Angrites, a small but diverse suite of ancient, silica-undersaturated volcanic-plutonic mafic meteorites, and the history of their parent asteroid

Keil, K.

doi:10.1016/j.chemer.2012.06.002

Cited by 127 publications

(114 citation statements)

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“…Therefore, the Si isotope composition of the Earth and the Moon may be consistent with Giant Impact models in which lunar material is derived primarily from the impactor. However, a homogenizing process may still be required to explain the Earth-Moon similarity for other isotope systems (e.g., O, Ti, W) (30), and it should be noted that angrites exhibit resolvable differences in O, Cr, and Ti isotope compositions compared with the Earth and Moon (15,32,33).…”

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confidence: 99%

“…Therefore, one core formation scenario that could explain the Si isotope composition of angrites is a planet-sized parent body that experienced metal-silicate equilibration at the base of a deep magma ocean, similar to conditions during terrestrial core formation. However, the early crystallization ages for angrites of ∼4.56 billion years ago argue for a small parent body that experienced early accretion, differentiation, and cooling only a few million years after CAI formation (15,16).…”

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confidence: 99%

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Silicon isotopes in angrites and volatile loss in planetesimals

Pringle

Moynier

Savage

et al. 2014

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

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Inner solar system bodies, including the Earth, Moon, and asteroids, are depleted in volatile elements relative to chondrites. Hypotheses for this volatile element depletion include incomplete condensation from the solar nebula and volatile loss during energetic impacts. These processes are expected to each produce characteristic stable isotope signatures. However, processes of planetary differentiation may also modify the isotopic composition of geochemical reservoirs. Angrites are rare meteorites that crystallized only a few million years after calcium-aluminum-rich inclusions and exhibit extreme depletions in volatile elements relative to chondrites, making them ideal samples with which to study volatile element depletion in the early solar system. Here we present high-precision Si isotope data that show angrites are enriched in the heavy isotopes of Si relative to chondritic meteorites by 50-100 ppm/amu. Silicon is sufficiently volatile such that it may be isotopically fractionated during incomplete condensation or evaporative mass loss, but theoretical calculations and experimental results also predict isotope fractionation under specific conditions of metal-silicate differentiation. We show that the Si isotope composition of angrites cannot be explained by any plausible core formation scenario, but rather reflects isotope fractionation during impact-induced evaporation. Our results indicate planetesimals initially formed from volatile-rich material and were subsequently depleted in volatile elements during accretion.volatiles | accretion | isotopes | angrites | silicon

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mentioning

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Silicon isotopes in angrites and volatile loss in planetesimals

Pringle

Moynier

Savage

et al. 2014

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

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“…We are interested in meteoritic samples that often span a very wide range in FeO contents compared to terrestrial mantle olivines (Criss, 2008 and references therein); for example, olivine phenocrysts in unequilibrated carbonaceous chondrites range from~Fa0 to Fa80 (e.g., Wasson and Rubin, 2003), olivine in martian meteorites is intermediate from~Fa20 to Fa50 (e.g., Mikouchi et al, 2001), olivine in HED meteorites is~Fa30 to Fa90 (Warren et al, 2014 and references therein), and olivine in angrites goes from~Fa10 to Fa86 (Keil, 2012). Previous studies of matrix effects in meteoritic olivine have come to different conclusions.…”

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Quantification of oxygen isotope SIMS matrix effects in olivine samples: Correlation with sputter rate

et al. 2017

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A B S T R A C TWe investigated the magnitude and reproducibility of instrumental mass-dependent fractionation of oxygen isotopes in secondary ion mass spectrometry (SIMS) analyses of olivine crystals of different major element chemistry (from Mg-rich to Fe-rich) in order to improve the accuracy of in-situ O-isotope measurements in geochemical/cosmochemical olivine samples. We found that oxygen isotope SIMS matrix effects are reproducible, and developed a model curve that can be used for correcting instrumental mass fractionation of olivine samples of intermediate chemical composition. The changes in instrumental mass fractionations were likely caused by differing Cs concentrations in the near surface regions of the samples due to different sample sputtering rates.

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“…Angrites, while being broadly basaltic in composition, are composed of augite with essentially pure anorthite, olivine and troilite, are critically understaturated with respect to SiO 2 content and have distinct oxygen isotopic compositions (Mittlefehldt et al, 1998;Greenwood et al, 2005;Keil, 2012). The aubrites are highly reduced pyroxenites that likely represent the melted surface of an enstatite-rich starting composition (Keil, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…Angrites have less SiO 2 and Na 2 O compared to eucrites (McCoy et al, 2006;Keil 2012 angrites is at trace element levels (average <0.03 %; Keil, 2012), while in basaltic and polymict eucrites the average value is 0.45 wt% (Mittlefelhdt, 2015). In addition, the molar Fe/Mn ratio in angrite pyroxenes falls between 90 to 130 (Papike et al 2003), while for eucrite pyroxenes ranges from 30 to 38.…”

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confidence: 99%

Bunburra Rockhole: Exploring the geology of a new differentiated asteroid

Benedix

Bland

Friedrich

et al. 2017

Geochimica et Cosmochimica Acta

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. We present the first Cr isotope results of this rock, which are also distinct from a majority of HEDs.Detailed computed tomographic scanning and back-scattered electron mapping do not indicate the presence of any other meteoritic contaminant (contamination is also unlikely based on trace element chemistry). We therefore conclude that Bunburra Rockhole represents a sample of a new differentiated asteroid, one that may have more variable oxygen isotopic compositions than 4 Vesta.The fact that Bunburra Rockhole chemistry falls on the eucrite trend perhaps suggests that multiple objects with basaltic crusts accreted in a similar region of the Solar System.

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Angrites, a small but diverse suite of ancient, silica-undersaturated volcanic-plutonic mafic meteorites, and the history of their parent asteroid

Cited by 127 publications

References 114 publications

Silicon isotopes in angrites and volatile loss in planetesimals

Silicon isotopes in angrites and volatile loss in planetesimals

Quantification of oxygen isotope SIMS matrix effects in olivine samples: Correlation with sputter rate

Bunburra Rockhole: Exploring the geology of a new differentiated asteroid

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