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Preliminary study of change in physical properties of coalified and graphitized phytoclasts with grade of metamorphis : correspondence between the reflectance and the crystallinit
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| Abstract | The reflectance of coalified phytoclast and the crystallinity of carbonaceous constituents from the Sanbagawa pelitic schists of the Asemi River area in central Shikoku and from thermally metamorphose...d elastic rocks of the Miocene Susa Group in Yamaguchi Prefecture have been investigated, and compared with the metamorphic zones previously reported. The values of reflectance and crystallinity by the X-ray difflaction mutually increase with advancing of metamorphic temperature, and are very consistent with the mineral zones of each district. And thus, the reflectance is very useful as a rank parameter for the metamorphic grade of the host rock within both the contact and the regional metamorphic belts. However, the increasing modes of the reflectance and the crystallinity do not always correspond each other with progressing of metamorphism. This phenomenon is probably due to the fact that the crystallinity, namely, the degree of graphitization is caused not only by rock temperature but also by pressure, the duration of metamorphism, parent material and its rank, and by heating rate, in contrast with the reflectance being surely determined by the rock temperature and the effective heating time for thermal maturation of orgainc matter. In the Asemi River area, the relfectance in the chlorite zone ranges from 4 to 6 % Romax, which supports that the greenschist facies begins beyond 4 %応max.The boundarys between the chlorite zone and the garnet zone, and between the albitebiotite zone and the oligoclase-biotite zone correspond to around 6 -7 % and around 8 % Romax respectively. The crystallinity of carbonaceous materials within the higher grade part of garnet zone and the biotite zone nearly reaches that of the fully ordered graphite. In the Susa area, the biotite is~grad and the cordierite isograd correspond to the isoreflectance line of 6 % and 8 % Romax respectively. The regional organic metamorphism of higher rank and the concentric isoreflectance surface in accordance with the distance from the Kohyama gabbroic body suggest that the thermal metamorphism by the gabbroic intrusion affected throughout the distribution area of the Susa Group.show more |
| Table of Contents | I. はじめに II. 試料採集地の地質および変成作用の概要 III. 研究方法 IV. 結果 V. 考察 VI. まとめ |
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| Created Date | 2021.10.18 |
| Modified Date | 2023.11.15 |