Geochemistry of the ungrouped carbonaceous chondrite Tagish Lake, the anomalous CM chondrite Bells, and comparison with CI and CM chondrites

Mittlefehldt, David W.

doi:10.1111/j.1945-5100.2002.tb00850.x

Cited by 56 publications

(50 citation statements)

References 27 publications

(45 reference statements)

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“…From its bulk oxygen isotopic composition, Clayton and Mayeda (2001) inferred that Tagish Lake was exposed to a high water/rock ratio, consistent with our observation of a relatively small anhydrous fraction. In CMs, this component is dominated by olivine (Grossman and Olsen 1974), so the smaller dense fraction should not necessarily be interpreted as a smaller refractory component; Tagish Lake is not depleted in bulk refractory trace elements relative to the CM chondrite average (Mittlefehldt 2002). Either Tagish Lake has a refractory inclusion content that is typical of CMs, or it originally had an abundance of refractory inclusions that was normal for a CM chondrite, and despite hydrous alteration, the elemental signature of this component was retained.…”

Section: Discussionmentioning

confidence: 99%

“…Studies that considered oxygen isotopes (Clayton and Mayeda 2001;Leshin et al 2001), bulk organic carbon , bulk chemistry (Friedrich et al 2002), and organic compounds (Pizzarello and Huang 2002) concluded that it is different from both CMs and CIs. Based on its bulk density, chondrule and inclusion types, and general mineralogy, Zolensky et al (2002) concluded that Tagish Lake is distinct from the known CIs, CRs, and CMs and suggested that it is a new kind of type 2 carbonaceous chondrite, while studies of the sulfides (Bullock et al 2002) and bulk chemistry (Mittlefehldt 2002) showed ways in which Tagish Lake is similar to CMs. Thus, a good understanding of Tagish Lake has remained elusive, and classification of Tagish Lake remains somewhat ambiguous.…”

Section: Introductionmentioning

confidence: 99%

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Petrography and mineral chemistry of the anhydrous component of the Tagish Lake carbonaceous chondrite

Simon¹,

Grossman²

2003

Meteorit & Planetary Scien

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Abstract-Most studies of Tagish Lake have considered features that were either strongly affected by or formed during the extensive hydrous alteration experienced by this meteorite. This has led to some ambiguity as to whether Tagish Lake should be classified a CI, a CM, or something else. Unlike previous workers, we have focused upon the primary, anhydrous component of Tagish Lake, recovered through freeze-thaw disaggregation and density separation and located by thin section mapping. We found many features in common with CMs that are not observed in CIs. In addition to the presence of chondrules and refractory forsterite (which distinguish Tagish Lake from the CIs), we found hibonite-bearing refractory inclusions, spinel-rich inclusions, forsterite aggregates, Cr-, Al-rich spinel, and accretionary mantles on many clasts, which clearly establishes a strong link between Tagish Lake and the CM chondrites. The compositions of isolated olivine crystals in Tagish Lake are also like those found in CMs. We conclude that the anhydrous inclusion population of Tagish Lake was, originally, very much like that of the known CM chondrites and that the inclusions in Tagish Lake are heavily altered, more so than even those in Mighei, which are more heavily altered than those in Murchison.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Petrography and mineral chemistry of the anhydrous component of the Tagish Lake carbonaceous chondrite

Simon¹,

Grossman²

2003

Meteorit & Planetary Scien

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“…Bells is considered an anomalous brecciated CM chondrite. Its bulk oxygen isotope composition (Rowe et al, 1994), noble gas signatures (Zadnik, 1985) and chemical composition (Mittlefehldt, 2002) Rubin et al (2007) as 2.1, whereas Browning et al (1996) suggest that Bells is in fact a weakly altered CM chondrite, similar to Murchison (CM2.5). Besides looking at Maribo and Jbilet Winselwan to identify mineralogical, isotopic and structural changes during the earliest stages of alteration, we chose Bells to determine whether this anomalous chondrite accreted to the CM chondrite parent body or belongs to a different parent body.…”

