14:15 〜 14:30
[SGC37-03] Geochemistry of diffuse gas emissions in Mount Melbourne, Antarctica
キーワード：Mount Melbourne , Antarctica, Volatiles, Carbon dioxide, Diffuse degassing
We report chemical and isotope compositions of volcanic gases collected from Mount Melbourne that is a stratovolcano with an altitude of 2,732m, located in Northern Victoria Land of Antarctica. Mount Melbourne is an active volcano with a history of eruption reported in the late 19th century according to volcanic ash layers. Currently, active volcanism is not observed, but diffuse gas emissions are found in areas with high surface temperatures around the crater (> 50°C), forming a number of ice towers and ice caves. Carbon dioxide (CO2) emissions were observed in the range of 100-10,000 g m-2 day-1 through CO2
flux meter in the crater area. Among them, the gas concentration and isotopes (C, N, and He) were measured by collecting volcanic gas samples, especially at six points where the surface temperature and CO2 are high. The CO2 concentration is in the range of 21 vol.% to 36 vol.%, and the carbon isotope ratios (δ13C vs. V-PDB = -6.1 ‰ to -13.9 ‰) suggest that CO2 originated from magma and shallow soil components. Nitrogen shows a concentration of 49-59 vol.% with nitrogen isotope ratios (δ15N vs. air) ranging from -0.5 ‰ to 0.2 ‰. In addition, hydrogen sulfide appears up to 3.8 vol.%, which probably indicates the release of sulfur from magma. The helium isotope ratios present up to 1.3 times the atmosphere value (3He/4He = 1.4 x 10-6), indicating the emission of mantle-derived helium. Furthermore, the oxygen and hydrogen isotope compositions (δ18O and δD vs. V-SMOW) of ice samples collected inside the ice towers and caves at high temperature areas are very similar to those of snow on the surface of Mount Melbourne. Thus, the source of the water vapor emitted suggests that the melting of the ice in
this area is probably due to the high temperature of the surface. Comprehensively considering the results, Mount Melbourne is currently showing quiet volcanic activity, but magma-derived volcanic gas is emitted in a diluted state with atmospheric components introduced by melting upper ice.
flux meter in the crater area. Among them, the gas concentration and isotopes (C, N, and He) were measured by collecting volcanic gas samples, especially at six points where the surface temperature and CO2 are high. The CO2 concentration is in the range of 21 vol.% to 36 vol.%, and the carbon isotope ratios (δ13C vs. V-PDB = -6.1 ‰ to -13.9 ‰) suggest that CO2 originated from magma and shallow soil components. Nitrogen shows a concentration of 49-59 vol.% with nitrogen isotope ratios (δ15N vs. air) ranging from -0.5 ‰ to 0.2 ‰. In addition, hydrogen sulfide appears up to 3.8 vol.%, which probably indicates the release of sulfur from magma. The helium isotope ratios present up to 1.3 times the atmosphere value (3He/4He = 1.4 x 10-6), indicating the emission of mantle-derived helium. Furthermore, the oxygen and hydrogen isotope compositions (δ18O and δD vs. V-SMOW) of ice samples collected inside the ice towers and caves at high temperature areas are very similar to those of snow on the surface of Mount Melbourne. Thus, the source of the water vapor emitted suggests that the melting of the ice in
this area is probably due to the high temperature of the surface. Comprehensively considering the results, Mount Melbourne is currently showing quiet volcanic activity, but magma-derived volcanic gas is emitted in a diluted state with atmospheric components introduced by melting upper ice.