ABSTRACT

Fumarolic and geothermal well gases from several volcanic areas in Northeastern Japan have been examined for the N₂/Ar and He/Ar ratios. The N₂/Ar and He/Ar ratios of the gas samples are 40 to 2, 000 and 10^-3 to 1, respectively, higher than those of the atmospheric air dissolved in groundwaters. The N₂/Ar ratio becomes larger with increasing ratio of He to Ar. The data also show that nitrogen and helium in gases increase with increasing contribution of magmatic gas to the discharges and with decreasing contribution of groundwater. This suggests that the observed volcanic and geothermal gases may be mixtures of magmatic gas of uniform N₂/Ar (≅4, 000) and He/Ar ratios (≅2) and local meteoric waters.