2014 Fiscal Year Annual Research Report
海底火山から採取した軽石試料を用いて、水中軽石中の気泡の成長履歴を明らかにする
| Project/Area Number |
14F03772
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| Research Institution | Japan Agency for Marine-Earth Science and Technology |
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Principal Investigator |
NICHOLS Alexande 独立行政法人海洋研究開発機構, 海洋掘削科学研究開発センター, 主任技術研究員 (00470120)
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| Co-Investigator(Kenkyū-buntansha) |
MCINTOSH Iona Margaret 独立行政法人海洋研究開発機構, 海洋掘削科学研究開発センター, 外国人特別研究員
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| Project Period (FY) |
2014-04-25 – 2016-03-31
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| Keywords | 海底噴出軽石 / 大室ダシ / 伊豆大島 / 水 / 水の溶存種 / 水和 / FTIR分光分析 / 海底微化石 |
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| Outline of Annual Research Achievements |
Submarine pumice is widely hydrated masking the magmatic H2O content. A model has been developed to reconstruct magmatic H2O contents from submarine pumice samples using the speciation of water measured by FTIR. Reconstructed H2O contents can be used to infer quench depths, and thus test different models of pumice formation and identify possible eruption sources of widely dispersed floating pumice rafts.
Submarine microfossils have been found in a pumice-bearing subaerial tephra layer on Izu-Oshima. This suggests that the tephra was produced in a submarine eruption whose plume entrained marine microorganisms before breaking the sea surface and being deposited subaerially. If so, this would be the first time microfossils have been used to identify submarine eruption deposits on land.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
The original objective was to reconstruct bubble growth histories of silicic pumice from submarine eruptions using FTIR and SIMS, in order to constrain the magma degassing processes of submarine volcanoes. Unfortunately, analyses of submarine pumice clasts have revealed that they are hydrated masking the degassing signal. Work has therefore had to focus on finding a way to reconstruct magmatic H2O contents of hydrated samples from measured hydroxyl contents (since hydration occurs through addition of molecular water only). This has required existing FTIR analytical techniques to be refined and new approaches to be developed.
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| Strategy for Future Research Activity |
The model proposed to reconstruct magmatic H2O contents in hydrated submarine samples will be rigorously tested using samples for which emplacement depths are well-constrained.
The pumice-bearing and adjacent tephra layers from Izu-Oshima will be examined further to test whether the submarine microfossils are unique to this layer or a common feature of the tephra outcrop.
Subaerial silicic obsidian and pumice will be collected from Kozushima and Niijima to investigate subaerial hydration of silicic deposits, and role of H2O diffusion and bubble resorption in obsidian formation.
H2O will be measured by SIMS to obtain high resolution diffusion profiles formed during quench resorption.
Data will be collated and presented at conferences and submitted for publication in international journals.
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Research Products
(3 results)
