Isotopic anomalies of noble gases in meteorites and their origins 2. Separated minerals from Allende

Journal Article · Thu Feb 10 04:00:00 EST 1977 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB082i005p00779· OSTI ID:7330042

Lewis, R S; Gros, J; Anders, E

Eleven mineral fractions from the Allende C3 chondrite were analyzed for He, Ne, Ar, Kr, and Xe by mass spectrometry. As was shown previously (Lewis et al., 1975), most of the heavy noble gases are contained in an ill-defined HNO/sub 3/-soluble mineral fraction ('Q') comprising 0.04% of the meteorite. The remaining noble gases, of decidedly nonsolar isotopic composition, are contained in chromite (0.2%) and amorphous carbon (0.2%). They have virtually identical concentrations and isotopic compositions in the two minerals: /sup 20/Ne//sup 22/Ne=8.7 and /sup 36/Ar//sup 38/Ar=4.82. Xenon is enriched up to twofold in both heavy and light isotopes, while Kr is enriched only in heavy isotopes. The enrichment of the heavy isotopes is presumably due to fission, but the fission spectra derived depend critically on the assumed composition of the trapped component. The enrichment patterns of the light xenon isotopes differ slightly for chromite and carbon. Partial destruction of the minerals by chemical treatments gave no evidence for other gas-rich phases or other gas components and only marginal evidence for heterogeneities within the known gas-rich phases. Spinel has very-much-less-than0.1 the gas content of other phases. The chromite-carbon fractions contain 30--60% more spallogenic /sup 21/Ne than does the bulk meteorite, although they are deficient in target elements for the production of /sup 21/Ne. A possible explanation is recoil of /sup 21/Ne from adjacent Mg-rich phases. All of the available isotopic and chemical data suggest that chromite, carbon, and Q, and hence their associated gas components, are of local rather than extra-solar system origin. The excess heavy Kr and Xe isotopes may have been produced by fission of a superheavy element, while the remaining isotopic anomalies may be due to mass fractionation during trapping. The virtual identity of the noble gas components of chromite and carbon suggests that both minerals formed simultaneously.

• Research Organization: Enrico Fermi Institute and Department of Chemistry, University of Chicago, Chicago, Illinois 60637
• OSTI ID: 7330042
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 82:5; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640107* -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CARBON
CHEMICAL COMPOSITION
CHONDRITES
ELEMENTS
ISOTOPE RATIO
ISOTOPE SEPARATION
MASS SPECTROSCOPY
METEORITES
NONMETALS
RARE GASES
SEPARATION PROCESSES
SPECTROSCOPY
STONE METEORITES