High-angular resolution electron backscatter diffraction as a new tool for mapping

14 Analysis of distortions of the crystal lattice within individual mineral grains is central to the 15 investigation of microscale processes that control and record tectonic events. These distortions are 16 generally combinations of lattice rotations and elastic strains, but a lack of suitable observational 17 techniques has prevented these components being mapped simultaneously and routinely in earth 18 science laboratories. However, the technique of high-angular resolution electron backscatter 19 diffraction (HR-EBSD) provides the opportunity to simultaneously map lattice rotations and 20 elastic strains with exceptional precision, on the order of 0.01° for rotations and 10 -4 in strain, 21 using a scanning electron microscope. Importantly, these rotations and lattice strains relate to 22 densities of geometrically necessary dislocations and residual stresses. Recent works have begun 23 to apply and adapt HR-EBSD to geological minerals, highlighting the potential of the technique to 24 provide new insights into the microphysics of rock deformation. Therefore, the purpose of this 25 overview is to provide a summary of the technique, to identify caveats and targets for further 26 development, and to suggest areas where it offers potential for major advances. In particular, HR27 EBSD is well suited to characterising the roles of different dislocation types during crystal plastic 28 deformation and to mapping heterogeneous internal stress fields associated with specific 29 deformation mechanisms/microstructures or changes in temperature, confining pressure, or 30 applied deviatoric stress. These capabilities make HR-EBSD a particularly powerful new 31 technique for analysing the microstructures of deformed geological materials. 32