LaPaz 04841: Comparative Petrology and Textural Study of a New Lunar Mare Basalt Meteorite

Introduction: Lunar mare basalt meteorites found in Antarctica and the hot deserts of Earth provide samples of the Moon that extend our knowledge beyond that gained during the Apollo and Luna missions. Through their study, we obtain a broader view of lunar magmatism and source rock composition. As impactexcavated samples, meteorites also offer the potential for the study of deeper regions of the Moon. To date, 20 mare basalt finds are catalogued on the List of Lunar Meteorites [1], of which 6 were found on the LaPaz Ice Field in Antarctica. Previous work (e.g., [2,3]) has presented strong arguments for 5 of these (LAP 02205, LAP 02224, LAP 02226, LAP 02436, and LAP 03632) to have originated from the same flow. The 2004 Antarctic search for meteorites season saw the addition of a 6 LaPaz lunar basalt to the collection. This find of LAP 04841 measured 5 x 2.5 x 2.5 cm and weighed 0.06 kg, bringing the total mass of LaPaz lunar basalts to 1.93 kg. Preliminary reports suggest that this new find is paired to the other 5 LaPaz meteorites [4], and is most similar to LAP 02205. We present here the first textural description, mineralogy, and mineral chemistry of LAP 04841 (thin sections LAP 04841,14 & 5, and thick section LAP 04841,18). We also confirm similarities between this meteorite and the other 5 LaPaz lunar basalts. Petrography and Textures: LAP 04841 is a coarse-grained basalt with subophitic texture. The major mineralogy consists of pyroxene and plagioclase, with interstitial ilmenite. Minor phases include olivine, Ti-chromite, and ulvospinel. Also present are shockinduced melt veins and a mesostasis, consisting of fayalite, SiO2, K-rich glass, and with trace amounts of FeNi, troilite, ilmenite, ulvospinel, phosphates, and baddeleyite. The order of crystallization, inferred from mineral associations, is believed to be Ti-chromite + olivine, pyroxene + ulvospinel, pyroxene + plagioclase + ilmenite, and mesostasis. The level of shock-induced deformations varies from slide to slide with the most-intense affected being LAP 04841,14, in which all plagioclases have been fully or partially converted to diaplectic glass, i.e., maskelynite. However, section 18 contains both plagioclase and maskelynite, and section 5 contains no maskelynite, only plagioclase. Mineralogy: Pyroxene is the most abundant phase and accounts for 56.2 vol% of the samples. Grains are anhedral and range in size up to ~0.5 mm. Pyroxenes have cores of augite, sometimes pigeonite (Wo14-20). Grain compositions grade continuously from core to rim with progressive Fe enrichment to high-Fe augite (Fs59Wo39), and pyroxferroite (Fs86Wo13).