New developments in EBSD analysis applied to characterization of fault rock microstructure

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During the last academic year Wallis accompanied a student to carry out field work in the Franciscan terrane of the western USA. We collected numerous samples for transport back to Japan and more detailed microstructural analysis. These samples were metamorphosed sandstone and mudstone and a variety of fault rocks including deformed serpentinite. Several samples of serpentinite were selected for EBSD analyses at University of Tokyo. Polished thin sections of the serpentinite samples were carefully prepared including 1/4 micron diamond polishing. The surface was then treated with colloidal silica following the polishing procedures established by the group at the University of Tokyo to optimize removal of surface damage. EBSD mapping of this sample were then prepared for an area of 0.5 mm^2 and the resulting data including all the Kikuchi patterns were saved to a hard disk. The resulting data set was in excess of 1TB. This data set was used as a test case to apply Dictionary Indexing to the difficult problem of defining the microstructure of serpentinite samples. The data were sent to De Graef at Carnegie Mello University along with the original sample for further complementary analysis using the Oxford Symmetry detector. No significant improvements in data quality were recognized using the more sensitive detectors. The results of DI indexing were used to plot a series of orientation maps that can in turn be used to reveal the microstructure of serpentinite samples with unprecedented completeness.