Die Zusammensetzung des Überschuß-Argon in Schwarzwälder Flußspäten

Abstract

The argon and potassium contents of eight fluorite samples with microinclusions from the Schwarzwald, Germany, were measured by isotope dilution technique. The samples contain .5 to 5 × 10-7 cc radiogenic Ar/g and there exists an approximate proportionality between the radiogenic and atmospheric argon component. In six samples the ratio Ar (rad) /Ar (total) at the time of mineral formation lies between .38 and .52 and probably represents the ratio in the mineral forming brine. These numbers are compatible with the argon ratios found in natural gases from bedrocks. ELINSON and POLYKOVSKII claim argon contents in fluid inclusions of pegmatitic feldspar ten times higher than the radioactive decay of K40 in the lattice would produce. Assuming this excess occuring frequently in pegmatitic feldspar and the pertinent ε0-values > 0, there could be a considerable source of error for K-Ar-determinations of such minerals.