| Co-Investigator(Kenkyū-buntansha) |
FUJINO Kuyoshi Faculty of Science, Ehime University (Now at : Faculty of Science, Hokkaido Univ, 理学部, 助教授 (40116968)
YOSHIDA Shizuo Faculty of Science, University of Tokyo Associate professor, 理学部, 助教授 (50011656)
TORIUMI Mitsuhiro Faculty of Science, University of Tokyo Professor, 理学部, 教授 (10013757)
OHNAKA Mitiyasu Earthquake Research Institute University of Tokyo Professor, 地震研究所, 教授 (00012956)
MATSUDA Tokihiko Earthquake Research Institute University of Tokyo (Now at : Faculty of Science,, 地震研究所・現九州大学理学部, 教授 (70012896)
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| Research Abstract |
The main tasks of the present research project have been (1) to determine whether the ultrafine matrix of PT is of melt origin or of crush origin, (2) to understand why PT are rare, and (3) to discuss the implications of the results from the former two tasks for the state-of-stress problem. The major results from the project are as follows.
The matrix of PT is so fine-grained that it is not easy to delineate its origin. However, an entirely new method was found as a result of this project for testing the validity of the crush origin based on the analysis of the size distribution of clasts contained in PT (Shimamoto and Nagahama, 1991,1992). They showed that clasts contained in PT from the Musgrave Range, central Australia, obey a power-law size distribution with a fractal dimension of 1.5. This size distribution predicts that the ultrafine-grained matrix should occupy an area of 4-5 %, whereas the area of the matrix of PT amounts to about 60 %. Hence, the major part of the matrix cannot
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be regarded as the crush products. This result, together with textural evidence such as the development of microlites and corroded textures of clasts, strongly suggests the melt origin of the matrix of pseudotachylytes. This result has been substatiated with updated analysis based on a modified fractal size distribution of clasts from two other localities (Nagahama et al., 1994).
We also have designed and built a new high-speed frictional testing machine to study the pseudotachylyte generating processes in laboratory. This was the major task for this project, and we have successfully produced frictional melt that is very similar to natural psedotachylytes. The findings from high-speed friction experiments are as follows. (1) Frictional melting is a disequilibrium phenomenon, (2) minerals with low melting temperature and presumably with less stability to rapid heating preferentially melt during the frictional melting, (3) frictional melt of granite is depleted in SiO_2 because quartz is most resistent to frictional melting, (4) temperature above 1,300 ﾟC was measured for the frictional melt of gabbro using a photo thermometer, and (5) thermal fracturing due to rapid temperature rise during frictional heating is important in the generation of clasts contained in pseudotachylytes. The results (3) is consistent with the results for some natural pseudotachylytes. Less
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