Meteorites & Asteroids

Meteorite Petrology Versus Genetics: Toward A Unified Binominal Classification

By Keith Cowing
Press Release
astro-ph.EP
October 3, 2022
Filed under , , , , , , , ,
Meteorite Petrology Versus Genetics: Toward A Unified Binominal Classification
A petrology-genetics diagram for current asteroidal meteorite groups with known C/NC affinities (e.g., Kleine et al., 2020; Weisberg et al., 2006). The abscissa is arbitrary and proximity between two groups does not imply genetic relationships unless they are explicitly boxed in a common higher level group (boxed low-level groups, whose names are written in the vertical direction, are meant to span the whole class range encompassed; gaps are bridged by a dotted line). The hypothetical assignations of chondritic winonaites and acapulcoites to the matrix-rich chondrite class are discussed in the section Chondrites. Here, the ordinary chondrite (OC) clan is distinguished from the more inclusive O group, which comprises differentiated meteorites (e.g., IIE irons); same for EC versus E and CC versus C (see the Chondrites section). I show in dotted magenta the nameless Rubin and Ma (2021) HED-MES-PMG-IIIAB “superclass,” which is a group in our parlance.10 All mentioned high-level groups are meaningful whether they represent one or several primary parent bodies, hence the impossibility to define a real hierarchy among them except locally for nested groups. While only established groups are exhaustively shown, any anomalous meteorite must land somewhere in this diagram, in its class, and a more or less broadly defined group (e.g., C, NC, O, E) and thus lend itself to a minimum standardized taxonomic characterization. As an illustration, the “eucrite-type” Ibitira and NWA 011 meteorites have been plotted in the same basaltic achondrite class as bona fide eucrites but they are discriminated from them on the group axis as “NC-an” and “C-an,” respectively. Abbreviations are the same as in Table 1. (Color figure can be viewed at wileyonlinelibrary.com.)

The current meteorite taxonomy, a result of two centuries of meteorite research and tradition, entangles textural and genetic terms in a less than consistent fashion, with some taxa (like shergottites) representing varied lithologies from a single putative parent body while others (like pallasites) subsume texturally similar objects of multifarious solar system origins.

The familiar concept of group as representative of one primary parent body is also difficult to define empirically. It is proposed that the classification becomes explicitly binominal throughout the meteorite spectrum, with classes referring to petrographically defined primary rock types, whereas groups retain a genetic meaning, but no longer tied to any assumption on the number of represented parent bodies.

The classification of a meteorite would thus involve both a class and a group, in a two-dimensional fashion analogous to the way Van Schmus and Wood decoupled primary and secondary properties in chondrites. Since groups would not substantially differ, at first, from those in current use de facto, the taxonomic treatment of normal meteorites, whose class would bring no new information, would hardly change.

Yet classes combined with high- or low-level groups would provide a standardized grid to characterize petrographically and/or isotopically unusual or anomalous meteorites (which make up the majority of represented meteorite parent bodies) for example, in relation to the carbonaceous/noncarbonaceous dichotomy. In the longer term, the mergers of genetically related groups, a more systematic treatment of lithology mixtures, and the chondrite/achondrite transition can further simplify the nomenclature.

Emmanuel Jacquet

Comments: 21 pages, 4 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2209.07377 [astro-ph.EP] (or arXiv:2209.07377v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2209.07377
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Journal reference: Jacquet E. (2022). Meteoritics and Planetary Science 57:1774-1794
Related DOI:
https://doi.org/10.1111/maps.13896
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Submission history
From: Emmanuel Jacquet
[v1] Thu, 15 Sep 2022 15:44:09 UTC (1,181 KB)
https://arxiv.org/abs/2209.07377
Astrobiology, Astrogeology, Astrochemistry

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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