The University of Arizona

An early I-Xe age for CB chondrite chondrule formation, and a re-evaluation of the closure age of Shallowater enstatite

J. D. GILMOUR, S. A. CROWTHER, A. BUSFIELD, G. HOLLAND, J. A. WHITBY

Abstract


The iodine-xenon system has been analyzed in samples of 7 chondrules from the CB chondrites Gujba and Hammadah al Hamra (HaH) 237. One sample from Gujba defined a high temperature iodine-xenon isochron corresponding to closure 1.87 ±  0.4 Ma before closure of Shallowater enstatite. Motivated by this result, we employ outlier rejection to re-evaluate the Shallowater age, leading to a modified value of 4562.3 ± 0.4 Ma (1σ). In this process, the datum obtained by combining our I-Xe age for Gujba with the literature Pb-Pb age is rejected as an outlier, indicating that in this sample the I-Xe system closed earlier than the accepted Pb-Pb age of chondrules from CB chondrites. The need for a formation environment distinct from that of chondrules from other meteorites is thus reduced.

Keywords


Xenon;Iodine-xenon ages;Chondrule formation;Chronology

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