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

Abstract : Ureilites displays  56 Fe values higher than average chondrite. 29-Segregation of Fe-sulfide melts explains the high  56 Fe values in ureilites. 30-Formation of a core can begin at very low degrees of melting through the circulation of a Fe-S melt 31 through a silicate mantle. 32 33 Earth and Planetary Science Letters, in press (11/3/15). 34 2 35 Abstract 36 37 Ureilite meteorites are achondrites that are debris of the mantle of a now disrupted 38 differentiated asteroid rich in carbon. They provide a unique opportunity to study the differentiation 39 processes of such a body. We analyzed the iron isotopic compositions of 30 samples from the Ureilite 40 Parent Body (UPB) including 29 unbrecciated ureilites and one ureilitic trachyandesite (ALM-A) 41 which is at present the sole large crustal sample of the UPB. The  56 Fe of the whole rocks fall within a 42 restricted range, from 0.01 to 0.11‰, with an average of +0.056 ± 0.008 ‰, which is significantly 43 higher than that of chondrites. We show that this difference can be ascribed to the segregation of S-44 rich metallic melts at low degrees of melting at a temperature close to the Fe-FeS eutectic, and 45 certainly before the onset of the melting of the silicates (< 1100 °C), in agreement with the marked S 46 depletions, and the siderophile element abundances of the ureilites. These results point to an efficient 47 segregation of S-rich metallic melts during the differentiation of small terrestrial bodies. 48 49
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Submitted on : Monday, March 30, 2015 - 11:38:12 AM
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Jean-Alix J-A Barrat, Olivier J. 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. ⟨insu-01133382⟩



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