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

在上个学年，沃利斯陪同一名学生在美国西部的方济各会地体进行实地考察。我们收集了大量样本，准备运回日本，并进行更详细的显微结构分析。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。蛇纹岩样品的抛光薄片经过精心准备，包括1/4微米的钻石抛光。然后，按照东京大学该小组建立的抛光程序，用胶体二氧化硅对表面进行处理，以优化表面损伤的去除。然后在0.5 mm^2的面积上绘制该样品的EBSD图，并将结果数据保存到硬盘上，其中包括所有菊池图案。最终得到的数据集超过1TB。将该数据集作为测试用例，将词典标引应用于蛇纹岩样品微结构的定义这一难题。这些数据与原始样本一起被发送给卡内基梅洛大学的德格拉夫，以便使用牛津对称探测器进行进一步的补充分析。使用更灵敏的探测器没有发现数据质量有显著改善。DI指数的结果被用来绘制一系列取向图，这些取向图可以用来揭示蛇纹岩样品的微结构，具有前所未有的完整性。

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.