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Crystal fabric development and slip systems in a quartz mylonite: an approach via transmission electron microscopy and viscoplastic self-consistent modelling

By
Luiz F. G. Morales
Luiz F. G. Morales
Géosciences Montpellier UMR CNRS 5243 & Université Montpellier 2, Place Eugène Bataillon, Batîment 22, 34095, Montpellier cedex 05, France
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David Mainprice
David Mainprice
Géosciences Montpellier UMR CNRS 5243 & Université Montpellier 2, Place Eugène Bataillon, Batîment 22, 34095, Montpellier cedex 05, France
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Geoffrey E. Lloyd
Geoffrey E. Lloyd
Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
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Richard D. Law
Richard D. Law
Department of Geosciences, Virginia Tech., Blacksburg, VA, 24061, USA
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Published:
January 01, 2011

Abstract

We have applied transmission electron microscopy (TEM) analyses coupled with viscoplastic self-consistent (VPSC) numerical modelling to identify the active slip systems and to better understand the crystal preferred orientation (CPO) development of the Torridon quartz mylonite (NW Scotland). TEM analyses showed evidence of activation of 1/3〈a〉{π′}, 1/3〈a〉{z} and possible 〈a〉(c) slip systems, as well as dislocation climb and dynamic recrystallization. All the CPOs generated by VPSC models share common characteristics with the Torridon quartz mylonite, but only Models 2 and 3 reproduce the [c]-axes maxima at low angle (<20°) to the foliation pole along the YZ plane, as observed in the mylonite. In Model 2, this concentration only occurs at γ≥2.6, whereas in Model 3 this maxima occurs at lower shear strains. The models that start with a previous preferred orientation acquire very strong CPOs after small-imposed strains, followed by the rapid rotation of the fabric in relation to the new imposed finite strain axes. The combined activation of 〈a〉{π′}, 〈a〉{z} and possibly 〈a〉(c) slip systems, as demonstrated by TEM analyses, suggests that the VPSC model that best predicts CPO development in the Torridon quartz mylonite is Model 2, where the critical resolved shear stress (CRSS) of 〈a〉{π/π′} is assumed to be slightly stronger than 〈a〉(c).

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Contents

Geological Society, London, Special Publications

Deformation Mechanisms, Rheology and Tectonics: Microstructures, Mechanics and Anisotropy

David J. Prior
David J. Prior
University of Otago, New Zealand
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Ernest H. Rutter
Ernest H. Rutter
University of Manchester, UK
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Daniel J. Tatham
Daniel J. Tatham
University of Liverpool, UK
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Geological Society of London
Volume
360
ISBN electronic:
9781862394483
Publication date:
January 01, 2011

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