Mass dependent fractionation of stable chromium isotopes in mare basalts: implications for the formation and the differentiation of the Moon

摘要: We present the first stable chromium isotopic data from mare basalts in order to investigate similarity between Moon and Earth’s mantle. A double spike technique coupled with MC-ICP-MS measurements was used analyse 19 basalts, comprising high-Ti, low-Ti KREEP-rich varieties. Chromium isotope ratios (δ53Cr) for are positively correlated indices of magmatic differentiation such as Mg# Cr concentration which suggests that isotopes were fractionated during differentiation. Modelling results provides evidence spinel pyroxene main phases controlling composition fractional crystallisation. The most evolved samples have lightest compositions, complemented by cumulates isotopically heavy. Two hypotheses proposed explain this fractionation: (i) equilibrium fractionation where heavy preferentially incorporated into lattice (ii) a difference Cr2+ Cr3+ melt. However, both processes require temperatures below 1200˚C appreciable be at low oxygen fugacities found (IW -1 -2 log units). There is no primitive KREEP suggest sources these homogeneous terms isotopes. least differentiated sample our set basalt 12016, characterised -0.222 ± 0.025 ‰, within error current BSE value (-0.124 0.101 ‰). mantles Earth consistent terrestrial origin major fraction lunar Cr. This also not core formation on Moon.