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Dislocation creep of olivine: Low-temperature plasticity controls transient creep at high temperatures
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  • Lars Hansen,
  • David Wallis,
  • Thomas Breithaupt,
  • Christopher Thom,
  • Imogen Kempton
Lars Hansen
University of Minnesota, University of Minnesota

Corresponding Author:lnhansen@umn.edu

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David Wallis
University of Cambridge, University of Cambridge
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Thomas Breithaupt
University of Oxford, University of Oxford
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Christopher Thom
University of Oxford, University of Oxford
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Imogen Kempton
University of Oxford, University of Oxford
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Transient creep occurs during geodynamic processes that impose stress changes on rocks at high temperatures. The transient is manifested as evolution in the viscosity of the rocks until steady-state flow is achieved. Although several phenomenological models of transient creep in rocks have been proposed, the dominant microphysical processes that control such behavior remain poorly constrained. To identify the intragranular processes that contribute to transient creep of olivine, we performed stress-reduction tests on single crystals of olivine at temperatures of 1250–1300°C. In these experiments, samples undergo time-dependent reverse strain after the stress reduction. The magnitude of reverse strain is ~10-3 and increases with increasing magnitude of the stress reduction. High-angular resolution electron backscatter diffraction analyses of deformed material reveal lattice curvature and heterogeneous stresses associated with the dominant slip system. The mechanical and microstructural data are consistent with transient creep of the single crystals arising from accumulation and release of backstresses among dislocations. These results allow the dislocation-glide component of creep at high temperatures to be isolated, and we use these data to recalibrate the low-temperature plasticity flow law for olivine to describe the glide component of creep over a wide temperature range. We argue that this flow law can be used to estimate both transient creep and steady-state viscosities of olivine, with the transient evolution controlled by the evolution of the backstress. This model is able to predict variability in the style of transient (normal versus inverse) and the load-relaxation response observed in previous work.
May 2021Published in Journal of Geophysical Research: Solid Earth volume 126 issue 5. 10.1029/2020JB021325