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Formation of metal and silicate globules in Gujba: a new Bencubbin-like meteorite fall
- Source :
- Geochimica et Cosmochimica Acta. 67:3283-3298
- Publication Year :
- 2003
- Publisher :
- Elsevier BV, 2003.
-
Abstract
- Gujba is a coarse-grained meteorite fall composed of 41 vol% large kamacite globules, 20 vol% large light-colored silicate globules with cryptocrystalline, barred pyroxene and barred olivine textures, 39 vol% dark-colored, silicate-rich matrix, and rare refractory inclusions. Gujba resembles Bencubbin and Weatherford in texture, oxygen-isotopic composition and in having high bulk delta N-15 values (approximately +685%0). The He-3 cosmic-ray exposure age of Gujba (26 +/- 7 Ma) is essentially identical to that of Bencubbin, suggesting that they were both reduced to meter-size fragments in the same parent-body collision. The Gujba metal globules exhibit metal-troilite quench textures and vary in their abundances of troilite and volatile siderophile elements. We suggest that the metal globules formed as liquid droplets either via condensation in an impact-generated vapor plume or by evaporation of preexisting metal particles in a plume. The lower the abundance of volatile elements in the metal globules, the higher the globule quench temperature. We infer that the large silicate globules also formed from completely molten droplets; their low volatile-element abundances indicate that they also formed at high temperatures, probably by processes analogous to those that formed the metal globules. The coarse-grained Bencubbin-Weatherford-Gujba meteorites may represent a depositional component from the vapor cloud enriched in coarse and dense particles. A second class of Bencubbin-like meteorites (represented by Hammadah a1 Hamra 237 and QUE 94411) may be a finer fraction derived from the same vapor cloud
Details
- ISSN :
- 00167037
- Volume :
- 67
- Database :
- OpenAIRE
- Journal :
- Geochimica et Cosmochimica Acta
- Accession number :
- edsair.doi...........74fc3bbed50071291c0de3dd26bec1be