Caffee, M. W. — Page 3

NASA NTRS1982

I-Xe ages of individual Bjurbole chondrules

Initial iodine isotopic compositions have been obtained for 10 individual chondrules from the meteorite Bjurbole, with a total range in well determined values of 6.5%, which would correspond to an age difference of 1.6 m.y. These results can be interpreted as distinct formation ages, metamorphic ages, or isotopic inhomogeneities in the early solar system, and can serve to constrain models for chondrule formation. Two of the chondrules show evidence of either isotopic inhomogeneities or disturbances of their I-Xe systems.

Caffee, M. W.↗

NASA NTRS1982

Shock disturbance of the I-Xe system

Three separate samples of the meteorite Bjurbole were artificially shocked at pressures of 70 kb, 200 kb, and 400 kb. Analysis of xenon released in stepwise heating shows that the I-Xe system of the 400 kb sample is substantially altered by the shock loading, and it is no longer possible to infer an age or trapped xenon composition for that sample. The 200-kb and 70-kb samples display isotopic structures progressively less altered demonstrating the gradations in shock disturbance likely to be found in natural systems. Interpretations of the I-Xe and Ar-40-Ar-39 systems for several naturally shocked meteorites are also presented. New data for Arapahoe do not confirm the previously reported age and trapped xenon composition, demonstrating instead that its I-Xe structure has been strongly disturbed by shock.

Caffee, M. W.↗