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

在上一学年，沃利斯陪同一名学生在美国西部的方济各会地区进行实地工作。我们收集了大量的样品运回日本，并进行了更详细的微观结构分析。这些样品为变质砂岩和泥岩以及包括变形蛇纹岩在内的各种断层岩。东京大学选择了几个蛇纹岩样品进行EBSD分析。精心制备了蛇纹石样品的抛光薄片，其中包括1/4微米的金刚石抛光。然后，按照东京大学的研究小组制定的抛光程序，用胶体二氧化硅处理表面，以优化表面损伤的去除。然后在0.5 mm^2的面积上制备该样品的EBSD映射，并将结果数据（包括所有菊池图案）保存到硬盘上。结果数据集超过1TB。该数据集作为测试用例，将字典索引应用于蛇纹石样品微观结构定义的难题。这些数据与原始样本一起被送到卡内基梅洛大学的De Graef，用牛津对称探测器进行进一步的补充分析。使用更灵敏的检测器，数据质量没有显著改善。DI标引的结果被用来绘制一系列的取向图，这些取向图反过来又可以用来揭示蛇纹岩样品的微观结构，其完整性前所未有。

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.