KAr and/or 40Ar39Ar plateau ages of Allende samples-whole rock, matrix, chondrules, white inclusions-range from 3.8 AE for matrix of ≳5 AE for some white inclusions, but cluster strongly near 4.53 AE. This age marks the dominant KAr resetting of Allende materials. Age spectra show disturbances due to 39Ar recoil or some other argon redistribution processes. Possible explanations for the apparent presolar ages (>4.6 AE) include: ≳20% loss of 39Ar; ≳40% loss of 40K ∼3.8 AE ago with no loss of 40Arl trapped argon of unique 40Ar/36Ar isotopic composition; admixture of "very old" presolar grains.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science