Direct Observation of Near-Equilibrium Pore Geometry in Synthetic Quartzites at 600°-800°C and 2-10.5 Kbar

A primary factor affecting geochemical transport and bulk-rock physical properties in the mid- and lower continental crust is the grain-scale distribution of fluid-filled porosity. Of particular significance is the continuity of the fluid phase in the direction of potential transport. SEM images reveal that H₂O-CO₂-NaCl fluids in quartzites synthesized at 600°-800°C and 2-6 kbar are present as isolated pores at the corners of mineral grains. At higher pressures (e.g., 10 kbar), pore connectivity is established for aqueous fluids in quartzite, providing a path for fluid flow and a short circuit for such processes as diffusion and electrical conduction. Pore geometries in synthetic quartzites resemble those predicted to exist in an ideal model of isotropic solid/solid and solid/fluid interfacial energies. To describe pore geometries in more complicated crustal lithologies, the equilibrium model should be modified to account for anisotropy of interfacial energies.