Experimental study of aqueous fluid infiltration into quartzite: Implications for the kinetics of fluid redistribution and grain growth driven by interfacial energy reduction

To investigate the kinetics of interfacial energy-driven fluid infiltration, experiments were carried out in a quartzitewater system at 621-925°C and 0.8 GPa. Infiltration couples were made by juxtaposing presynthesized dry quartzite cylinders and fluid reservoirs. The infiltration process was confirmed by the presence of pores at the quartzite grain edges. As predicted from theoretical considerations and previous experiments, wetting fluids such as pure water and NaCI aqueous solution infiltrated into quartzite, whereas nonwetting CO₂-rich fluids did not. Newly precipitated quartz layers at the surfaces of the infiltrated sample proved that infiltration took place by a dissolution-precipitation mechanism. The enhancement of grain growth by fluid infiltration was observed over the entire range of experimental temperatures. The fluid fraction, gauged by the porosity of the run products, increases at the infiltration front and then decreases towards the fluid reservoir to form a high-porosity zone with a maximum porosity of 2.3-2.9%. As infiltration proceeds, the high-porosity zone advances like a travelling wave. This porosity wave is probably caused by a grain curvature gradient resulting from preferential grain growth in the infiltrated part of the quartzite, perhaps combined with other factors. The infiltration kinetics were modelled with a steady-state diffusion model over the high-porosity zone. The solubility difference between dissolving and precipitating grains was deduced to be 2 × 10^-2-3× 10^-1wt%. The experimentally obtained infiltration rate of aqueous fluid in the steady-state diffusion regime (2±0.5 × 10^-8m sec^-1 at 823°C) is much faster than the estimated metamorphic fluid flux rates, so that interfacial energy-driven fluid redistribution in quartz-rich layers could significantly contribute to the fluid flux in high-grade metamorphism, at least over a short distance. Cathodoluminescence observations of the run products revealed that the grain growth of quartzite in the presence of fluid proceeds extensively, which would promote the chemical equilibration between fluid and rock more effectively than would volume diffusion in quartz crystals.