Statistical chronometry of meteorites. I. A Test of 26Al homogeneity and the Pb-Pb age of the solar system’st= 0

摘要: We use rapidly cooled achondrites to test the assumption of 26 Al homogeneity in the solar nebula, by checking if there is a single value of t SS, the absolute “Pb-Pb” age of the Solar System’s t= 0, that makes concordant their ages from the Al-Mg and Pb-Pb systems. We find that values t SS= 4568. 42±0. 24 Myr do make these ages concordant, and therefore the hypothesis of homogeneous 26 Al is not falsified. This age, defined to be when the solar nebula had (26 Al/27 Al)= 5. 23× 1 0− 5, is significantly older than the≈ 4567.3 Myr inferred from direct measurements of Pb-Pb ages in CAIs. Discrepancies between the Al-Mg and Pb-Pb chronometers in chondrules and CAIs have previously been interpreted as arising from heterogeneities in 26 Al, under the presumption that the Al-Mg and Pb-Pb systems in CAIs closed simultaneously. We examine this assumption and show that resetting is to be expected in CAIs. In …