Alkali (Rb/K) abundances in Allende barred-olivine chondrules - Implications for the melting conditions of chondrules
- Kobe Univ. (Japan)
Twenty five petrographically characterized chondrules, including 18 barred olivine (BO) chondrules from the Allende (CV3) meteorite, were analyzed for alkalis (K and Rb) and alkaline earths (Sr, Ba, Ca and Mg) by mass spectrometric isotope dilution. Most BO chondrules with higher alkalis (greater than the CI level) have nearly CI-chondritic Rb/K ratios, while those with lower alkalis clearly show higher Rb/K ratios than the CI-chondritic. In general, BO chondrules with higher Rb/K exhibit more depletion of alkalis relative to Ca. The mean olivine Fa for individual chondrules positively correlates with bulk alkali concentrations in BO type but not in porphyritic type chondrules. These observations suggest that some BO chondrules formed from more reducing assemblages of precursor minerals, which experienced more intensive vaporization losses of alkalis, accompanied by Rb/K fractionation, during the chondrule-formation melting. 30 refs.
- OSTI ID:
- 6576428
- Journal Information:
- Meteoritics; (USA), Vol. 25; ISSN 0026-1114
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
CHONDRITES
CHEMICAL COMPOSITION
ALKALINE EARTH METALS
CRYSTAL GROWTH
ELEMENT ABUNDANCE
ISOTOPES
MASS SPECTROMETERS
OLIVINE
PETROGRAPHY
POTASSIUM COMPOUNDS
RUBIDIUM COMPOUNDS
ABUNDANCE
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
ELEMENTS
IRON COMPOUNDS
IRON SILICATES
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MEASURING INSTRUMENTS
METALS
METEORITES
MINERALS
OXYGEN COMPOUNDS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SPECTROMETERS
STONE METEORITES
TRANSITION ELEMENT COMPOUNDS
640107* - Astrophysics & Cosmology- Planetary Phenomena