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

Abstract

Abstract-sfAr/39Ar ages offour tektites (moldavites) from southern Bohemia (near Ceske 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 ofthe Bohemian and Lusatian samples. 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 Nordlinger 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.

40Ar/39Ar laser probe dating of the Central European tektite‐producing impact event

“…Baksi et al (1996) recommend a value of 18.51 Myr for B4M, and they obtained an age of 18.54 ± 0.05 Myr (1σ) versus 27.95 Myr for FCTb. The ages displayed here are equal within error to the 14.4 ± 0.25 Myr ; recalculated at 14.52 ± 0.40 Myr in Schwarz and Lippolt [2002]) of a moldavite from Lusatia and to recent ages on Lusatian and Bohemian samples (14.38 ± 0.44 Myr and 14.50 ± 0.42 Myr, respectively, 2σ error; Schwarz and Lippolt 2002). These data were obtained using the age monitor HD-B1 bt, with an assigned age of 24.21 ± 0.32 Myr (1σ) (Hess and Lippolt 1994), and no cross-calibration of HD-B1 bt relative to FCTb exists.…”

“…The ages reported in the literature for this strewn field are spread over a wide interval of time (14-15.3 Myr) , and the majority were obtained with the K/Ar and fission-track methods in the 1960s (Gentner et al 1963;Zähringer 1963;Gentner et al 1967;McDougall and Lovering 1969). The few published 40 Ar/ 39 Ar plateau ages differ slightly (15.21 ± 0.15 Myr [Staudacher et al 1982] and 14.4 ± 0.25 Myr , recalculated to 14.52 ± 0.40 Myr (2σ) due to a revision of monitor age in Schwarz and Lippolt (2002)]) or are affected by an error of about 2 Myr (Mader et al 2001). In a recent paper, Schwarz and Lippolt (2002) report a younger mean 40 Ar/ 39 Ar plateau age on moldavites from the Bohemian and Lusatian strewn field: 14.50 ± 0.42 Myr and 14.38 ± 0.24 Myr, respectively, with errors at the 2σ level.…”

“…The few published 40 Ar/ 39 Ar plateau ages differ slightly (15.21 ± 0.15 Myr [Staudacher et al 1982] and 14.4 ± 0.25 Myr , recalculated to 14.52 ± 0.40 Myr (2σ) due to a revision of monitor age in Schwarz and Lippolt (2002)]) or are affected by an error of about 2 Myr (Mader et al 2001). In a recent paper, Schwarz and Lippolt (2002) report a younger mean 40 Ar/ 39 Ar plateau age on moldavites from the Bohemian and Lusatian strewn field: 14.50 ± 0.42 Myr and 14.38 ± 0.24 Myr, respectively, with errors at the 2σ level. The interval of variation of these ages is too large considering the state of the art of modern geochronology and when compared with data on other strewn fields.…”

Integrated stratigraphy and 40Ar/39Ar chronology of the Early to Middle Miocene Upper Freshwater Molasse in eastern Bavaria (Germany)

“…Although this explanation could account for the 200 kyr offset between our 40 Ar/ 39 Ar and ATNTS04 ages, several observations argue against it. Relict minerals have, to our knowledge, not been reported from moldavites and their absence is convincingly demonstrated in the extensive data set of Laurenzi et al (2003) and Schwarz and Lippolt (2002). Laurenzi et al (2003) obtained 76 plateau ages from analysis of seven different moldavites, of which the ages varied by 400 ka only.…”

“…Schwarz and Lippolt (2002) report plateau ages of 14.50 ± 0.16 and 14.38 ± 0.26 Ma for tectites from Bohemia and Lutetia, respectively. Laurenzi et al (2003) obtained an average laser total fusion age of 14.34 ± 0.08 Ma for Bohemian and Moravian moldavites while Buchner et al (2003) found a 40 Ar/ 39 Ar laser total fusion value of 14.32 ± 0.28 Ma for a Ries suevite.…”