The I-Xe chronometer

• 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
• ISSN: 0253-4126; 0973-774X
• DOI: 10.1007/BF02841607

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.