2022 Fiscal Year Research-status Report
New developments in EBSD analysis applied to characterization of fault rock microstructure
| Project/Area Number |
20KK0079
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| Research Institution | The University of Tokyo |
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Principal Investigator |
WALLIS R・Simon 東京大学, 大学院理学系研究科(理学部), 教授 (30263065)
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| Co-Investigator(Kenkyū-buntansha) |
瀬戸 雄介 神戸大学, 理学研究科, 講師 (10399818)
永冶 方敬 東京大学, 大学院理学系研究科(理学部), 助教 (10795222)
吉田 健太 国立研究開発法人海洋研究開発機構, 海域地震火山部門(火山・地球内部研究センター), 副主任研究員 (80759910)
大柳 良介 国立研究開発法人海洋研究開発機構, 海域地震火山部門(火山・地球内部研究センター), 特別研究員(PD) (90835729)
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| Project Period (FY) |
2020-10-27 – 2024-03-31
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| Keywords | EBSD / Serpentinite / Hough Indexing / Dictionary Indexing / Microstructure |
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| Outline of Annual Research Achievements |
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.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The international collaboration that is an important part of this project could be fruitfully pursued after the long interruption by the pandemic. We were able to collect a series of important samples for future work and produced concrete results from one sample. These results have shown the viability of the procedure that has been suggested and opened the way for more samples to be studies in a similar way. The results for the analysis of the antigorite rich serpentine sample have been analyzed and the results are far enough advanced to be able to write up the results in the form of a publication in the near future.
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| Strategy for Future Research Activity |
In the coming academic year we intend to write up the results that have already been obtained for the antigorite sample and expand the methodology to analyze samples consisting dominantly of talc and chrysotile. In the case of talc there are only a handful of published EBSD mapping studies. These include one by members of the research team for this project. However, there have been no published studies that clearly reveal the microstructure of the talc rich deformed rocks. This is important because talc is proposed as an important low strength domain that forms at the base of the mantle wedge. Low-T serpentinite samples are also highlighted as potentially important but even less is known about the CPO patterns and microstructure of these samples.
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| Causes of Carryover |
It was difficult to have an effective international collaboration with only limited travel. These costs were carried over to the next financial year. We are looking for an appropriate time for our partner researcher at the Carnegie Mellon University to travel to Japan to contribute to developing our understanding of the most effective systems when employing DI.
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