Formation of the Bencubbin polymict meteoritic breccia

Gregory W. Kallemeyn, William V. Boynton, John Willis, John T. Wasson

Research output: Contribution to journalArticle

42 Citations (Scopus)

Abstract

The Bencubbin meteorite is a polymict breccia consisting of a host fraction of ~60% metal and ~40% ferromagnesian silicates and a selection of carbonaceous, ordinary and 'enstatite' chondritic clasts. Concentrations of 27 elements were determined by neutron activation in replicate samples of the host silicates and the ordinary and carbonaceous chondritic clasts; 12 elements were determined in the host metal. Compositional data for the ordinary chondrite clast indicate a classification of LL4 ± 1. Refractory element data for the carbonaceous chondrite clast indicate that it belongs to the CI-CM-CO clan; its volatile element abundances are intermediate between those of CM and CO chondrites. Abundances of nonvolatile elements in the silicate host are similar to those in the carbonaceous chondrite clast and in CM chondrites; the rare earths are unfractionated. We conclude that it is not achondritic as previously designated, but chondritic and that it is probably related to the CI-CM-CO clan; its volatile abundances are lower than those in CO chondrites. Oxygen isotope data are consistent with these classifications. Host metal in Bencubbin and in the closely related Weatherford meteorite has low abundances of moderately volatile siderophiles; among iron meteorite groups its nearest relative is group IIIF. We suggest that Bencubbin and Weatherford formed as a result of an impact event on a carbonaceous chondrite regolith. The impact generated an 'instant magma' that trapped and surrounded regolithic clasts to form the polymict breccia. The parent of this 'magma' was probably the regolith itself, perhaps mainly consisting of the so-called 'enstatite' chondrite materials. Accretion of such a variety of materials to a small parent body was probably only possible in the asteroid belt.

Original languageEnglish (US)
Pages (from-to)507-515
Number of pages9
JournalGeochimica et Cosmochimica Acta
Volume42
Issue number5
DOIs
StatePublished - 1978
Externally publishedYes

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Carbon Monoxide
Meteorites
breccia
Silicates
clast
carbonaceous chondrite
Metals
chondrite
Oxygen Isotopes
silicate
regolith
Asteroids
meteorite
metal
magma
Refractory materials
Rare earths
enstatite chondrite
volatile element
iron meteorite

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Formation of the Bencubbin polymict meteoritic breccia. / Kallemeyn, Gregory W.; Boynton, William V.; Willis, John; Wasson, John T.

In: Geochimica et Cosmochimica Acta, Vol. 42, No. 5, 1978, p. 507-515.

Research output: Contribution to journalArticle

Kallemeyn, Gregory W. ; Boynton, William V. ; Willis, John ; Wasson, John T. / Formation of the Bencubbin polymict meteoritic breccia. In: Geochimica et Cosmochimica Acta. 1978 ; Vol. 42, No. 5. pp. 507-515.
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