20-EPN-050: 26-Aluminium-26-Magnesium systematics of chondrules and clasts in unequilibriated ordinary chondrites
In-person visit by Audrey Bouvier (Universität Bayreuth, Germany) to TA2.9 Ion probe facility (IPF), CRPG (France).
Dates of visit: 7-11 June 2021
Chondrules are a major component of chondritic meteorites whose time and mechanism of formation are still debated. Inconsistencies in formation ages of chondrules have been found between ages determined by the absolute Pb-Pb chronometer or using the relative 26Al-26Mg chronometer. While the Pb-Pb ages suggest that chondrules formed continuously for about 4 Ma from the time of CAI formation, the 26Al-26Mg data show evidence that chondrules did not form until about 1.8 Ma after CAIs. One possible explanation could be a heterogeneous distribution of 26Al in the solar nebula.
To evaluate this hypothesis, we used secondary ionization mass spectrometry (SIMS) to date chondrules and clasts from unequilibrated ordinary chondrites with the 26Al-26Mg chronometer. Three chondrules from ordinary chondrites show resolvable excesses in 26Mg due to the decay of 26Al and formed around 2 Ma after CAI formation, consistent with previous studies. Analysis of a large igneous inclusion from Paposo 004 supports a formation age within 1 Ma after CAI. The presence of a relict olivine chondrule in this inclusion provides contextual evidence that chondrule formation must have taken place prior to this time.