Gas Compositions and Tectonic Setting
Symonds, Rose, Bluth, and Gerlach (1994) published a list of compositions of high-temperature volcanic-gas samples. They also have a comprehensive list of published sources for high-quality volcanic-gas data .
Equilibrium compositions, temperatures, and log fO2 values of high-temperature and low-pressure (1 bar) volcanic gases. Concentrations are in mole %; log fO2 given in log bars.
H20, CO2, and SO2 are the most common gases in all samples.
Minor gases are H2, H2S, HCl, CO, and S2.
Based on elemental compositions, convergent-plate volcanoes tend to have higher H (reflected in H2O) and lower C and S (CO2 and SO2) relative to divergent-plate volcanoes and hot-spot volcanoes (which have high relative C and S and low H). HCl is higher at Etna and does not fit the pattern, perhaps because of its alkaline magma composition. Plate tectonics influences these abundances. The subducted slab contributes H2O and Cl to convergent-plate magmas. Magma sources for divergent-plate volcanoes and hot-spot volcanoes are located in the mantle and have moderate amounts of C and S and are relatively depleted in H2O and HCl.
Sources of Information:
Giggenbach, W.F., and LeGuern, Francois, 1976, The chemistry of magmatic gases from Erta Ale, Ethiopia: Geochimica et Cosmochimica Acta, v. 40, p. 25-30.
Symonds, Rose, Bluth, and Gerlach, 1994, Volcanic-gas studies: Methods, results, and applications in Carroll, M.R., and Holloway, J.R., editors, 1994, Volatiles in magmas: Mineralogical Society of America, Reviews in Mineralogy, v. 30, 517 p.