P-bearing olivines of lunar rocks: sources and localization in the lunar crust

Fragments of P-bearing olivine have been studied in lunar highland, mare and mingled meteorites and in «Apollo-14», «Luna-16, -20, -24» lunar samples. Olivine contains up to 0.5 wt.% P 2 O 5 and has variable MG# number. It is associated with anorthite, pyroxene and accessory spinel group minerals, Ti and Zr oxides, phosphates, troilite and Fe-Ni metal. Three possible sources of P-bearing olivine were found in lunar material: 1) highland anorthositic-noritic-troctolitic rocks enriched in incompatible elements and thought to be related to high-Mg suite rocks: 2) late-stage products of mare basalts crystallization; 3) unusual olivine-orthopyroxene intergrowths either of meteoritic or lunar origin. Enrichment in incompatible elements may be resulted from both crystallization processes (source 2) and KREEP assimilation (sources 1 and 3). However following metasomatic processes can lead to some addition of phosphorus and other elements. The rarity of P-bearing olivines points either to the low abundance or local distribution of their sources in the lunar crust. Association with mare basalts specifies the highland-mare boundary. The presence of the evolved rocks in the studied breccias suggests possible connection of some sources with recently discovered granitic domes in Procellarum Ocean. That means the P-bearing sources are mainly localized on the visible side of the Moon.