Other
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....11414b&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #11414
Other
Scientific paper
Angrites are a particularly interesting group of differentiated meteorites with only seven members at present. They are mafic igneous rocks not showing any signatures of brecciation, impact and shock metamorphism. This points to an origin from a small parent body or a region of the solar system protected against severe collisions. Angrites are among the oldest objects in the solar system showing no later disturbance and almost instantaneous cooling as inferred from various chronometers, fission track analyses and the presence of fission Xe originating from the now extinct 244Pu (T1/2 = 82 Ma). Crystallization ages of 8--18 Ma after Allende CAIs have been reported, indicating that the angrite parent body must have accreted and differentiated rapidly -- possibly from a chondritic precursor parent body. The most recent find, D'Orbigny, found 1979 in Argentina, is a unique angrite containing significant amounts of ancient glass. In a first analysis of a D'Orbigny bulk sample, we determined a cosmic-ray exposure age of 12.3±0.9 Ma, which is different from those determined for the other five angrites, suggesting that five impact events have occurred. In addition, we detected fissiogenic Xe, which largely originate from 244Pu, reflecting once more their early formation. D'Orbigny glass has an unreasonably high apparent Pb-Pb age of 4.7 Ma, indicating some excess 207Pb contributions e.g. from 235Curium (T1/2 = 2.4h). To further assess this important observation, we will analyze the noble gases including Xe in an aliquot of D'Orbigny glass. The low abundances of trapped Xe should allow us to determine a precise 244Pu--136Xe age as well as the fissiogenic Xe composition.
Busemann Henner
Eugster Otto
Jagoutz Emil
Lorenzetti Silvio
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