Correlated morphological, chemical, and isotopic characteristics of hibonites from the Murchison carbonaceous chondrite

Journal Article · Thu Dec 01 00:00:00 EST 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90150-0· OSTI ID:5013954

Ireland, T R ^[1]

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1. Australian National Univ., Canberra (Australia)

Twenty-four hibonite-dominated refractory grains from the Murchison carbonaceous chondrite have been identified from polished grain-mounts of density separates, and have been morphologically and chemically divided into three groups: (1) 14 colorless PLAty Crystal fragments (PLACs) with less than 2.7% TiO{sub 2}; (2) 3 pleochroic Blue AGgregates (BAGs) which are composed of crystal plates and fragments and have TiO{sub 2} concentrations between 5.1% and 6.5%; (3) Six Spinel-HIBonite spherules and crystal aggregates (SHIBs), often with spinel, Fe-silicate, and clino-pyroxene rims. The maximum TiO{sub 2} concentrations of hibonite in the SHIBs ranges from 3.5 to 7.6%, but the TiO{sub 2} concentration in one grain was heterogeneous and ranged from 0.5% to 5.0%. Hibonite in all types is stoichiometric with Ti and Mg predominantly in a coupled substitution of Mg{sup 2+} and Ti{sup 4+} for 2Al{sup 3+}. One grain with a rounded hibonite core does not clearly fit into the three designated groups. The hibonites have been analyzed by ion microprobe mass spectrometry for their Mg and Ti isotopic compositions. The presence of hibonite populations with distinct morphological, chemical and Mg isotopic systematics suggests that there were several hibonite formation episodes within the early solar system. The hibonites probably formed by the melting of refractory dust aggregates during local transient thermal events.

• OSTI ID: 5013954
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 52:12; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CHONDRITES
CHEMICAL COMPOSITION
MINERALOGY
QUANTITATIVE CHEMICAL ANALYSIS
REFRACTORY METALS
ALUMINIUM 26
CARBONACEOUS MATERIALS
DECAY
GEOCHEMISTRY
GEOLOGIC HISTORY
ISOTOPE RATIO
MAGNESIUM 26
MASS SPECTROSCOPY
PETROGENESIS
PETROGRAPHY
STOICHIOMETRY
TITANIUM 48
TITANIUM 50
ALKALINE EARTH ISOTOPES
ALLOYS
ALUMINIUM ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
CHEMICAL ANALYSIS
CHEMISTRY
ELEMENTS
EVEN-EVEN NUCLEI
INTERMEDIATE MASS NUCLEI
ISOTOPES
LIGHT NUCLEI
MAGNESIUM ISOTOPES
MATERIALS
METALS
METEORITES
NUCLEI
ODD-ODD NUCLEI
RADIOISOTOPES
SECONDS LIVING RADIOISOTOPES
SPECTROSCOPY
STABLE ISOTOPES
STONE METEORITES
TITANIUM ISOTOPES
YEARS LIVING RADIOISOTOPES
580000* - Geosciences