The Irradiation History of the H-Chondritic Regolith Breccia ACFER 111

Details The Irradiation History of the H-Chondritic Regolith Breccia ACFER 111 The Irradiation History of the H-Chondritic Regolith Breccia ACFER 111

Jul 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27r.273p&link_type=abstract

Meteoritics, vol. 27, no. 3, volume 27, page 273

Computer Science

6

Scientific paper

To investigate the irradiation history of the H3-6 chondritic regolith breccia Acfer 111 two perpendicular slabs were sawn from the meteorite for sampling. The cut surfaces revealed some cm- sized solar-gas-free clasts embedded in the solar-gas-rich matrix. We analyzed the noble gases in several 5-15 mg samples of the matrix and 20-100 mg samples of the clasts. For matrix samples there is a correlation between the concentrations of ^20Ne(sub)solar and ^21Ne(sub)cosm. (Fig. 1). A similar correlation was observed previously in the gas-rich meteorites Kapoeta (1) and Fayetteville (2,3). This correlation was attributed to an admixture, prior to the final compaction of the meteorite, of variable proportions of unirradiated debris into the irradiated asteroidal regolith. This implies that the pre-irradiated fraction of the matrix accumulated at least 0.5 to 3.0 *10^-8 cm^3 STP/g ^21Ne(sub)c in the regolith, with minimum regolith exposure ages of 4-20 Ma. The ordinate intercept of the line fitted to the matrix samples (Fig. 1) suggests that the less irradiated component of the regolith acquired 7.6+-0.4 *10^-8 cm^3 STP/g ^21Ne(sub)c in a subsequent irradiation, presumably during the meteoroid stage of Acfer 111. Relative to this value, all clasts have ^21Ne(sub)c excesses of at least 0.5 *10^-8 cm^3 STP/g, since their concentrations of ^21Ne(sub)c range between 8.3 and 11.5 *10^-8 cm^3 STP/g. A similar pattern was observed also for clasts in Fayetteville (Fig. 1) but not in Kapoeta. For samples with ^21Ne(sub)c < 9.1 *10^-8 cm^3 STP/g, the shielding sensitive ratio (^22Ne/^21Ne)(sub)cosm. ranges from 1.165 to 1.22 and correlates with the position of the sample in the meteorite. This strongly suggests that most of the cosmogenic Ne was produced by 4-pi irradiation of a relatively small object (R=12-30 cm) while travelling in space. At present is is not clear whether clasts having ^21Ne(sub)c excesses in the range of 0.5 to 1.5 *10^-8 cm^3 STP/g were pre-irradiated in the regolith or if they have a target chemistery differing from that of the matrix. The ^21Ne(sub)c excess of at least one of the clasts is, however, too large to be caused by differing chemical composition. References: (1) Pedroni (1989) Ph.D. Thesis ETH-Zurich. (2) Wieler et al. (1989) GCA 53, 1441-1448. (3) Wieler et al. (1989) GCA 53, 1449-1460. Figure 1, which in the hard copy appear here, shows solar ^20Ne and cosmogenic ^21Ne in matrix and clast samples of Acfer 111. The correlation line fitted to the data for the matrix samples of Acfer 111 is interpreted as mixing line between materials having differing precompaction irradiations. As suggested by the dotted areas, which cover data fields obtained previously for Fayetteville (2,3), the irradiation features of Fayetteville and Acfer 111 are nearly identical.

Affiliated with

Also associated with

No associations

Rating

The Irradiation History of the H-Chondritic Regolith Breccia ACFER 111 does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with The Irradiation History of the H-Chondritic Regolith Breccia ACFER 111, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Irradiation History of the H-Chondritic Regolith Breccia ACFER 111 will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1209839