129I-129Xe Dating of Chondrites
The 129I-129Xe formation intervals of the Bjurböle, Bruderheim, Bruderheim chondrules, Renazzo, and the dark and light regions of Pantar are calculated by comparing the amount of radiogenic 129Xe associated with iodine in each thermal fraction. Unlike the sharp 129I-129Xe isochronism reported for the high-temperature minerals, the lower-temperature minerals show progressively longer formation intervals. A plot of formation times versus extraction temperatures yields an apparent 129I-129Xe cooling rate for these chondrites. Below 800°C all of the chondrites except Renazzo and Pantar Dark display 129I-129Xe cooling rates of 5-9°C per million years. Pantar Dark and Renazzo appear to have cooled rapidly to 600° and 400°C, respectively. An inversion of the I-Xe correlation of chondrites is noted in the slow temperature minerals of Shallowater. This enstatite achondrite displays a maximum 129I-129Xe cooling rate of 2.4°C per million years.
O. Manuel et al., "129I-129Xe Dating of Chondrites," Icarus, vol. 9, pp. 291-304, Academic Press Inc., Feb 1968.
The definitive version is available at http://dx.doi.org/10.1016/0019-1035(68)90021-3
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