The I-Xe chronometer

129Xe, from the decay of the now-extinct 16.7 Ma129I, accumulates in iodine-bearing sites and since most iodine host phases are secondary, the I-Xe system is typically a chronometer for post-formational processes. The validity of the I-Xe chronometer is confirmed by comparison with Pb-Pb ages on pho...

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Bibliographic Details
Published in:Academy Proceedings in Earth and Planetary Sciences 1998-12, Vol.107 (4), p.413-423
Main Authors: HOHENBERG, C. M, BRAZZLE, R. H, PRAVDIVTSEVA, O. V, MESHIK, A. P
Format: Article
Language:English
Subjects:
Age
Apatite
Chondrites
Chronometers
Cosmochemistry. Extraterrestrial geology
Earth sciences
Earth, ocean, space
Exact sciences and technology
Feldspars
Geochronology
Iodine
Irradiation
Isotope geochemistry. Geochronology
Lead
Measuring instruments
Meteorites. Tectites. Impactites
Mineralization
Phosphates
Radiometric dating
Xenon 129
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Summary:129Xe, from the decay of the now-extinct 16.7 Ma129I, accumulates in iodine-bearing sites and since most iodine host phases are secondary, the I-Xe system is typically a chronometer for post-formational processes. The validity of the I-Xe chronometer is confirmed by comparison with Pb-Pb ages on phosphate and feldspar separates from twelve meteorites. Phosphate separates are found to be concordant with Pb-Pb for all six samples in which useful I-Xe data were obtained. Feldspar is a better iodine host than apatite in H chondrites, typically providing good I-Xe isochrons. These too are concordant with the Pb-Pb ages of the corresponding phosphates for five out of six feldspar separates. The exception is Allegan whose feldspar yields one of the oldest I-Xe ages observed, similar to those for CI and CM magnetites. We attribute this to a more primary mineralization, predating the secondary phosphate from which the comparison Pb-Pb age was obtained. Absolute I-Xe ages, found using the reported Pb-Pb age of Acapulco phosphate provide an absolute I-Xe age of 4.566 ± 0.002 Ga for both Shallowater and Bjurböle irradiation standards. This allows relative I-Xe ages to be interpreted in the context of absolute ages.
ISSN:0253-4126
0973-774X
DOI:10.1007/BF02841607