A new type of Al-rich inclusion in Axtell CV3 chondrite

Details A new type of Al-rich inclusion in Axtell CV3 chondrite A new type of Al-rich inclusion in Axtell CV3 chondrite

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..453c&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 453-454

Computer Science

2

Abundance, Aluminum Oxides, Chondrites, Inclusions, Meteoritic Composition, Meteoritic Microstructures, Chemical Composition, Chromium Oxides, Crystal Structure, Mineralogy, Olivine, Petrography

Scientific paper

Petrographic observations of an unusual compact inclusion from the newly available Axtell chondrite show that it contains essentially Al-rich oxides and lacks metals. The blue-green isotropic core composed or rare ferroan spinel becomes intergrown with fan-shaped hibonite crystals projecting toward the inclusion's core forming a marginal irregular colorless zone. The inclusion appears to be crossed by multiple ilmenite microchannels. These small tubes penetrate toward the core of the inclusion but are more concentrated at its border. Two areas are altered and seem porous. The first contains fine-grained mineral assemblages including acicular crystals that might be ilmenite. The second area, located on the inclusion's opposite narrow end, shows a disorganized network of altered spinel partially replaced by Al-rich phase(s) also present near the inclusion's border. A narrow rim (up to 8 microns thick) consists primarily of an agglomerate of micrometer-sized aluminous diopside crystals. Small olivine clusters occurring on the outer margin of the diopside layer could be patches of an irregular outermost layer. The surrounding weathered Fe-rich matrix contains micrometric elongated olivines resembling those found in the matrix of Allende meteorite. The abundance of Al-rich phases demonstrates that the inclusion is Al enriched but Si depleted relative to CV3 inclusions. Preliminary calculated bulk analysis confirms the high content of refractory Al2O3 (59.2 wt%) similar to some CM inclusions. Contrasted with normal CV3 CAIs, this inclusion has quite abundant, moderately volatile Fe (FeO = 22.5) and very low CaO (1.4) in inverse proportion. Thus it probably did not stop equilibrating with the nebular gas at higher temperatures. The mineral paragenesis of this Al-rich inclusion is inconsistent with the predicted condensation sequence. Indeed Fe should be absent in high-temperature condensates from a gas of solar composition. Therefore this unusual inclusion could represent a residue of incomplete volatilization of a preexisting rock that later remelted.

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