The lodranite class: Asteroid break-up and chemical composition

Details The lodranite class: Asteroid break-up and chemical composition The lodranite class: Asteroid break-up and chemical composition

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.548w&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 548

Computer Science

5

Achondrites, Asteroids, Chemical Composition, Fragmentation, Abundance, Neutron Activation Analysis, Radioactive Age Determination, Rare Gases

Scientific paper

We continued our work on lodranites and present the cosmic-ray-produced noble gas abundances of EET 84302, FRO 90011, Gibson, and Y 74357. Additionally, we determined the target element abundances for the production of cosmogenic noble gases in aliquots of our samples by neutron activation analysis (INAA and RNAA). We calculated production rates using the chemistry-dependent equations for achondrites determined by Eugster and Michel (1994). Since the Mg/Si ratio in lodranites is similar to that of H chondrites. Because the contents of trapped He and Ne in lodranites are low we can derive reliable He-3 and Ne-21 cosmic-ray exposure ages. All lodranites fall within 30% of the average exposure age T21 of 4.6 Ma and within 20% of the average exposure age T3 of 6.1 Ma, except MAC 88177, with obvious diffusion loss of He-3. Our exposure ages agree with those based on Al-26 and Be-10 measurements that range from 3.8 to 6.4 Ma. The average exposure age T3 is about 30% higher than the average T21. Most lodranites show a high (Ne-22/Ne-21)c ratio, which is an indication for a small preatmospheric size. Perhaps the production rate ratio P3/P21 is underestimated for very small meteoroids. We conclude that one break-up event on the lodranite parent asteroid is responsible for the production of all eight lodranites dated till now. The chemical abundances presented allow us to derive more reliable production rates than in our previous work. We, thus deduce that the common break-up occurred 5 +/- 1 Ma.

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