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

Jean-Alix Barrat, Pierre Sansjofre, Akira Yamaguchi, Richard C. Greenwood, Philippe Gillet

Earth and Planetary Science Letters
Volume 478, 15 November 2017, Pages 143–149
Available online 19 September 2017


• δ13C in ureilites correlate with the Fe/Mg ratios of the cores of their olivines.
• The ureilitic mantle has recorded the involvement of two C-rich reservoirs.
• The UPB’s diameter was larger than 690 km.
• C-rich matter, unlike carbonaceous chondrites, was present in the inner Solar System.”

“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.”