Chromium isotopic homogeneity between the Moon, the Earth, and enstatite chondrites

Abstract

Among the elements exhibiting non-mass dependent isotopic variations in meteorites, chromium (Cr) has been central in arguing for an isotopic homogeneity between the Earth and the Moon. However, the 54Cr isotope composition of the Moon relies on 2 samples only, which define an average value that is slightly different from the terrestrial standard. Here, by determining the Cr isotopic composition of 17 lunar, 9 terrestrial and 5 enstatite chondrite samples, we re-assess the isotopic similarity between these different planetary bodies, and provide the first robust estimate for the Moon. In average, terrestrial and enstatite samples show similar eps_54Cr. On the other hand, lunar samples show variables excesses of 53Cr and 54Cr compared to terrestrial and enstatite chondrites samples with correlated eps_53Cr and eps_54Cr (per 10,000 deviation of the 53Cr/52Cr and 54Cr/52Cr ratios normalized to the 50Cr/52Cr ratio from Cr standard). Unlike previous suggestions, we show for the first time that cosmic irradiation can affect significantly the Cr isotopic composition of lunar materials. Moreover, we also suggest that rather than spallation reactions, neutron capture effects are the dominant process controlling the Cr isotope composition of lunar igneous rocks. This is supported by the correlation between eps_53Cr and eps_54Cr, and 150Sm/152Sm ratios. After correction of these effects, the average eps_54Cr of the Moon is indistinguishable from the terrestrial and enstatite chondrite materials reinforcing the idea of an Earth-Moon-Enstatite chondrite system homogeneity. This is compatible with the most recent scenarios of Moon formation suggesting an efficient physical homogenization after a high-energy impact on a fast spinning Earth, and/or with an impactor originating from the same reservoir in the inner proto-planetary disk as the Earth and enstatite chondrites and having similar composition.

References in corpus (3)

• Equilibration in the Aftermath of the Lunar-Forming Giant Impact
• Extreme 54Cr-rich nano-oxides in the CI chondrite Orgueil -Implication for a late supernova injection into the Solar System
• Chromium isotope evidence in ejecta deposits for the nature of Paleoproterozoic impactors

Cited by in corpus (8)

• Early evolution of the solar accretion disk inferred from Cr-Ti-O isotopes in individual chondrules
• Volatile loss following cooling and accretion of the Moon revealed by chromium isotopes
• Isotopic evolution of the inner Solar System inferred from molybdenum isotopes in meteorites
• Composition, Structure and Origin of the Moon
• Accretion regions of meteorite parent bodies inferred from a two-endmember isotopic mixing model
• Spatial distribution of isotopes and compositional mixing in the inner protoplanetary disk
• Origin of nucleosynthetic isotope variability in the NC reservoir: Evidence from Ti, Cr, and Mo isotopes
• Earth's accretion inferred from iron isotopic anomalies of supernova nuclear statistical equilibrium origin