Analyses of noble gases in whole rock samples of the howardites Bholghati and Kapoeta and grain-size separates of Kapoeta yield evidence for excesses of the Xe isotopes 129Xe, 131Xe, 132Xe, 134Xe, and 136Xe in a low-temperature component, similar to lunar excess fission Xe. Such a component may be able to provide Chronometric information if the relative abundances of radioactive progenitors (129I, 244Pu, and 238U) can be determined, but the isotopic spectra we obtain are not sufficiently precise to do so. Eucritic clast BH-5 in Bholghati contains Xe produced in situ by the decay of 244Pu. Calculated fission Xe retention ages are 30-70 Ma after the formation of the solar system, consistent with the apparent presence of 146Sm decay products. Both the clast and the matrix of Bholghati have K-Ar ages of about 2 Ga, suggesting a common thermal event at least that recently.
ASJC Scopus subject areas
- Geochemistry and Petrology