Micromechanics of Semi-Brittle Flow

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9903307EvansThe transition in deformation mechanism from brittle fracture to plastic flow is important in understanding tectonophysics, the strength of the crust, and the style of deformation at the field scale, but as yet, there are only a few suggestions for constitutive laws for semi-brittle deformation. Using a new deformation apparatus, the investigators are measuring permeability and storage capacity during deformation in rocks composed dominantly of either calcite or olivine. The proposed work extends initial studies to a range of temperature, pressure and effective pressures spanning the transition from brittle to plastic flow in both rock types. In situ measurements of dilatancy are an important part of the macroscopic description of the deformation mode, and the experiments will concentrate on making axial and volumetric strain measurements during the mechanical tests. The macroscopic measurements will be accompanied with detailed, quantitative observations of the microstructure, including crack surface area per unit volume, crack length, crack number density, dislocation density, dislocation orientation, and crack-dislocation interactions.