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Petrology and mineralogy of Type II, FeO-rich chondrules in Semarkona (LL3.0) - Origin by closed-system fractional crystallization, with evidence for supercoolingThe petrology of type II porphyritic olivine chondrules in Semarkona (LL3.0) has been studied in detail. Olivines in these chondrules are euhedral, Fe-rich, and are strongly zoned from cores to rims of grains in FeO (Fa10-30), Cr2O3 (0.2-0.6 wt pct), MnO (0.2-0.7 wt pct), and CaO (0.1-0.4 wt pct). Interstitial mesostasis is rich in Si, Al, and Ca and is glassy with abundant microcrystallites. Minor minerals include troilite, Fe,Ni metal, and chromite. Some olivine grains contain euhedral, fayalite-rich cores that are probably produced during initial supercooling of the chondrule melt. Rare relict grains of forsteritic olivine have compositions very similar to olivines in type IA chondrules in Semarkona and may result from disaggregation of such chondrules. Apart from these relics, all properties of type II chondrules can be described by closed-system fractional crystallization of droplets which were essentially entirely molten. Type IA chondrules may have formed from type II chondrules by loss of Fe and volatiles. Alternatively, the two chondrule types may have formed in regions of considerable diversity in the solar nebula from precursor materials with different Fe/Mg ratios.
Document ID
19900052103
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Jones, Rhian H.
(New Mexico, University Albuquerque, United States)
Date Acquired
August 14, 2013
Publication Date
June 1, 1990
Publication Information
Publication: Geochimica et Cosmochimica Acta
Volume: 54
ISSN: 0016-7037
Subject Category
Lunar And Planetary Exploration
Accession Number
90A39158
Funding Number(s)
CONTRACT_GRANT: NAG9-30
Distribution Limits
Public
Copyright
Other

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