Anomalously old Ar-40 - Ar-39 ages of Antarctic meteorites due to weathering

Details Anomalously old Ar-40 - Ar-39 ages of Antarctic meteorites due to weathering Anomalously old Ar-40 - Ar-39 ages of Antarctic meteorites due to weathering

Jul 1983

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983natur.304..146k&link_type=abstract

Nature (ISSN 0028-0836), vol. 304, July 14, 1983, p. 146-148. Sponsorship: Ministry of Education, Science, and Culture.

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Antarctic Regions, Argon Isotopes, Meteoritic Composition, Radioactive Age Determination, Weathering, Degassing, Mineralogy, Neutron Irradiation, Phase Transformations, Meteorites, Antarctic Meteorites, Argon, Isotopes, Ages, Anomalies, Weathering, Oxidation, Thermal Properties, History, Temperature, Data, Hamatite, Irradiation, Allan Hills Meteorites, Alha761

Scientific paper

The effect of weathering on the Ar isotope contents of oxidized meteorite surfaces was examined in consideration of observed anomalous abundance ratios which indicated ages exceeding 4.6 Gyr. Two chemically identical large meteorites were irradiated for 25 days in a fast neutron flux and nine temperature steps from 600-1300 C in 100 C intervals. Differences of up to 200 Myr were calculated for the ages, based on the releases of Ar-40 - Ar-39. However, the older of the two also released Ar-36, which was concluded of terrestrial atmospheric origin. It is suggested that goethite was changed into haematite during neutron irradiation, as happened in the reactor. The same results were found to hold true for other samples displaying ages of over 5 Gy. It is concluded that weathering in Antarctica can increase the Ar-40 - Ar-39 in meteorites over a long peroid of time.

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