ABSTRACT

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.