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NWA 7034 (Morocco) – Mars, polymict breccia


Meteoritical Bulletin 101

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.

Meteoritical Bulletin 107

The nomenclature committee accepted a petition to reclassify the NWA 7034 pairing group as “Martian (polymict breccia)”. The older term, “basaltic breccia,” was held to be unsuitable because the stones contain a variety of clast types, including impact melts, sedimentary rocks, and a wide variety of other lithologies.

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