Dislocation Creep of Olivine: Backstress Evolution Controls Transient Creep at High Temperatures

Lars N. Hansen, David Wallis, Thomas Breithaupt, Christopher A. Thom, Imogen Kempton

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

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 1,250°C–1,300°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 calibrate a 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 vs. inverse) and the load-relaxation response observed in previous work.

Original languageEnglish (US)
Article numbere2020JB021325
JournalJournal of Geophysical Research: Solid Earth
Volume126
Issue number5
DOIs
StatePublished - May 1 2021

Bibliographical note

Funding Information:
The authors benefited greatly from conversation with H. Jay Melosh on the rheological behavior of planetary bodies. His passing represents a great loss to our community. The authors would also like to acknowledge fruitful discussions with Greg Hirth, Ben Holtzman, and David Kohlstedt. The manuscript was greatly improved by constructive and thoughtful reviews from Reid Cooper and Brian Evans. L. N. Hansen and D. Wallis acknowledge support from the Natural Environment Research Council, grant NE/M000966/1, LH and CT acknowledge support from the Natural Environment Research Council, Grant 1710DG008/JC4, and D. Wallis acknowledges support from the Netherlands Organization for Scientific Research, User Support Program Space Research, grant ALWGO.2018.038, and startup funds from Utrecht University. L. N. Hansen recognizes funds used to develop the uniaxial apparatus from the John Fell Fund at the University of Oxford.

Funding Information:
The authors benefited greatly from conversation with H. Jay Melosh on the rheological behavior of planetary bodies. His passing represents a great loss to our community. The authors would also like to acknowledge fruitful discussions with Greg Hirth, Ben Holtzman, and David Kohlstedt. The manuscript was greatly improved by constructive and thoughtful reviews from Reid Cooper and Brian Evans. L. N. Hansen and D. Wallis acknowledge support from the Natural Environment Research Council, grant NE/M000966/1, LH and CT acknowledge support from the Natural Environment Research Council, Grant 1710DG008/JC4, and D. Wallis acknowledges support from the Netherlands Organization for Scientific Research, User Support Program Space Research, grant ALWGO.2018.038, and startup funds from Utrecht University. L. N. Hansen recognizes funds used to develop the uniaxial apparatus from the John Fell Fund at the University of Oxford.

Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.

Keywords

  • Backstress
  • dislocation creep
  • dislocation interactions
  • mantle viscosity
  • olivine
  • stress-reduction tests
  • transient creep

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