Carbon isotopic variation in ureilites: Evidence for an early, volatile-rich Inner Solar System

1Jean-Alix Barrat, 1Pierre Sansjofre, 2,3Akira Yamaguchi, 4Richard C. Greenwood, 5Philippe Gillet
Earth and Planetary Science Letters 478, 143-149 Link to Article [https://doi.org/10.1016/j.epsl.2017.08.039]
1Laboratoire Geosciences Océan (UMR CNRS 6538), Université de Bretagne Occidentale et Institut Universitaire Européen de la Mer, Place Nicolas Copernic, 29280 Plouzané, France
2National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
3Department of Polar Science, School of Multidisciplinary Science, Graduate University for Advanced Sciences, Tachikawa, Tokyo 190-8518, Japan
4Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
5Earth and Planetary Science Laboratory (EPSL), Ecole Polytechnique Fédérale de Lausanne, Institute of Condensed Matter Physics, Station 3, CH-1015 Lausanne, Switzerland
Copyright Elsevier

We analyzed the C isotopic compositions of 32 unbrecciated ureilites, which represent mantle debris from a now disrupted, C-rich, differentiated body. The δ13C values of their C fractions range from −8.48 to +0.11‰. The correlations obtained between δ13C, δ18O and Δ17O values and the compositions of the olivine cores, indicate that the ureilite parent body (UPB) accreted from two reservoirs displaying distinct O and C isotopic compositions. The range of Fe/Mg ratios shown by its mantle was not the result of melting processes involving reduction with C (“smelting”), but was chiefly inherited from the mixing of these two components. Because smelting reactions are pressure-dependent, this result has strong implications for the size of the UPB, and points to a large parent body, at least 690 km in diameter. It demonstrates that C-rich primitive matter distinct from that represented by carbonaceous chondrites was present in some areas of the early inner Solar System, and could have contributed to the growth of the terrestrial planets. We speculate that differentiated, C-rich bodies, or debris produced by their disruption, were an additional source of volatiles during the later accretion stages of the rocky planets, including Earth.

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