To accurately predict cavern convergence and subsidence caused by solution mining of K- and Mg-bearing salt bodies, a good understanding of the creep behaviour of bischofite, carnallite and mixed salts rocks is required. We studied the mechanical properties of these materials aiming to produce flow laws that can be applied at in situ conditions. We performed triaxial deformation experiments on natural polycrystalline samples of bischofite, carnallite (starting grain size similar to 5 mm), and their mixtures with halite, at in situ PT conditions of 40 MPa and 70 degrees C. All deformation tests were done in strain rate stepping mode, with intervening stress relaxation to reach low strain rates. We found that carnallite is 4-5 times stronger than bischofite, and that bischofite-carnallite-halite mixtures are stronger than carnallite. The constant strain rate parts of the multistep experiments allowed dislocation creep laws to be defined for bischofite and carnallite at relatively high stress, with a power law stress exponent n similar to 5. During stress relaxation, n changes to similar to 1 at a strain rate of similar to 10(-9) s(-1). This is interpreted as reflecting a change from dislocation creep at the faster strain rates to solution-precipitation behaviour at slow strain rate, mediated by changing grain size.
Two novel techniques, photo based reconstruction (photogrammetry) and computed tomography (CT), are used to investigate the formation of an exceptional array of sigmoidal veins in a hand sample from Cape Liptrap, Southern Victoria, and to provide constraint on models for their development. The accuracies of the photogrammetric models were tested by comparison with a laser scan generated three dimensional (3D) model. The photogrammetric model was found to be accurate to at least 0.25 mm and substantially more detailed than the laser scan. A methodology was developed by which 3D structural measurements could be extracted from the photogrammetric model. This was augmented with the CT model which, through its capacity to elucidate internal structure, was used to constrain the geometry and linkage of structures within the rock volume. The photogrammetric and CT data were then combined with detailed photomicrographs to evaluate the evolution of the sigmoidal veins in the sample.The angle between the sigmoidal vein margins and an inferred shear zone, as well as the orientations of the crystal fibres, were found to imply a rotation of >27 degrees. However coeval pressure solution seams and older veinlets in the rock bridges between the veins were only found to have rotated by similar to 10 degrees, an observation not easily explained using existing models for sigmoidal vein formation.A new model is proposed in which a significant component of sigmoidal vein geometry is due to localised dilation caused by slip on the pressure solution seams. The process involves strain partitioning onto pressure solution seams, which leads to exaggeration of sigmoidal vein geometries. If not accounted for, the apparent vein rotation due to slip partitioning introduces errors into calculations of simple shear and volume strain based on sigmoidal arrays of this type. Furthermore, the CT data demonstrated that in 3D the veins are continuous and channel-like, implying a far higher degree of connectivity and fluid transport than is suggested by their 2D form. (C) 2015 Elsevier Ltd. All rights reserved.
The newest generation of satellites have greatly improved the capabilities of optical imagery over the last decade. Ground resolution has increased by one order of magnitude (to sub-metric pixel images), and improved sensors allow images to be located with an absolute accuracy of within a few meters. Better-resolved images facilitate refined tectonic studies of faults, basins, terraces, and other geomorphic features as it provides the opportunity to extract detailed topographic information. We have developed high-resolution digital elevation models (DEMs) in eight locations in Greece from tri-stereo satellite images acquired by the new Pleiades platform of CNES. With 0.5m resolution, these DEMs are state-of-the-art in comparison to previous DEMs made from satellite imagery. In this study we explore the potential of one of these DEMs, in the eastern Gulf of Corinth, for the analysis of a flight of marine terraces.
