Europium isotopic variations in Allende CAIs and the nature of mass-dependent fractionation in the solar nebula

Frédéric Moynier (1) , Audrey Bouvier (1) , Janne Blichert-Toft (1) , Philippe Telouk , Daniela Gasperini , Francis Albarède (1)

1 LST - Laboratoire de Sciences de la Terre

We measured the 153Eu/151Eu ratio by MC-ICP-MS for a terrestrial basalt, two terrestrial soils, and four meteorites (whole rocks and/ or chondrules of Bjurbo¨ le, Forest City, Murchison, and Allende) and found no isotopic variations. By contrast, two CAI separates from two different pieces of Allende show a 153Eu deficit of up to one per mil. Such a shortage in the heavy isotopes, which had also been identified in Allende CAIs for Sr [Patchett, P.J. 1980b. Sr isotopic fractionation in Allende chondrules: a reflection of solar nebular processes. Earth Planet. Sci. Lett. 50, 181–188], cannot reflect evaporative fractionation. The lack of Sm isotope fractionation in the same samples further makes fractionation by purely kinetic processes an unlikely cause of the anomalous Eu isotopic composition. An alternative interpretation is condensation from a vapor already significantly depleted in Eu, but in such a scenario the fate of the missing material is unclear. We therefore prefer yet another interpretation, based on the low ionization potential of Eu (and Sr), in which electromagnetic separation of the ionized gas preferentially depletes the nebular gas in heavy isotopes.

Domaines: Géochimie

Frédéric Moynier, Audrey Bouvier, Janne Blichert-Toft, Philippe Telouk, Daniela Gasperini, et al.. Europium isotopic variations in Allende CAIs and the nature of mass-dependent fractionation in the solar nebula. Geochimica et Cosmochimica Acta, 2006, 70, pp.4287-4294. ⟨10.1016/j.gca.2006.06.1371⟩. ⟨hal-00096155⟩