Contribution of mantle-derived gases to subsurface gases in a tectonically quiescent area, the Carpathian Basin, Hungary revealed by noble gas measurements
1986 年 20 巻 3 号 p. 119-125
詳細
1986 年 20 巻 3 号 p. 119-125
A noble gas study including measurements of relative abundances and isotopic ratios of noble gases was carried out for gas samples collected from gas wells in the Carpathian Basin, Hungary. 3He/4He ratios in gases in which CO2 predominates were 2.6 to 5.5 × 10-6, in contrast to 0.42 to 0.62 × 10-6 of those in gases in which CH4 prevails. The strainer depth of the former wells is in the range from 1, 400 to 1, 438 m, and that of the latter is 860 to 1, 183m. Contribution of the mantle He to the helium in the CO2 gases estimated to be 19 to 42% and that to the helium in the CH4 gases to be 2.5 to 4.0%. The δ13C (PDB) value of CO2 with the high 3He/4He ratio was in the range from -6.2 to -5.2‰, suggesting high contribution of the mantle CO2. A high contribution of mantle-derived gases to the tectonically quiescent area can be related to the thin crust and high heat flow in this region. CH4 predominant gases seem to be derived from an environment rich in K, Th and U. No isotopic anomalies were found for Kr and Xe.
