Structure and properties of loaded silica contacts during pressure solution: impedance spectroscopy measurements under hydrothermal conditions

Abstract

In order to investigate directly the structure and properties of grain boundaries in silicatematerials undergoing pressure solution, in situmeasurements of these properties are required. We report electrical impedance spectroscopy measurements, performed, under hydrothermal conditions, on individual glass–glass and glass-quartz contacts undergoing pressure solution. Resulting estimates of the average grain boundary diffusivity product (Z ¼ DdavC ) for silica transport and of the average grain boundary fluid film thickness (dav) fall in the ranges 6.3 ± 1.4 9 10-18 m3 s-1 and 350 ± 210 nm, respectively. However, the average values for Z and dav obtained were likely influenced by cracking and irregular dissolution of the dissolving contact surfaces, rather than representing uniformly wetted grain boundary properties. Post-mortem SEM observations indicate that the contact surfaces were internally rough. Taken together, our data support the notion that during pressure solution of quartz, grain boundary diffusion is rapid, and interface processes (dissolution and precipitation) are more likely to be ratelimiting than diffusion.