XENON AND NEON FROM ACID-RESISTANT RESIDUES OF INMAN AND TIESCHITZ

Xenon and neon from highly oxidized acid residues of the unequilibrated ordinary chondrites Inman and Tieschitz are dominated by Xe-HL and Ne-A2, although Xe-S is also present in the oxidized Inman residue. The isotopic composition of Xe released at lower temperatures from the Inman residues most likely represents mixtures of trapped Xe and Xe-HL at all isotopes except Xe-129 and Xe-128 where significant and correlated excesses are observed. These are clearly both derived from I, the former from decay of extinct I-129 and the latter from neutron capture by I-127, requiring a thermal equivalent fluence of approximately 3 x 10(17) n/cm2, or 2-3 x 10(16) n/cm2 in the resonance region, confirmed by artificial irradiation of an aliquot. The I-129/I-127 ratio at Xe closure is about 1 x 10(-4), similar to the canonical meteoritic value which, given the short half-life of I-129, suggests closure times similar to other meteorites and subsequent irradiation within the solar system. In Tieschitz there may be some evidence for separation of Xe-L from Xe-H as would be expected if the neutron-deficient end of the Xe-HL spectrum is not produced by the same processes as the neutron-rich end and is not completely homogenized with it. Ne-E(H) is measured in oxidized residues from both of these meteorites, but no evidence is found for Ne-E(L). Correlations are observed between cosmogenic Ne-21 and Ne-E(H) in the higher temperature fractions of both Inman and Tieschitz. These may not be due to a common host phase, but could instead be due to high temperature reactions between spinel and SiC.