Abstract
AbstractAnalysis of distortions of the crystal lattice within individual mineral grains is central to the investigation of microscale processes that control and record tectonic events. These distortions are generally combinations of lattice rotations and elastic strains, but a lack of suitable observational techniques has prevented these components being mapped simultaneously and routinely in earth science laboratories. However, the technique of high‐angular resolution electron backscatter diffraction (HR‐EBSD) provides the opportunity to simultaneously map lattice rotation and elastic strain gradients with exceptional precision, on the order of 0.01° for rotations and 10−4 in strain, using a scanning electron microscope. Importantly, these rotations and lattice strains relate to densities of geometrically necessary dislocations and residual stresses. Recent works have begun to apply and adapt HR‐EBSD to geological minerals, highlighting the potential of the technique to provide new insights into the microphysics of rock deformation. Therefore, the purpose of this review is to provide a summary of the technique, to identify caveats and targets for further development, and to suggest areas where it offers potential for major advances. In particular, HR‐EBSD is well suited to characterizing the roles of different dislocation types during crystal plastic deformation and to mapping heterogeneous internal stress fields associated with specific deformation mechanisms/microstructures or changes in temperature, confining pressure, or macroscopic deviatoric stress. These capabilities make HR‐EBSD a particularly powerful new technique for analyzing the microstructures of deformed geological materials.
Highlights
The rates and styles of geodynamic processes on rocky planets emerge from a complex ensemble of underlying processes operating at scales down to the crystal lattices of their constituent minerals
high‐angular resolution electron backscatter diffraction (HR‐EBSD) is well suited to characterizing the roles of different dislocation types during crystal plastic deformation and to mapping heterogeneous internal stress fields associated with specific deformation mechanisms/microstructures or changes in temperature, confining pressure, or macroscopic deviatoric stress
The ability to precisely map intragranular lattice rotations, geometrically necessary dislocations (GNDs) densities, elastic strains, and residual stresses using EBSD data collected in a standard scanning electron microscope (SEM) has led to a wealth of developments in the materials sciences over the past decade
Summary
The rates and styles of geodynamic processes on rocky planets emerge from a complex ensemble of underlying processes operating at scales down to the crystal lattices of their constituent minerals. The ability to precisely map intragranular lattice rotations, GND densities, elastic strains, and residual stresses using EBSD data collected in a standard SEM has led to a wealth of developments in the materials sciences over the past decade. Examples include mapping GNDs and residual stress heterogeneity in single crystals of olivine (Kumamoto et al, 2017; Wallis et al, 2016; Wallis, Hansen, et al, 2017) and mapping GNDs in aggregates of olivine (Boneh et al, 2017; Kumamoto et al, 2017; Qi et al, 2018) and quartz (Wallis, Parsons, et al, 2017) These examples demonstrate the great potential of the technique and highlight some subtle but important considerations for analysis of geological materials in particular. We finish by discussing the strengths and limitations of the technique and summarizing potential research directions
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