Analytical results for the material of the Chelyabinsk meteorite

Geochemistry International (Impact Factor: 0.47). 51(7). DOI: 10.1134/S0016702913070100

ABSTRACT This paper presents the results of the mineralogical, petrographic, elemental, and isotopic analysis of the Chelyabinsk meteorite and their geochemical interpretation. It was shown that the meteorite can be assigned to LL5-group ordinary chondrites and underwent moderate shock metamorphism (stage S4). The Chelyabinsk meteorite contains a significant fraction (approximately one-third by volume) of shock-melted material similar in composition to the main volume of the meteorite. The results of isotopic analysis suggest that the history of meteorite formation included an impact event approximately 290 Ma ago.

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    ABSTRACT: Many equilibrated ordinary chondrites contain (besides chromites of constant composition) Cr spinel with a large spread in Cr/(Cr + Al) ratios. They occur mainly as large grains in chondrules rich in mesostasis, preventing complete equilibration in Cr/Al but not in Fe/Mg. This partially equilibrated Cr spinel turned out to be particularly useful for the selection of an appropriate olivine/spinel thermometer and for the determination of equilibration temperatures. The main results are:1) The H3.7 to 3.8 and the L3.7 to 3.8 chondrites analyzed show temperatures of 625 to 680 °C;2) Equilibrated chondrites show a range of olivine/Cr-spinel temperatures between 700 and 820 °C, and the same average temperatures for type 4 to 6 (number of analyzed meteorites in brackets): H4 (9) 766 °C, H5 (7) 774 °C, H6 (3) 775 °C, L4 (5) 752 °C, L5 (4) 754 °C, L6 (1) 754 °C. These temperatures are interpreted as equilibration temperatures. One indication is that the measured isotherms are straight lines down to low Cr/(Cr + Al) ratios, which have a higher Fe/Mg interdiffusion coefficient than grains with high ratios. And there is no correlation of measured temperature with grain size of Cr spinel.3) Chromites sensu stricto show temperatures about 50 to 100 °C lower than Cr spinel, and a correlation with grain size. This is a closure temperature established during cooling and in situ crystallization.These results can best be interpreted by a "rubble pile" model of parent body evolution. This model cannot explain, however, the absence of type 4 to 6 chondrites with temperatures as low as for type 3.7 to 3.8.
    Meteoritics & planetary science 01/2005; · 2.80 Impact Factor
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    ABSTRACT: We present new INAA results for bulk metal from H and LL chondrites. Both have characteristic elemental patterns similar to L chondrite metal, in particular increasing abundances of W and Ga from unequilibrated to equilibrated chondrites but a reverse variation of V and Cr abundances. These characteristics indicate that metal in ordinary chondrites formed by melting and reduction of highly oxidized material. The similarities of melting features and the complementary nature of compositions between metal and chondrules suggest that these two components were derived from a common precursor, similar to CI or CM material in redox state and compositionally related to the matrix of highly unequilibrated ordinary chondrites. abundance ratios are similarly low for bulk metal in the least metamorphosed ordinary chondrites of all three chemical groups. This suggests that metal in ordinary chondrites initially had the same composition and formed under the same melting conditions. The chondrites that accreted earliest have preserved their melting characteristics, while those that accreted later reequilibrated with the ambient gas at different temperatures. The differences in redox state between equilibrated and unequilibrated chondrites show that formation of chondritic metal and chondrules by melting occurred during the accretion of ordinary chondrite parent bodies. The initial metal composition established during the melting stage (13 wt% Ni; ) is inferred from the metal in highly unequilibrated chondrites. The accretion temperatures of about 600 k for ordinary chondrites are calculated from the reequilibration reaction. H chondrites were accreted at the highest temperature and are most reduced among the three ordinary chondrite groups. LL chondrites were accreted at the lowest temperature and are most oxidized. Compositionally, the metal component that would account for the fractionation among H, L, and LL chondrites is different from the metal formed by melting, indicating that the different ratios of H, L, and LL chondrites were established before their accretion.
    Geochimica et Cosmochimica Acta 01/1997; · 3.88 Impact Factor
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    ABSTRACT: A suite of 134 ordinary chondrites (OCs) was analyzed by electron microprobe to determine olivine and kamacite compositions. Equilibrated members of the three main OC groups have the following ranges of olivine Fa and kamacite Co: H (17.3–20.2 mol% Fa; 4.4–5.1 mg/g Co); L (23.0–25.8 mol% Fa; 7.0–9.5 mg/g Co); LL (26.6–32.4 mol% Fa; 14.2–370 mg/g Co). However, the high-Co (200–370 mg/g Co) metal phase in highly oxidized LL chondrites is probably not kamacite. Group ranges of kamacite Ni content overlap, but mean Ni values of equilibrated OCs decrease from H (69.2 mg/g) to L (65.4 mg/ g) to LL (49.8 mg/g). The concomitant increase in kamacite Co and decrease in kamacite Ni in the H-L-LL sequence is probably due to a combination of two effects: 1.(1) the decrease in kamacite grain size from H through LL (the smaller LL grains reach equilibrium faster and thereby acquire lower Ni contents), and2.(2) the greater oxidizability of Fe relative to Co (kamacite grains thus become richer in Co as the oxidation state increases from H through LL).There are significant intragroup differences in olivine and kamacite composition: type-3 and type-4 OCs tend to have lower olivine Fa and kamacite Co and Ni values than type-6 OCs. The lower Fa in H-L-LL3 chondrites may be due either to the lack of equilibration between fine FeO-rich and coarse FeOpoor silicates in type-3 OCs, or to the acquisition of less FeO-rich material (possibly type-II chondrules or fine-grained matrix material) by type-3 OCs during agglomeration. The lower kamacite Co and Ni contents of H-L-LL3 chondrites may reflect the presence in type-3 OCs of a relict nebular metal component with positively correlated Co and Ni; such a component has previously been inferred for the primitive, ungrouped chondrites, Al Rais, Renazzo, and ALH85085.Aberrant olivine and/or kamacite grains with compositions significantly different than the majority in the whole-rock occur in at least half and probably virtually all equilibrated OCs. Aberrant kamacite grains are not uniformly distributed among the OCs; they are more common in L and LL than in H chondrites. Chondrites containing aberrant grains are fragmental breccias that were brecciated after cooling from high metamorphic temperatures.The different OC parent bodies accreted at different heliocentric distances and acquired distinct bulk and mineralogical compositions. It is probable that more than three OC parent bodies were formed: Netschaevo is from an OC body more reduced than H chondrites; Tieschitz and Bremervörde may be from an OC body intermediate in its properties between H and L chondrites; and ten other OCs may be from a body intermediate between L and LL.Within each individual OC group, there are many chondrites with non-overlapping olivine compositional distributions. These meteorites clearly have not equilibrated with each other; they may have agglomerated at opposite extremes of the parent body's accretion zone. Their existence is consistent with maximum metamorphic temperatures having occurred in small planetesimals prior to the accretion of large asteroids.
    Geochimica et Cosmochimica Acta 01/1990; · 3.88 Impact Factor


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