Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.498m&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 498
Astronomy and Astrophysics
Astronomy
Astronomical Models, Inclusions, Iron Meteorites, Meteoritic Composition, Xenon Isotopes, Anomalies, Phase Transformations, Rare Gases, Silicates, Temperature Effects
Scientific paper
The IAB and IIICD groups of iron meteorites contain silicate inclusions of nearly unequilbrated chondritic type, and models have been proposed to explain the origin of these groups, which are different from the magmatic group of iron meteorites. We analyzed acid residues of IAB Campo del Cielo (El Taco) for their noble gases; the Xe isotopic composition in the C phase of these residues is discussed. About 12-15 g of the meteorite, which also contained parts of several macro inclusions were treated with 4M HNO3 and the residue separated into different parts according to their density. These separates were analyzed for noble gases following standard mass spectrometric procedures. In the major silicates there are correlated excesses at Kr-80 and Kr-82 due to (n, gamma) capture reactions on Br-79 and Br-81 respectively. For the Xe isotopes, there are correlated excesses at Xe-128 and Xe-129 showing that these inclusions have incorporated live I-129 in them. The Xe isotopic composition obtained in the graphite phase of these inclusions is discussed. The measured Xe amounts in these graphic samples are in the range of 10-20 x 10-10/cu cm/STP, which is much larger than those in the silicates. The low-temperature runs of the stepwise heating experiments have a Xe isotopic composition similar to atmospheric, probably due to adsorption. The temperature steps above 1000 C, where the contribution from atmospheric adsorbed Xe should be minimal, have isotopic compositions distinctly different from the low-temperature steps and are significantly different from the terrestrial values. The heavier Xe isotopes are clearly enhanced by about 2.5% per amu relative to solar Xe, which is the same tendency, although not quite as pronounced, as is observed for terrestrial Xe.
Begemann Friedrich
Mathew K. J.
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