[SVC38-P12] Varying chemical and isotopic compositions of fumarolic gases from the summit and from the 1962-63 eruptive vents at Yakedake Volcano, Japan
Discharge temperatures of the fumaroles around the 1962-63 vents were 95-100°C: slightly lower temperatures than those from the summit fumaroles but higher than the boiling temperature at the elevation. Chemical analysis revealed that fumarolic gases from the 1962-63 vents contain lower amounts of SO2 than the summit fumaroles. Higher CO2/total S ratio and lower apparent equilibrium temperatures of the 1962-63 fumaroles coincide with lower discharge temperatures. On the other hand, the 1962-63 fumaroles show higher He/Ar ratio than the summit fumaroles, suggesting higher contribution of magmatic fluid.
The isotopic compositions of water (D, 18O) show that the fumarolic fluids from the summit fumaroles were probably formed by mixing of the magmatic fluids and local meteoric water. The isotopic compositions of the 1962-63 fumaroles show much lower values not only than the summit fumaroles but than local meteoric water, suggesting that the fluids suffered isotopic fractionation due to evaporation of the fumarolic gases.
Our results possibly indicate that volcanic hydrothermal system beneath the summit region differ from that under the 1962-63 vents.