Geochemistry of Yamato-82192, -86032 and -793274 lunar meteorites

The major and trace element compositions of lunar meteorites Yamato (Y)-82192,Y-86032 and Y-793274 were determined by neutron activation analysis. Y-82192 and Y-86032 are anorthositic lunar meteorites rich in Al_2O_3 and CaO and poor in FeO, MgO and incompatible elements. Although these meteorites are similar in composition to each other and other anorthositic lunar meteorites, they are distinct in several key compositional characteristics. Y-793274 is a basaltic lunar meteorite rich in FeO, MgO, Sc, Cr, Co, and incompatible elements and poor in Al_2O_3 and CaO compared to anorthositic lunar meteorites. It is similar in many ways to lunar meteorite EET87521 which is also a basaltic breccia. It is distinct from EET87521 in its higher proportion of highland material, its meteoritic contamination and regolith glass, and in the composition of its dominant basalt component. Y-793274 contains 65-75% magnesian VLT basalt, while EET87521 consists of ferroan VLT basalt. The eleven lunar meteorites probably represent eight distinct falls. Four are anorthositic and four are basaltic. This 50-50 proportion of highlands-mare material contrasts strongly with the 83-17 proportion derived from photogeologic mapping. The dominance of VLT basalt among lunar meteorites contrasts with its scarcity among Apollo samples. The resolution of these discrepancies awaits further studies of basaltic lunar meteorites and further discoveries of new lunar meteorites.