Carbonaceous chondrites—II. Carbonaceous chondrite phyllosilicates and light element geochemistry as indicators of parent body processes and surface conditions

Bunch, T. E.; Chang, Sherwood

doi:10.1016/0016-7037(80)90118-0

Cited by 454 publications

(300 citation statements)

References 76 publications

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“…Table 1. Shaded ellipses represent compositional ranges from CR, CI and CM chondrites using data from Weisberg et al (1993), Bunch and Chang (1980) and Tomeoka and Buseck (1988). Also given are solid solution lines for serpentine and saponite.…”

Section: Jbilet Winselwanmentioning

confidence: 99%

Isotope record of mineralogical changes in a spectrum of aqueously altered CM chondrites

Kooten

Nagashima

Kasama

et al. 2018

Geochimica et Cosmochimica Acta

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The recent fall of the relatively unaltered CM chondrite Maribo provides a unique opportunity to study the early stages of aqueous alteration on the CM chondrite parent body. We show using transmission electron microscopy of a matrix FIBsection from Maribo that this meteorite mainly appears to consist of tochilinite-cronstedtite intergrowths (TCIs), but also contains regions of amorphous or nanocrystalline silicates, anhydrous silicates and FeNi metal aggregates with thin iron oxide rims, suggesting that it experienced aqueous alteration to a relatively small degree. A comparison of Maribo with increasingly altered CM chondrites such as Jbilet Winselwan and Bells shows that during progressive aqueous alteration (1) the TCIs are replaced by coarser sulfides and increasingly Mg-rich serpentine, and (2) the abundance of 15 N-rich hotspots increases, whereas the magnitude of their 15 N enrichment decreases. We observe that the overall N isotope variability related to aqueous alteration is an order of magnitude lower than the variability observed between different chondrite groups. We suggest these high order differences are the result of heterogeneous accretion of insoluble or soluble organic carriers of 15 N to the different chondrite parent bodies. D/H ratios of matrices from Maribo, Jbilet Winselwan and Bells increase with progressive aqueous alteration, a trend that is opposite to expectations of mixing between D-poor water and D-rich organic matter. We argue that this behaviour cannot be related to Fe oxidation or serpentinization reactions and subsequent loss of D-poor H 2 gas. We offer an alternative hypothesis and suggest that CM chondrites experienced two-stage aqueous alteration. During the first stage occurring at relatively low temperature, mixing of increasing amounts of D-poor water with D-rich organic matter results in a decrease of D/H ratio with increasing degree of alteration. During the second stage of alteration occurring at relatively high temperature (T < 300°C), decomposition of TCIs in CMs of petrologic type <2.7 releases gaseous D-poor water that results in increase of the D/H ratio of the CM matrices. Finally, we report on changes in the organic structure of Maribo, Jbilet Winselwan and Bells using Carbon-K and Nitrogen-K edge electron energy loss spectroscopy. The organic matter initially has higher aromatic/aliphatic ratios (e.g., Maribo) and lower abundances of ketone and carboxyl functional groups, which we suggest are the result of chemical degradation of double bonded carbon from oxidation during hydrothermal

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Section: Jbilet Winselwanmentioning

confidence: 99%

Isotope record of mineralogical changes in a spectrum of aqueously altered CM chondrites

Kooten

Nagashima

Kasama

et al. 2018

Geochimica et Cosmochimica Acta

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“…CM chondrites contain ~9 wt% indigenous water (Jarosewich 1990) bound in phyllosilicates formed during parent-body aqueous alteration (McSween 1979;Bunch and Chang 1980;Barber 1981;Tomeoka and Buseck 1985;Zolensky and Browning 1994;Zolensky et al 1997;Browning et al 2000;Trigo-Rodríguez et al 2006). CM properties that change with progressive whole-rock alteration were explored by McSween (1979), Browning et al (1996), and Hanowski and Brearley (2001).…”

Section: Summary Of CM Alterationmentioning

confidence: 99%

Petrography of refractory inclusions in CM2.6 QUE 97990 and the origin of melilite‐free spinel inclusions in CM chondrites

Rubin

2007

Meteorit & Planetary Scien

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Abstract-Queen Alexandra Range (QUE) 97990 (CM2.6) is among the least-altered CM chondrites known. It contains 1.8 vol% refractory inclusions; 40 were studied from a single thin section. Inclusion varieties include simple, banded and nodular structures as well as simple and complex distended objects. The inclusions range in mean size from 30 to 530 μm and average 130 ± 90 μm. Many inclusions contain 25 ± 15 vol% phyllosilicate (predominantly Mg-Fe serpentine); several contain small grains of perovskite. In addition to phyllosilicate, the most abundant inclusions in QUE 97990 consist mainly of spinel-pyroxene (35%), followed by spinel (20%), spinel-pyroxene-olivine (18%), pyroxene (12%), pyroxene-olivine (8%) and hibonite ± spinel (8%). Four pyroxene phases occur: diopside, Al-rich diopside (with ≥8.0 wt% Al 2 O 3 ), Al-Ti diopside (i.e., fassaite), and (in two inclusions) enstatite. No inclusions contain melilite. Aqueous alteration of refractory inclusions transforms some phases (particularly melilite) into phyllosilicate; some inclusions broke apart during alteration. Melilite-free, phyllosilicate-bearing, spinel inclusions probably formed from pristine, phyllosilicate-free inclusions containing both melilite and spinel. Sixty-five percent of the refractory inclusions in QUE 97990 appear to be largely intact; the major exception is the group of spinel inclusions, all of which are fragments. Whereas QUE 97990 contains about 50 largely intact refractory inclusions/cm 2 , estimates from literature data imply that more-altered CM chondrites have lower modal abundances (and lower number densities) of refractory inclusions: Mighei (CM ~ 2.3) contains roughly 0.3-0.6 vol% inclusions (~10 largely intact inclusions/cm 2 ); Cold Bokkeveld (CM2.2) contains ~0.01 vol% inclusions (on the order of 6 largely intact inclusions/cm 2 ).

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“…An investigation of relative amounts of organic compounds, especially structural isomers, found in carbonaceous chondrites may contribute to the understanding of aqueous and low temperature alteration processes that affected these meteorites (McSween, 1979;Bunch and Chang, 1980;Kojima et al, 1984;Tomeoka and Buseck, 1985).…”

Section: Application To Thermal Historymentioning

confidence: 99%

Analyses of carboxylic acids and hydrocarbons in Antarctic carbonaceous chondrites, Yamato-74662 and Yamato-793321.

et al. 1989

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Carbonaceous chondrites—II. Carbonaceous chondrite phyllosilicates and light element geochemistry as indicators of parent body processes and surface conditions

Cited by 454 publications

References 76 publications

Isotope record of mineralogical changes in a spectrum of aqueously altered CM chondrites

Isotope record of mineralogical changes in a spectrum of aqueously altered CM chondrites

Petrography of refractory inclusions in CM2.6 QUE 97990 and the origin of melilite‐free spinel inclusions in CM chondrites

Analyses of carboxylic acids and hydrocarbons in Antarctic carbonaceous chondrites, Yamato-74662 and Yamato-793321.

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