Foreign inclusions in stony meteorites—I. Carbonaceous chondritic xenoliths in the Kapoeta howardite

Wilkening, L. L.

doi:10.1016/0016-7037(73)90152-x

Cited by 70 publications

(35 citation statements)

References 18 publications

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“…Very small inclusions rich in light or heavy isotopes of zinc could significantly alter the isotopic composition of these small chips. For example, carbonaceous chondrite xenoliths have been reported in Kapoeta (Wilkening, 1973) and Pasamonte (Metzler et al, 1995) and could alter the measured Zn ratios; these may have been introduced by an impactor. CM-and CR-like clasts, ranging in size from 25 lm to 5 mm, have been reported in HEDs by Buchanan et al (2009); their wide distribution in the breccias suggested efficient energetic mixing of impactors as the most likely source.…”

Section: Isotopic Variation Within An Individual Meteoritementioning

confidence: 99%

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: 99%

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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“…MacPherson et al (1993) described one such clast in the Magombedze H3-5 chondrite breccia. Relatively unshocked CM clasts are also present in various HED breccias (e.g., Wilkening 1973;Bunch et al 1979; Table 2 of determined by broad-beam electron microprobe techniques; they also reported 0.12 wt% TiO 2 , 0.22 wt% P 2 O 5 and 1.2 wt% Ni.The composition of the rim determined in this study was derived from electron-microprobe analysis using a 6 µm diameter beam and combining the analyses of two 100 × 100 µm grids located on different sides of the PV3 clast. CM2 data from Table 4 was used in conjunction with H-chondrite data from Jarosewich (1990).…”

Section: Low-velocity Accretion Of CM Projectiles To H-chondrite and mentioning

confidence: 99%

“…CM clasts are also the most abundant foreign materials in HED breccias (Wilkening 1973;Bunch et al 1979; Kozul and Hewins 1988;Pun 1992;Zolensky et al 1992;Buchanan et al 1993;Brearley 1993;Zolensky et al 1996;Gounelle et al 2003), constituting ~5 vol% of the Kapoeta howardite (Zolensky et al 1996).…”

Section: Introductionmentioning

confidence: 99%

On the origin of shocked and unshocked CM clasts in H‐chondrite regolith breccias

Rubin

Bottke

2009

Meteorit & Planetary Scien

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Abstract--CM chondrite clasts that have experienced different degrees of aqueous alteration occur in H-chondrite and HED meteorite breccias. Many clasts are fragments of essentially unshocked CM projectiles that accreted at low relative velocities to the regoliths of these parent bodies. A few clasts were heated and dehydrated upon impact; these objects most likely accreted at higher relative velocities. We examined three clasts and explored alternative scenarios for their formation. In the first scenario, we assumed that the H and HED parent bodies had diameters of a few hundred kilometers, so that their high escape velocities would effectively prevent soft landings of small CM projectiles. This would imply that weakly shocked CM clasts formed on asteroidal fragments (family members) associated with the H and HED parent bodies. In the second scenario, we assumed that weakly shocked CM clasts were spall products ejected at low velocities from larger CM projectiles when they slammed into the H and HED parent bodies. In both cases, if most CM clasts turn out to have ancient ages (e.g., ~3.4-4

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“…This is generally attributed to repeated impact processing on their parent bodies (e.g., Scott and Taylor, 1982;Scott et al, 1989Scott et al, , 1992Stoffler et al, 1991;Metzler et al, 1992;Bogard, 1995). Many chondritic breccias contain foreign inclusions (e.g., Wilkening, 1973Wilkening, , 1977Wilkening, , 1978Wilkening and Clayton, 1974;Leitch and Grossman, 1977;Anders, 1978;Wasson and Wetherill, 1979;Bunch and Rajan, 1988;Lipschutz ef al., 1989). Anders (1 978), Wasson and Wetherill (1979), and Lipschutz et al (1989) summarize the findings of foreign clasts in chondritic meteorites and reach the conclusion that >6O% of the clasts are related to carbonaceous material (mostly CI-and CM-related), whereas clasts described as OC-like are much less abundant.…”

Section: Foreign Clasts In Chondritic Brecciasmentioning

confidence: 99%

Evidence for the insignificance of ordinary chondritic material in the asteroid belt

Meibom

Clark

1999

Meteorit & Planetary Scien

101

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We review the meteoritical and astronomical literature to answer the question: What is the evidence for the importance of ordinary chondritic material to the composition of the asteroid belt? From the meteoritical literature, we find that currently (1) our meteorite collections sample at least 135 different asteroids; (2) out of 25+ chondritic meteorite parent bodies, 3 are (by definition) ordinary chondritic; (3) out of 14 chondritic grouplets and unique chondrites, 1 1 are affiliated with a carbonaceous groupklan of chondrites; (4) out of 24 differentiated groups of meteorites, only the IIE iron meteorites clearly formed from ordinary chondritic precursor material; (5) out of 12 differentiated grouplets and unique differentiated meteorites, 8 seem to have had carbonaceous chondritic precursors; (6) a high frequency of carbonaceous clasts in ordinary chondritic breccias suggests that ordinary chondrites have been embedded in a swarm of carbonaceous material. The rare occurrence (only one example) of ordinary chondritic clasts in carbonaceous chondritic breccias indicates that ordinary chondritic material has not been widespread in the asteroid belt; (7) cosmic spherules, micrometeorites, and stratospheric interplanetary dust particles-believed to represent a less biased sampling of asteroidal material-show that only a very small fraction (less than-1%) of asteroidal dust has an ordinary chondritic composition. From the astronomical literature, we find that currently (8) spectroscopic surveys of the main asteroid belt are finding more and more nonordinary chondritic primitive material in the inner main belt; (9) the increase in spectroscopic data has increased the inferred mineralogical diversity of main belt asteroids; and (10) no ordinary chondritic asteroids have been directly observed in the main belt. These lines of evidence strongly suggest a scenario in which ordinary chondritic asteroids were never abundant in the main belt. The S-type asteroids may currently be primarily differentiated, but the precursor material is more likely to have been carbonaceous chondritic, not ordinary chondritic. Historically, carbonaceous material could have dominated the entire main belt. This could explain the presence in the inner main belt of asteroids linked to the primitive carbonaceous chondrites, and the absence of asteroids linked to the ordinary chondrites. The implications of this scenario for the asteroid heating mechanism(s) are briefly discussed.

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Foreign inclusions in stony meteorites—I. Carbonaceous chondritic xenoliths in the Kapoeta howardite

Cited by 70 publications

References 18 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

On the origin of shocked and unshocked CM clasts in H‐chondrite regolith breccias

Evidence for the insignificance of ordinary chondritic material in the asteroid belt

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