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Microstructural stability and the kinetics of textural evolution

Lind, Andrew (1996) Microstructural stability and the kinetics of textural evolution. PhD thesis, University of Leeds.

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Abstract

This thesis is concerned with constraining the processes by which a rock texture may be altered in the geological history after a rock has been deformed and the rates at which that microstructural modification may occur. The area which has been chosen to investigate microstructural change is the Ballachulish aureole in the NW Highlands of Scotland, using samples from the Appin Quartzite. Rocks in this region were deformed during the Caledonian orogeny. Post-dating the deformation was the intrusion of the Ballachulish granite. As a consequence of the thermal perturbation associated with the granite intrusion, deformation microstructures were gradually altered. This process is known as annealing. The Ballachulish aureole is essentially a ‘natural laboratory’ which preserves an annealing experiment over geological time; rocks are gradually annealed along the traverse towards the intrusive complex where higher temperatures were attained. Rocks have been sampled along a traverse from outside the igneous aureole towards the contact. A variety of microstructural elements have been characterised using image analysis and crystallographic techniques, some of which have been developed during this study. The changes in rock fabrics along the traverse are used as a basis for developing models of annealing for many microstructural features, including dislocations, subgrains, subgrain walls and grains. The relative stability of each of these microstructures is assessed to show that dislocations are the least stable, then subgrains and grains. An interesting ‘mesh’ microstructure is identified, preserving evidence of fracturing on a grain scale. These mesh-grains are very stable, surviving annealing in some cases altogether. The presence of impurities on all scales of observation are shown to greatly influence the mechanisms of microstructural change. The kinetics of microstructural modification are examined using theoretical models based on the processes of annealing which have been identified during this investigation. Again these indicate that impurities can have marked implications on the rates of microstructural change. Kinetic models for rocks undergoing regional prograde and retrograde metamorphosis are developed to indicate how this work may be applied on a more regional tectonic scale.

Item Type: Thesis (PhD)
Academic Units: The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Earth Sciences (Leeds)
Identification Number/EthosID: uk.bl.ethos.690140
Depositing User: Digitisation Studio Leeds
Date Deposited: 02 Aug 2016 13:32
Last Modified: 06 Oct 2016 14:43
URI: http://etheses.whiterose.ac.uk/id/eprint/13739

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