Strength of orthoenstatite single crystals at mantle pressure and temperature and comparison with olivine

Raterron, Paul; Fraysse, G.; Girard, Jennifer; Holyoke, C. W.

doi:10.1016/j.epsl.2016.06.025

Cited by 17 publications

(27 citation statements)

References 46 publications

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“…For these low‐pressure experiments, the somewhat elongated grains perpendicular to the compression axis and the EBSD data suggest that dislocation creep takes place predominantly by activation of the (100)[001] slip system. As noted in Mackwell [] and Raterron et al [], this slip system is expected to be the easiest one under our experimental deformation conditions.…”

Section: Discussionsupporting

confidence: 54%

“…The addition of Al under dry conditions however yielded a CPO consistent with dominant activation of (010)[001]. Finally, Raterron et al [] observed that the enstatite (100)[001] slip system is also prevalent over the (010)[001] slip system at higher pressures.…”

Section: Discussionmentioning

confidence: 99%

“…These results are much weaker than those of Mackwell [] for protoenstatite and are also somewhat weaker than those for dry deformation of olivine single crystals and polycrystals. Recently, Raterron et al [] reported results of deformation experiments on oriented enstatite single crystals at confining pressures of 3–6 GPa and temperatures from 1313 to 1645 K. They concluded that the orthopyroxene (100)[001] slip system is weaker than the (010)[001] slip system and that both orthopyroxene slip systems are significantly stronger than olivine slip systems.…”

Section: Introductionmentioning

confidence: 99%

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High‐temperature deformation of enstatite aggregates

et al. 2016

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Synthesized polycrystalline enstatite samples were deformed in a Paterson gas‐medium apparatus at 1200–1300°C, oxygen fugacity buffered at Ni/NiO, and confining pressures of 300 MPa (protoenstatite field) or 450 MPa (orthoenstatite field). At both confining pressures, the mechanical data display a progressive increase of the stress exponent from n = 1 to n~3 with increasing differential stress, suggesting a transition from diffusional to dislocation creep. Nonlinear least squares fits to the high‐stress data yielded dislocation creep flow laws with a stress exponent of 3 and activation energies of 600 and 720 kJ/mol for orthoenstatite and protoenstatite, respectively. Deformed samples were analyzed using optical microscopy and scanning and transmission electron microscopy. Microstructures show undulatory extinction and kink bands, evidence of dislocation processes. Crystallographic preferred orientations measured by electron backscatter diffraction are axisymmetric and indicate preferential slip on (100)[001]. Most deformed grains comprise an interlayering of orthoenstatite and clinoenstatite lamellae. While many lamellae may have formed during quenching from run conditions, those in samples deformed in the orthoenstatite field are often bordered by partial [001] dislocations, suggesting transformation due to glide of partial [001] dislocations in (100) planes. Comparison of our orthoenstatite creep law with those for dislocation creep of olivine indicates that orthoenstatite deforms about a factor of 2 slower than olivine at our experimental conditions. However, as orthoenstatite has a higher activation energy and smaller stress exponent than olivine, this strength difference is likely smaller at the higher temperatures and lower stresses expected in much of the upper mantle.

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Section: Discussionsupporting

confidence: 54%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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High‐temperature deformation of enstatite aggregates

et al. 2016

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“…These microstructures are often observed in samples deformed by a dislocation‐accommodated process in nature and experiment (e.g., Hansen et al, ; Linckens et al, ). In the pyroxene‐rich layers, the pyroxene grains form a weak texture with [010] approximately parallel to the Y direction (Figure b), an orientation typical of slip on the (100)[001] slip system in a sample deformed by dislocation creep, as observed in naturally and experimentally deformed orthopyroxene (e.g., Bystricky et al, ; Christensen & Lundquist, ; Raterron et al, ; Skemer et al, ). In contrast, as secondary phases (pyroxene in olivine‐rich aggregates and olivine in pyroxene‐rich aggregates), both phases show weak textures typical of uniform distributions (Figures d and e).…”

