Oxygen isotope evidence for rapid mixing of the HED meteorite parent body

Wiechert, Uwe; Halliday, Alex N.; Palme, H.; Rumble, Douglas

doi:10.1016/s0012-821x(04)00090-1

Cited by 142 publications

(188 citation statements)

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“…Ghosh and McSween (1998) proposed a model for Vesta of a melted center with an unmelted outer shell which would be expected to retain some isotopic heterogeneity. This idea was further sup- ported by Wiechert et al (2004), who reported heterogeneous oxygen isotope measurements in HEDs consistent with a very rapid early history of large-scale, incomplete mixing on Vesta. The Zn isotopic heterogeneity found in our study fits with both of these models if the Zn was initially isotopically heterogeneous in Vesta or if some isotopic fractionation occurred early in Vesta history.…”

Section: Isotopic Variation Within An Individual Meteoritementioning

confidence: 79%

Zinc isotopes in HEDs: Clues to the formation of 4-Vesta, and the unique composition of Pecora Escarpment 82502

Paniello¹,

Moynier²,

Beck

et al. 2012

Geochimica et Cosmochimica Acta

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The d 66 Zn (permil deviation of the 66 Zn/ 64 Zn ratio from a terrestrial standard) values for a suite of 20 non-Antarctic HED (howardite-eucrite-diogenite) meteorites and one mesosiderite, and for eight Antarctic eucrites and diogenites, were measured in order to determine the role of volatization in the formation of their presumed parent body, the asteroid 4-Vesta. The 20 non-Antarctic HEDs had d 66 Zn values that ranged from À2.0& to +1.67&, with a mean value of À0.01 ± 0.39& (2 se); this range likely represents a small-scale heterogeneity due to brecciation induced by multiple impacts. The non-Antarctic eucrites (d 66 Zn = +0.00 ± 0.58& (2 se), n = 12) were isotopically the same as the diogenites (d 66 Zn = À0.31 ± 0.80& (2 se), n = 4), and the howardites (d 66 Zn = +0.26 ± 0.37& (2 se), n = 4). On average, non-Antarctic eucrite falls were isotopically heavier (+0.50&) than non-Antarctic finds (À1.00&). The Antarctic finds studied were all unbrecciated samples, and they were significantly heavier than the non-Antarctic samples with a d 66 Zn range of +1.63& to +6.22& for four eucrites (mean, +4.32&) and +0.94& to +1.60& for three diogenites (mean + 1.23&), excluding one anomalous sample, while their Zn concentration is significantly lower than the brecciated samples. These data suggest that the unbrecciated eucrites probably represent the eucritic crust shortly after differentiation and cooling of the parent asteroid, at which time volatization of lighter zinc isotopes led to an isotopically heavy crust. Early impact events caused the ejection of these unbrecciated meteorites, which were subsequently spared from brecciation caused by multiple additional impacts on the much larger Vesta. The range of d 66 Zn values and Zn concentration for the brecciated HEDs in this study supports a major contribution to the Vestan surface by chondritic impactors (À1.30 < d 66 Zn < +0.76& for ordinary and carbonaceous chondrites). The anomalous eucrite PCA 82502 (d 66 Zn = À7.75&) is significantly isotopically lighter than the other HEDs and is the natural sample with the lightest Zn isotopic composition reported in the solar system to date. This meteorite most likely originated from a distinct parent body.

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Section: Isotopic Variation Within An Individual Meteoritementioning

confidence: 79%

Zinc isotopes in HEDs: Clues to the formation of 4-Vesta, and the unique composition of Pecora Escarpment 82502

Paniello¹,

Moynier²,

Beck

et al. 2012

Geochimica et Cosmochimica Acta

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“…Does this conclusion hold for other asteroid vesicular basalts or if vesicular eucrites did not originate on Vesta? Recent work found that Ibitira differed in Δ 17 O [30] and pyroxene Fe/Mn ratio [31] from other eucrites and may sample a separate parent body. Additional basaltic asteroids have also been identified [32], including 17 Thetis, whose average semimajor axis at 2.47 AU is close to the meteorite-delivering 3:1 resonance in the asteroid belt.…”

