Classification of Meteorites and Their Genetic Relationships

Krot, Alexander N.; Keil, K.; Scott, E. R. D.; Goodrich, C. A.; Weisberg, M. K.

doi:10.1016/b978-0-08-095975-7.00102-9

Cited by 137 publications

(184 citation statements)

References 377 publications

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“…The classification of meteorites has been described in detail by Krot et al [62], so it is only briefly outlined here. The major subdivision of meteorites is between the unmelted chondrites and the non-chondrites (achondrites, stony irons and irons) that come from asteroids that experienced variable degrees of melting and differentiation.…”

Section: Meteorites In Briefmentioning

confidence: 99%

The origin of inner Solar System water

Alexander¹

2017

Phil. Trans. R. Soc. A.

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Of the potential volatile sources for the terrestrial planets, the CI and CM carbonaceous chondrites are closest to the planets' bulk H and N isotopic compositions. For the Earth, the addition of approximately 2–4 wt% of CI/CM material to a volatile-depleted proto-Earth can explain the abundances of many of the most volatile elements, although some solar-like material is also required. Two dynamical models of terrestrial planet formation predict that the carbonaceous chondrites formed either in the asteroid belt (‘classical’ model) or in the outer Solar System (5–15 AU in the Grand Tack model). To test these models, at present the H isotopes of water are the most promising indicators of formation location because they should have become increasingly D-rich with distance from the Sun. The estimated initial H isotopic compositions of water accreted by the CI, CM, CR and Tagish Lake carbonaceous chondrites were much more D-poor than measured outer Solar System objects. A similar pattern is seen for N isotopes. The D-poor compositions reflect incomplete re-equilibration with H 2 in the inner Solar System, which is also consistent with the O isotopes of chondritic water. On balance, it seems that the carbonaceous chondrites and their water did not form very far out in the disc, almost certainly not beyond the orbit of Saturn when its moons formed (approx. 3–7 AU in the Grand Tack model) and possibly close to where they are found today. This article is part of the themed issue ‘The origin, history and role of water in the evolution of the inner Solar System’.

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Section: Meteorites In Briefmentioning

confidence: 99%

The origin of inner Solar System water

Alexander¹

2017

Phil. Trans. R. Soc. A.

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“…However, if a D N metal/silicate of 15-20 is used, the calculated C N BE is 220-1600 ppm and the C N core is 660-5000 ppm. The high end of these C N BE values may be higher than the nitrogen concentration in any known chondrites (Krot et al, 2014), which thus indicates that a hybrid Rayleigh-equilibrium model may be more realistic for the segregation of nitrogen in Earth's core if D N metal/silicate is 15-20. Such a hybrid model (Rubie et al, 2015) assumes that during the early stages of accretion, the impacting objects are relatively small and their metal phase sequentially extracts nitrogen from the magma ocean according to a Rayleigh model; however, towards the end of accretion, large, differentiated planetesimals collide with the growing Earth.…”

Section: Resultsmentioning

confidence: 99%

Nitrogen isotope fractionation during terrestrial core-mantle separation

Li¹,

Marty²,

Shcheka³

et al. 2016

Geochem. Persp. Let.

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doi: 10.7185/geochemlet.1614The origin and evolution of the terrestrial nitrogen remains largely unresolved. In order to understand the potential influence of core-mantle separation on terrestrial nitrogen evolution, experiments were performed at 1.5 to 7.0 GPa and 1600 to 1800 °C to study nitrogen isotope fractionation between coexisting liquid Fe-rich metal and silicate melt. The results show that the metal/silicate partition coefficient of nitrogen D N metal/silicate ranges from 1 to 150 and the nitrogen isotope fractionation d15 N metal-silicate is −3.5 ± 1.7 ‰. Calculations show that the bulk Earth is more depleted in d 15 N than the present-day mantle, and that the presentday mantle d 15 N of −5 ‰ could be derived from an enstatite chondrite composition via terrestrial core-mantle separation, with or without the addition of carbonaceous chondrites. These results strongly support the notion that enstatite chondrites may be a main component from which the Earth formed and a main source of the terrestrial nitrogen. Moreover, in the deep reduced mantle, the Fe-rich metal phase may store most of the nitrogen, and partial melting of the coexisting silicates may generate oceanic island basalts (OIBs) with slightly positive d15 N values.

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“…However, in contrast to the μ 26 Mg*-μ 54 Cr systematics, the oxygen isotopic compositions of metal-rich carbonaceous chondrites and their chondrules are not anomalous. In a three-isotope oxygen diagram, these objects define compositions that approach the terrestrial fractionation line (33)(34)(35). In addition, the bulk oxygen isotopic composition of the primordial thermally unprocessed molecular cloud material is currently debated.…”

Section: Accretion Region Of Metal-rich Carbonaceous Chondritesmentioning

confidence: 99%

Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites

Kooten

Wielandt

Schiller

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

170

124

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The short-lived 26 Al radionuclide is thought to have been admixed into the initially 26 Al-poor protosolar molecular cloud before or contemporaneously with its collapse. Bulk inner Solar System reservoirs record positively correlated variability in mass-independent 54 Cr and 26 Mg*, the decay product of 26 Al. This correlation is interpreted as reflecting progressive thermal processing of infalling 26 Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last addition of stellar-derived 26 Al has not been identified yet but may be preserved in planetesimals that accreted in the outer Solar System. We show that metal-rich carbonaceous chondrites and their components have a unique isotopic signature extending from an inner Solar System composition toward a 26 Mg*-depleted and 54 Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived 26 Al. The 26 Mg* and 54 Cr compositions of bulk metal-rich chondrites require significant amounts (25-50%) of primordial molecular cloud matter in their precursor material. Given that such high fractions of primordial molecular cloud material are expected to survive only in the outer Solar System, we infer that, similarly to cometary bodies, metal-rich carbonaceous chondrites are samples of planetesimals that accreted beyond the orbits of the gas giants. The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants. molecular cloud | outer Solar System | metal-rich chondrites | isotopes | chondrite accretion regions L ow-mass stars like our Sun form by the gravitational collapse of the densest parts of molecular clouds comprising stellarderived dust and gas. Collapsing clouds swiftly evolve into deeply embedded protostars that rapidly accrete material from their surrounding envelopes via a protoplanetary disk (1), in which planetesimals and planetary embryos form over timescales of several million years (2). Chondritic meteorites (chondrites) are fragments of early-formed planetesimals that avoided melting and differentiation and, therefore, provide a record of the earliest evolutionary stages of the Sun and its protoplanetary disk. Most chondrites contain calcium−aluminum-rich inclusions (CAIs) and chondrules, which formed by high-temperature processes that included evaporation, condensation, and melting during short-lived heating events (3). CAIs represent the oldest dated solids and, thus, define the age of the Solar System at 4,567.3 ± 0.16 Ma (4). It is inferred that CAIs formed near the proto-Sun during a brief time interval (<0

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Classification of Meteorites and Their Genetic Relationships

Cited by 137 publications

References 377 publications

The origin of inner Solar System water

The origin of inner Solar System water

Nitrogen isotope fractionation during terrestrial core-mantle separation

Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites

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