| In order to attain a better understanding of the Earth's origin and its relationship to extraterrestrial materials, noble gas mass spectrometric analysis was carried out with a rare terrestrial Ni-Fe alloy, josephinite, and a specimen of the coarse octahedrite, Canyon Diablo.; Isotopic abundances measured in josephinite display a pattern analogous to those of iron meteorites containing little spallogenic noble gas. This information has lead us to suggest that either the Ni-Fe alloy has effectively survived the metamorphic processes that have homogenized nearly all of Earth's upper crustal material or alternately, the stone could be of more "recent" meteoritic origin, having been mechanically reprocessed in Earth's crust. Either view could adequately explain the primordial type ('3)He and excess radiogenic ('129)Xe present in josephinite.; If iron meteorites condensed in a region common with the iron that formed the Earth's core, then identification of a primordial rare gas component in iron meteorites would be valuable in deciphering the origin and evolution of Earth and its atmosphere.; In pursuit of the trapped component in iron meteorites, a novel system was developed for the extraction of noble gases from Canyon Diablo having the advantages of (i) convenient analysis of large metallic samples which is significant because of the low concentrations of gases in iron meteorites and (ii) effectively eliminating the release of terrestrial contamination due to the fluxing of the crucible during the melt phase. The results obtained show no clear evidence for a trapped component of Helium, Neon or Argon, but instead that, in our sample, they are derived from spallation reactions, perhaps before meteorite assembly. An upper limit for the trapped ('40)Ar/('36)Ar value was measured as 0.39 (+OR-) 0.04. Analyses of the heavy noble gases indicate a trapped component resembling type-Y, terrestrial-like, gases and not type-X, as seen in chondritic material. Ratios measured for ('129)Xe/('131)Xe suggest the presence of products of neutron capture on Te requiring neutrons of E > 0.4 eV. In addition, the amount of excess ('136)Xe observed sets an upper limit on the number of atoms of siderophilic superheavy elements that could have been trapped in Canyon Diablo at 6 x 10('6) atoms/g. |
