Chondrule heritage and thermal histories from trace element and oxygen isotope analyses of chondrules and amoeboid olivine aggregates

1Emmanuel Jacquet,2Yves Marrocchi
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12985]
1Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, CNRS & Muséum National d’Histoire Naturelle, UMR 7590, Paris, France
2Centre de Recherches Pétrographiques et Géochimiques, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre-lès-Nancy, France
Publishedby arrangement with John Wiley & Sons

We report combined oxygen isotope and mineral-scale trace element analyses of amoeboid olivine aggregates (AOA) and chondrules in ungrouped carbonaceous chondrite, Northwest Africa 5958. The trace element geochemistry of olivine in AOA, for the first time measured by LA-ICP-MS, is consistent with a condensation origin, although the shallow slope of its rare earth element (REE) pattern is yet to be physically explained. Ferromagnesian silicates in type I chondrules resemble those in other carbonaceous chondrites both geochemically and isotopically, and we find a correlation between 16O enrichment and many incompatible elements in olivine. The variation in incompatible element concentrations may relate to varying amounts of olivine crystallization during a subisothermal stage of chondrule-forming events, the duration of which may be anticorrelated with the local solid/gas ratio if this was the determinant of oxygen isotopic ratios as proposed recently. While aqueous alteration has depleted many chondrule mesostases in REE, some chondrules show recognizable subdued group II-like patterns supporting the idea that the immediate precursors of chondrules were nebular condensates.

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