Constraints on the viscosity of water at high pressures and temperatures using particle tracking analysis

Abstract The viscosity (η) of a geofluid dictates its roles within the Earth, such as migration in subduction zones and volcanism. High pressures and temperatures at depth influence visocity (η). The falling sphere method is effective to measure viscosity at high-pressures for geofluids that form solids at ambient temperature. A typically metallic sphere is placed atop a solid sample, which is then compressed to high-pressure and later melted by heating. This method is more challenging for geofluids that do not form solids at ambient temperature. A diamond-anvil-cell (DAC) is often used to contain such geofluids, but requires a small sample chamber and that the sphere either falls parallel to the diamond culet faces or rolls along one face. This geometry produces complicated drag effects on a sphere fall and additional frictional forces for a roll. The sphere may also adhere to chamber surfaces, preventing its fall/roll. To circumvent these issues, in this study, we quantify the viscosity of a geofluid (H 2 O) at pressures