Large spinel grains in a CM chondrite (Acfer 331): Implications for reconstructions of ancient meteorite fluxes
Identifieur interne : 000305 ( Main/Exploration ); précédent : 000304; suivant : 000306Large spinel grains in a CM chondrite (Acfer 331): Implications for reconstructions of ancient meteorite fluxes
Auteurs : Karolina Bj Rnborg [Suède] ; Birger Schmitz [Suède, États-Unis]Source :
- Meteoritics & Planetary Science [ 1086-9379 ] ; 2013-02.
Abstract
By dissolving 30–400 kg of marine limestone in HCl and HF acid, our group has previously recovered common relict chromite grains (approximately 63–250 μm) from ordinary chondritic micrometeorites that fell on ancient sea floors, up to 500 Myr old. Here, we evaluate if CM group carbonaceous chondritic material, which makes up an important fraction of the micrometeorite flux today, contains analogous grains that can be searched for in acid residues. We dissolved 8 g of CM2 meteorite Acfer 331 in HF, which yielded a characteristic assemblage of both transparent Mg‐Al‐ and opaque Cr‐spinels >28 μm. We find on average 4.6 and 130 Mg‐Al‐spinel grains per gram in the 63–250 and 28–63 μm size fractions, respectively. These grains are mostly pink or colorless, and often characterized by heterogeneous Cr‐content. Black, opaque Cr‐spinel grains are absent from the >63 μm fraction, but in the 28–63 μm fraction we find approximately 65 such grains per gram meteorite. The individual grains have a characteristic composition, with heterogeneous major element compositions (e.g., 44.4–61.7 wt% Cr2O3), but narrow ranges for maximum TiO2 (0.6–1.6 wt%) and V2O3 (0.5–1.0 wt%) concentrations. The content of spinel grains in the 28–63 μm fraction of CM meteorites appears comparable at the order of magnitude level with the content of >63 μm sized chromite grains in fossil L‐chondrites from Ordovician limestone. Our approach of recovering meteoritic spinel from sediment may thus be extended to include CM meteorites, but the smaller size fraction of the acid residues should be searched.
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DOI: 10.1111/maps.12050
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Box 118, SE‐22100, Lund</wicri:regionArea><wicri:noRegion>Lund</wicri:noRegion></affiliation><affiliation wicri:level="3"><country xml:lang="fr">États-Unis</country><wicri:regionArea>Robert A. Pritzker Center for Meteoritics and Polar Studies, Department of Geology, The Field Museum, 1400 S. Lake Shore Drive, Illinois, 60605, Chicago</wicri:regionArea><placeName><settlement type="city">Chicago</settlement><region type="state">Illinois</region></placeName></affiliation></author></analytic><monogr></monogr><series><title level="j">Meteoritics & Planetary Science</title><title level="j" type="abbrev">Meteorit Planet Sci</title><idno type="ISSN">1086-9379</idno><idno type="eISSN">1945-5100</idno><imprint><publisher>Blackwell Publishing Ltd</publisher><date type="published" when="2013-02">2013-02</date><biblScope unit="volume">48</biblScope><biblScope unit="issue">2</biblScope><biblScope unit="page" from="180">180</biblScope><biblScope unit="page" to="194">194</biblScope></imprint><idno type="ISSN">1086-9379</idno></series><idno type="istex">A16513BD8B844A6759E0E1B5CB78DFD18C25E397</idno><idno type="DOI">10.1111/maps.12050</idno><idno type="ArticleID">MAPS12050</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">1086-9379</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass><langUsage><language ident="en">en</language></langUsage></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">By dissolving 30–400 kg of marine limestone in HCl and HF acid, our group has previously recovered common relict chromite grains (approximately 63–250 μm) from ordinary chondritic micrometeorites that fell on ancient sea floors, up to 500 Myr old. Here, we evaluate if CM group carbonaceous chondritic material, which makes up an important fraction of the micrometeorite flux today, contains analogous grains that can be searched for in acid residues. We dissolved 8 g of CM2 meteorite Acfer 331 in HF, which yielded a characteristic assemblage of both transparent Mg‐Al‐ and opaque Cr‐spinels >28 μm. We find on average 4.6 and 130 Mg‐Al‐spinel grains per gram in the 63–250 and 28–63 μm size fractions, respectively. These grains are mostly pink or colorless, and often characterized by heterogeneous Cr‐content. Black, opaque Cr‐spinel grains are absent from the >63 μm fraction, but in the 28–63 μm fraction we find approximately 65 such grains per gram meteorite. The individual grains have a characteristic composition, with heterogeneous major element compositions (e.g., 44.4–61.7 wt% Cr2O3), but narrow ranges for maximum TiO2 (0.6–1.6 wt%) and V2O3 (0.5–1.0 wt%) concentrations. The content of spinel grains in the 28–63 μm fraction of CM meteorites appears comparable at the order of magnitude level with the content of >63 μm sized chromite grains in fossil L‐chondrites from Ordovician limestone. Our approach of recovering meteoritic spinel from sediment may thus be extended to include CM meteorites, but the smaller size fraction of the acid residues should be searched.</div></front></TEI><affiliations><list><country><li>Suède</li><li>États-Unis</li></country><region><li>Illinois</li></region><settlement><li>Chicago</li></settlement></list><tree><country name="Suède"><noRegion><name sortKey="Bj Rnborg, Karolina" sort="Bj Rnborg, Karolina" uniqKey="Bj Rnborg K" first="Karolina" last="Bj Rnborg">Karolina Bj Rnborg</name></noRegion><name sortKey="Schmitz, Birger" sort="Schmitz, Birger" uniqKey="Schmitz B" first="Birger" last="Schmitz">Birger Schmitz</name></country><country name="États-Unis"><region name="Illinois"><name sortKey="Schmitz, Birger" sort="Schmitz, Birger" uniqKey="Schmitz B" first="Birger" last="Schmitz">Birger Schmitz</name></region></country></tree></affiliations></record>Pour manipuler ce document sous Unix (Dilib)
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