富山県立山地獄谷の噴気孔ガスおよび温泉水の化学組成と同位体比

概要

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The Tateyama-Jigokudani geothermal area, located about 40 km east of Toyama city, central Japan, is composed of two explosion craters which were formed at the foot of Tateyama volcano between 3000 and 6000 years B. P. and later than 3000 years B. P., respectively. Fumarolic gases and bubbling hot spring waters were analyzed for chemical and isotopic compositions during the period from 1989 to 1991. The Giggenbach method was used with some modifications for collecting fumarolic gases. The measured temperatures of fumaroles are from 88 to 123℃. The fumarolic gas is characterized by relatively high carbon dioxide concentration and high N_2/Ar ratios. Hot spring waters are of the acid sulfate and acid chloride-sulfate types. Apparent equilibrium temperatures of fumarolic gases estimated for 2H_2S+SO_2=3S (s, l)+2H_2O and 3H_2+SO_2=H_2S+2H_2O reactions are from 121 to 206℃ and 183 to 310℃, respectively. The δD and δ^<18>O of fumarolic condensates and hot spring waters suggest that they are mixtures of magmatic water and local meteoric water. Variations in CO_2, N_2 and He concentrations of fumarolic gases with δD of fumarolic condensates support the idea of mixing of magmatic gas with local meteoric water. The δ^<13>C of CO_2 and duN of N_2 are in narrow ranges from -4.0 to -4.3‰ and +4.0 to + 4.2‰, respectively, probably indicating those of magmatic origin.
2000-06-10