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  • Print publication year: 2018
  • Online publication date: June 2018

7 - Chondrules in Enstatite Chondrites

from Part I - Observations of Chondrules
Summary

We review silicate chondrules and metal-sulfide nodules in unequilibrated enstatite chondrites (EH3 and EL3). Their unique mineral assemblages, with a wide diversity of opaque phases, nitrides, and nearly FeO-free enstatite, testify to exceptionally reduced conditions. While those have long been ascribed to a condensation sequence at supersolar C/O ratios, with the oldhamite-rich nodules among the earliest condensates, evidence for relatively oxidized local precursors suggests that their peculiarities may have been acquired during the chondrule-forming process itself. Silicate phases may have been then sulfidized in an O-poor and S-rich environment; whereas metal-sulfide nodules in EH3 chondrites could have originated in the silicate chondrules, those in EL3 may be impact products. The astrophysical setting (nebular or planetary) where such conditions were achieved, whether by depletion in water or enrichment in dry organics-silicate mixtures, is uncertain, but was most likely sited inside the snow line, consistent with the Earth-like oxygen isotopic signature of most EC silicates, with little data constraining its epoch yet.

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Chondrules
  • Online ISBN: 9781108284073
  • Book DOI: https://doi.org/10.1017/9781108284073
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