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Computational studies of point defects and dislocations in forsterite (Mg₂SiO₄) and some implications for the rheology of mantle olivine

Walker, Andrew Mark; (2004) Computational studies of point defects and dislocations in forsterite (Mg₂SiO₄) and some implications for the rheology of mantle olivine. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Convection in the Earths solid mantle, accompanied by long time-scale viscous creep, is the mechanism operating on the global scale that allows internally generated heat to escape from the Earths deep interior. This process drives plate tectonics and, ultimately, almost every other geological process occurring at the Earths surface. On a small scale, the mantle deforms by plastic deformation of its constituent crystals - a process that involves the movement of a range of crystal defects (point defects, dislocations and grain boundaries). An understanding of the defect properties of mantle phases is thus essential to any unified, multi-scale view of the behaviour of the Earth. This thesis describes research on a range of defect phenomena in olivine ([Mg,Fe]₂SiO₄) undertaken using atomic scale computational modelling techniques. Following an outline of the theoretical background, the structure, energetics and properties of a range of point defects are studied using an inter-atomic parameterised potential model and the Mott-Littleton method. A combined electronic structure - parameterised potential embedded cluster approach has also been employed for selected defects. Bulk diffusion occurring by point defect motion is then considered using static lattice techniques with the parameterised model. The diffusion of oxygen is treated in some detail and an explanation of a range of experimental observations is proposed by considering the formation and motion of defects on the oxygen sub-lattice coupled to the redox behaviour of iron. The second part of the thesis concentrates on modelling line defects. First a methodology for studying screw and edge dislocations in structurally complex ionic materials is developed from an earlier approach limited to studies of ionic materials with the rock salt structure. This methodology is then applied to MgO, zeolite A (a technologically significant material) and finally forsterite, the pure magnesium end member of the olivine solid solution.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Computational studies of point defects and dislocations in forsterite (Mg₂SiO₄) and some implications for the rheology of mantle olivine
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Earth sciences; Forsterite
URI: https://discovery.ucl.ac.uk/id/eprint/10101276
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