The Chlorine Isotope Composition of the Moon and Implications for an Anhydrous Mantle

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Science  05 Aug 2010:
DOI: 10.1126/science.1192606


Arguably, the most dramatic geochemical distinction between the Earth and Moon has been the virtual lack of water (hydrogen) in the latter. This conclusion was recently challenged on the basis of geochemical data for lunar materials that suggest that the water content of the Moon might be far higher than previously believed. We have measured the Cl isotope composition of Apollo basalts and find that the range of isotopic values (from –1 to +24‰ vs. SMOC) is 25 times greater than for Earth. The huge isotopic spread is explained by volatilization of metal halides during basalt eruption, a process that could only occur if the Moon had H concentration ~104 to 105 lower than Earth, implicating that the lunar interior is essentially anhydrous.