Composition and mineralogy of refractory-metal-rich assemblages from a Ca,Al-rich inclusion in the Allende meteorite

Journal Article · Thu Oct 01 00:00:00 EDT 1987 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(87)90153-0· OSTI ID:7253953

Bischoff, A ^[1]; Palme, H ^[2]

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1. Institut fuer Planetologie, Muenster (West Germany) Institut fuer Mineralogie, Muenster (West Germany)
2. Max-Planck-Institut fuer Chemie, Mainz (West Germany)

The authors have separated four refractory metal-rich samples (10 {mu}g to 190 {mu}g) from a single Ca,Al-inclusion of the Allende meteorite. Chemical analyses were performed by INAA. From the analyzed samples polished sections were prepared. Mineral phases from six large Fremdlinge and the surrounding inclusion were analyzed by EDS. Three of the four separated samples have variable absolute but similar relative abundances of refractory metals. The pattern is controlled by volatility. The most refractory metals W, Os, and Re are enriched relative to the less refractory metals Ir, Mo, Ru, and Pt. This pattern can be reproduced by condensation calculations. A metal alloy in equilibrium with a gas of solar composition at a temperature of 1672 K, a pressure of 10{sup {minus}3} atm, and an H{sub 2}O/H{sub 2}-ratio of 5 {times} 10{sup {minus}3} would have the same abundance pattern. All six Fremdlinge have similar texture and mineralogy. They are composed of Ni-rich metal containing 2-9% Ir, surrounded by a fine-grained intergrowth of V-magnetite and FeS. The Ni-Fe metal poikilitically encloses tiny Os-particles, domains of a W- and Mo-rich solid solution (Ca(W,Mo)O{sub 4}) and V-magnetite. Based on chemical and textural information obtained in this study the formation of these aggregates in four steps is suggested: (1) condensation of a refractory metal alloys (W, Os, Re, Ir, Mo, Ru); (2) oxidation of the refractory metal alloy, allowing formation of Ca(W,Mo)O{sub 4}; (3) condensation of Ni-rich metal and V-magnetite at high oxygen fugacity (relative to the f{sub O{sub 2}} in a solar gas); (4) reaction of the existing assemblage with S to form FeS at lower temperatures.

• OSTI ID: 7253953
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 51:10; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
INCLUSIONS
ALUMINIUM COMPOUNDS
CALCIUM COMPOUNDS
CHEMICAL COMPOSITION
MINERALOGY
REFRACTORY METAL COMPOUNDS
METEORITES
CHEMICAL ANALYSIS
CHEMICAL REACTION KINETICS
EQUILIBRIUM
GEOCHEMISTRY
OXIDATION
PETROLOGY
REFRACTORY METALS
ALKALINE EARTH METAL COMPOUNDS
ALLOYS
CHEMICAL REACTIONS
CHEMISTRY
ELEMENTS
GEOLOGY
KINETICS
METALS
REACTION KINETICS
580000* - Geosciences