Northwest Africa 8632 (NWA 8632)
Classification: Lunar meteorite (basalt)
History: Purportedly found near Chwichiya in 2013 and purchased by Luc Labenne in June 2014 from a dealer in Ouarzazate, Morocco.
Physical characteristics: A single, small, dense black stone (23.8 g) with a flat, squarish shape and no fusion crust. Magnetic susceptibility log ? = 3.08 (X in nm3/kg) (J. Gattacceca, CEREGE).
Petrography: (A. Irving and S. Kuehner, UWS) Porphyritic texture. Subhedral zoned olivine phenocrysts (up to 2.3 mm long, yellowish in thin section) are set in a groundmass composed mainly of elongate, zoned clinopyroxene grains (clear with pink rims), smaller olivine grains and interstitial regions (opaque in thin section) consisting of ilmenite needles, Ti-chromite, fine clinopyroxene, fayalite and glass. No plagioclase was found. Small patches and veinlets of pale yellow devitrified glass are present.
Geochemistry: Olivine phenocrysts (cores Fa32.5-32.8, FeO/MnO = 90-100, N = 3; rim Fa48.8, FeO/MnO = 98), groundmass olivine (Fa72.6-74.1, FeO/MnO = 91-97, N = 3), augite (Fs23.7-27.1Wo40.1-40.5, FeO/MnO = 53-55, TiO2 = 2.4-2.6 wt.%, Al2O3 = 5.9- 6.1 wt.%, N = 2), subcalcic augite (Fs26.6-27.0Wo30.8-36.1, FeO/MnO = 54-60, TiO2 = 1.9-2.1 wt.%, Al2O3 = 4.7-5.6 wt.%, N = 2), ferroan subcalcic augite rim (Fs41.9Wo34.1, FeO/MnO = 63, TiO2 = 3.2 wt.%, Al2O3 = 8.1 wt.%).
Bulk composition: (R. Korotev, WUSL) INAA of subsamples gave the following mean abundances (in wt.%) FeO 22.6, Na2O 0.28; (in ppm) Sc 51.1, Ni 70, La 7.8, Sm 4.7, Eu 0.89, Yb 4.1, Lu 0.58, Hf 3.4, Th 1.25.
Classification: Lunar (mare basalt).
Specimens: 4.6 g including one polished thin section, one polished thick section and one polished mount at UWB. The main mass is held by Labenne.
Northwest Africa 8632 compositionally distinct from any other basaltic lunar meteorite. The major-element composition, however, is matched well by a mixture of 83% NWA 032/479, 13% Fo68 olivine, and 3% ilmenite, so it may be a sample from the bottom of the NWA 032 basalt flow, one that contains denser minerals and slightly less trapped liquid than NWA 032 (Korotev and Irving, 2021). The 40Ar/39Ar crystallization age of 3038 ± 60 Ma obtained by Assis Fernandes et al. (2022) for NWA 8632 is greater than the ~2800 usually cited for NWA 032, however, so the ages do not support a launch-pairing hypothesis but also do not refute it.
Meteoritical Bulletin Database
Assis Fernandes V., Pfänder J. A., Bizzarro M., Hoefnagels B., Khan A., and Zhang A.-C. (2022) 40Ar/39Ar ages for lunar basaltic meteorites Northwest Africa 8632 and 12008. Forming and Exploring Habitable Worlds, Edinburgh.
Cato M. J., Fagan A. L. Gross J. (2016) Crystal size distribution of low-Ti lunar basalt-Northwest Africa 8632. 47th Lunar and Planetary Science Conference, abstract no. 2751.
Fagan A. L., Gross J., Ramsey S., and Turrin B. (2018) Northwest Africa 8632- Recording young lunar volcanism. 49th Lunar and Planetary Science Conference, abstract no. 2584.
Fagan A. L., Udry A., Gannon J. P., Cato M. J., and the Spring 2017 WCU Petrology (GEOL 355) class1 (2018) Northwest Africa 8632 – Crystal size distribution variation & potential link to Northwest Africa 032. 49th Lunar and Planetary Science Conference, abstract no. 2601.
Korotev R. L. and Irving A. J. (2021) Lunar meteorites from northern Africa. Meteoritics & Planetary Science, 206–240.
Korotev R. L., Irving A. J., Wittmann A., Kuehner S. M., Chennaoui-Aoudjehane H., and Labenne L. (2015) Petrology and composition of lunar mare basalt meteorite Northwest Africa 8632 from Chwichiya, Morocco. 46th Lunar and Planetary Science Conference, abstract no. 1195.
Madera A., Gross J., and Fagan A. L. (2023) Sector-zoned pyroxenes in young lunar mare basalt, Northwest Africa (NWA) 8632: Insights into crystallization kinetics during late-stage volcanism on the Moon. 86th Annual Meeting of the Meteoritical Society, abstract no. 6053.
Schiller M., Bizzarro M., and Fernandes V. A. (2018) Isotopic evolution of the protoplanetary disk and the building blocks of Earth and the Moon. Nature 555, 507-510.
Tang C. P, Sawchuk K, and Warren P. H. (2018) A textural/mineralogical gradient within vitrophyric mare basalt Northwest Africa (NWA) 8632. 49th Lunar and Planetary Science Conference, abstract no. 2029.
Webb S., Neal C. R., Gawronska A., and Day J. M. D. (2019) Crystal size distribution patterns for lunar meteorites Northwest Africa 12008, 4898, 8632, 3136 and three LaPaz Icefield lunar meteorites. 50th Lunar and Planetary Science Conference, abstract no. 2686.