Mineralogical studies of lunar meteorite Yamato-793169, a mare basalt

Abstract

A preliminary mineralogical study of the lunar meteorites Yamato (Y)-793169 and Asuka (A)-881757,which were apparently derived from a mare region of the Moon, has been performed to identify crystallization trends of their pyroxenes. Y-793169 is a crystalline basalt with similar basaltic components to lunar breccias EET87521 and Y-793274,containing strongly zoned Fe-Ca-rich pyroxenes. Their zoning trends in the pyroxene quadrilateral are closest to those found in the basaltic clast in an Apollo 16 breccia. Differentiation trends expressed by Ti/(Ti+Cr) versus Fe/(Fe+Mg) of Y-793169 and A-881757 pyroxenes are similar but they differ from those of EET87521. The Y-793169 trend starts at a more Mg-rich composition point than the A-881757 trend. Based on differences in textures and ranges of zoning trends, the pyroxene of A-881757 could represent growth deeper in the lava unit under conditions more closely approaching equilibrium, than Y-793169,which appears to have formed from a lava flow of similar bulk composition. Although Y-793169 has been described as the VLT basalt, some mesostases contain significant amounts of ilmenite and ulvospinel, together with fayalite, troilite, chromite and a silica mineral. Mg-rich pyroxenes as found in Y-793274 and EET87521 are not present in Y-793169 and A-881757 basalts