EBSDinterp 1.0: A MATLAB<sup>®</sup> Program to Perform Microstructurally Constrained Interpolation of EBSD Data

Pearce, Mark A.

doi:10.1017/s1431927615000781

Cited by 11 publications

(7 citation statements)

References 18 publications

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“…The stability of the sample surface at these very low temperatures made it possible to acquire such large data sets. We processed the raw EBSD data using the band contrast as a template [ Pearce , ] and generated microstructural information using the open‐source MTEX toolbox [ Bachmann et al , ]. We use eigenvectors calculated from the EBSD data to describe the shape and strength of alignment of c axes [ Woodcock , ].…”

Section: Methodsmentioning

confidence: 99%

Insights into anisotropy development and weakening of ice from in situ P wave velocity monitoring during laboratory creep

et al. 2017

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Polycrystalline ice weakens significantly after a few percent strain, during high homologous temperature deformation. Weakening is correlated broadly with the development of a crystallographic preferred orientation (CPO). We deformed synthetic polycrystalline ice at −5°C under uniaxial compression, while measuring ultrasonic P wave velocities along several raypaths through the sample. Changes in measured P wave velocities (Vp) and in the velocities calculated from microstructural measurements of CPO (by cryo‐electron backscatter diffraction) both show that velocities along trajectories parallel and perpendicular to shortening decrease with increasing strain, while velocities on diagonal trajectories increase. Thus, in these experiments, velocity data provide a continuous measurement of CPO evolution in creeping ice. Samples reach peak stresses after 1% shortening. Weakening corresponds to the start of CPO development, as indicated by divergence of P wave velocity changes for different raypaths, and initiates at ≈3% shortening. Selective growth by strain‐induced grain boundary migration (GBM) of grains favorably oriented for basal slip may initiate weakening through the formation of an interconnected network of these grains by 3% shortening. After weakening initiates, CPO continues to develop by GBM and nucleation processes. The resultant CPO has an open cone (small circle) configuration, with the cone axis parallel to shortening. The development of this CPO causes significant weakening under uniaxial compression, where the shear stresses resolved on the basal planes (Schmid factors) are high.

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Section: Methodsmentioning

confidence: 99%

Insights into anisotropy development and weakening of ice from in situ P wave velocity monitoring during laboratory creep

et al. 2017

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“…While calcite EBSD patterns were of a high quality, anhydrite proved difficult to index despite reasonable quality patterns. The raw EBSD pixel data were cleaned using the pixel‐interpolation toolbox EBSDinterp (v.1.0) [ Pearce , ], applying band contrast masking to improve the robustness of the interpolation. EBSD data were thereafter processed in the MTEX toolbox for MATLAB (v.4.3.2) [ Bachmann et al ., ].…”

Section: Methodsmentioning

confidence: 99%

Ultramylonite generation via phase mixing in high‐strain experiments

Cross

Skemer

2017

JGR Solid Earth

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Dynamic recrystallization and phase mixing are considered to be important processes in ductile shear zone formation, as they collectively enable a permanent transition to the strain‐weakening, grain‐size sensitive deformation regime. While dynamic recrystallization is well understood, the underlying physical processes and timescales required for phase mixing remain enigmatic. Here, we present results from high‐strain phase mixing experiments on calcite‐anhydrite composites. A poorly mixed starting material was synthesized from fine‐grained calcite and anhydrite powders. Samples were deformed in the Large Volume Torsion apparatus at 500°C and shear strain rates of 5 × 10−5 to 5 × 10−4 s−1, to finite shear strains of up to γ = 57. Microstructural evolution is quantified through analysis of backscattered electron images and electron backscatter diffraction data. During deformation, polycrystalline domains of the individual phases are geometrically stretched and thinned, causing an increase in the spatial density of interphase boundaries. At moderate shear strains (γ ≥ 6), domains are so severely thinned that they become “monolayers” of only one or two grain's width and form a thin compositional layering. Monolayer formation is accompanied by a critical increase in the degree of grain boundary pinning and, consequently, grain‐size reduction below the theoretical limit established by the grain‐size piezometer or deformation mechanism field boundary. Ultimately, monolayers neck and disaggregate at high strains (17 <γ <57) to complete the phase mixing process. This “geometric” phase mixing mechanism is consistent with observations of mylonites, where layer (i.e., foliation) formation is associated with strain localization, and layers are ultimately destroyed at the mylonite‐ultramylonite transition.

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“…EBSD data were cleaned using the EBSDinterp toolbox for MATLAB (Pearce, 2015). In the first pass of cleaning, nonindexed pixels were filled if they had three or more neighboring pixels of a common orientation.…”

Section: Microstructural Analysismentioning

confidence: 99%

How Does Viscosity Contrast Influence Phase Mixing and Strain Localization?

et al. 2020

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Ultramylonites—intensely deformed rocks with fine grain sizes and well‐mixed mineral phases—are thought to be a key component of Earth‐like plate tectonics, because coupled phase mixing and grain boundary pinning enable rocks to deform by grain‐size‐sensitive, self‐softening creep mechanisms over long geologic timescales. In isoviscous two‐phase composites, “geometric” phase mixing occurs via the sequential formation, attenuation (stretching), and disaggregation of compositional layering. However, the effects of viscosity contrast on the mechanisms and timescales for geometric mixing are poorly understood. Here, we describe a series of high‐strain torsion experiments on nonisoviscous calcite‐fluorite composites (viscosity contrast, ηca/ηfl ≈ 200) at 500°C, 0.75 GPa confining pressure, and 10−6–10−4 s−1 shear strain rate. At low to intermediate shear strains (γ ≤ 10), polycrystalline domains of the individual phases become sheared and form compositional layering. As layering develops, strain localizes into the weaker phase, fluorite. Strain partitioning impedes mixing by reducing the rate at which the stronger (calcite) layers deform, attenuate, and disaggregate. Even at very large shear strains (γ ≥ 50), grain‐scale mixing is limited, and thick compositional layers are preserved. Our experiments (1) demonstrate that viscosity contrasts impede mechanical phase mixing and (2) highlight the relative inefficiency of mechanical mixing. Nevertheless, by employing laboratory flow laws, we show that “ideal” conditions for mechanical phase mixing may be found in the wet middle to lower continental crust and in the dry mantle lithosphere, where quartz‐feldspar and olivine‐pyroxene viscosity contrasts are minimized, respectively.

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EBSDinterp 1.0: A MATLAB^® Program to Perform Microstructurally Constrained Interpolation of EBSD Data

Cited by 11 publications

References 18 publications

Insights into anisotropy development and weakening of ice from in situ P wave velocity monitoring during laboratory creep

Insights into anisotropy development and weakening of ice from in situ P wave velocity monitoring during laboratory creep

Ultramylonite generation via phase mixing in high‐strain experiments

How Does Viscosity Contrast Influence Phase Mixing and Strain Localization?

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EBSDinterp 1.0: A MATLAB® Program to Perform Microstructurally Constrained Interpolation of EBSD Data

Cited by 11 publications

References 18 publications

Insights into anisotropy development and weakening of ice from in situ P wave velocity monitoring during laboratory creep

Insights into anisotropy development and weakening of ice from in situ P wave velocity monitoring during laboratory creep

Ultramylonite generation via phase mixing in high‐strain experiments

How Does Viscosity Contrast Influence Phase Mixing and Strain Localization?

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EBSDinterp 1.0: A MATLAB^® Program to Perform Microstructurally Constrained Interpolation of EBSD Data