Coeval argon-40/argon-39 ages of moldavites from the Bohemian and Lusatian strewn fields

Abstract

40Ar/39Ar ages of four tektites (moldavites) from southern Bohemia (near Cesk Budejovice, Czech Republic) and a tektite from Lusatia (near Dresden, Germany) have been determined by 11 step-degassing experiments. The purpose of the study was to enlarge the 40Ar/39Ar data base of moldavites and to check the age relations of the Bohemian and Lusatian samples. The mean plateau-age of the Bohemian samples, which range from 14.42 to 14.70 Ma, is 14.50 +/- 0.16 (0.42) (2-sigma) Ma (errors in parentheses include age error and uncertainty of standard monitor age). The plateau age of the Lusatian sample of 14.38 +/- 0.26 (0.44) (2-sigma) Ma confirms the previously published 40Ar/39Ar age of 14.52 +/- 0.08 (0.40) (2-sigma) Ma, and demonstrates that the fall of Lusatian and Bohemian tektites were contemporaneous. Because of their geochemistry and their ages there is no doubt that the Lusatian tektites are moldavites. Accepting that moldavites are ejecta from the Nӧrdlinger Ries impact, the new ages also date the impact event. This age is slightly younger (about 0.2-0.3 Ma) than the age suggested by earlier K-Ar determinations.