Griesshaber, Erika; O’Nions, R. K.; Oxburgh, E. R.
Helium and carbon isotope systematics in crustal fluids from the Eifel, the Rhine Graben and Black Forest, F.R.G.
In: Chemical Geology, Vol. 99, No. 4: pp. 213-235
Full text not available from 'Open Access LMU'.
Helium and carbon isotope analyses are reported for groundwater samples from the Rhenish Massif, the Rhine Graben and Black Forest. Most of the samples contain a resolvable component of mantle-derived 3He, which varies from < 1\% up to ∼ 70\% of the total He present. The presence of mantle-derived 3He in deep groundwaters is discussed in relation to the distribution of surface volcanics, tectonic activity, regional seismicity and heat flow. Although there is a crude relationship between the presence of mantle-derived 3He and surface volcanics, 3He occurs over a larger geographic area than do surface volcanics. A correlation between the distribution pattern of mantle-derived 3He and tectonic activity, local seismicity or heat flow is not apparent from the present data set. δ13CCO2-values for CO2-rich mineral waters vary from - 25 to - 5‰ (PDB) and indicate a contribution of organicderived carbon to the CO2-bearing groundwater. In geographically restricted areas simple mixing relationships exist between the isotope composition of carbon and that of helium. This can be approximated by a two-component model, where a \"magmatic\" end-member with ( R R1)c6 and -8‰<δ13CCO2<- 5‰ is diluted by a \"crustal\" end-member with ( R Ra)c<0.1 and δ13CCO2<-15‰. The observed relationship between He and C strongly points to the presence of mantlederived CO2 in some groundwaters, particularly in waters from the East and West Eifel districts, and the Vogelsberg and Kaiserstuhl volcanic sites.