Clues to the origin of sulfide minerals in CI chondrites
Abstract
The dominant sulfide in CI carbonaceous chondrites is an Fe-deficient pyrrhotite containing about 1% Ni. Alais, Ivuna and Orgueil also contain minor cubanite, CuFe 2S 3, and Alais minor pentlandite, (Fe,Ni) 9S 8. All pyrrhotites contain 39.4 ± 0.1% S; Ni contents range from 0.7 to 1.3%. The phase diagrams reveal no temperature at which the observed pentlandite-pyrrhotite assemblage is at equilibrium. Similarly, the pyrrhotite compositions alone are inconsistent with equilibrium formation from a gas of solar composition. In Xe from high-purity submilligram Orgueil pyrrhotite separates, the ratios 129Xe/ 132Xe are not significantly larger than those in trapped meteoritic Xe. The lack of positive evidence for extinct 129I in pyrrhotite does not permit any inferences regarding cooling rates in the early solar nebula. We conclude that sulfides in CI chondrites cannot be nebular condensates formed under equilibrium conditions. Argon isotopic abundances reveal the presence of significant spallation and trapped gas components in Orgueil pyrrhotite. The Orgueil exposure age is calculated to be ≳ 10m.y.
- Publication:
-
Earth and Planetary Science Letters
- Pub Date:
- June 1979
- DOI:
- 10.1016/0012-821X(79)90091-8
- Bibcode:
- 1979E&PSL..43..359K
- Keywords:
-
- Abundance;
- Carbonaceous Chondrites;
- Chemical Composition;
- Minerals;
- Sulfides;
- Electron Microscopy;
- Mineralogy;
- Phase Diagrams;
- Planetary Evolution;
- Tables (Data);
- Xenon Isotopes;
- CHONDRITES;
- METEORITES;
- C1 CHONDRITES;
- SULFIDES;
- CARBONACEOUS CHONDRITES;
- MINERALOGY;
- ALAIS METEORITE;
- ORGUEIL METEORITE;
- CHEMICAL COMPOSITION;
- XENON;
- MICROPROBE ANALYSIS;
- KRYPTON;
- ARGON;
- ISOTOPES;
- ORIGIN;
- PHASES;
- PYRRHOTITE;
- ABUNDANCE;
- ISOTOPIC RATIOS;
- PENTLANDITE;
- IVUNA METEORITE