Section: Discussionmentioning

confidence: 86%

“…The dashed line is the best fit for data from Hansen et al (2012). Journal of Geophysical Research: Solid Earth 10.1002/2017JB014311 orthopyroxene (e.g., Bystricky et al, 2016;Christensen & Lundquist, 1982;Raterron et al, 2016;Skemer et al, 2006). In contrast, as secondary phases (pyroxene in olivine-rich aggregates and olivine in pyroxene-rich aggregates), both phases show weak textures typical of uniform distributions (Figures 9d and 9e).…”

Section: Development Of Crystallographic Fabricmentioning

confidence: 99%

Rheological Weakening of Olivine + Orthopyroxene Aggregates Due To Phase Mixing: Part 2. Microstructural Development

et al. 2017

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To understand the processes involved in phase mixing during deformation and the resulting changes in rheological behavior, we conducted torsion experiments on samples of iron‐rich olivine plus orthopyroxene. The experiments were conducted at a temperature, T, of 1200°C and a confining pressure, P, of 300 MPa using a gas‐medium deformation apparatus. Samples composed of olivine plus 26% orthopyroxene were deformed to outer radius shear strains up to γ ≈ 26. In samples deformed to lower strains of γ ≲ 4, elongated olivine and pyroxene grains form a compositional layering. Already by this strain, mixtures of small equant grains of olivine and pyroxene begin to develop and continue to evolve with increasing strain. The ratios of olivine to pyroxene grain size in deformed samples follow the Zener relationship, indicating that pyroxene grains effectively pin the grain boundaries of olivine and inhibit grain growth. Due to the reduction in grain size, the dominant deformation mechanism changes as a function of strain. The microstructural development forming more thoroughly mixed, fine‐grained olivine‐pyroxene aggregates can be explained by the difference in diffusivity among Me (Fe or Mg), O, and Si, with transport of MeO significantly faster than that of SiO2. These mechanical and associated microstructural properties provide important constraints for understanding rheological weakening and strain localization in upper mantle rocks.

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Diffusion Creep of Enstatite at High Pressures Under Hydrous Conditions

et al. 2017

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Mantle convection and large‐scale plate motion depend critically on the nature of the lithosphere‐asthenosphere boundary and thus on the viscosity structure of Earth's upper mantle, which is determined by the rheological properties of its constituent minerals. To constrain the flow behavior of orthopyroxene, the second most abundant constituent of the upper mantle, deformation experiments were carried out in triaxial compressive creep on fine‐grained (~6 μm) samples of enstatite at high pressures (3.8–6.3 GPa) and high temperatures (1323–1573 K) using a deformation‐DIA apparatus. Based on results from this study, the deformation behavior of enstatite is quantitatively presented in the form of a flow law that describes the dependence of deformation rate on differential stress, water fugacity, temperature, and pressure. Specifically, the creep rate depends approximately linearly on stress, indicating deformation in the diffusion creep regime. A least squares regression fit to our data yielded a flow law for diffusion creep with an activation energy of ~200 kJ/mol and an activation volume of ~14 × 10−6 m3/mol. The magnitude of the water‐weakening effect is similar to that for olivine with a water fugacity exponent of r ≈ 0.7. This strong dependence of viscosity on water fugacity (concentration) indicates that the viscosity of an orthopyroxene‐bearing mantle varies from one geological setting to another, depending on the large‐scale water distribution. Based on the rheology contrast between olivine and enstatite, we conclude that olivine is weaker than enstatite throughout most of the upper mantle except in some shallow regions in the diffusion creep regime.

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Strength of orthoenstatite single crystals at mantle pressure and temperature and comparison with olivine

Cited by 17 publications

References 46 publications

High‐temperature deformation of enstatite aggregates

High‐temperature deformation of enstatite aggregates

Rheological Weakening of Olivine + Orthopyroxene Aggregates Due To Phase Mixing: Part 2. Microstructural Development

Diffusion Creep of Enstatite at High Pressures Under Hydrous Conditions

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