Refractory inclusions in carbonaceous chondrites: Records of early solar system processes

Krot, Alexander N.

doi:10.1111/maps.13350

Cited by 83 publications

(45 citation statements)

References 236 publications

(599 reference statements)

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“…1995, 1998a, 2010, 2020; Fagan et al. 2007; Brearley and Krot 2013; Krot 2019). Thus, it is not a surprise that the three CAI samples have unusually high K contents (0.48–0.57 wt%) that are higher than all other chondritic components (i.e., chondrules and matrix).…”

Section: Resultsmentioning

confidence: 99%

Early solar system aqueous activity: K isotope evidence from Allende

Jiang

Koefoed

Pravdivtseva

et al. 2020

Meteorit & Planetary Scien

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The alkali element K is moderately volatile and fluid mobile; thus, it can be influenced by both primary processes (evaporation and recondensation) in the solar nebula and secondary processes (thermal and aqueous alteration) in the parent body. Since these primary and secondary processes would induce different isotopic fractionations, K isotopes could become a potential tracer to distinguish them. Using recently developed methods with improved precision (0.05‰, 95% confidence interval), we systematically measured the K isotopic compositions and major/trace elemental compositions of chondritic components (18 chondrules, 3 CAIs, 2 matrices, and 5 bulks) in the carbonaceous chondrite fall Allende. Among all the components analyzed in this study, CAIs, which formed initially under high‐temperature conditions in the solar nebula and were dominated by nominally K‐free refractory minerals, have the highest K2O content (average 0.53 wt%) and have K isotope compositions most enriched in heavy isotopes (δ41K: −0.30 to −0.25‰). Such an observation is consistent with previous petrologic studies that show CAIs in Allende have undergone alkali enrichment during metasomatism. In contrast, chondrules contain lower K2O content (0.003–0.17 wt%) and generally lighter K isotope compositions (δ41K: −0.87‰ to −0.24‰). The matrix and bulks are nearly identical in K2O content and K isotope compositions (0.02–0.05 wt%; δ41K: −0.62 to − 0.46‰), which are, as expected, right in the middle of CAIs and chondrules. This strongly indicates that most of the chondritic components of Allende suffered aqueous alteration and their K isotopic compositions are the ramification of Allende parent‐body processing instead of primary nebular signatures. Nevertheless, we propose the small K isotope fractionations observed (< 1‰) among Allende components are likely similar to the overall range of K isotopic fractionation that occurred in nebular environment. Furthermore, the K isotope compositions seen in the components of Allende in this study are consistent with MC‐ICP‐MS analyses of the components in ordinary chondrites, which also show an absence of large (10‰) isotope fractionations. This is not expected as evaporation experiments in nebular conditions suggest there should be large K isotopic fractionations. Nevertheless, possible nebular processes such as chondrules back exchanging with ambient gas when they formed could explain this lack of large K isotopic variation.

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Section: Resultsmentioning

confidence: 99%

Early solar system aqueous activity: K isotope evidence from Allende

Jiang

Koefoed

Pravdivtseva

et al. 2020

Meteorit & Planetary Scien

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“…Chondritic meteorites consist of three main components: refractory inclusions (CAIs, hibonite-rich CAIs, and amoeboid olivine aggregates), chondrules, and matrix (e.g., Hezel et al 2019;Krot 2019). Recent advances have established a chronology of formation of CAIs and chondrules in the context of plausible formation models that account for their chemical and isotopic compositions.…”

Section: Meteorites and Their Componentsmentioning

confidence: 99%

The NC-CC Isotope Dichotomy: Implications for the Chemical and Isotopic Evolution of the Early Solar System

et al. 2020

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Understanding the formation of our planetary system requires identification of the materials from which it originated and the accretion processes that produced the planets. The compositional evolution of the solar system can be constrained by synthesizing astronomical datasets and numerical models with elemental and isotopic compositions from objects that directly sampled the disk: meteorites and their constituents (chondrules, refractory inclusions, and matrix). This contribution reviews constraints on early solar system evolution provided by the so-called non-carbonaceous (NC) and carbonaceous chondrite (CC) groups and their relationship to the volatile element characteristics of chondritic meteorites. In previous work, the NC or CC character of a parent body was used to infer its accretion location in the protoplanetary disk. The NC groups purportedly originated in the inner disk, and the CC groups were derived from the outer disk, where the NC and CC regions of the disk may have been separated early on by proto-Jupiter, a pressure maximum, or a dust trap in the disk. The tenet that all CC parent bodies accreted in the outer disk is, in part, based on evidence that a handful of CC meteorites are enriched in volatile species compared to NC meteorites. Here, it is reviewed if and how the volatile element and nucleosynthetic isotope compositions of meteorites can be linked to accretion locations within the disk. The nucleosynthetic isotope compositions of whole rock meteorite samples contrast the trends found for their major volatile element compositions (i.e., C, N, and O). Although there may be an increase in volatile abundances when comparing some stony NC and CC meteorites and their inferred accretion locations within the disk, this is not necessarily a general rule. The difficulties with inferring parent body accretion locations are discussed. It is found that it cannot always be assumed that parent bodies which formed in the CC reservoir are "volatile-rich" relative to those that formed in the NC reservoir which are "volatilepoor". Consequently, tracing the origin of terrestrial volatiles using the NC-CC isotope dichotomy remains challenging.

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“…Formation and pre-accretional thermal processing of Ca-Al-rich inclusions (CAIs) -the oldest known material of the solar system (e.g., Amelin et al, 2010;Bouvier and Wadhwa, 2010;Connelly et al, 2012) -remains a major unsolved problem in cosmochemistry. Although recent advances in analytical instrumentation have generated a large volume information on the mineralogy and chemical and isotopic compositions of CAIs (see reviews of MacPherson, 2014 andKrot, 2019 andreferences therein), which has greatly improved our understanding of the formation and evolution of these early solar system materials, the quantitative interpretation of these data still requires their experimental calibration under conditions close to those of the natural systems.…”

Section: Introductionmentioning

confidence: 99%