Transport processes at quartz–water interfaces: constraints from hydrothermal grooving experiments

Abstract

Abstract. We performed hydrothermal annealing experiments on quartzite samples at temperatures of 392 to 568 • C and fluid pressures of 63 to 399 MPa for up to 120 h, during which hydrothermal grooves developed on the free surfaces of the samples. An analysis of surface topology and groove characteristics with an atomic force microscope revealed a range of surface features associated with the simultaneous and successive operation of several processes partly depending on crystal orientation during the various stages of an experiment. Initially, dissolution at the quartzite-sample surface occurs to saturate the fluid in the capsule with SiO 2 . Subsequently, grooving controlled by diffusion processes takes place parallel to dissolution and precipitation due to local differences in solubility. Finally, quench products develop on grain surfaces during the termination of experiments. The average groove-root angle amounts to about 160 • , varying systematically with misorientation between neighboring grains and depending slightly on temperature and run duration. The grooving is thermally activated, i.e., groove depth ranging from 5 nm to several micrometers for the entire suite of experiments generally increases with temperature and/or run time. We use Mullins' classical theories to constrain kinetic parameters for the transport processes controlling the grooving. In the light of previous measurements of various diffusion coefficients in the system SiO 2 -H 2 O, interface diffusion of Si is identified as the most plausible rate-controlling process. Grooving could potentially proceed faster by diffusion through the liquid if the fluid were not convecting in the capsule. Characteristic times of healing of microfractures in hydrous environments constrained from these kinetic parameters are consistent with the order of magnitude of timescales over which postseismic healing occurs in situ according to geophysical surveys and recurrence intervals of earthquakes.

The Relationship Between Microfracture Damage and the Physical Properties of Fault‐Related Rocks: The Gole Larghe Fault Zone, Italian Southern Alps

“…Actual crack healing occurs by diffusional processes on the crystal scale leaving (secondary) fluid‐inclusion planes as evidence of the initial crack surface (Smith & Evans, ; Sprunt & Nur, ). At depth, this process can occur on a timescale of days (Smith & Evans, ; see also Klevakina et al, ) and might explain the recovery of the in situ seismic wave velocities. Additionally, closure of cracks due to confining pressure or loss of fluid (pressure) diminishes the influence of the cracks on the elastic properties of the material without a healing process.…”

Evaluation of grain boundaries as percolation pathways in quartz-rich continental crust using Atomic Force Microscopy

“…to study in-situ dissolution precipitation of minerals such as barite, celestite and calcite and for studying calcite surface structure 20 , 21 . It has also been used to study grooving and wetting along grain boundaries in quartz during hydrothermal annealing 4 . In this study, we demonstrate that systematic changes in grain boundary morphology in quartzite samples metamorphosed at different metamorphic grades can be directly visualized using AFM.…”

Direct Visualization of Grain Boundaries in Quartzites using Atomic Force Microscopy: Application to Study of Fluid Percolation in Continental Crust

“…A number of mechanisms have been proposed in material and geological sciences to explain how uids percolate through a medium under ductile and brittle conditions [1][2][3][4][5][6][7][8][9][10] . Most postulated mechanisms agree that in a 3-dimensional material framework, grain/phase boundaries play a major role in uid percolation 7,11,12 .…”

“…to study in-situ dissolution precipitation of minerals such as barite, celestite and calcite and for studying calcite surface structure 20,21 . It has also been used to study grooving and wetting along grain boundaries in quartz during hydrothermal annealing 4 . In this study, we demonstrate direct visualization of systematic changes in grain boundary morphology in quartzite samples metamorphosed at different metamorphic grades using AFM.…”