1997 Fiscal Year Final Research Report Summary
Magma degassing processes in view of hydrogen isotopic variations
| Project/Area Number |
08454166
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
地球化学
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| Research Institution | Okayama University |
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Principal Investigator |
KUSAKABE Minoru Institute for Study of the Earth's Interior, Okayama University Professor, 固体地球研究センター, 教授 (20015770)
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| Co-Investigator(Kenkyū-buntansha) |
YAMASHITA Shigeru Institute for Study of the Earth's Interior, Okayama University Research Associa, 固体地球研究センター, 助手 (30260665)
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| Project Period (FY) |
1996 – 1997
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| Keywords | magma degassing / water content / hydrogen isotopic ratio / Unzen volcano / Mt.Fuji volcano |
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| Research Abstract |
Hydrogen isotopic variation of water in volcanic eject is a good indicator to understand the degassing processes of magma, because large hydrogen isotopicfractionation between vapor and water dissolved in melt is significantly large even at magmatic temperatures (-800ﾟC). This research aimed at studying the degassing processes magmas with different chemical properties that lead to different eruption styles.
(1) Water contents and hydrogen isotopic ratios were determined for whole rocks and mineral separates (hornblende and biotite) from lavas and bombs obtained from the 1991 eruption of Unzen volcano. The eruption was of typical dacite dome formation. The data indicated that the deep-seated magma characterized by a high initial water conten (5-6 wt.%) and hydrogen isotopic ratio (deltaD=-50) lost most of water during ascent to the Earth's surface, resulting in the low H_2O lavas (0.5 wt% or lower). The observed H_2O-deltaD relationship followed neither the closed- nor open-system degassing models, suggesting that a kinetic isotopic effect playd an important role during degassing of highly viscous magma. These results will be published shortly in Journal of Volcanology and Geothermal Research.
(2) Water contents and hydrogen isotopic ratios were determined for basaltic scoria samples from the 1707 eruption of Mt.Fuji. It was found that the deltaD values negatively correlate with H_2O contents. The same trend was found for basaltic scoria from Kilauea volcano, Hawaii. This suggests that part of water dissolved in basaltic melt was reduced to hydrogen through reaction with abundant Fe^<2+> in the melt, resulting in the negative correlation between deltaD and H_2O.
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Research Products
(10 results)
