Mathematics – Logic
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.504m&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 504-505
Mathematics
Logic
Antarctic Regions, Meteoritic Composition, Radiation Effects, Radioactive Age Determination, Temperature Profiles, Chemical Composition, Cosmic Rays, Mineralogy, Petrography, Rare Gases
Scientific paper
More than 100 specimens of eucrites have been recovered in Antarctica. Several pieces of them have been identified as paired meteorites based on chemical, mineralogical, petrographical, and isotopic observation. In order to investigate the cosmic ray exposure and thermal histories as well as the grouping, we newly determined noble gas elemental and isotopic compositions for 11 Antarctic eucrites. We report results on cosmogenic noble gases. The concentrations of cosmogenic Ne-21 and Ar-38 and cosmic ray exposure ages calculated based on cosmogenic Ar-38 are listed. The cosmic ray exposure ages of the 11 eucrites belong to exposure age clusters at 6 Ma, 12 Ma, 21 Ma, or 38 Ma. The cosmogenic Kr-81 was measured for all the eucrites. The terrestrial ages calculated using the apparent ages based on Kr-81 and the cosmic ray exposure age T38 are from 0.05 Ma to 0.37 Ma. The terrestrial age of PCA 91007, 0.37 Ma, is the longest among those reported for eucrites. A plot of exposure age vs. terrestrial age and histograms of the ages for Antarctic eucrites are included. Data obtained based on noble gas isotopes given in this study and in the literature are plotted. We calculated an average age for apparently recognized paired eucrites, and only the average is counted in the histograms. Many Antarctic eucrites show terrestrial ages of 0.1-0.2 Ma. Since pairing has not been identified completely, the number in the histograms may be an upper limit. For the eucrites measured here, noble gas data do not indicate possible pairing among them except for ALH polymict eucrites, for which pairing was already suggested.
Miura Yayoi N.
Nagao Keiichi
Sugiura Norimasa
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