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Constraints on the viscosity of water at high pressures and temperatures using particle tracking analysis
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DOI：10.1180/mgm.2026.10195.png)
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Abstract
En 中文
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 (H2O) at pressures <2.5 GPa using the Brownian motions of suspended particles in DAC. Previous high-pressure efforts used particles of polystyrene; which are unstable at ≥300°C; or silica; but only at ambient temperatures. Such temperatures are relatively low for hydrothermal to supercritical geofluids. We tested quartz particles (∼1–2 µm diameter) with heating; as quartz does not significantly dissolve/melt until ≥600°C. Although three times denser than water; the particles remained suspended and displayed Brownian motions for long timescales at temperatures ≤200°C. The measured viscosities are relatively high due to drag from the culets and particle–particle interactions. Regardless; our measured pressure-effect on viscosity shows excellent agreement with the standard reference for water. After correcting for the drag; the η are very low (< 2 mPa s) highlighting that H2O-rich geofluids should be highly mobile at depth.
Keywords:
water
viscosity
geofluid
subduction zone
aqueous fluid
Brownian motion
high pressure
particle tracking
differential dynamic microscopy
Journal
IF:
1.4
Papers:
178
Citations:
4.8K