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

Accepted version
Peer-reviewed

Type

Article

Change log

Abstract

jats:titleAbstract</jats:title>jats:pTransient 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 ∼10jats:sup−3</jats:sup> 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.</jats:p>

Description

Keywords

Backstress, dislocation creep, dislocation interactions, mantle viscosity, olivine, stress&#8208, reduction tests, transient creep

Journal Title

Journal of Geophysical Research: Solid Earth

Conference Name

Journal ISSN

2169-9313
2169-9356

Volume Title

126

Publisher

American Geophysical Union (AGU)

Rights

All rights reserved
Sponsorship
LH and DW 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 DW acknowledges support from the Netherlands Organisation for Scientific Research, User Support Programme Space Research, grant ALWGO.2018.038, and startup funds from Utrecht University. LH recognizes funds used to develop the uniaxial apparatus from the John Fell Fund at the University of Oxford.