Modal abundances of coarse-grained (&gt;5 μm) components within CI-chondrites and their individual clasts – Mixing of various lithologies on the CI parent body(ies)

Alfing, Julian; Patzek, M.; Bischoff, A.

doi:10.1016/j.chemer.2019.08.004

Cited by 42 publications

(61 citation statements)

References 33 publications

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“…2015, 2017; Alfing et al. 2019). The characterization of CM breccias gives insight into the formation processes of CM parent bodies as well as into the evolution of asteroid surfaces.…”

Section: Discussionmentioning

confidence: 99%

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Classification of CM chondrite breccias—Implications for the evaluation of samples from the OSIRIS‐REx and Hayabusa 2 missions

Lentfort

Bischoff

Ebert

et al. 2020

Meteorit & Planetary Scien

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CM chondrites are complex impact (mostly regolith) breccias, in which lithic clasts show various degrees of aqueous alteration. Here, we investigated the degree of alteration of individual clasts within 19 different CM chondrites and CM‐like clasts in three achondrites by chemical analysis of the tochilinite‐cronstedtite‐intergrowths (TCIs; formerly named “poorly characterized phases”). To identify TCIs in various chondritic lithologies, we used backscattered electron (BSE) overview images of polished thin sections, after which appropriate samples underwent electron microprobe measurements. Thus, 75 lithic clasts were classified. In general, the excellent work and specific criteria of Rubin et al. (2007) were used and considered to classify CM breccias in a similar way as ordinary chondrite breccias (e.g., CM2.2‐2.7). In BSE images, TCIs in strongly altered fragments in CM chondrites (CM2.0‐CM2.2) appear dark grayish and show a low contrast to the surrounding material (typically clastic matrix), and can be distinguished from TCIs in moderately (CM2.4‐CM2.6) or less altered fragments (CM2.7‐CM2.9); the latter are bright and have high contrast to the surroundings. We found that an accurate subclassification can be obtained by considering only the “FeO”/SiO2 ratio of the TCI chemistry. One could also consider the TCIs’ S/SiO2 ratio and the metal abundance, but these were not used for classification due to several disadvantages. Most of the CM chondrites are finds that have suffered terrestrial weathering in hot and cold deserts. Thus, the observed abundance of metal is susceptible to weathering and may not be a reliable indicator of subtype classification. This study proposes an extended classification scheme based on Rubin’s scale from subtypes CM2.0‐CM2.9 that takes the brecciation into account and includes the minimum to maximum degree of alteration of individual clasts. The range of aqueous alteration in CM chondrites and small spatial scale of mixing of clasts with different alteration histories will be important for interpreting returned samples from the OSIRIS‐REx and Hayabusa 2 missions in the future.

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“…2015, 2017; Alfing et al. 2019). The characterization of CM breccias gives insight into the formation processes of CM parent bodies as well as into the evolution of asteroid surfaces.…”

Section: Discussionmentioning

confidence: 99%

“…2015, 2017; Alfing et al. 2019). Some of these rocks even contain fragments that were formed in water‐free environments or that have completely lost their volatiles due to heating (Kerraouch et al.…”

Section: Introductionmentioning

confidence: 99%

Classification of CM chondrite breccias—Implications for the evaluation of samples from the OSIRIS‐REx and Hayabusa 2 missions

Lentfort

Bischoff

Ebert

et al. 2020

Meteorit & Planetary Scien

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“…This composition is similar to that of Bennu's presumed meteorite analogs, the CM and CI groups of carbonaceous chondrites, which are dominated by Feand Mg-bearing phyllosilicates, respectively. In the most intensely aqueously altered CI chondrites, the Fe is contained in oxides, sulfides, carbonates, and other minor species (61,62,63).…”

