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Title (Primary) Upper mantle-derived free gas exhalations in central Europe - an isotope study
Title (Secondary) EGS-AGU-EUG Joint Assembly, Nice, France, 06-11 April 2003
Author Bräuer, K.; Kämpf, H.; Niedermann, S.; Strauch, G.; Weise, S.M.;
Journal Geophysical Research Abstracts
Year 2003
Department HDG; ISOHYD;
Volume 5
Language englisch;
Abstract The results of geochemical mapping (about 100 locations) of free gas exhalations in the western Eger Rift (Czech-German border region) are compared with data of free gas exhalations from the surroundings of the Laacher See (East Eifel, Germany) and Le Mont Dore (Massif Central, France). In the western Eger Rift, three gas exhalation centres characterized by high gas flux (> 85 m^3 h-1), CO_2 concentrations > 99 vol. -%, d13C between -2 and -4 per mil, and ^3He/^4He ratios up to 6 R_a could be distinguished. CO_2-rich gases consist of mantle-derived components with only small admixtures of dissolved air due to sampling after passing a water phase. The scatter in d13C values of CO_2-rich gases is due to isotope fractionation between gaseous CO_2, dissolved CO_2 and HCO_3, respectively. As a result of long-term monitoring studies at four locations in the western Eger Rift, the natural variation range of the gas and isotope composition could be evaluated and as a consequence of numerous data sets reliable d15N mean values could be specified. At the Bublak mofette (NW Bohemia), the transport velocity in the upper crust is estimated at about 400 m/d. The Bublak CO_2 is enriched in 13C (d13C -2 per mil) relative to MORB values and its CO_2/^3He is 6.5x10^9. In addition to the ^3He/^4He ratio of 5.9 R_a, which is in the range of values for European sub-continental mantle xeno-liths, also the uncorrected d15N values (-3.2±0.7, n=16) show an upper mantle signature. Corrected for air via O_2 contents and/or 40Ar/36Ar ratios, the 15N/14N ratios yield d15N <= -5 per mil, corresponding to mantle-derived nitrogen contributions of about 50 %. The channel-like fluid supply at the Bublak mofette related with the high transport velocity indicates that its isotope ratios are not significantly altered during transport through the crust and represent probably the signature of the magmatic source in the European sub-continental mantle. Comparable distribution patterns of gases and isotopic compositions were found in the studied areas of the East Eifel and the Massif Central. Their ^3He/^4He and 13C/12C ratios are similar to data of the Czech-German border region and compare well to the xenolith data from the European sub-continental mantle, indicating a common reservoir.
ID 4751
Persistent UFZ Identifier
Bräuer, K., Kämpf, H., Niedermann, S., Strauch, G., Weise, S.M. (2003):
Upper mantle-derived free gas exhalations in central Europe - an isotope study
EGS-AGU-EUG Joint Assembly, Nice, France, 06-11 April 2003
Geophysical Research Abstracts 5
European Geosciences Union (EGU), p. abstract #784