Meteoritical Bulletin: Entry for Northwest Africa 7034

Writeup from MB 100:

Northwest Africa 7034 (NWA 7034)

Morocco

Purchased: 2011

Classification: Ungrouped achondrite

History: Purchased by Jay Piatek from AHabibi in Morocco, 2011.

Physical characteristics: Single stone, shiny, black surface, saw cut reveals porphyritic breccia with numerous dark and light colored phenocrysts and clasts of variable size and texture, set in a dark groundmass, many reflective opaques visible.

Petrography: (C. Agee, UNM) Microprobe examination of two polished epoxy mounts show a porphyritic, brecciated texture with plagioclase and pyroxene phenocrysts to 5 mm, ubiquitous chlorapatite, ilmenite, magnetite, and trace K-feldspar. Fine-grained groundmass composed of plagioclase, pyroxene, oxides, and trace Fe-sulfides. Poikilitic pyroxene-plagioclase clasts and quench melt clasts present. No Fe-Ni metal observed.

Geochemistry: (C. Agee , N. Wilson, F. McCubbin, UNM) Plagioclase Ab_52±6An_45±7Or_3±1, n=10, low-Ca pyroxene Fs_31.6±6.7Wo_3.1±0.8, Fe/Mn=37±3, n=23, pigeonite Fs_35.5±3.5Wo_8.0±3.3, Fe/Mn=34±1, n=8, augite Fs_24.3±4.5Wo_38.7±4.6, Fe/Mn=32±6, n=12, apatite with Cl=4.85±0.34 F=0.70±0.13 F+Cl=-O 1.38±0.06 (wt%) n=16, ilmenite with up to 5.3 wt% MgO, magnetite with up to 22.5 wt% Cr₂O₃, K-feldspar Or₇₇Ab₂₁An_3.Oxygen isotopes (Z. Sharp, UNM): acid-washed material analyzed in replicate by laser fluorination gave, respectively δ¹⁸O=6.00, 5.79, 6.51, 6.32; δ¹⁷O=3.76, 3.52, 4.09, 3.89; Δ¹⁷O= +0.59, +0.46, +0.65, +0.55 (all per mil).

Classification: Achondrite ungrouped (basaltic breccia). Plagioclase and pyroxene compositions similar to basaltic shergottites, however the oxygen isotopic values are higher than the SNC fractionation array.

Specimens: 30 g including a probe mount on deposit at UNM, Jay Piatek holds the main mass.

Northwest Africa 7034 (NWA 7034), updated information, based on Agee et al. (2013)

Revised classification: Martian, Basaltic Breccia

Updated petrography (C. Agee, UNM): Porphyritic basaltic monomict breccia, with a few euhedral phenocrysts up to several millimeters and many phenocryst fragments of dominant andesine, low-Ca pyroxene, pigeonite, and augite set in a very fine-grained, clastic to plumose, groundmass with abundant magnetite and maghemite; accessory sanidine, anorthoclase, Cl-rich apatite, ilmenite, rutile, chromite, pyrite, and goethite, identified by electron microprobe analyses on eight different sections at UNM. X-ray diffraction analyses conducted at UNM on a powdered sample and on a polished surface show that plagioclase feldspar is the most abundant phase (38.0±1.2%), followed by low-Ca pyroxene (25.4±8.1%), clinopyroxenes (18.2±4.0%), iron-oxides (9.7±1.3%), alkali feldspars (4.9±1.3%), and apatite (3.7±2.6%). The x-ray data also indicate a minor amount of iron-sulfide and chromite. The data are also consistent with magnetite and maghemite making up ~70% and ~30%, respectively, of the iron oxide detected.

Additional geochemical data. Rb-Sr age (V. Polyak, Y. Asmerom, N. Wilson, UNM): 2.089±0.081 Ga (2-σ). REE: La=58 × CI, (La/Yb)=2.3. Hydrogen isotopes (Z. Sharp, K. Ziegler, UNM): six whole-rock combustion measurements yielded a bulk water content of 6190±620 ppm. The mean δD value for the bulk combustion analyses was +46.3±8.6‰. The maximum δD values in two separate stepwise heating experiments were +319‰ and +327‰, reached at 804°C and 1014°C respectively. Oxygen isotopes (Z. Sharp, K. Ziegler, UNM; M. Nunn, UCSD): 21 analyses of bulk NWA 7034 were carried out. The mean value obtained at UNM was Δ¹⁷O=0.58±0.05‰ n=13 for acid washed samples and Δ¹⁷O=0.60±0.02‰ n=6 for non-acid-washed samples; at UCSD the mean value was Δ¹⁷O=0.50±0.03‰ n=2 for vacuum pre-heated samples that were dewatered and decarbonated. The combined data give Δ¹⁷O=0.58±0.05‰ n=21.