LITHOLOGIC DIVERSITY WITHIN LUNAR REGOLITH BRECCIA METEORITE NORTHWEST AFRICA 8783: CLASTS 1 AND 7

In this project the lunar regolith breccia meteorite Northwest Africa (NWA) 8783 was analyzed. NWA 8786 is paired with NWA 8455 and has had very few analyses conducted to date; this, along with two companion abstracts, is the first detailed study of the lithologic diversity of clasts within the sample. NWA 8783 contains lithologic clasts and isolated mineral grains set in a dark, fine-grained matrix with cross-cutting impact glass veins. The goal of this project is to classify the individual lithologic clasts in the breccia using petrography, modal mineralogy, and mineral chemistry in order to better understand the lithologic diversity of the Moon. Major and minor element contents were collected for olivine, pyroxene, and plagioclase on two clasts using the Cameca SX 100 electron microprobe at the University at Tennessee, Knoxville; further analyses, including those for ilmenite, are ongoing. Modal mineralogies were approximated using backscattered electron images and X-ray composite maps collected by the electron microprobe. This abstract is a part of a larger study on NWA 8783 and will only discuss lithologic clasts #1 and #7, with the companion abstracts describing clasts 2 & 5 and 3 & 6, respectively. Clast 1 is approximately 0.4 to 0.6 mm, and the preliminary modal mineralogy is 75.5%Enstatite (avg En60.5Fs37.2Wo2.3), 24.2% Augite (avg En40.9Fs15.5Wo43.5), 0.2%Olivine (avg Fo 49.8), and 0.1% Ilmenite. Clast 7 is approximately 2.5 to 5 mm with a modal mineralogy of 84.7% plagioclase (avg An91.2), 5.3% pyroxene, 4.8% olivine (Fo67.6-76.3), 3.5% silica- and potassium-rich interstitial glass, 0.9% ilmenite, and 0.8% iron metal. Pyroxenes in Clast 7are pigeonite (En65.6-72.7Fs20-28.5Wo7.2-13.1) and augite (En47.9Fs14.25Wo37.8). Clast 1 contains pyroxene and olivine that are chemically similar to lunar ferroan anorthosites (FANs) such as NWA 5744, suggesting that this clast may simply represent a pyroxene-rich portion of a FAN, despite its complete lack of plagioclase. Clast 7 is classified as an impact melt based on textural and some chemical similarities (e.g., pyroxene) to some Apollo 16 impact melts.