Petrologic and Minerochemical Trends of Acapulcoites, Winonaites and Lodranites: New Evidence from Image  Analysis and EMPA Investigations

Cecchi, V. Moggi; Caporali, Stefano

doi:10.3390/geosciences5030222

Cited by 5 publications

(4 citation statements)

References 28 publications

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“…Because diffusion is particularly slow in clinopyroxene, diffusive exchange of Fe, Mg, and Ca between the pyroxenes effectively ceases at relatively high temperatures on the cooling path (particularly when cooling is rapid), at which point individual pyroxene grains effectively become closed systems. There are many reported two‐pyroxene thermometry results for type 6 ordinary chondrites in the range 950–1000 °C (see compilation in Mare et al 2014), and for primitive achondrites in the range 1000–1100 °C (Folco et al 2006; Li et al 2011; Cecchi and Caporali 2015), implying that the closure temperature of typical chondritic systems is close to the solidus temperature (cf. Fig.…”

Section: Discussionmentioning

confidence: 99%

A review of the chondrite–achondrite transition, and a metamorphic facies series for equilibrated primitive stony meteorites

Tomkins

Johnson

Mitchell

2020

Meteorit & Planetary Scien

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Here, the petrological features of numerous primitive achondrites and highly equilibrated chondrites are evaluated to review and expand upon our knowledge of the chondrite-achondrite transition, and primitive achondrites in general. A thermodynamic model for the initial silicate melting temperature and progressive melting for nearly the entire known range of oxidation states is provided, which can be expressed as T m = 0.035Fa 2 À3.51Fa + 1109 (in°C, where Fa is the proportion of fayalite in olivine). This model is then used to frame a discussion of textural and mineralogical evolution of stony meteorites with increasing temperature. We suggest that the metamorphic petrology of these meteorites should be based on diffusive equilibration among the silicate minerals, and as such, the chondrite-achondrite transition should be defined by the initial point of silicate melting, not by metal-troilite melting. Evidence of silicate melting is preserved by a distinctive texture of interconnected interstitial plagioclase AE pyroxene networks among rounded olivine and/or pyroxene (depending on ƒO 2 ), which pseudomorph the former silicate melt network. Indirectly, the presence of exsolution lamellae in augite in slowly cooled achondrites also implies that silicate melting occurred because of the high temperatures required, and because silicate melt enhances diffusion. A metamorphic facies series is defined: the Plagioclase Facies is equivalent to petrologic types 5 and 6, the Subcalcic Augite Facies is bounded at lower temperatures by the initiation of silicate melting and at higher temperatures by the appearance of pigeonite, which marks the transition to the Pigeonite Facies. 857

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Section: Discussionmentioning

confidence: 99%

A review of the chondrite–achondrite transition, and a metamorphic facies series for equilibrated primitive stony meteorites

Tomkins

Johnson

Mitchell

2020

Meteorit & Planetary Scien

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“…Pontlyfni does not fit with the other eight samples for any criteria (e.g., petrography, mineralogy, chemistry, or isotopy). In fact, the relict chondrules in Pontlyfni are not straightforward to identify (Benedix et al, 1998) and were not even identified by Graham et al (1977), while relict chondrules in the other samples are numerous (1.5-5 vol%) and barely altered (Cecchi & Caporali, 2015;Farley et al, 2015;Rubin, 2007;Zeng et al, 2019). As such, it seems that Pontlyfni does not belong to this particular "chondritic achondrite" group and might be the only real winonaite-bearing relict chondrule.…”

Section: Oxygen Isotopic Compositionmentioning

confidence: 91%

“…The modal abundances of NWA 090 and its olivine/opaque ratio (Fig. 3) are evocative of winonaites (Cecchi & Caporali, 2015;Hunt et al, 2017;Zeng et al, 2019). The overlapping of Fs and Fa signatures between NWA 090 and acapulcoites (Fig.…”

Section: Oxygen Isotopic Compositionmentioning

confidence: 93%

“…To date, 9 of 69 classified winonaites (as of May 2022) contain relict chondrules: Dhofar 1222; Pontlyfni; Mont Morris (Wisconsin); Northwest Africa (NWA) 725, NWA 1463; NWA 1052 and its pairs NWA 1054; and NWA 8614 (Benedix et al, 1998(Benedix et al, , 2003Cecchi & Caporali, 2015;Farley et al, 2015;N eri, 2019;Rubin, 2007;Zeng et al, 2019). One should note that Mount Morris is an ambiguous member of this subgroup; while this meteorite is often cited as containing relict chondrules in the literature (Benedix et al, 1998;Greenwood et al, 2012;Schrader et al, 2017), Benedix et al (1998) actually identified only one suspected chondrule, while Davis et al (1977), Graham et al (1977), and Bevan and Grady (1988) did not report any.…”

Section: Introductionmentioning

confidence: 99%

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Tissemouminites: A new group of primitive achondrites spanning the transition between acapulcoites and winonaites

Stephant

Carli

Anand

et al. 2022

Meteorit & Planetary Scien

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The Northwest Africa (NWA) 090 meteorite, initially classified as an acapulcoite, presents petrological, chemical, and isotopic characteristics comparable to a group of seven primitive winonaites: Dhofar 1222, NWA 725, NWA 1052, NWA 1054, NWA 1058, NWA 1463, and NWA 8614. Five of these samples were previously classified as acapulcoites or ungrouped achondrites before being reclassified as winonaites based on their oxygen isotopic compositions. These misclassifications are indicative of the particular compositional nature of these primitive achondrites. All contain relict chondrules and a lower closure temperature of metamorphism of 820 AE 20 °C compared to other typical winonaites, as well as mineral elemental compositions similar to those of acapulcoites. The oxygen isotopic signature of these samples, d 17 O of 1.18 AE 0.17&, d 18 O of 3.18 AE 0.30&, and D 17 O of À0.47 AE 0.02, is in fact resolvable from both acapulcoites and winonaites. We investigate the relationship between these eight primitive achondrites, typical winonaites, and acapulcoites, to redefine petrological, mineralogical, and geochemical criteria of primitive achondrite classification. Distinguishing between winonaites, acapulcoites, and this group of eight primitive achondrites can be unambiguously done using a combination of several mineralogical and chemical criteria. A combination of olivine fayalite content and FeO/ MnO ratio, as well as plagioclase potassium content allow us to separate these three groups without the absolute necessity of oxygen isotope analyses. NWA 090 as well as the other seven primitive achondrites, although related to winonaites, are most likely derived from a parent body distinct from winonaites and acapulcoites-lodranites, and define a new group of primitive achondrites that can be referred to as tissemouminites.

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Petrography of the carbonaceous, diamond-bearing stone “Hypatia” from southwest Egypt: A contribution to the debate on its origin

Belyanin

Kramers

Andreoli

et al. 2018

Geochimica et Cosmochimica Acta

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Petrologic and Minerochemical Trends of Acapulcoites, Winonaites and Lodranites: New Evidence from Image Analysis and EMPA Investigations

Cited by 5 publications

References 28 publications

A review of the chondrite–achondrite transition, and a metamorphic facies series for equilibrated primitive stony meteorites

A review of the chondrite–achondrite transition, and a metamorphic facies series for equilibrated primitive stony meteorites

Tissemouminites: A new group of primitive achondrites spanning the transition between acapulcoites and winonaites

Petrography of the carbonaceous, diamond-bearing stone “Hypatia” from southwest Egypt: A contribution to the debate on its origin

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