Chondrules and matrix in the Ornans CO3 meteorite: Possible precursor components
TL;DR: In this paper, a bulk composition of 17 chondrules and one sample of matrix from CO3 Ornans were determined by instrumental neutron activation analysis, which indicated that the siderophile/lithophile and refractory lithophile/common lithophile fractionations recorded in chondrite whole-rocks were established prior to chondrule formation at all nebular locations.
About: This article is published in Geochimica et Cosmochimica Acta.The article was published on 1988-02-01. It has received 59 citations till now. The article focuses on the topics: Chondrite & Chondrule.
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01 Jan 2014
TL;DR: In this article, the properties of carbonaceous, ordinary and enstatite chondrites focusing on the most pristine samples are reviewed to establish the chemical, isotopic, and mineralogical properties and origins of their components and to elucidate the asteroidal processes that modified them.
Abstract: Chondrites are extraordinary mixtures of materials with diverse origins that formed around other stars, in the solar nebula, and in their parent asteroids. Most chondrites were so severely altered by aqueous fluids, thermal metamorphism, and impacts that the original characteristics of their components have been largely erased. But a few pristine chondrites have preserved an exquisite mineralogical, chemical, isotopic, and chronological record of the first few million years of solar system history. The properties of diverse types of carbonaceous, ordinary, and enstatite chondrites focusing on the most pristine samples are reviewed to establish the chemical, isotopic, and mineralogical properties and origins of their components and to elucidate the asteroidal processes that modified them. Refractory inclusions – amoeboid olivine aggregates and Ca–Al-rich inclusions – were the first solids to form in the solar nebula near to the protosun. Chondrules and associated metallic Fe–Ni grains were still forming several million years later when the earliest planetesimals, which melted due to heat from 26 Al decay, were colliding. In the least-altered chondrites, matrix material, which coats chondrules and other components, is largely composed of micrometer-sized silicates and amorphous materials, which formed at high temperatures, plus small amounts (up to 200 ppm) of presolar oxides and silicates.
305 citations
TL;DR: The spectral reflectance properties of 16 CO-type carbonaceous chondrites (CCs) were examined in this paper to better understand their range of spectral properties, develop spectral-compositional correlations, and provide information that may aid in the search for CO parent bodies.
244 citations
Cites background from "Chondrules and matrix in the Ornans..."
...Chondrule olivines are generally Fa-poor (Fa<7), as are chondrule pyroxenes (Fs<6) (Rubin and Wasson, 1988)....
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...% in porphyritic pyroxene chondrules, and 0% in one barred olivine chondrule that was examined (Rubin and Wasson, 1988)....
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TL;DR: It is inferred that carbonaceous chondrite matrices are not pristine: they formed from a material reservoir that was already depleted in volatile and moderately volatile elements, which produces a highly nonmonotonic trace element pattern that requires a complementary depletion in chondrule compositions to achieve a monotonic bulk.
Abstract: Bulk chondritic meteorites and terrestrial planets show a monotonic depletion in moderately volatile and volatile elements relative to the Sun's photosphere and CI carbonaceous chondrites. Although volatile depletion was the most fundamental chemical process affecting the inner solar nebula, debate continues as to its cause. Carbonaceous chondrites are the most primitive rocks available to us, and fine-grained, volatile-rich matrix is the most primitive component in these rocks. Several volatile depletion models posit a pristine matrix, with uniform CI-like chemistry across the different chondrite groups. To understand the nature of volatile fractionation, we studied minor and trace element abundances in fine-grained matrices of a variety of carbonaceous chondrites. We find that matrix trace element abundances are characteristic for a given chondrite group; they are depleted relative to CI chondrites, but are enriched relative to bulk compositions of their parent meteorites, particularly in volatile siderophile and chalcophile elements. This enrichment produces a highly nonmonotonic trace element pattern that requires a complementary depletion in chondrule compositions to achieve a monotonic bulk. We infer that carbonaceous chondrite matrices are not pristine: they formed from a material reservoir that was already depleted in volatile and moderately volatile elements. Additional thermal processing occurred during chondrule formation, with exchange of volatile siderophile and chalcophile elements between chondrules and matrix. This chemical complementarity shows that these chondritic components formed in the same nebula region.
157 citations
TL;DR: In this article, the Mg/Si ratios of chondrules and matrices in carbonaceous chondrites are complementary, indicating that chond rules and matrix are chemically connected.
147 citations
TL;DR: The physical properties of chondrules have generally received less emphasis than other properties of meteorites such as their mineralogy, petrology, and chemical and isotopic compositions as discussed by the authors.
