Early stages of core segregation recorded by Fe isotopes in an asteroidal mantle

J. A. Barrat (1) , O. Rouxel (2) , K. Wang , F. Moynier (3) , A. Yamaguchi , A. Bischoff , J. Langlade (4)

1 LDO - Domaines Océaniques
2 IFREMER - Institut Français de Recherche pour l'Exploitation de la Mer
3 IUF - Institut universitaire de France
4 CNRS - Centre National de la Recherche Scientifique

Ureilite meteorites are achondrites that are debris of the mantle of a now disrupted differentiated asteroid rich in carbon. They provide a unique opportunity to study the differentiation processes of such a body. We analyzed the iron isotopic compositions of 30 samples from the Ureilite Parent Body (UPB) including 29 unbrecciated ureilites and one ureilitic trachyandesite (ALM-A) which is at present the sole large crustal sample of the UPB. The δ⁵⁶Fe of the whole rocks fall within a restricted range, from 0.01 to 0.11‰, with an average of + 0.056 ± 0.008‰, which is significantly higher than that of chondrites. We show that this difference can be ascribed to the segregation of S-rich metallic melts at low degrees of melting at a temperature close to the Fe-FeS eutectic, and certainly before the onset of the melting of the silicates (< 1100 °C), in agreement with the marked S depletions, and the siderophile element abundances of the ureilites. These results point to an efficient segregation of S-rich metallic melts during the differentiation of small terrestrial bodies.

Mots clés: iron isotopes; achondrite; ureilite; core

Domaines: Planète et Univers [physics]

J. A. Barrat, O. Rouxel, K. Wang, F. Moynier, A. Yamaguchi, et al.. Early stages of core segregation recorded by Fe isotopes in an asteroidal mantle. Earth and Planetary Science Letters, 2015, 419, pp.93-100. ⟨10.1016/j.epsl.2015.03.026⟩. ⟨insu-03579972⟩