1Yves Marrocchi,1Johan Villeneuve,2Emmanuel Jacquet,1Maxime Piralla,3Marc Chaussidon
Proceedings of the National Academy of Sciences of the United States of America (PNAS) (in Press) Link to Article [DOI:https://doi.org/10.1073/pnas.1912479116]
1Centre de Recherches Pétrographiques et Géochimiques (CRPG), CNRS, Université de Lorraine, UMR 7358, 54501 Vandoeuvre-lès-Nancy, France;
2Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), CNRS & Muséum national d’Histoire naturelle, UMR 7590, 75005 Paris, France;
3Institut de Physique du Globe de Paris, Université de Paris, CNRS, 75238 Paris, France
Chondritic meteorites are composed of primitive components formed during the evolution of the Solar protoplanetary disk. The oldest of these components formed by condensation, yet little is known about their formation mechanism because of secondary heating processes that erased their primordial signature. Amoeboid Olivine Aggregates (AOAs) have never been melted and underwent minimal thermal annealing, implying they might have retained the conditions under which they condensed. We performed a multiisotope (O, Si, Mg) characterization of AOAs to constrain the conditions under which they condensed and the information they bear on the structure and evolution of the Solar protoplanetary disk. High-precision silicon isotopic measurements of 7 AOAs from weakly metamorphosed carbonaceous chondrites show large, mass-dependent, light Si isotope enrichments (–9‰ < δ30Si < –1‰). Based on physical modeling of condensation within the protoplanetary disk, we attribute these isotopic compositions to the rapid condensation of AOAs over timescales of days to weeks. The same AOAs show slightly positive δ25Mg that suggest that Mg isotopic homogenization occurred during thermal annealing without affecting Si isotopes. Such short condensation times for AOAs are inconsistent with disk transport timescales, indicating that AOAs, and likely other high-temperature condensates, formed during brief localized high-temperature events.