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Substructure dynamics in halite: Comparison of 2D in-situ annealing experiments with 3D X-ray diffraction annealing
Stockholm University, Faculty of Science, Department of Geology and Geochemistry. (Petrotectonics)
Stockholm University, Faculty of Science, Department of Geology and Geochemistry. (Petrotectonics)
Denmarks Technical University, Materials Research Department.
Lund University, MaxLab.
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2009 (English)In: Deformation Mechanisms, Rheology and Tectonics 2009, 2009Conference paper (Other academic)
Abstract [en]

The understanding of substructural behaviour during post-deformational annealing is key to interpreting rheological adjustments during tectonic change, and the processes which cause them. The focus of this study is to use in-situ experimental techniques to increase understanding of substructure dynamics in geological materials. 2D in-situ annealing experiments have been conducted in the scanning electron microscope, using electron backscatter diffraction (EBSD) to collect information about the crystallographic orientation of the surface. A single crystal of halite, pre-deformed under uniaxial compression at temperatures of ~450 ºC with a strain rate of 6.9x10-6s-1, and to a final strain of 0.165, was examined. Different temperature time-paths were investigated with temperatures between 280-470 ºC and durations of heating between 30 min and 6 h. EBSD maps were taken before, during and after heating. Behaviour during annealing was found to be temperature dependent and could be divided into three main phases of development. Subgrain boundaries could be divided into five categories based on behaviour during annealing, morphology and orientation. Annealing behaviour could be directly related to preferential activation of one set of slip systems due to the chosen aspect ratio of the crystal.

While the 2D experiments provided valuable information, it is impossible to rule out the potential influence surface effects may have on annealing behaviour. In order to verify the results of these experiments, a 3D X-ray diffraction experiment was conducted at the synchrotron in Grenoble, France. The experiment followed a similar heating procedure as that for the 2D experiments and was performed on the same sample. This newly developed technique allows non-destructive internal examination of the crystal. Data was collected before, during and after each heating stage. During heating crystallographic information was collected within a limited rotation threshold (12-30º) in order to illuminate one or two subgrains and allow us to follow their progress. Comparison of the shape and strength of intensity spots has allowed us to draw some early conclusions from the data without a full crystallographic analysis. Preliminary results suggest that similar processes may be occurring as those observed in the 2D experiments, including spots becoming more distinct as well as some spots rotating away from the bulk of the subgrain indicating some subdivision and potential polygonisation. We can thus suggest that some of the behaviour exhibited in the 3D experiment is similar to that from the 2D experiment. Full crystallographic analysis of large maps taken after heating will allow us to examine the behaviour of the substructure in more detail and potentially rule out surface effects from the 2D experiments.

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URN: urn:nbn:se:su:diva-33831OAI: diva2:283722
Deformation Mechanisms, Rheology and Tectonics 2009
Available from: 2009-12-30 Created: 2009-12-30 Last updated: 2012-06-19Bibliographically approved

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Borthwick, VerityPiazolo, Sandra
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Department of Geology and Geochemistry
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