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NWA 2986 (Sahara) – Mars, shergottite


Northwest Africa 2986 (NWA 2986)


Purchased: 2006

Classification: Martian meteorite (shergottite)

History: Three partially crusted stones with a weight of 201 g were purchased in Erfoud, Morocco, in 2006.

Petrography: (T. Bunch and J. Wittke, NAU): A basaltic shergottite that contains 54 vol% Ca-pyroxene (pigeonite and augite), 41 vol% plagioclase (maskelynite) and minor ulvöspinel, ilmenite, merrillite, chlorapatite, pyrrhotite, and K-Si-rich, late stage glasses. Pyroxene shows mottled compositional zoning. Dark, shock pocket glasses and veins are also present. A few melt inclusions of K-Si-rich glass, phosphates, ferroan pigeonite, and ilmenite were found in ulvöspinel.

Geochemistry: Pigeonite Fs37.4-53.8Wo10.8-15.8 (FeO/MnO = 34); augite Fs27.8-40.6Wo33.4-36.0; maskelynite An54.7Or1.6. Oxygen isotopes (D. Rumble, CIW): Replicate analyses of acid-washed whole rock samples by laser fluorination gave, respectively δ18O = 4.65, 4.59, 4.45, 4.78, δ17O = 2.73, 2.67, 2.58, 2.80, Δ17O = 0.280, 0.260, 0.240, 0.284 (all permil). Bulk composition (ICPMS, C. Herd, UAb): (mean of 2 replicate analyses, in ppm) La 0.97, Ce 2.32, Nd 1.70, Sm 0.71, Eu 0.43, Gd 1.71, Dy 1.12, Yb 0.85, Lu 0.12, Hf 1.07, Ba 21, Cr 646, V 236, Ni 47, Co 29.

Classification: Martian (shergottite) with an “enriched” chondrite-normalized rare earth element pattern, and probably paired with NWA 2975 and related stones. Low weathering grade and a moderate shock level.

Specimens: 21.3 g is on deposit at NAU. MFarmer and Strope are the main mass holders.

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