Section: Discussionmentioning

confidence: 99%

Formation of vesicles in asteroidal basaltic meteorites

McCoy

Ketcham

Wilson

et al. 2006

Earth and Planetary Science Letters

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“…(They did not analyze Ibitira, Caldera, and ALHA78132.) Contrary to Wiechert et al (2004), they attributed Pasamonte's anomalous oxygen isotopic composition to contamination by an ordinary or CI carbonaceous chondrite projectile. More importantly, they inferred from the homogeneity of the 17 other meteorites that Vesta had been isotopically homogenized and had therefore probably melted to form a magma ocean, favoring an origin for eucrites and diogenites as residual liquids and cumulates.…”

Section: Introductionmentioning

confidence: 91%

“…However, the two groups differed in their interpretation of the data for the few eucrites that were found to have aberrant oxygen isotopic compositions. Wiechert et al (2004), who analyzed 26 eucrites and diogenites, concluded that four of the eucrites, Ibitira, Pasamonte, Caldera and ALHA78132, had significantly higher ∆ 17 O values, which deviated by 13σ, 3σ, 2.5σ and 2σ, respectively from the mean value for the other eucrites and diogenites. From this they inferred that Vesta retained some primary isotopic heterogeneity, consistent with the formation of the basaltic eucrites by partial melting.…”

Section: Introductionmentioning

confidence: 99%

“…Two groups, Wiechert et al (2004) and Greenwood et al (2005), have used infrared laserassisted fluorination to analyze the oxygen isotopic compositions of the HED achondrites to much higher precision than had been achieved by Clayton and Mayeda (1996) using the externally heated Ni-rod bomb technique. Both groups agreed that most HEDs have indistinguishable ∆ 17 O values (see section 3 for a definition of this term), consistent with an origin from a single homogeneous source, and that some howardites have significantly lower ∆ 17 O values because of contamination by a few vol.…”

Section: Introductionmentioning

confidence: 99%

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Oxygen isotopic constraints on the origin and parent bodies of eucrites, diogenites, and howardites

Scott

Greenwood

Franchi

et al. 2009

Geochimica et Cosmochimica Acta

149

177

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A few eucrites have anomalous oxygen isotopic compositions. To help understand their origin and identify additional samples, we have analyzed the oxygen isotopic compositions of 18 eucrites and four diogenites. Except for five eucrites, these meteorites have ∆ 17 O values that lie within 2σ of their mean value viz., -0.242±0.016‰, consistent with igneous isotopic homogenization of Vesta. The five exceptional eucrites-NWA 1240, Pasamonte (both clast and matrix samples), PCA 91007, A-881394, and Ibitira-have ∆ 17 O values that lie respectively 4σ, 5σ, 5σ, 15σ, and 21σ away from this mean value. NWA 1240 has a δ 18 O value that is 5σ below the mean eucrite value. Four of the five outliers are unbrecciated and unshocked basaltic eucrites, like NWA 011, the first eucrite found to have an anomalous oxygen isotopic composition. The fifth outlier, Pasamonte, is composed almost entirely of unequilibrated basaltic clasts. Published chemical data for the six eucrites with anomalous oxygen isotopic compositions (including NWA 011) exclude contamination by chondritic projectiles as a source of the oxygen anomalies. Only NWA 011 has an anomalous Fe/Mn ratio, but several anomalous eucrites have exceptional Na, Ti, or Cr concentrations. We infer that the six anomalous eucrites are probably derived from five distinct Vesta-like parent bodies (Pasamonte and PCA 91007 could come from one body). These anomalous eucrites, like many unbrecciated eucrites from Vesta, are probably deficient in brecciation and shock effects because they were sequestered in small asteroids (~10 km diameter) during the Late Heavy Bombardment following ejection from Vesta-like bodies. The preservation of Vesta's crust and the lack of deeply buried samples from the hypothesized Vestalike bodies are consistent with the removal of these bodies from the asteroid belt by gravitational perturbations from planets and protoplanets, rather than by collisonal grinding.

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Oxygen isotope evidence for rapid mixing of the HED meteorite parent body

Cited by 142 publications

References 32 publications

Zinc isotopes in HEDs: Clues to the formation of 4-Vesta, and the unique composition of Pecora Escarpment 82502

Zinc isotopes in HEDs: Clues to the formation of 4-Vesta, and the unique composition of Pecora Escarpment 82502

Formation of vesicles in asteroidal basaltic meteorites

Oxygen isotopic constraints on the origin and parent bodies of eucrites, diogenites, and howardites

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