11 Undergraduate Research I (Posters)

Thursday, 12 April 2018
8:00 AM - 12:00 PM
Room 301 DE/Henley Concourse

A COMPARATIVE LOOK AT LUNAR METEORITES NWA 8632 AND NWA 032

Paper number: 11-2
Program: Theme Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

The lunar meteorite Northwest Africa (NWA) 8632 has not undergone extensive research since its finding in 2014. Lunar meteorites are significant because they provide samples from areas of the Moon that were likely not visited during Apollo missions. This study presents an examination of the mineral compositions and quantitative textural analysis of NWA 8632. NWA 8632 is a Low-Ti, basaltic meteorite primarily composed of subhedral olivine phenocrysts in a groundmass of skeletal clinopyroxene and quenched glass with a porphyritic vitrophyric texture. Pale yellow impact melt glass is also found and the accessory mineral chromite is present as inclusions within olivine phenocrysts that also may contain melt inclusions. Compositional analyses of the olivine and pyroxene were obtained by using the Electron Microprobe at the University of Tennessee, Knoxville; textural analyses were determined by crystal size distributions (CSD). Olivine crystals were divided into two size fractions. Olivine phenocryst (300 μm to 1500 μm) compositions averaged Fo60 while smaller crystals (50 μm to 300 μm) averaged Fo53. Pyroxenes had an average composition of En36 Wo32 Fs32. By using a combination of aforementioned methodologies the crystallization sequence was determined to be as follows: Chromite±Olivine→Olivine→Pyroxene±Olivine→Quenched glass→Impact glass.

Despite being unpaired, NWA 8632 does exhibit some bulk compositional (e.g., TiO2) and textural similarities to the lunar meteorite, NWA 032. Similar cooling histories are suggested by textural parallels between NWA 8632 and NWA 032. NWA 8632 and NWA 032 olivine crystal size distribution profiles have a similar shape and slope. Similar crystallization sequences also exist between NWA 8632 and NWA 032. Chromite crystallizes first in both NWA 8362 and NWA 032 and is followed by the crystallization of olivine phenocrysts, then a period with olivine and pyroxenes crystallizing contemporaneously. In NWA 032 pyroxene and plagioclase crystallized together before a rapid cooling event quenched the groundmass. NWA 8632 does not contain plagioclase and after the crystallization of olivine and pyroxene, it was quenched. Impact melt features occur in the meteorites. NWA 8632 and NWA 032 have textural similarities but remain chemically distinct from one another and thus unpaired.

Geological Society of America Abstracts with Programs. Vol. 50, No. 3

doi: 10.1130/abs/2018SE-312644

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