Physics
Scientific paper
Aug 1970
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1970gecoa..34..873f&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 34, Issue 8, pp.873-881
Physics
9
Scientific paper
The rare gases and the K and U were measured in whole-rock and chondrule samples of the Allende meteorite, a type-3 carbonaceous chondrite. There is an enrichment of the He 4 , Ar 40 , K, and U, and a depletion of the primordial gas in the chondrules. The U, Th-He 4 age of the chondrules is (4.2 ± 0.2) × 10 9 years , and the K-Ar 40 age of the chondrules is (4.44 ± 0.14) × 10 9 years. The chondrules are gas tight and old. With a maximum but reasonable correction for primordial He 4 , the U, Th-He 4 age of the whole rock is (3.4 ± 0.2) × 10 9 years. The K-Ar 40 age of the whole rock is 4.55 × 10 9 years, but this determination is less reliable than that for the chondrules because of the primordial Ar. The chondrules are enriched in excess Xe 129 and depleted in primordial Xe. The Xe 129 / Xe 132 ratios and the Xe 129 excess in the chondrules are exceptionally high. Two troilite-bearing chondrules have a Xe 129 / Xe 132 ratio of 92, which is the highest ever observed, and a Xe 129 excess of 4.1 × 10 -9 cc / g , which is also very large. For chondrules, which contain little primordial Xe, the I contents can be obtained from the Xe 128 excesses, the Co 60 content, and the exposure age. In spite of the high Xe 129 excesses, the I contents of the chondrules are not very high, ranging from 59 to 135 ppb. The ( Xe 129 / I max ) ratios range from 0.42 to 1.39 × 10 -4 . Some chondrules of Allende may predate slightly the I-Xe 129 isochronism in chondrules even with no Xe 129 loss.
Defelice J. J.
Fireman Edward L.
Norton Elinor
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