TY - JOUR
T1 - Dislocation Creep of Olivine
T2 - Backstress Evolution Controls Transient Creep at High Temperatures
AU - Hansen, Lars N.
AU - Wallis, David
AU - Breithaupt, Thomas
AU - Thom, Christopher A.
AU - Kempton, Imogen
N1 - Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.
PY - 2021/5
Y1 - 2021/5
N2 - 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.
AB - 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.
KW - Backstress
KW - dislocation creep
KW - dislocation interactions
KW - mantle viscosity
KW - olivine
KW - stress-reduction tests
KW - transient creep
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U2 - 10.1029/2020JB021325
DO - 10.1029/2020JB021325
M3 - Article
AN - SCOPUS:85106860764
SN - 2169-9313
VL - 126
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
IS - 5
M1 - e2020JB021325
ER -