Fig. 10
a Fumarolic gas compositions in the He–N2–Ar ternary system; broken circle indicates the expected magmatic end member. ASW is the composition of air dissolved in water. Broken lines indicate the mixing between the magmatic and atmospheric end members. b Fumarolic gas compositions in the He–N2–CO2 ternary system; broken circle indicates the expected magmatic end member. Broken lines indicate the mixing between the magmatic and atmospheric end members. c Fumarolic gas composition in the He–N2–CH4 ternary system; broken circle indicates the expected magmatic end member. d Fumarolic gas composition in the SO2–CO2–H2S ternary system classified as a hydrothermal system (Stix and de Moor 2018). SLS, HD, DHM, SHM, DM, SM and SR indicate the types of volcanic gas with the following geneses: “S loss scrubbing”, “hydrothermally dominated”, “deep hydrothermal-magmatic”, “shallow hydrothermal-magmatic”, “deep magmatic”, “shallow magmatic” and “sulfur remobilization”, respectively. PF indicates the estimated parental magmatic fluid in the Kirishima volcanic area (Ohba et al. 1997). The CO2/SO2 and H2S/SO2 molar ratios are calibrated on the left and bottom sides, respectively. The CO2/St isomolar ratio is indicated by broken lines where St is the summation of SO2 and H2S