Quartz-rich aggregates provide a good analog for Earth's upper crust. Previous workers have shown the presence of water can greatly decrease the strength of quartz and can shift the brittle-ductile transition conditions to lower temperatures/pressures for quartz-rich rocks in the Earth. In this study, a combination of Fourier Transform Infrared Spectrometry, optical light microscopy, Scanning Electron Microscopy, and Cathodoluminescence Microscopy analyses were used to determine the distribution and transport of water and water-related species within natural quartz aggregates using dehydration, rehydration, and isotope exchange experiments.
Water within natural quartz arenites is distributed along grain boundaries, at grain junctions, and within the grain interiors. Fluid inclusions trapped along healed microfractures are the main source of molecular water within the grains. The concentration of water within the quartz arenite samples is proportional to the amount of deformation and type of deformation-related microstructures present. At brittle-ductile transition conditions (between 150 degrees C and 300 degrees C), water transport appears to be influenced by both brittle and ductile factors. Water is transported by oxygen volume diffusion, oxygen grain boundary diffusion, and as molecular water along microfractures within natural quartz arenites. Microfracture-assisted transport may play an important role in the transport of water throughout natural quartz arenites around the brittle-ductile transition conditions.