INVESTIGATION OF LOADED HALITE-SIO2 INTERFACES UNDERGOING DISSOLUTION-PRECIPITATION PROCESSES

Abstract

Deformation assisted by transport in aqueous solutions is important for the rheology of earth materials, and models commonly used to describe deformation by dissolution-precipitation creep assume a steady state process in a closed system which is driven by the potential energy of the system. Here, we studied the effect of uni-axial stress on the convergence of halite crystals in contact to SiO2 at dry conditions and in presence of saturated solution by optical interferometry. Adding saturated solution caused the convergence to increase strongly. Simultaneously, Linnik-based phase shift interference microscopy was used to in situ monitor the nano-scale morphology of the loaded surface of the crystal. These investigations revealed that the measured crystal convergence is not dominated by dissolution within the loaded halite-SiO2 interface but rather by an increased plasticity of the halite crystal due to the addition of saturated solution. Temporarily reducing the stress reduces the elastic strain energy of the crystal and potential energy of the system as driving force for dissolution, but increases the potentiality for material transport from the interface into the bulk fluid. Thus, mechanisms which cause a remanent excess energy contribute to increased solubility and material flux during periods of reduced stress. Local plastic deformation satisfies this condition. We expect from our results that episodic cycling of tectonic stress, pore pressure, or solute activity significantly enhances deformation rates in rocks. © 2005 E. Schweizerbart'sche Verlagsbuchhandlung.