, Chemical features of fumarolic discharges from magmatic-hydrothermal system of Deception Island (Antartica).

AGUSTO, M., A. CASELLI, F. TASSI, O. VASELLI,

Buenos Aires

Congreso; SCAR; 2010

DNA

Deception Island (62°43´S, 60°57´W) is an active basaltic-andesitic volcano, whose last eruptive cycle took place in 1967-1970. Gases (10 samples) were collected during January-March 2007 from three fumaroles (94-100°C) located in Fumarole Bay. Fumarolic chemical composition is dominated by CO2 and characterized by relatively high concentrations of N2 and H2S (up to 8000 and 6500 μmol/mol, respectively). Relatively high concentrations of H2 and CH4 (up to 1400 and 50 μmol/mol, respectively) were also measured. Sulphur dioxide, HCl and HF gases are below the detection limit (0.0001 μmol/mol). Argon, He and Ne concentrations are up to 170, 17 and 0.1 μmol/mol, respectively. Predominance of typical hydrothermal species, such as H2S, H2 and CH4, suggests that the discharged fluids are produced by boiling of liquid-dominated reservoir able to completely dissolve the highly-soluble magmatic-related compounds, i.e. SO2, HCl and HF. Relatively high R/Ra values (6.7 to 7.0) and δ 13C-CO2 values of -6‰ suggest that He and CO2 are derived from a mantle source geochemically similar to MORB (Kusakabe et al.,2009). Gas geothermometric calculations in the CO2-H2-Ar (Giggenbach 1991) system provide temperature up to 300 °C, in agreement with those calculated by Kusakabe et al.(2009) on the basis of the H2-Ar geothermometer (Chiodini et al., 2001). Similar temperatures are indicated by the CO2-CH4-H2 geothermometer (Giggenbach 1993) at RH (log(H2/H2O)) values of -3.4, i.e. redox condition consistent with those typical of hydrothermal fluids (Giggenbach, 1987), when vapor-liquid interaction at temperature ~200 °C are considered. References: Chiodini et al, 2001. Geochim. Cosmochim. Acta, 65, 2129-2147. Giggenbach, 1987. Applied Geochemistry 2, 143-161. Giggenbach, 1991. In: Application of Geochemistry in Geothermal Reservoir Development. UNITAR, New York, 253-273. Giggenbach, 1993. Geothermics 22, 575-587. Kusakabe et al.,2009. Antarctic Science, 21 (3), 255-267.