Recent data from Apollo samples demonstrate the presence of water in the lunar interior and at the surface, challenging previous assumption that the Moon was free of water. However, the source(s) of this water remains enigmatic. The external flux of particles and solid materials that reach the surface of the airless Moon constitute a hydrogen (H) surface reservoir that can be converted to water (or OH) during proton implantation in rocks or remobilization during magmatic events. Our original goal was thus to quantify the relative contributions to this H surface reservoir. To this end, we report NanoSIMS measurements of D/H and 7 Li/ 6 Li ratios on agglutinates, volcanic glasses, and plagioclase grains from the Apollo sample collection. Clear correlations emerge between cosmogenic D and 6 Li revealing that almost all D is produced by spallation reactions both on the surface and in the interior of the grains. In grain interiors, no evidence of chondritic water has been found. This observation allows us to constrain the H isotopic ratio of hypothetical juvenile lunar water to δD ≤ −550‰. On the grain surface, the hydroxyl concentrations are significant and the D/H ratios indicate that they originate from solar wind implantation. The scattering distribution of the data around the theoretical D vs. 6Li spallation correlation is compatible with a chondritic contribution <15%. In conclusion, (i) solar wind implantation is the major mechanism responsible for hydroxyls on the lunar surface, and (ii) the postulated chondritic lunar water is not retained in the regolith.hydrogen | lithium | moon | chondrites T hree types of sources could contribute to lunar superficial and mantle water, namely: (i) a primordial indigenous source identified in apatites (1-4), volcanic glasses (5, 6), and plagioclase phases (7) supporting a common origin of water for the Earth−Moon system (8-10); (ii) an addition of H 2 O-rich material via impacts of carbonaceous chondrites (CCs) and cometary materials (11, 12); and (iii) a proton implantation by the solar wind (SW) (13-18). Because magmatic water was incorporated in apatites, i.e., in the last minerals crystallized from lunar melts, the D/H ratio of these minerals was used to identify the source of this water. Indeed, all inner solar system objects (Earth, Moon, CCs) show an average water D/H ratio around 150 × 10 −6 with variations lying between 125 × 10 −6 and 220 × 10. However, in lunar materials, a variety of processes may have altered this D/H ratio, namely: isotopic fractionation during the outgassing of the melt under vacuum, the reduction of water into H 2 by the highly reduced lunar melts, or the contribution of D from spallation reactions. The possible oxidation of SW H into water during silicate melting could also be considered as a possible source for this mantellic water. Indeed, production of water by SW implantation is now considered as a ubiquitous process in the solar system (13, 19) and one of the possible mechanisms for bringing water to the Moon's surface. However, its c...
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