HR: 14:00h
AN: U13C-02    [Abstracts]
TI: Volatiles in the Lunar Volcanic Glasses, Evidence for the Presence of Indigenous Water in the Moon's Interior
AU: * Saal, A E
EM: asaal@brown.edu
AF: Department of Geological Sciences, Brown University, 324 Brook St., Providence, RI 02912, United States
AU: Hauri, E H
EM: hauri@dtm.ciw.edu
AF: DTM, Carnegie Institution of Washington, 5241 Broad Branch Road, NW Washington, DC 20015, United States
AU: Lo Cascio, M
EM: Mauro_Lo_Cascio@brown.edu
AF: Department of Geological Sciences, Brown University, 324 Brook St., Providence, RI 02912, United States
AU: Van Orman, J
EM: jav12@pop.cwru.edu
AF: Department of Geological Sciences, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, United States
AU: Rutherford, M
EM: malcolm_rutherford@brown.edu
AF: Department of Geological Sciences, Brown University, 324 Brook St., Providence, RI 02912, United States
AU: Cooper, R
EM: reid_cooper@brown.edu
AF: Department of Geological Sciences, Brown University, 324 Brook St., Providence, RI 02912, United States
AB: The composition and origin of the lunar volatiles has been the subject of considerable interest and one of the most important unsolved questions regarding the formation of the Moon. Volatiles influence mantle melting, magma crystallization and volcanic eruption, and their abundances and spatial distribution provide important constraints on models for the thermal and chemical evolution of the Moon's interior. The general consensus today is that the Moon formed and evolved through a single or series of catastrophic heating events in which most of the highly volatile elements were either stripped or evaporated away. Hydrogen being the lightest element is thought to have been completely lost during this period. Most of the geochemical inferences about the deepest section of the moon have been based on studies of the most primitive melts erupted on the Moon's surface, the lunar volcanic glasses. We reported new volatile contents (CO₂, H₂O, F, S, Cl) for the lunar volcanic glasses, which by virtue of SIMS analysis provide improved detection limits by almost an order of magnitude. All volcanic glasses have CO₂ below or within the 2 standard deviation of the detection limit for our runs (6 ppm CO₂) and will not be considered further. The volatile contents after background correction have the following ranges: 4-46 ppm (±2 ppm 2σ) for H₂O; 4-40 ppm (±0.2 ppm 2σ) for F; 115-576 ppm (±3 ppm 2σ) for S; and 0.06-2 ppm (±0.03 ppm 2σ) for Cl. Two outstanding features of the data is the significant correlation among H₂O, Cl, F and S contents, and the clear relationship between the volatile and the major and trace element contents of the glasses. Most importantly, the correlations among the volatiles suggest that the measured H₂O content in the volcanic glasses is indigenous. To test this hypothesis we determined concentration profiles for the volatiles within a single selected glass bead. Our data define concentration profiles with decreasing volatile contents from the core to the rim of the glass bead. This is especially significant for H₂O, which decreases from ~30 ppm in the center to ~14 ppm in the margin of the bead, supporting the hypothesis of the indigenous origin of H₂O subsequently affected by degassing processes during melt decompression and eruption. To our knowledge this is the first definitive confirmation of the presence of indigenous H₂O in primitive lunar basalts. Our results suggest that, contrary to the prevailing ideas, the bulk Moon is not uniformly depleted in highly volatile elements, and the presence of water in particular must be included to constrain models for the thermal and chemical evolution of the Moon's interior.
DE: 1026 Composition of the moon
SC: Union [U]
MN: 2007 Fall Meeting