Section: Evidence For Parent Body Heterogeneitymentioning

confidence: 99%

Variations in color and reflectance on the surface of asteroid (101955) Bennu

DellaGiustina

Burke

Walsh

et al. 2020

Science

113

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Visible-wavelength color and reflectance provide information about the geologic history of planetary surfaces. We present multispectral images (0.44 to 0.89 microns) of near-Earth asteroid (101955) Bennu. The surface has variable colors overlain on a moderately blue global terrain. Two primary boulder types are distinguishable by their reflectance and texture. Space weathering of Bennu surface materials does not simply progress from red to blue (or vice versa). Instead, freshly exposed, redder surfaces initially brighten in the near-ultraviolet (become bluer at shorter wavelengths), then brighten in the visible to near-infrared, leading to Bennu’s moderately blue average color. Craters indicate that the timescale of these color changes is ~105 years. We attribute the reflectance and color variation to a combination of primordial heterogeneity and varying exposure ages.

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“…Such characteristics are fundamental because (1) OCs are by far the most common meteorites falling on Earth (~80%) and (2) CMs represent 25% of all carbonaceous chondrite falls (Gounelle et al 2005). Even rarer chondrite types like CI carbonaceous chondrites (Alfing et al 2019), Rumuruti chondrites (Bischoff et al 2011), C1 chondrites (Bischoff et al 2021), CB/CH chondrites (Briani et al 2009;Bonal et al 2010), and enstatite chondrites (Fig. 1B) (Piani et al 2016(Piani et al , 2020 have brecciated textures, thus implying that all chondrite types have been reprocessed after the accretion of their respective parent bodies.…”

Section: Meteoritic Evidence Of Widespread Collision Processes In the Asteroid Beltmentioning

confidence: 99%

The astrophysical context of collision processes in meteorites

Marrocchi

Delbò

Gounelle

2021

Meteorit & Planetary Scien

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Chondrites are leftover solids from the early evolution of the solar protoplanetary disk that never experienced melting since their formation. They comprise unequilibrated assemblages of low-and high-temperature components, including volatile-rich, fine-grained matrices, Fe-Ni metal, sulfides, refractory inclusions, and chondrules. Consequently, chondrites are commonly described as pristine, primitive, or primordial rocks of the solar system. However, impact-generated secondary features are abundant in chondrites, suggesting that collisions among early-formed planetesimals and their fragmentation and reassembly have been effective throughout the evolution of the solar system. In this report, we review evidence of the major role of impacts in generating the current mineralogical and petrographic characteristics of chondrites. We provide perspective to these meteoritic features by discussing recent analyses of large-scale structures of the main asteroid belt and remote-sensing observations of asteroids. Observations at various spatial scales all attest that the "primitive" materials formed during the evolution of the solar system have largely been reprocessed, confirming previous studies that primitivity is relative, not absolute. This implies that (1) chondrites (and some differentiated meteorites) should systematically be envisioned as reprocessed and heterogeneous materials and (2) brecciated meteorites should be considered the norm and unbrecciated meteorites the exception.

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Modal abundances of coarse-grained (>5 μm) components within CI-chondrites and their individual clasts – Mixing of various lithologies on the CI parent body(ies)

Cited by 42 publications

References 33 publications

Classification of CM chondrite breccias—Implications for the evaluation of samples from the OSIRIS‐REx and Hayabusa 2 missions

Classification of CM chondrite breccias—Implications for the evaluation of samples from the OSIRIS‐REx and Hayabusa 2 missions

Variations in color and reflectance on the surface of asteroid (101955) Bennu

The astrophysical context of collision processes in meteorites

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Modal abundances of coarse-grained (>5 μm) components within CI-chondrites and their individual clasts – Mixing of various lithologies on the CI parent body(ies)

Cited by 42 publications

References 33 publications

Classification of CM chondrite breccias—Implications for the evaluation of samples from the OSIRIS‐REx and Hayabusa 2 missions

Classification of CM chondrite breccias—Implications for the evaluation of samples from the OSIRIS‐REx and Hayabusa 2 missions

Variations in color and reflectance on the surface of asteroid (101955) Bennu

The astrophysical context of collision processes in meteorites

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Product

Resources

About

Modal abundances of coarse-grained (>5 μm) components within CI-chondrites and their individual clasts – Mixing of various lithologies on the CI parent body(ies)