Abstract: The examination of the physical properties of chondrules has generally received less emphasis than other properties of meteorites such as their mineralogy, petrology, and chemical and isotopic compositions. Among the various physical properties of chondrules, chondrule size is especially important for the classification of chondrites into chemical groups, since each chemical group possesses a distinct size-frequency distribution of chondrules. Knowledge of the physical properties of chondrules is also vital for the development of astrophysical models for chondrule formation, and for understanding how to utilize asteroidal resources in space exploration. To examine our current knowledge of chondrule sizes, we have compiled and provide commentary on available chondrule dimension literature data. We include all chondrite chemical groups as well as the acapulcoite primitive achondrites, some of which contain relict chondrules. We also compile and review current literature data for other astrophysically-relevant physical properties (chondrule mass and density). Finally, we briefly examine some additional physical aspects of chondrules such as the frequencies of compound and “cratered” chondrules. A purpose of this compilation is to provide a useful resource for meteoriticists and astrophysicists alike.
122 citations
Cites background from "Chondrules and matrix in the Ornans..."
...ameters for whole chondrules, so we set this work aside for the CO chondrites as well as the rest of the carbonaceous chondrites examined by King and King (1978). In a personal communication cited by Rubin and Wasson (1988), King and King 13 found a mean diameter of 196 µm for CO chondrules. It is unreported how many chondrules were measured to arrive at this value. Rubin (1989a) reported on the size frequency distribut...
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References
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TL;DR: In this paper, the calibration curve in a binary metal alloy system can, within the variance of data points, be described by the linear expression $$C_{A}/K{A} = \alpha_{AB} + (1 - α_{AB})C{A]$$, where C is the concentration of element A in alloy  relative to pure A, and K is the background-corrected intensity of a characteristic radiation line of A in the alloy relative to that of pure A. This linear variation of the correction factor with composition can be extended to multicomp
Abstract: Given suitable correction factors, the use of pure oxides and binary oxide phases as standards would make electron microanalysis independent of chemical analyses and problems of sample inhomogeneity. Ziebold and Ogilvie (1964) have shown that the calibration curve in a binary metal alloy system can, within the variance of data points, be described by the linear expression $$C_{A}/K_{A} = \alpha_{AB} + (1 - \alpha_{AB})C_{A}$$, where $$C_{A }$$ is the concentration of element A in alloy Ârelative to pure A, and $$K_{A}$$ is the background-corrected intensity of a characteristic radiation line of A in the alloy relative to that of pure A. This linear variation of the correction factor with composition can be extended to multicomponent systems by using the weighted average of the binary correction factors. Correction factors have been determined empirically for characteristic lines of ten major elements (Na, Mg, Al, Si, K, Ca, Ti, Cr, Mn, and Fe) in the corresponding oxides using phases on binary and pseudob...
2,162 citations
TL;DR: N abundance and isotopic compositions can differentiate existing taxonomic groups with close to 100% reliability and there are hints that both CI and CM groups may each be divisible into two subgroups.
396 citations
TL;DR: Renazzo chondrites have a lineation possibly caused by fluid-lubricated, impact-induced shearing as mentioned in this paper, which can be represented by six or more closely related fall events.
386 citations
TL;DR: A petrographic survey of > 1600 chondrules in thin-sections of 12 different mildly to highly unequilibrated H-, L-, and LL-chondrites, as well as morphological and textural study of 141 whole chond rules separated from 11 of the same chondrites was used to determine the relative abundances of definable chondrule primary textural types as discussed by the authors.
Abstract: A petrographic survey of > 1600 chondrules in thin-sections of 12 different mildly to highly unequilibrated H-, L-, and LL-chondrites, as well as morphological and textural study of 141 whole chondrules separated from 11 of the same chondrites, was used to determine the relative abundances of definable chondrule primary textural types Percentage abundances of various chondrule types are remarkably similar in all chondrites studied and are ∼ 47–52 porphyritic olivine-pyroxene (POP), 15–27 porphyritic olivine (PO), 9–11 porphyritic pyroxene (PP), 3–4 barred olivine (BO), 7–9 radial pyroxene (RP), 2–5 granular olivine-pyroxene (GOP), 3–5 cryptocrystalline (C), and ≤ 1 metallic (M) Neither chondrule size nor shape is strongly correlated with textural type Compound and cratered chondrules, which are interpreted as products of collisions between plastic chondrules, comprise ∼ 2–28% of nonporphyritic (RP, GOP, C) but only ∼ 2–9% of porphyritic (POP, PO, PP, BO) chondrules, leading to a model-dependent implication that nonporphyritic chondrules evolved at number densities (chondrules per unit volume of space) which were 102 to 104 times greater than those which prevailed during porphyritic chondrule formation (total range of ∼ 1 to ∼ 106 m−3) Distinctive “rims” of fine-grained sulfides and/or silicates occur on both porphyritic and nonporphyritic types and appear to post-date chondrule formation Apparently, either the same process(es) contributed chondrules to all unequilibrated ordinary chondrites or, if genetically different, the various chondrule types were well mixed before incorporation into chondrites Melting of pre-existing materials is the mechanism favored for chondrule formation
273 citations