Phosphorus-bearing Olivines of Lunar Rocks: Sources and Localization in the Lunar Crust

Аннотация

Abstract—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. The olivines contain up to 0.5 wt % P₂O₅ and have variable MG# numbers. They are 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 the lunar material: 1) highland anorthositic–noritic–troctolitic rocks enriched in incompatible elements and interpreted to be related to high-Mg suite rocks: 2) late-stage products of mare basalts crystallization; and 3) unusual olivine–orthopyroxene intergrowths of meteoritic or lunar origin. Enrichment in incompatible elements may result from both crystallization processes (source 2) and KREEP assimilation (sources 1 and 3). However, superimposed 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 evolved rocks in the studied breccias suggests a possible connection of some sources with recently discovered granitic domes in Procellarum Ocean. This means the P-bearing sources are mainly localized on the nearside of the Moon.