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          Institute: MPI für Chemie     Collection: Publikationen MPI für Chemie     Display Documents

ID: 6427.0, MPI für Chemie / Publikationen MPI für Chemie
Chemistry of glass inclusions in olivines of the CR chondrites Renazzo, Acfer 182, and El Djouf 001
Authors:Varela, M. E.; Kurat, G.; Hoppe, P.; Brandstätter, F.
Date of Publication (YYYY-MM-DD):2002-05
Title of Journal:Geochimica et Cosmochimica Acta
Journal Abbrev.:Geochim. Cosmochim. Acta
Issue / Number:9
Start Page:1663
End Page:1679
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:Glass inclusions in olivines of the Renazzo, El Djouf 001, and Acfer 182 CR-type chondrites are chemically divers and can be classified into Al-rich, Al-poor, and Na-rich types. The chemical properties of the glasses are independent of the occurrence of the olivine (isolated or part of an aggregate or chondrule) and its composition. The glasses are silica- saturated (Al-rich) or oversaturated (Al-poor, 24% normative quartz). All glasses have chondritic CaO/Al2O3 ratios, unfractionated Cl-normalized abundances of refractory trace elements and are depleted in moderately volatile and volatile elements. Thus the glasses are likely to be of a primitive condensate origin whose chemical composition has been established before chondrule formation and accretion, rather then the product of either crystal fractionation from chondrule melts or part melting of chondrules. Rare Na-rich glasses give evidence for elemental exchange between the glass and a vapor phase. Because they have Al2O3 contents and trace element abundances very similar to those of the Al-rich glasses, they likely were derived from the latter by Ca exchange (for Na) with the nebula. Elemental exchange reactions also have affected practically all olivines (e.g., exchange of Mg of olivine for Fe2+, Mn2+, and Cr3+). Glasses formed contemporaneously with the host olivine. As the most likely process for growing nonskeletal olivines from a vapor we consider the VLS (vapor-liquid-solid) growth process, or liquid-phase epitaxy. Glasses are the possible remnants of the liquid interface between growing crystal and the vapor. Such liquids can form stably or metastably in regions with enhanced oxygen fugacity as compared to that of a nebula of solar composition. Copyright (C) 2002 Elsevier Science Ltd.
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Chemie/Kosmochemie
External Affiliations:UNS, CONICET, Dept Geol, San Juan 670, RA-8000 Bahia Blanca, Buenos Aires, Argentina; Naturhist Museum, A-1014 Vienna, Austria
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