Lunar apatite with terrestrial volatile abundances

The Moon is thought to be depleted relative to the Earth in volatile elements such as H, Cl and the alkalis(1-3). Nevertheless, evidence for lunar explosive volcanism(4,5) has been used to infer that some lunar magmas exsolved a CO-rich and CO(2)-rich vapour phase before or during eruption(6-8). Although there is also evidence for other volatile species on glass spherules(9), until recently(10) there had been no unambiguous reports of indigenous H in lunar rocks. Here we report quantitative ion microprobe measurements of late-stage apatite from lunar basalt 14053 that document concentrations of H, Cl and S that are indistinguishable from apatites in common terrestrial igneous rocks. These volatile contents could reflect post-magmatic metamorphic volatile addition or growth from a late-stage, interstitial, sulphide-saturated melt that contained similar to 1,600 parts per million H(2)O and similar to 3,500 parts per million Cl. Both metamorphic and igneous models of apatite formation suggest a volatile inventory for at least some lunar materials that is similar to comparable terrestrial materials. One possible implication is that portions of the lunar mantle or crust are more volatile-rich than previously thought.