^1,2Tu-Han Luu, ³Edward D. Young, ^4,5Matthieu Gounelle, ²Marc Chaussidon
¹Centre de Recherches Pétrographiques et Géochimiques (CRPG) – Institut National des Sciences de l’Univers CNRS – Université de Lorraine – UMR 7358, 54501 Vandoeuvre-lès-Nancy Cedex, France;
²Institut de Physique du Globe de Paris (IPGP), CNRS UMR 7154, Sorbonne Paris Cité, 75238 Paris Cedex 05, France;
³Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095-1567;
⁴Institut de Minéralogie et de Physique des Milieux Condensés, Muséum National d’Histoire Naturelle, Sorbonne Universités, CNRS, Université Pierre et Marie Curie & L’Institut de Recherche pour le Développement, 75005 Paris, France; and
⁵Institut Universitaire de France, 75005 Paris, France

Chondritic meteorites are made of primitive components that record the first steps of formation of solids in our Solar System. Chondrules are the major component of chondrites, yet little is known about their formation mechanisms and history within the solar protoplanetary disk (SPD). We use the reconstructed concentrations of short-lived 26Al in chondrules to constrain the timing of formation of their precursors in the SPD. High-precision bulk magnesium isotopic measurements of 14 chondrules from the Allende chondrite define a 26Al isochron with 26Al/27Al = 1.2(±0.2) × 10−5 for this subset of Allende chondrules. This can be considered to be the minimum bulk chondrule 26Al isochron because all chondrules analyzed so far with high precision (∼50 chondrules from CV and ordinary chondrites) have an inferred minimum bulk initial (26Al/27Al) ≥ 1.2 × 10−5. In addition, mineral 26Al isochrons determined on the same chondrules show that their formation (i.e., fusion of their precursors by energetic events) took place from 0 Myr to ∼2 Myr after the formation of their precursors, thus showing in some cases a clear decoupling in time between the two events. The finding of a minimum bulk chondrule 26Al isochron is used to constrain the astrophysical settings for chondrule formation. Either the temperature of the condensation zone dropped below the condensation temperature of chondrule precursors at ∼1.5 My after the start of the Solar System or the transport of precursors from the condensation zone to potential storage sites stopped after 1.5 My, possibly due to a drop in the disk accretion rate.

Reference
Luua T-H, Young ED, Gounelle M, Chaussidon M (2015) Short time interval for condensation of high-temperature silicates in the solar accretion disk. Proceedings of the National Academy of Sciences 112,5, 1298–1303
Link to Article [doi: 10.1073/pnas.1414025112]