| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1996: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1995: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
Significant subsurface boiling of the deep circulating geothermal waters in Kuju-Iwoyama Volcano, Kyushu, Japan, was demonstrated by the hydrogen and oxygen isotopic study of hot spring waters and fumarolic steam condensates.
(1) Single-stage and continuous steam separations result in greatly different chloride and isotope contents of remaining liquid. Because of phase separation at high temperatures, deuterium contents of hot spring arehigher than those recharge waters, and part of the observed oxygen isotope shift may be due to boiling as well as water-rock reactions. The highest contents of chloride, oxygen-18 and deuterium observed in hot spring waters are considered to have resulted from boiling at shallow levels under single-stage steam separation of deep thermal water at its critical point. The lower contents of chloride, oxygen-18 and deuterium may have resulted from boiling under multi-stage steam separation of thermal waters, coupled with dilution with meteoric waters.
(2) Thus
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, we proposed that part of meteoric water is heated to the critical point of water during a hydrologic cycle through the volcano, forming a single-phase seam. The linear deltaD-delta^<18>O,deltaD-Cl, and delta^<18>O-Cl relationships for fumarolic condensates appear to have resulted from mixing at depths of the volcano between a magmatic steam and the super-critical steam of meteoric water origin.
(3) The tritium contents in fumarolic condensates suggest a short residence time (within about 6 years) of meteoric water circulating in the steam region, while those in hot spring waters are corresponded to a very long residence time over 100 years for the liquid region. The fumarolic discarge, therefore, is considered to be from the main water circulation system containing a vapor-dominated zone in the volcano and the hot spring discharge must be from the subsystem of liquid water circulation surrounding the vapor-dominated system.
(4) A sulfur hydrolysis in high temperature solution may occur as a possible mechanism of the formation of strongly sulfuric acid in the hot spring water. The new geothermometer for strongly acidic hot spring water by using its main chemical composition was developed by hydrothermal experiments of anhydrite-water system. Less
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