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Roosevelt County 075: A petrologic chemical and isotopic study of the most unequilibrated known H chondriteRoosevelt County (RC) 075 was recovered in 1990 as a single 258-gram stone. Classification of this meteorite is complicated by its highly unequilibrated nature and its severe terrestrial weathering, but we favor H classification. This is supported by O isotopes and estimates of the original Fe, Ni metal content. The O isotopic composition is similar to that of a number of reduced ordinary chondrites (e.g., Cerro los Calvos, Willaroy), although RC 075 exhibits no evidence of reduced mineral compositions. Chondrule diameters are consistent with classification as an L chondrite, but large uncertainties in chondrule diameters of RC 075 and poorly constrained means of H, L and LL chondrites prevent use of this parameter for reliable classification. Other parameters are compromised by severe weathering (e.g., siderophile element abundances) or unsuitable for discrimination between unequilibrated H, L and LL chondrites (e.g., Co in kamacite delta C-13). Petrologic subtype 3.2 +/- 0.1 is suggested by the degree of olivine heterogeneity, the compositions of chondrule olivines, the thermoluminescence sensitivity, the abundances and types of chondrules mapped on cathodoluminescence mosaics, and the amount of presolar SiC. The meteorite is very weakly shocked (S2), with some chondrules essentially unshocked and, thus, is classified as an H3.2(S2) chondrite. Weathering is evident by a LREE enrichment due to clay contamination, reduced levels of many siderophile elements, the almost total loss of Fe, Ni metal and troilite, and the reduced concentrations of noble gases. Some components of the meteorite (e.g., type IA chondrules, SiC) appear to preserve their nebular states, with little modification from thermal metamorphism. We conclude that RC 075 is the most equilibrated H chondrite yet recovered and may provide additional insights into the origin of primitive materials in the solar nebula.
Document ID
19950047185
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Mccoy, T. J.
(University of Hawaii at Manoa, Honolulu, HI United States)
Keil, K.
(University of Hawaii at Manoa, Honolulu, HI United States)
Ash, R. D.
(Open University Miton Keynes, United Kingdom)
Morse, A. D.
(Open University Miton Keynes, United Kingdom)
Pillinger, C. T.
(Open University Miton Keynes, United Kingdom)
Wieler, R.
(ETH Zurich Zurich, Switzerland)
Mayeda, T. K.
(University of Chicago, Chicago, IL United States)
Clayton, R. N.
(University of Chicago, Chicago, IL United States)
Benoit, P. H.
(University of Arkansas, Fayetteville, AR United States)
Sears, D. W. G.
(University of Arkansas, Fayetteville, AR United States)
Date Acquired
August 16, 2013
Publication Date
December 1, 1993
Publication Information
Publication: Meteoritics
Volume: 28
Issue: 5
ISSN: 0026-1114
Subject Category
Lunar And Planetary Exploration
Accession Number
95A78784
Funding Number(s)
CONTRACT_GRANT: NAGW-3281
CONTRACT_GRANT: NAG9-183
CONTRACT_GRANT: NAG9-81
CONTRACT_GRANT: NAG9-454
CONTRACT_GRANT: NSF EAR-89-20584
Distribution Limits
Public
Copyright
Other

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