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Published October 1, 2015 | Supplemental Material
Journal Article Open

Water, fluorine, and sulfur concentrations in the lunar mantle


The concentrations of volatile elements in the moon have important implications for the formation of the earth–moon system. There is currently a debate regarding the water content of the lunar mantle: Authors studying H_2O in lunar pyroclastic glass beads and in olivine-hosted melt inclusions in such pyroclastic samples and in plagioclase crystals in lunar highland anorthosites infer hundreds of ppm H_2O in the lunar mantle. In contrast, authors studying Zn/Fe ratios infer that the H_2O concentration in the lunar mantle is ≤1 ppm, and they argue that the glassy lunar basalts are a local anomaly. We contribute to a resolution of the debate by a broader examination of the concentrations of H_2O and other volatile components in olivine-hosted melt inclusions in a wider range of lunar mare basalts, including crystalline melt inclusions that are homogenized by melting in the laboratory. We find that F, Cl, and S concentrations in various lunar melt inclusions (including those in glassy lunar basalts) are similar to one another, and previously studied glassy lunar basalts are not a local anomaly in terms of these volatile concentrations. Furthermore, we estimate the pre-degassing H_2O/Ce, F/Nd, and S/Dy ratios of mare basaltic magmas to be at least 64, 4.0 and 100 respectively. These ratios are lower than those of primitive earth mantle by a factor of 3, 5, and 4 respectively. The depletion factors of these volatile elements relative to the earth's primitive mantle do not correlate strongly with volatility or bonding energy, and indeed they are roughly constant and similar to those of other volatile elements such as Li, Cs, Rb and K. This approximate constancy of volatile depletion in the moon relative to the earth can be explained by assuming that both the earth and the moon acquired volatiles from a similar source or by a similar mechanism but the earth was more efficient in acquiring the volatiles. We estimate the H_2O, F and S concentrations in the primitive lunar mantle source to be at least 110, 5.3, and 70 ppm, respectively – similar to or slightly lower than those in terrestrial MORB mantle.

Additional Information

© 2015 Elsevier B.V. Received 13 January 2015, Revised 22 June 2015, Accepted 23 June 2015, Available online 15 July 2015. We thank NASA CAPTEM for providing the lunar samples, K.P. Jochum for providing the MPI-Ding glass standards, F. Albarede, Cin-Ty Lee, and three anonymous reviewers for comments. This research is supported by NASA grants NNX10AH74G and NNX15AH37G, and University of Michigan funds. YL acknowledges NASA grant NNN13D465T and support from Jet Propulsion Laboratory, which is managed by California Institute of Technology under a contract with NASA. EMS acknowledges NASA grant NNX12AH63G.

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