The depletion in moderately volatile elements in the Moon relative to Earth and comparison of the isotope compositions of the Moon and Earth have placed important constraints on models of lunar formation. A liquid–vapour protolunar disk from a high-energy giant impact has been proposed to explain some of these constraints. Here we present high-precision tin isotope data for lunar rocks, measured by double-spike MC-ICP-MS (multicollector inductively coupled plasma mass spectrometry). The lunar rocks are enriched in light tin isotopes compared to the Earth (Δ124/116SnMoon–Earth = −0.48 ± 0.15‰). On the basis of our data and constraints on tin speciation, we show that this tin isotope fractionation is inconsistent with volatile loss from a lunar magma ocean. Instead, we propose a scenario with vigorous mixing between the protolunar disk and the Earth in high-energy conditions during the impact, followed by liquid–vapour equilibration and phase separation at around 2,500 K while the disk was cooling. This scenario is consistent with the depletion in moderately volatile elements and isotope composition of the Moon.
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We thank the CAPTEEM of NASA for providing the lunar rocks. This project was funded by ANR project ISOVOL and by LABEX LIO (Lyon Institute of Origins). B.F. was funded by grants AST-1517541 and AST-1412175 from the NSF Astronomy Program and NASA grant NNX17AC02G (XRP Program), and thanks N. S. Jacobson for useful discussions. We thank J. Creech for insightful comments that helped improve this manuscript.
The authors declare no competing interests.
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