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Book Chapter

Grain growth and the lifetime of diffusion creep deformation

By
Mark A. Pearce
Mark A. Pearce
Geospatial Research Ltd., Department of Earth Science, Durham University, Durham DH1 3LE, UK
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John Wheeler
John Wheeler
Department of Earth & Ocean Sciences, University of Liverpool, Liverpool L69 3GP, UK
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Published:
January 01, 2011

Abstract

Extreme grain-size reduction due to cataclasis, neocrystallization or phase change results in a switch to diffusion creep and dramatic weakening in deforming rocks. Grain growth increases strength until dislocation creep becomes a significant deformation mechanism. We quantify the ‘lifetime’ of diffusion creep by substituting the normal grain growth law into the diffusion creep flow law to calculate the time taken for dislocation creep to become significant. Stress-temperature and strain-rate-temperature space is outlined where diffusion creep may accommodate significant strain: these regions have an upper temperature limit beyond which grain growth is fast enough to move the rock quickly into the dislocation creep field. For plagioclase the limit lies in the amphibolite facies. Rocks in a mantle upwelling experience grain-size reduction during phase changes. Pressure-dependent grain growth limits the deformation that can be accommodated by diffusion creep. This time limit and associated strain limit is independent of starting grain size with a small dependence on upwelling rate and plume width. In both these tectonic environments, second phases are likely to play a role in the maximum achievable grain size due to grain-boundary pinning. Hence we predict the minimum lifetimes of diffusion-creep-dominated deformation following extreme grain-size reduction.

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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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