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

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. © The Meteoritical Society, 2009.