The Northwest Africa 8159 martian meteorite: Expanding the martian sample suite to the early Amazonian

Herd, Christopher D. K.; Walton, E. L.; Agee, C. B.; Muttik, N.; Ziegler, K.; Shearer, C. K.; Bell, A. S.; Santos, A. R.; Burger, P. V.; Simon, Justin I.; Tappa, M. J.; McCubbin, F. M.; Gattacceca, J.; Sanborn, M. E.; Yin, Qing‐Zhu; Cassata, William S.; Borg, L. E.; Lindvall, Rachel E.; Kruijer, T. S.; Brennecka, G. A.; Kleine, T.; Nishiizumi, K.; Caffee, Marc W.

doi:10.1016/j.gca.2017.08.037

Cited by 62 publications

(87 citation statements)

References 104 publications

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“…This heterogeneity within each sample likely results from a combination of one or more of the following: (i) the compositionally heterogeneous nature of the starting materials (e.g., interactions between the shock wave and materials of different densities within the sample), (ii) heterogeneity of crystal orientation within the sample, or (iii) the heterogeneous nature of the shock wave itself prior to interacting with the sample. For example, recent microscopic observations of the NWA 8159 shergottite by Herd et al () demonstrated that the partial amorphization of larger plagioclase crystals coincided with their proximity to shock veins. They noted that the deviatoric stresses and temperature gradients associated with shock vein margins likely resulted in a distribution of shock states in nearby plagioclase grains, consistent with the results of Daniel et al () and Kubo et al ().…”

Section: Discussionmentioning

confidence: 99%

Microspectroscopic and Petrographic Comparison of Experimentally Shocked Albite, Andesine, and Bytownite

et al. 2018

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Plagioclase feldspars are common on the surfaces of planetary objects in the solar system such as the Moon and Mars, and in meteorites. Understanding their response to shock deformation is important for interpretations of data from remote sensing, returned samples, and naturally shocked samples from impact craters. We used optical petrography, micro‐Raman, and micro–Fourier transform infrared spectroscopy to systematically document vibrational spectral differences related to structural changes in experimentally shocked (0–56 GPa) albite‐, andesine‐, and bytownite‐rich rocks as a function of pressure and composition. Across all techniques, the specific composition of feldspars was confirmed to affect shock deformation, where more Ca‐rich feldspars transform to an amorphous phase at lower shock conditions than more Na‐rich feldspars. Onset of amorphization occurs at ~50 GPa for albite, between 28 and 30 GPa for andesine, and between 25 and 27 GPa for bytownite. Complete amorphization occurred at pressures greater than ~55 GPa for albite, ~47 GPa for andesine, and ~38 GPa for bytownite. Petrographically, these experimentally shocked samples do not exhibit the planar microstructures common in naturally shocked plagioclase, despite showing the expected trends of internal disordering and deformation as seen in the micro‐Raman and infrared spectra. Average spectra of hyperspectral images of these samples mimic macroscale measurements acquired previously. However, we see micro‐scale heterogeneity in the shock response, resulting from variations in either composition, crystal orientation, or the inherent heterogeneity of the shock wave topology. This is an important factor to consider when deducing shock pressures in naturally shocked samples.

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Section: Discussionmentioning

confidence: 99%

Microspectroscopic and Petrographic Comparison of Experimentally Shocked Albite, Andesine, and Bytownite

et al. 2018

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“…The Martian meteorite collection consists of shergottites (basalts and basaltic cumulates), nakhlites (clinopyroxenites), chassignites (dunites), Allan Hills 84001 (orthopyroxenite), regolith breccias (Northwest Africa, NWA 7034 and paired stones), two ancient (~2.4 Ga) shergottitic‐type rocks (NWA 8159 and NWA 7635), and is expanding in terms of diversity of samples (e.g., Agee et al, , ; Goodrich, ; Herd et al, ; Lapen et al, ; McCoy et al, ; McSween & Treiman, ; Treiman, ). Shergottites still represent the largest portion of the collection and can be further classified on the basis of mineralogy and textures into the subclasses: basaltic, olivine‐phyric (ol‐phyric), and poikilitic—previously called lherzolitic (e.g., Goodrich, ; McSween, ).…”

