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A comparison of FeO-rich, porphyritic olivine chondrules in unequilibrated chondrites and experimental analoguesExperimentally produced analogues of porphyritic olivine (PO) chondrules in ordinary chondrites provide an important insight into chondrule formation processes. We have studied experimental samples with PO textures grown at three different cooling rates (2, 5 and 100 C/h), and samples that have been annealed at high temperatures (1000-1200 C) subsequent to cooling. These are compared with natural chondrules of similar composition and texture from the ordinary chondrites Semarkona (LL3.0) and ALH 81251 (LL3.3). Zoning properties of olivine grains indicate that the Semarkona chondrules cooled at comparable rates to the experiments. Zoning in olivine from chondrules in ALH 81251 is not consistent with cooling alone but indicates that the chondrules underwent an annealing process. Chromium loss from olivine is very rapid during annealing and calculated diffusion coefficients for Cr in olivine are very similar to those of Fe-Mg interdiffusion coefficients under the same conditions. Annealed experimental samples contain an aluminous, low-Ca pyroxene which forms by reaction of olivine and liquid. No similar reaction texture is observed in ALH 81251 chondrules, and this may be evidence that annealing of the natural samples took place at considerably lower temperatures than the experimental analogues. The study supports the model of chondrule formation in a cool nebula and metamorphism of partly equilibrated chondrites during reheating episodes on the chondrite parent bodies.
Document ID
19930062738
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Jones, Rhian H.
(New Mexico Univ. Albuquerque, United States)
Lofgren, Gary E.
(NASA Johnson Space Center Houston, TX, United States)
Date Acquired
August 16, 2013
Publication Date
June 1, 1993
Publication Information
Publication: Meteoritics
Volume: 28
Issue: 2
ISSN: 0026-1114
Subject Category
Lunar And Planetary Exploration
Accession Number
93A46735
Funding Number(s)
CONTRACT_GRANT: NAG9-497
Distribution Limits
Public
Copyright
Other

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