Ohio
Circulation of deep crustal fluids is responsible for transporting super critical fluids such as H2O and CO2 across great distances while reacting with the host rock. The viscosity of such super-critical fluids is a first-order constraint on the fluid transport mechanisms in the deep crust and upper mantle, with viscosities varying by up to 10 orders of magnitude between the limits of pure water fluid and silicate melts. Accurate determination of fluid viscosity at high pressures (>30 kbar or 3 GPa) and temperatures (~900 °C) is hampered by the geometry and sample size of high-pressure devices. The goal of this research is to quantify the viscosity of water at pressures representative of the deep crust and upper mantle using a new experimental method. By observing the Brownian motion of polystyrene spheres suspended in fluid contained in a hydrothermal diamond anvil cell, the in-situ viscosity of the fluid at high pressures and temperatures can be determined by Einstein’s relation. The hydrothermal diamond anvil cell is an experimental apparatus that can compress samples 0.02 mm3 to >50 kbar and > 900 °C. Initial experimental results conducted at room temperature up to the freezing point of water (~0.8 GPa) show that particle tracking of 5-10 particles for 30 seconds of video at 150 X magnification results in viscosities accurate to within 0.3 log units of known values, with greater accuracy for lower viscosity fluids. This new method will allow for viscosity measurements of water enriched in silica and hydrated minerals.
AAPG Search and Discovery Article #90094 © 2009 AAPG Foundation Grants in Aid