Section: Methodsmentioning

confidence: 99%

“…Recently, the least altered CM chondrite Paris was found to have a bulk d 15 N value of +19.5‰ (Vinogradoff et al, 2017), on the upper end of CM chondrite values. Bells, often described as an anomalous CM chondrite (Kallemeyn, 1995;Mittlefehldt, 2002) . Therefore, we provide an alternative explanation for our samples and suggest that this discrepancy is the result of variations in the ionization efficiency of organic components with different N isotope signatures.…”

Section: Bellsmentioning

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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“…The Tagish Lake meteorite harbors (1) unusual petrologic and mineralogical characteristics in between those of CI1 and CM2 chondrites such as a fine-grained opaque matrix consisting mainly of phyllosilicates (intergrowth of serpentine and saponite), sulfides, and magnetites and within this matrix, the presence of altered CAIs and chondrules, isolated olivine grains, magnetite, carbonates, and Fe-Ni sulfides (Zolensky et al 2002); (2) mineralogical indications of high degree of aqueous alteration such as the presence of altered CAIs, and of carbonates ranging in composition from pure calcite (CaCO 3 ) to siderite (FeCO 3 ) and magnesite (MgCO 3 ), the last two endmembers not present in any other type of meteorites (Zolensky et al 2002); (3) a bulk refractory lithophile element abundances similar to the one of CM2 chondrites, while bulk moderately volatile and volatile element abundances are between those of CI1 chondrites and CM2 chondrites (Mittlefehldt 2002); (4) an oxygen isotopic composition near those of CI1 chondrites and some metamorphosed carbonaceous chondrites but different from either of these and from the O-isotopic field of the CM2 chondrites (Engrand et al 2001;Leshin et al 2001); and (5) a bulk rock carbon isotopic composition distinct from those of CI1 chondrites and CM2 chondrites, although the carbonates in Tagish Lake have carbon isotopic compositions similar to those of these two meteorite groups (Grady et al 2002). All these characteristics suggest that Tagish Lake is a new type of meteorite.…”

Section: Tagish Lakementioning

confidence: 99%

The Chromium Isotopic Composition of the Ungrouped Carbonaceous Chondrite Tagish Lake

Petitat

Birck

Luu

et al. 2011

ApJ

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Early solar materials bear a variety of isotopic anomalies that reflect compositional differences deriving from distinct stellar nucleosynthetic processes. As shown in previous studies, the stepwise dissolution with increasing acid strengths of bulk rock carbonaceous chondrites liberates Cr with both excesses and deficits in 53 Cr and 54 Cr relative to the terrestrial standard. The magnitude of the 54 Cr variations within a meteorite decreases in the sequence CI1 > CR2 > CM2 > CV3 > CO3 > CK4 and correlates with the degree of metamorphism of each carbonaceous chondrite class. This study shows that the Tagish Lake meteorite presents the highest excesses in 54 Cr ever measured in a bulk silicate phase. According to this study, the Tagish Lake meteorite is composed of the least re-equilibrated material known at this time. The magnitude of 54 Cr variation decreases now in the following sequence: Tagish Lake (ungrouped CI2) > Orgueil (CI1) > Murchison (CM2) > Allende (CV2). Moreover, this study shows that excesses in 53 Cr relative to Earth can be interpreted as representing the extent of aqueous alteration on meteorite parent bodies. Finally, the high 54 Cr anomalies measured in this meteorite make Tagish Lake one of the major targets to decipher the host of these anomalies.

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Geochemistry of the ungrouped carbonaceous chondrite Tagish Lake, the anomalous CM chondrite Bells, and comparison with CI and CM chondrites

Cited by 56 publications

References 27 publications

Petrography and mineral chemistry of the anhydrous component of the Tagish Lake carbonaceous chondrite

Petrography and mineral chemistry of the anhydrous component of the Tagish Lake carbonaceous chondrite

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

The Chromium Isotopic Composition of the Ungrouped Carbonaceous Chondrite Tagish Lake

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