Determination of volatiles in magma by micro-gas-analysis of melt inclutions in phenocrysts
| Project/Area Number |
63470031
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
分析・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, 地球内部研究センター, 教授 (20015770)
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| Project Period (FY) |
1988 – 1989
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| Project Status |
Completed (Fiscal Year 1989)
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| Budget Amount *help |
¥5,100,000 (Direct Cost: ¥5,100,000)
Fiscal Year 1989: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1988: ¥4,400,000 (Direct Cost: ¥4,400,000)
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| Keywords | phenocryst / melt inclusions / magma / volatiles in magma / laser / quadrupole mass spectrometer / 斑晶中のガラス包有物 / レーザー溶融法 |
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| Research Abstract |
The volatile compositions in maama can be obtained by micro-gas-analysis of glass inclusions in phenocrysts which can be regarded as a part of a "quenched magma". The system for gas extraction by laser heating followed by QMS analysis was assembled to determine H_2O and CO_2 contents in glasses on a 100 mum scale. A ND-YAG laser with a beam diameter of 10 mum And the energy of 7W was used to melt glasses in vacuum. The evolved gases were collected in a liquid air cold trap. CO_2 was separated from H_2O by trap work. In order to avoid the absorption of H_2O onto walls of the extraction line, H_2O was reduced to H_2 by reaction with a heated uranium metal. The resulting H_2 and CO_2 were determined by a statically operated QMS. The linear calibration curves were obtained in the range between 0.04-99 ng for H_2O and 0.01-18 ng for CO_2. The pit volume which released H_2O and CO_2 was estimated from the diameter and depth of the pit. The mass of the glass melted was calculated from the pit volume and the density of the glass. The gas concentrations were obtained by dividing the amount of H_2 and CO_2 determined by the mass of the glass melted.
Glassy margin of the Mariana Trough basalt (H_2O=1.37 wt% and CO_2=326 ppm) was used to test this technique. The amount of the evolved gases from each pit with a size ranging from 90 to 300 mum in diameter and from 15 to 110 mum in depth was between 30-120 ng for H_2O and between 0.08-1.2 ng for CO_2. The microanalysis showed 1.4<plus-minus>0.2 (S.E.) wt% for H_2O and 390<plus-minus>40 (S.E.) ppm for CO_2 based on 6 independent analyses. With the present technique, a melt inclusion with a diameter of ca. 150 mum can be analyzed, assuming the inclusion has the above gas composition.
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Report
(3 results)
Research Products
(5 results)
