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The H (sub 2) O content of andesitic magmas from three volcanoes in Japan, inferred from the infrared analysis of clinopyroxene

Satoshi Okumura
The H (sub 2) O content of andesitic magmas from three volcanoes in Japan, inferred from the infrared analysis of clinopyroxene
European Journal of Mineralogy (October 2011) 23 (5): 771-778

Abstract

In this study, we have determined the H (sub 2) O content of arc andesitic magmas erupted from three volcanoes in Japan [the 1929 A.D. eruption of Hokkaido-Komagatake (Ko-a), Tenmei eruption of Asama (As-A), and Taisho eruption of Sakurajima Volcanoes (Sz-Ts/P1)]. The amount of H (sub 2) O dissolved in the melt at magma chamber was estimated by analyzing the H (sub 2) O content of clinopyroxene phenocrysts and using the partition coefficient of H (sub 2) O between melt and clinopyroxene. On the basis of infrared spectroscopic analyses, the H (sub 2) O contents of clinopyroxene were 329 + or - 65, 247 + or - 72, and 213 + or - 36 ppm for Ko-a, As-A, and Sz-Ts/P1, respectively. The partition coefficient was calculated from the H (sub 2) O content of Ko-a clinopyroxene and that of rhyolitic melt inclusions included in clinopyroxene (3.1 wt% H (sub 2) O). Assuming that clinopyroxene was in equilibrium with melt inclusions, the partition coefficient is 0.011 + or - 0.003, which results in H (sub 2) O contents of the melts at the magma chamber of 2.3 + or - 0.9 and 2.0 + or - 0.6 wt% for As-A and Sz-Ts/P1, respectively. The H (sub 2) O content of magma in the magma chamber calculated at saturation on the basis of magma-chamber depth estimated from geophysical observation shows good agreement with the measured value for As-A; those of Ko-a and Sz-Ts/P1 are slightly higher than the measured values. These results indicate that arc andesitic magmas are saturated with H (sub 2) O or are ready to saturate before the eruptions.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 23
Serial Issue: 5
Title: The H (sub 2) O content of andesitic magmas from three volcanoes in Japan, inferred from the infrared analysis of clinopyroxene
Author(s): Okumura, Satoshi
Affiliation: Tohoku University, Department of Earth Science, Division of Earth and Planetary Materials Science, Sendai, Japan
Pages: 771-778
Published: 201110
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 41
Accession Number: 2012-010014
Categories: Geochemistry of rocks, soils, and sedimentsIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch map
N42°03'48" - N42°03'48", E140°40'38" - E140°40'38"
N31°34'60" - N31°34'60", E130°39'00" - E130°39'00"
N36°25'60" - N36°25'60", E138°30'00" - E138°30'00"
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201205
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