Lunar meteorite Yamato-793274: Mixture of mare and highland components,and barringerite from the Moon

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Two small samples of the new lunar meteorite Yamato-793274 have been studied for mineralogical, petrological, and geochemical composition. The meteorite has a coarse grained texture and consists of a dense breccia that contains relatively large and abundant mineral fragments (clinopyroxene, plagioclase, olivine, ilmenite), rare fine-grained granulitic (poikilitic) breccias, and some mostly brownish devitrified glass. The matrix is abundant, dense, and consists of mineral fragments and interstitial mostly recrystallized glass. One large recrystallized melt breccia of anorthositic-noritic-troctolitic (ANT) composition was found. All plagioclase fragments are highly anorthitic, and olivine compositions range from Fo_<46-72>. The occurrence of these breccias and plagioclases, as well as the chemistry of some matrix glass, is consistent with an origin from the lunar highlands. However, some glasses have a considerably more mafic composition and show admixture of a low mg-component. Pyroxenes are unusually abundant when compared with other lunar meteorites. They usually show exsolution lamellae, are heavily shocked, and their compositions show a bimodal distribution, with low-mg pyroxenes most probably of mare origin. Among opaque phases, kamacite, and a Co-rich taenite were found, and, for the first time in lunar rocks, the rare higher phosphide barringerite, (Fe, Ni)_2 P. The bulk major and trace element composition is unlike the anorthositic lunar highland meteorites (e. g., ALHA81005,Y-791197,Y-86032,MAC88104/5), but somewhat similar to the newly identified mare meteorite EET87521. The mineral compositions as well as the major and trace element compositions of the bulk show a close similarity to certain VLT mare basalts, e. g., the Luna 24 ferrobasalts. This is obvious, for example, in a plot of molar Mg/(Mg+Fe) vs. TiO_2 content. The lithophile trace element abundances in Y-793274 are similar to EET87521 and Apollo 17 and Lunar 24 VLT's. The REE patterns show higher abundances (about 20-10×Cl) than the anorthositic meteorites and a small negative Eu anomaly. They are similar to EET87521 and some Apollo 14 green volcanic glasses. From the mineralogical and chemical data, pairing with any other lunar meteorite is very unlikely. Y-793274 is a shock lithified fragmental breccia containing a minor regolith component and numerous mafic mineral fragments and glasses. It is a mixture of about two thirds mare material and one third highland component, and therefore different from all previously known lunar meteorites.

Lunar meteorite Yamato-793274: Mixture of mare and highland components,and barringerite from the Moon

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