抄録
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 N2/Ar ratios. Hot spring waters are of the acid sulfate and acid chloride-sulfate types. Apparent equilibrium temperatures of fumarolic gases estimated for 2H2S+SO2=3S (s, l)+2H2O and 3H2+SO2=H2S+2H2O reactions are from 121 to 206℃ and 183 to 310℃, respectively. The δD and δ18O of fumarolic condensates and hot spring waters suggest that they are mixtures of magmatic water and local meteoric water. Variations in CO2, N2 and He concentrations of fumarolic gases with δD of fumarolic condensates support the idea of mixing of magmatic gas with local meteoric water. The δ13C of CO2 and δ14N of N2 are in narrow ranges from -4.0 to -4.3‰ and +4.0 to + 4.2‰, respectively, probably indicating those of magmatic origin.
