05035 and Meteorite Hills 01210 : Two Basaltic Lunar Meteorites

Introduction: The lunar meteorites Miller Range 05035 (MIL) and Meteorite Hills 01210 (MET) were collected during the 2005 and 2001 ANSMET (Antarctic Meteorite Search) field seasons [1,2]. MET is a 22.8 g regolith breccia composed primarily of basaltic material [3-6]. MIL is a 142.2 g coarse-grained basalt [2]. The bulk composition, mineral assemblage, and texture of MIL is similar to lunar meteorites Asuka 881757 (A88) and Yamato 793169 (Y79), as are the reported mineral compositions [1]. The texture, mineral assemblage, and mineral chemistry of the basalt clasts in MET 01210 are also similar to Asuka/Yamato basalts. The bulk composition of MET is consistent with a mixture of Asuka/Yamato basalt and some moderately incompatible-trace-element (ITE) rich feldspathic material. It is likely that MET is also source-crater paired with A88 and Y79 (and MIL). Methods: We determined the bulk composition of meteorites in this study by INAA (trace elements, Fe, Na) and EMPA (major elements) of fused beads made from the INAA samples. We analyzed 240 mg of MET and 423 mg MIL. EMPA (electron microprobe analysis) was also used to determine quantitative mineral compositions for MET. Petrography: MET is a glassy matrix regolith breccia containing lithic clasts of basalt, gabbro, and plagioclase-rich impact-melt breccia, as well as abundant pyroxene, olivine, and minor plagioclase mineral clasts. Mafic mineral compositions in MET clasts are typically ferroan (Fs25-83Wo6-41; Fo0-56; Figs. 1-2) and plagioclase compositions are moderately Na-rich (An8596Or<0.9) [for more petrographic detail see 3-6]. MIL is an unbrecciated coarse-grained (2-3 mm) basalt consisting of pyroxene (Fs31-55Wo15-42), maskelynite (An8392Or0-2), Fe-Ti oxide, and symplectite intergrowths [1]. The symplectite is principally composed of fayalitesilica-hedenbergite, with associated K-feldspar and Sirich glass [1]. Geochemistry: MET 01210 has a bulk composition that is relatively rich (for a breccia) in elements associated with ferromagnesian minerals (16 wt% FeO; 54 ppm Sc; 1621 ppm Cr). Concentrations of incompatible trace elements are typical of basaltic samples (3.6 ppm Sm; 0.85 ppm Th). MIL is an Fe-rich basalt (21 wt% FeO) that also has high concentrations of Sc (93 ppm), but relatively low concentrations of Cr (1634 ppm), caused by the high proportion of high-Ca pyroxene and low proportion of olivine in MIL. ITE concentrations in MIL are near the low end of the range of basaltic lunar meteorites (2.8 ppm Sm; 0.45 ppm Th), and are one of the only basaltic lunar meteorites (along with A88, Y79, and NEA 003) that don’t have an enrichment in light REEs [7]. Discussion: There is strong petrographic, geochemical, and isotopic evidence that the A88 and Y79 basaltic lunar meteorites are source crater paired and could be samples of the same lunar basalt flow [8-13]. The texture, mineral assemblage and compositions, and bulk composition of MIL are markedly similar to A88 and Y79, suggesting that MIL could be from the same basalt flow as A88 and Y79, and, thus, all were likely ejected from the Moon by a common impact. The Di