1990 Fiscal Year Final Research Report Summary
Estimation of Primary Magma Composition of Esan-Aosoyama New Volcanic Front.
| Project/Area Number |
63540640
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
鉱物学(含岩石・鉱床学)
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| Research Institution | Tohoku University |
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Principal Investigator |
FUJIMAKI Hirokazu. Tohoku Univ. Fac. Sci., Assoc. Prof., 理学部, 助教授 (90133933)
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| Co-Investigator(Kenkyū-buntansha) |
HASENAKA Toshiaki ditto Assist. Prof, 理学部, 助手 (50202429)
AOKI Ken-ichiro ditto Prof., 理学部, 教授 (00004276)
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| Project Period (FY) |
1988 – 1990
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| Keywords | New volcanic front / Esan volcano / Aosoyama volcano / Low-K tholeiite / Low-K calc-alkali / Volcanic zone |
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| Research Abstract |
The Sr and Nd isotopic compositions for the 65 rock samples from Nanatsumori, Narugo, Onikobe volcanoes to clarify the isotopic nature of the new volcanic front and to examine whether the volcanic rocks of the new volcanic front follow the common chemical and isotopic regularities to the Quarternay volcanic rocks in Japan. The 87Sr/86Sr ratios of the same rocks from Nanatsumori volcano are as high as 0.7054, while the lowest ratio for them is 0.7047. It seems that the rocks can be divided into two groups in terms of Sr isotopic ratio. One has rather high ratios (0.7051-0.7054), and the other has low ratios (0.7047-0.7050). Only a few samples have intermediate ratios. The frequency distribution of each group forms Gaussian. In contrast, Narugo and Onikobe volcanoes erupted isotopically quite similar volcanic rocks. The rocks from Narugo volcano have 87Sr/86Sr ratios ranging from 0.070475 to 0.70505, while the ratios of those from Okikobe volcano are in 0.70477-0.70502. Both seem to have Gaussian distributions. The dacitic rocks of those volcanoes can be highly differentiated products of presumably basic magma. The basic magma is parental and have 87Sr/86Sr ratios of 0.7047-0.7051. On the other hand, some of the rocks from Nanatsumori volcano have similar ratios to those of the Narugo and Onikobe volcanoes, but some have higher ratios. The latter may imply crustal contamination to some extent. Therefore, the Sr isotopic compositions of the volcanic rocks from Esan-Aosoyama new volcanic front are consistent with lateral variation of the Sr isotopic composition of the Quarternary volcanic rocks in Japan and the parental magma of the new volcanic front must be related with the Pacific plate subduction.
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Research Products
(10 results)
