Multiple Break-up of the Angrite Parent Asteroid: Asuka 881371 and Other Angrites

Details Multiple Break-up of the Angrite Parent Asteroid: Asuka 881371 and Other Angrites Multiple Break-up of the Angrite Parent Asteroid: Asuka 881371 and Other Angrites

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30..504e&link_type=abstract

Meteoritics, vol. 30, no. 5, page 504

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Achondrites, Angra Dos Reis, Angrite, Cosmic Ray, Exposure Ages, Meteorites, Asuka 881371, Lewis Cliff 86010, Lewis Cliff 87051, Noble Gases

Scientific paper

Angrite Asuka-881371 (subsequently named "Asuka") is presently being studied by a consortium organized by Paul Warren (UCLA). We obtained a sample of 35.5 mg for the determination of the cosmic-ray, fission, radiogenic, and trapped noble gas isotope abundances, of the cosmic-ray exposure age, and of the 244Pu-fission Xe age. A first analysis of a 10 mg sample yielded the following results: based on the concentrations of cosmic-ray produced 3He, 21Ne, and 38Ar cosmic-ray exposure ages T3, T21, T38, respectively were calculated. The target element abundances for Asuka were taken form Yanai (1994). The production rates were derived using the method given by Eugster and Michel (1995), adopting the same shielding dependency as for HED's. For Asuka we obtained T3 = 5.0 Ma, T21 = 5.5 Ma, and T38 = 5.4 Ma. In Table 1 the cosmic-ray exposure ages of the four known angrites are compared. It is evident that Asuka does not originate from the same break-up event as Angra dos Reis (Lugmair and Marti, 1977) or LEW 86010 (Eugster et al., 1991). Since LEW 87051 lost gases, only a lower limit of its break-up time could be determined. Also the concentrations of radiogenic 4He and 40Ar in Asuka differ from those in the other angrites indicating differences in U and K concentrations. As in the other angrites solar gases are absent in Asuka. The relatively low cosmogenic ratio 22Ne/ 21Ne indicates that the mass of the Asuka meteoroid was much larger than the recovered weight of 11 g, probably more than 1 kg. The analyses of the Kr and Xe isotopes are in progress. With knowledge of the concentrations of fission Xe, U, and 244Pu (derived from the Nd abundance) we plan to calculate the 244Pu-Xe formation age for Asuka. Acknowledgments: We thank the National Institute of Polar Research, Tokyo for the Asuka sample and P. Warren for organizing the consortium study. This work was supported by the Swiss NSF. References: [1] Yanai K. (1994) Proc. NIPR Symp. Antarc. Meteorites, 7, 30-41. [2] Eugster O. and Michel Th. (1995) GCA, 59, 177-199. [3] Lugmair G. W. and Marti K. (1977) EPSL, 35, 273-284. [4] Eugster O. et al. (1991) GCA, 55, 2957-2964. Table 1 shows comparison of the break-up times from parent body and cosmogenic and radiogenic gases for the four known angrites.

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