The relative isotopic abundance of K^(40) in terrestrial and meteoritic samples

Fowler, Greenstein, and Hoyle have proposed that the inner solar system was heavily irradiated during its formation. A consequence of this proposal is that sizable differences in meteoritic and terrestrial K^(41)/K^(40) ratios are possible if the fraction of material which was irradiated was different in the two cases. The isotopic composition of potassium was measured by mass spectrometry for nine stone meteorites, silicate from the Vaca Muerta mesosiderite and the Weekeroo Station iron meteorite, and four terrestrial samples. The measured K^(41)/K^(40) ratios were corrected by normalizing the measured K^(39)/K^(41) ratio to the Nier value of 13.47. This normalization procedure approximately cancels out any variations in the isotopic abundance except those due to nuclear processes. Measurements on enriched standards showed that any variations greater than 1% would certainly have been detected, and variations greater than ½% would probably have been detected with replicate analyses. Within these limits, no variations in the K^(40) abundance between the terrestrial and meteoritic samples could be found which could be ascribed to particle irradiation in the early history of the solar system. Small K^(40) enrichments were observed in Norton County, Weekeroo Station, and Vaca Muerta; however, these appear to have been produced during cosmic-ray irradiation by the Ca^(40)(n, p) reaction. The present results set relatively strong limitations on possible mechanisms for the formation of the earth and the meteorites if the idea of a large-scale irradiation in the early history of the solar system is to be retained. Independent of the model of Fowler et al., limits have been placed on any differential uniform irradiation. The implications of the present work on the K-Ar ages of stone and iron meteorites are discussed. The possibility that iron meteorites are considerably older than the solar system as a whole appears unlikely

Kalium-Argon-Daten zum Alter des Laacher Vulkanismus, der Rheinterrassen und der Eiszeiten

Die Vulkanite des Laacher-See-Gebietes in der Eifel können mit den Terrassenbildungen des Rheines zeitlich korreliert und ihre Föderfolge auf diese Weise stratigraphisch festgelegt werden. Dadurch bietet sich eine Möglichkeit, die K-Ar-Datierungsmethode an Proben von pleistozänem Alter zu testen und zu prüfen, ob die physikalisch bestimmte Sequenz mit der geologischen übereinstimmt. Datierungen wurden vorgenommen an 13 Sanidinen, 7 Biotiten, 2 Augiten und 14 Gesteinen der Eifel, ferner als Ergänzung an 6 Gesteinen der Umgebung von Agde, Dept. Hérault, Südfrankreich. Die meisten Datierungen ergaben geologisch wahrscheinliche Alter. Sie reichen in der Eifel von 570.10³a bis 100.10³a, bei Agde von 1400.10³a bis 640.10³a. Diffusionsexperimente an Sanidinen und Biotiten zeigten, daß das atmosphärische Argon durch Ausheizen nicht zufriedenstellend entfernt werden kann, ohne daß radiogenes Argon verloren geht. Eine Kontrollprobe des abgeheizten radiogenen Gases mit radioaktivem Ar(39) wurde getestet und erwies sich als nützliche Korrekturgröße.researc

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

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.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202