島弧火山の地球化学的研究(1994年度日本地球化学会賞受賞記念論文)

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This paper summarizes advances in three topics of geochemical studies on island arc volcanoes, which I and my colleagues have been investigating. First one is strontium isotope studies of arc volcanic rocks mainly from Japanese island arcs. We have shown that the precise spatial distribution of the ^<87>Sr/^<86>Sr ratio reflects natures of the subduction structure and slab-mantle interaction. Based on the ^<87>Sr/^<86>Sr ratio of volvanic rocks in the northern Kanto district, where two plates subduct concurrently with different directions, the existence of an aseismic portion of the Philippine Sea plate ahead of the seismic one was suggested. Second one is geochemical monitoring of active arc volcanoes. ^3He/^4He ratio of volcanic volatiles was shown to be a good indicator to monitor the behavior of magma: ascent and drain- back of magma result in an increase and decrease in the ratio, respectively. In the case of 1986 eruptions of Izu-Oshima volcano, the ratio began to increase two months after big eruptions, reaching the maximum and decreased. Such delayed response is explained in terms of travelling time of magmatic helium from the vent area to the observation site along the underground steam flow. Third one is remote observation of volcanic gas chemistry of arc volcanoes, using an infrared absorption spectroscopy. During Unzen eruptions starting in 1990, absorption features of SO_2 and HCl of volcanic gas were detected from the observation station at 1.3km distance. This was the first ground-based remote detection of HCl in volcanic gas. In the recent work at Aso volcano, we could identify 5 species (CO, COS, CO_2, SO_2 and HCl) simultaneously in the volcanic plume spectra.
日本地球化学会の論文
1998-08-25

島弧火山の地球化学的研究(1994年度日本地球化学会賞受賞記念論文)

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