I-Xe dating: From adolescence to maturity |
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Authors: | C.M. Hohenberg O.V. Pravdivtseva |
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Affiliation: | Department of Physics and McDonnell Center for Space Sciences, Washington University, CB1105, One Brookings Drive, St. Louis, MO 63130, USA |
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Abstract: | The I-Xe chronometer is based upon decay of now-extinct 129I where the ratio of accumulated daughter 129Xe to stable 127I reflects the iodine isotopic ratio at closure of the host mineral. Since none of the parent remains, I-Xe is by nature a relative chronometer but, when referenced by a standard mineral of known age, the I-Xe system becomes an absolute chronometer reflecting true closure times. Most iodine hosts are secondary minerals so the I-Xe system is unique in providing details of post-formational chronometry not readily available with other chronometers. The short half-life of 129I gives it exceptional precision. However, the secondary nature of iodine host minerals, combined with the inherent precision of I-Xe, were responsible for a large database of “whole-rock” I-Xe ages that were not easily interpreted. As this problem evolved historically, doubts were cast upon the viability of the I-Xe system as a chronometer which persisted until it was tested against other chronometers in single-mineral systems. Properly calibrated, absolute I-Xe ages reflect the true closure time of the host minerals, and sequences of closure times in different hosts provide cooling rates for the parent object. |
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Keywords: | I-Xe chronometer Meteorite evolution Cooling rates |
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