Section: Introductionmentioning

confidence: 99%

Shergottite Northwest Africa 6963: A Pyroxene‐Cumulate Martian Gabbro

et al. 2018

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Northwest Africa (NWA) 6963 was found in Guelmim‐Es‐Semara, Morocco, and based on its bulk chemistry and oxygen isotopes, it was classified as a Martian meteorite. On the basis of a preliminary study of the textures and crystal sizes, it was resubclassified as a gabbroic shergottite because of the similarity with terrestrial and lunar gabbros. However, the previous work was not a quantitative investigation of NWA 6963; to supplement the original resubclassification and enable full comparison between this and other Martian samples; here we investigate the mineralogy, petrology, geochemistry, quantitative textural analyses, and spectral properties of gabbroic shergottite NWA 6963 to constrain its petrogenesis, including the depth of emplacement (i.e., base of a flow versus crustal intrusion). NWA 6963 is an enriched shergottite with similar mineralogy to the basaltic shergottites but importantly does not contain any fine‐grained mesostasis. Consistent with the mineralogy, the reflectance (visible/near‐infrared and thermal infrared) spectrum of powdered NWA 6963 is similar to other shergottites because they are all dominated by pyroxene, but its reflectance is distinct in terms of albedo and spectral contrast due to its gabbroic texture. NWA 6963 represents a partial cumulate gabbro that is associated with the basaltic shergottites. Therefore, NWA 6963 could represent a hypabyssal intrusive feeder dike system for the basaltic shergottites that erupted on the surface.

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“…), has so far revealed no sulfides (Herd et al. ). In comparison to other meteorites with ~1 Ma ejection ages, the next largest sulfide sulfur abundance was measured for NWA 5990 (2363 ± 47 ppm; Franz et al.…”

Section: Discussionmentioning

confidence: 99%

“…NWA 8159, which may be launch paired with NWA 7635, possesses similar crystallization and cosmic ray exposure ages and geochemical characteristics, providing evidence for late‐stage interaction with an oxidizing fluid (Herd et al. ). However, no sulfides were observed in the samples of NWA 8159 examined by Herd et al.…”

Section: Discussionmentioning

confidence: 99%

A new type of isotopic anomaly in shergottite sulfides

Franz

Farquhar

et al. 2019

Meteorit & Planetary Scien

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The isotopic composition and abundance of sulfur in extraterrestrial materials are of interest for constraining models of both planetary and solar system evolution. A previous study that included phase‐specific extraction of sulfur from 27 shergottites found the sulfur isotopic composition of the Martian mantle to be similar to that of terrestrial mid‐ocean ridge basalts, the Moon, and nonmagmatic iron meteorites. However, the presence of positive Δ33S anomalies in igneous sulfides from several shergottites, indicating incorporation of atmospherically processed sulfur into the subsurface, complicated this interpretation. The current study expands upon the previous work through analyses of 20 additional shergottites, enabling tighter constraints on the isotopic composition of juvenile Martian sulfur. The updated composition (δ34S = −0.24 ± 0.05‰, Δ33S = 0.0015 ± 0.0016‰, and Δ36S = 0.039 ± 0.054‰, 2 s.e.m.), representing the weighted mean for all shergottites within the combined population of 47 without significant Δ33S anomalies, strengthens our earlier result. The presence of sulfur isotopic anomalies in igneous sulfides of some meteorites suggests that their parent magmas may have assimilated crustal material. We observed small negative Δ33S anomalies in sulfides from two meteorites, NWA 7635 and NWA 11300. Although negative Δ33S anomalies have been observed in nakhlites and ALH 84001, previous anomalies in shergottites have all shown positive values of Δ33S. Because NWA 7635 has formation age of 2.4 Ga and is much more ancient than shergottites analyzed previously, this finding expands our perspective on the continuity of Martian atmospheric sulfur photochemistry over geologic time.

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The Northwest Africa 8159 martian meteorite: Expanding the martian sample suite to the early Amazonian

Cited by 62 publications

References 104 publications

Microspectroscopic and Petrographic Comparison of Experimentally Shocked Albite, Andesine, and Bytownite

Microspectroscopic and Petrographic Comparison of Experimentally Shocked Albite, Andesine, and Bytownite

Shergottite Northwest Africa 6963: A Pyroxene‐Cumulate Martian Gabbro

A new type of isotopic anomaly in shergottite sulfides

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