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Chemical and petrographic constraints on the origin of chondrules and inclusions in carbonaceous chondrites

Authors
Journal
Geochimica et Cosmochimica Acta
0016-7037
Publisher
Elsevier
Publication Date
Volume
41
Issue
12
Identifiers
DOI: 10.1016/0016-7037(77)90216-2
Disciplines
  • Chemistry

Abstract

Abstract Bulk chemical compositions of the various petrographie types of chondrules and inclusions in Type 3 carbonaceous chondrites (excluding those affected by metamorphism) have been determined by microprobe defocused beam analysis. Inclusion compositions follow approximately the theoretical compositional trajectory for equilibrium condensation. Analyses of chondrules occurring in the same meteorites have higher silica contents and show only slight overlap with inclusion compositions. Dust fusion is apparently an inadequate mechanism for producing the wide chemical variations observed among chondrules. Impact melting models require sampling of complex target rocks which are unknown as components of meteorites; this mechanism also demands efficient mechanical processing of chondrules before accretion. A genetic relationship between chondrules and inclusions in carbonaceous chondrites is suggested by the compositional continuum between these objects. A condensation sequence which dips into the liquid stability field at lower temperatures is advocated for the production of both inclusions and chondrules. Textural relationships between intergrown chondrules and inclusions support such a sequence. This model suggests that the assembled components (inclusions and chondrules) of carbonaceous chondrites are related by a common process.

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