Dissolution of a stressed calcite crystal- high resolution strain measurements and interface observations

Pressure solution, the stress-mediated transport of mass by dissolution and precipitation, is one of the most important deformation mechanisms operating in the earth's upper crust. It affects both hydraulic and mechanical properties of rocks by redistributing material on relatively short spatial scales. We present here a unique experimental platform designed to study pressure solution by loading small (∼3mm) fluid-immersed samples against various flat surfaces, and observing the samples' axial strain and their morphologies in real time. The platform measures axial displacement rates smaller than 5Å/h over weeks, and resolves micron-size structures in 3D. A corner of a cleaved calcite single crystal rhomb was polished into a triangular face (edge length ∼ 200ìm) and pressed against a muscovite disc to yield a nominal stress of 80MPa. Immersing the sample in a pre-saturated water solution resulted in an axial displacement rate of ∼1nm/h, with no significant changes in contact morphology. However, when pre-saturated NH4Cl solution was added, the highly reactive fluid caused an increase in axial displacement rates to ∼50nm/h, and the contact roughened, with load-bearing surfaces becoming smaller.