Water in the lunar interior

Presence and distribution of water and other volatiles in the lunar interior could have played a key role in the early evolution of the Moon. We report abundance of water along with F and Cl, in apatite present in the Apollo 15 lunar basalt 15555, considered to be the primitive end member of the low-Ti mare basalt suite. Apatites are rare in this basalt and are devoid of significant spatial variation in volatile content. Considering a late-stage crystallization of apatite, we infer 100–160 ppm water, 80–90 ppm fluorine and 10–20 ppm chlorine in the parent magma of 15555. The inferred water content is much lower than that reported for the parent magma of lunar volcanic glasses, as well as in melt inclusions trapped within the glasses that sampled much deeper regions of Moon. This difference suggests a non-uniform distribution of water and other volatiles in lunar mantle source regions, that could have significantly influenced early thermochemical evolution of the Moon.