Metamorphosed calcium-aluminum-rich inclusions in CK carbonaceous chondrites

Noël Chaumard, Bertrand Devouard, Audrey Bouvier, Meenakshi Wadhwa

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Abstract

CK chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6. Although CKs are described as calcium-aluminum-rich inclusion (CAI)-poor objects, the abundance of CAIs in the 18 CK3-6 we analyzed ranges from zero to approximately 16.4%. During thermal metamorphism, some of the fine-grained CAIs recrystallized as irregular assemblages of plagioclase + Ca-rich pyroxene ± olivine ± Ca-poor pyroxene ± magnetite. Coarse-grained CAIs display zoned spinel, fassaite destabilization, and secondary grossular and spinel. Secondary anorthite, grossular, Ca-rich pyroxene, and spinel derive from the destabilization of melilite, which is lacking in all CAIs investigated. The Al-Mg isotopic systematics measured in fine- and coarse-grained CAIs from Tanezrouft (Tnz) 057 was affected by Mg redistribution. The partial equilibration of Al-Mg isotopic signatures obtained in the core of a coarse-grained CAI (CG1-CAI) in Tnz 057 may indicate a lower peak temperature for Mg diffusion of approximately 540-580 °C, while grossular present in the core of this CAI indicates a higher temperature of around 800 °C for the metamorphic event on the parent body of Tnz 057. Excluding metamorphic features, the similarity in nature and abundance of CAIs in CK and CV chondrites confirms that CVs and CKs form a continuous metamorphic series from type 3 to 6.

Original languageEnglish (US)
Pages (from-to)419-452
Number of pages34
JournalMeteoritics and Planetary Science
Volume49
Issue number3
DOIs
StatePublished - Mar 2014

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ASJC Scopus subject areas

  • Geophysics
  • Space and Planetary Science

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