The stress dependence of olivine creep rate: Implications for extrapolation of lab data and interpretation of recrystallized grain size

Hirth, Greg; Kohlstedt, D. L.

doi:10.1016/j.epsl.2015.02.013

Cited by 61 publications

(92 citation statements)

References 42 publications

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“…We also compare our grain size piezometer with previous studies under anhydrous conditions [ Karato et al ., ; van der Wal et al ., ; Hansen et al ., ; Hirth and Kohlstedt , ]. The normalized grain size as a function of stress determined in previous studies and this study agree within half an order of magnitude.…”

Section: Discussionsupporting

confidence: 85%

“…The normalized grain size as a function of stress determined in previous studies and this study agree within half an order of magnitude. Hirth and Kohlstedt [] also demonstrated that the same piezometric relationship is effective under both anhydrous and hydrous conditions for a wide range of stress and temperature, as well as modest variations in hydrogen content.…”

Section: Discussionmentioning

confidence: 99%

“…Values of 63,510 MPa for Van der Wal et al . [] and Hirth and Kohlstedt [], 62,150 MPa for Jung and Karato [], and 59,107 MPa for Karato et al . [], respectively, were used for their samples of Fo 90 .…”

Section: Discussionmentioning

confidence: 99%

“…[] (HMK) for Fo 50 under anhydrous conditions. Gray solid line: Hirth and Kohlstedt [] (HK) for Fo 90 assuming screw dislocation.…”

Section: Discussionmentioning

confidence: 99%

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Evolution of the rheological and microstructural properties of olivine aggregates during dislocation creep under hydrous conditions

2016

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Since hydrogen plays an important role in dynamic processes in Earth's mantle, we conducted torsion experiments to shear strains of 0.6 to 5.0 on Fe‐bearing olivine aggregates [(Mg0.5Fe0.5)2SiO4: Fo50] under hydrous conditions at T = 1200°C and P = 300 MPa. We deformed samples to high enough strains that a steady state microstructures were achieved, which allowed us to investigate the evolution of both the rheological and microstructural properties. The stress exponent of n ≈ 5.0 and the grain size exponent of p ≈ 0 determined by fitting the strain rate, stress, and grain size data indicate that our samples deformed by dislocation creep. Fourier transform infrared spectroscopy measurements on embedded olivine single crystals demonstrated that our samples were saturated with hydrogen during the deformation experiments. The lattice preferred orientation (LPO) of olivine changes as a function of strain due to competition among three slip systems: (010)[100], (100)[001], and (001)[100]. Observed strain weakening can be attributed to geometrical softening associated with development of LPO, which reduces the stress by ~1/3 from its peak value in constant strain rate experiments. The geometrical softening coefficient determined in this study is an important constraint for modeling and understanding dynamical processes in the upper mantle under hydrous conditions.

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Section: Discussionsupporting

confidence: 85%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…[] (HMK) for Fo 50 under anhydrous conditions. Gray solid line: Hirth and Kohlstedt [] (HK) for Fo 90 assuming screw dislocation.…”

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Evolution of the rheological and microstructural properties of olivine aggregates during dislocation creep under hydrous conditions

2016

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“…The flow laws in Hirth and Kohlstedt (), Mei et al (), and Hansen et al () were used to determine total strain rate based on the relation

\overset{ε}{true} = {\overset{true.}{ε}}_{diff} + {\overset{true.}{ε}}_{GBS} + {\overset{true.}{ε}}_{disl} + {\overset{true.}{ε}}_{lowT}

, where

{\overset{true.}{ε}}_{diff}

{\overset{true.}{ε}}_{GBS}

{\overset{true.}{ε}}_{disl}

, and

{\overset{true.}{ε}}_{lowT}

are strain rates in diffusion, disGBS with subgrain boundaries, dislocation, and low‐temperature plasticity creep, respectively. The red dashed line (K80) is the previously determined grain size piezometer from Karato et al (); the red dotted line (vdW93) is the piezometer from van der Wal et al (); and the red line (H&K15) is the piezometer from Hirth and Kohlstedt (). The solid blue line is the deformation mechanism boundary between disGBS with subgrain boundaries and diffusion creep.…”

Section: Discussionmentioning

confidence: 99%

Rheological Weakening of Olivine + Orthopyroxene Aggregates Due to Phase Mixing: 1. Mechanical Behavior

2017

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To understand the processes involved in rheological weakening due to phase mixing in olivine + orthopyroxene aggregates, we conducted high‐strain torsion experiments on two‐phase samples at a temperature of 1200°C and a confining pressure of 300 MPa. Samples composed of iron‐rich olivine plus 26% orthopyroxene were deformed to outer radius shear strains of up to γ ≈ 26. Values for the stress exponent, n, and grain size exponent, p, were determined based on least squares fits of the strain rate, stress, and grain size data to a power law creep equation both at smaller strains (γ ≤ 3) and at larger strains (γ ≥ 24). Microstructural observations demonstrate that with increasing shear strain, grain size decreased and mixtures of small, equant grains of olivine and pyroxene developed. The values of n and p combined with associated changes in microstructure demonstrate that our samples deformed (i) by dislocation‐accommodated grain‐boundary sliding with subgrains present at lower strains and (ii) by dislocation‐accommodated grain‐boundary sliding with subgrains absent at higher strains. The evolution of both the mechanical and the microstructural properties observed in this study provide insights into the dynamic processes associated with rheological weakening and strain localization in the plastically deforming portion of the lithosphere.

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Creep behavior of Fe‐bearing olivine under hydrous conditions

2015

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To understand the effect of iron content on the creep behavior of olivine, (MgxFe(1 − x))2SiO4, under hydrous conditions, we have conducted tri‐axial compressive creep experiments on samples of polycrystalline olivine with Mg contents of x = 0.53, 0.77, 0.90, and 1. Samples were deformed at stresses of 25 to 320 MPa, temperatures of 1050° to 1200°C, a confining pressure of 300 MPa, and a water fugacity of 300 MPa using a gas‐medium high‐pressure apparatus. Under hydrous conditions, our results yield the following expression for strain rate as a function of iron content for 0.53 ≤ x ≤ 0.90 in the dislocation creep regime: trueε˙=ε˙0.901−x0.11true/2exp[]226×1030.9−xRT. In this equation, the strain rate of San Carlos olivine, ε˙0.90, is a function of T, σ, and fH2normalO. As previously shown for anhydrous conditions, an increase in iron content directly increases creep rate. In addition, an increase in iron content increases hydrogen solubility and therefore indirectly increases creep rate. This flow law allows us to extrapolate our results to a wide range of mantle conditions, not only for Earth's mantle but also for the mantle of Mars.

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The stress dependence of olivine creep rate: Implications for extrapolation of lab data and interpretation of recrystallized grain size

Cited by 61 publications

References 42 publications

Evolution of the rheological and microstructural properties of olivine aggregates during dislocation creep under hydrous conditions

Evolution of the rheological and microstructural properties of olivine aggregates during dislocation creep under hydrous conditions

Rheological Weakening of Olivine + Orthopyroxene Aggregates Due to Phase Mixing: 1. Mechanical Behavior

Creep behavior of Fe‐bearing olivine under hydrous conditions

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