Fibrous veins are generally interpreted in terms of the crack-seal mechanism. Several aspects of fibrous veins (fibrous structure, curved fibres, symmetry of antitaxial veins) are however better explained by vein formation without fracturing. Mass transfer to such veins would be by diffusional transport rather than by fluid flow through the veins. Deformation by dissolution-precipitation creep can provide the driving force for the necessary mass transfer. Veins form when mass transfer is heterogeneous and precipitation is localised.Experiments were performed which enforced a chemical potential gradient, acting as the driving force for diffusional mass transfer. These experiments resulted in fibrous growths in aggregates of soluble salts (NaCl and KCl) saturated with brine. The experimental results support the theory that fibrous veins may form without fracturing and that rather than providing evidence for major fluid pathways, fibrous veins may instead represent localised precipitation during diffusional material transfer.
A technique is presented for the multiply-constrained inversion of geological and potential field data. This technique speeds up the process of testing simplified kinematic structural models of structural and potentialfield data collected by field geologists and geophysicists. The scheme uses pre-existing software (Noddy) to calculate possible solutions, and as the inverse modeling scheme requires flexibility and speed over a potentially large parameter space with many local minima, a genetic programming approach to the global optimization problem is used.The Noddy integrated forward modeling package calculates geometries and potential-field anomalies resulting from a specified geologic structure. These models are then compared to the target data using correlation of potential-field anomaly images to assign the fitness of the model, with the genetic algorithm breeding successive generations of models. Initial testing of the inversion scheme was successful for a spherical plug, and a planar dike.
The localization of deformation in recrystallizing materials is investigated via a series of two-dimensional grain-scale numerical simulations. These simulations couple a grain size and strain dependant viscous rheology with grain size reduction and grain growth processes. The simulations are able to predict the mechanical, microstructural and strain evolution of the polycrystals to high strain, and allow us to examine the nature of the time dependent feedback between mechanical and
microstructural behavior. It was found that significant strain localization occurred only when the grain size dependence of the viscosity was non-linear, and was greatly enhanced by the activity of the grain size modifying processes. The intensity and location of the zone of strain localization varied spatially and temporally, with the result that the finite strain state showed a much broader, and hence less intense, zone of localized deformation than the instantaneous state.
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