Gabbroic lunar mare meteorites Asuka-881757(Asuka-31) and Yamato-793169:Geochmical and mineralogical study

Asuka-31 (Asuka-881757) is a new type of gabbroic mare basalt which is similar to VLT mare basalts from Apollo 17 and Luna 24. The small lunar meteorite Yamato-793169 was described to have petrologic characteristics that are similar to those of A-881757; this similarity is confirmed here for trace element compositions. We studied bulk (powder) samples and mineral and rock fragments of A-881757. The mineralogy and mineral chemistry of the separates from A-881757,111 is that of a coarse-grained gabbroic rock of VLT composition; the texture of the mesostases suggests some metamorphic recrystallization with highly unequilibrated mineral compositions. As for mineral phases, we found plagioclase, pyroxene, fayalite, Fe-Ni metal, silica, apatite, and some trace minerals. In addition, we found ulvospinels associated with Na-rich plagioclase, fayalite, apatite, ilmenite, SiO_2,Fe-sulfide, and a rare metal (0.3wt% Ni, 2.0wt% Co) which has a composition unknown so far from any lunar rocks. The trace element contents found in the mineral separates and fragments correspond closely to the mineralogical findings. The chondrite normalized REE patterns for the bulk samples of A-881757 and Y-793169 are relatively flat, with some light REE depletion that is typical of mare basalts. The plagioclasedominated subsamples A31-CL, A31-CL2,and A31-YC show a distinct positive Eu anomaly. The bulk trace element composition of Y-793169 is almost identical to that of A-881757. Solar-wind dervved noble gas and exposure age studies of A-881757 and Y-793169 have indicated marked differences between the two meteorites, indicating that they might have been ejected in different events. These two new gabbroic, VLT-like, mare basalts are therefore valuable new additions to the lunar meteorite collection