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GEOREF RECORD

Orthopyroxenes from granulite rocks of the Wilson Terrane (Victoria Land, Antarctica); crystal chemistry and cooling history

Mario Tribaudino and Franco Talarico
Orthopyroxenes from granulite rocks of the Wilson Terrane (Victoria Land, Antarctica); crystal chemistry and cooling history
European Journal of Mineralogy (June 1992) 4 (3): 453-463

Abstract

The compositions of 17 orthopyroxenes from granulites facies rocks of the Wilson Terrane (Ross Orogen), determined by microprobe analysis, are consistent with a metamorphic origin. Three groups may be distinguished: orthopyroxenes with high Al2O3 content (2.85-5.33 weight%) and XMg=0.46-0.60, from garnet-cordierite granulites; orthopyroxenes with low Al2O3 (less than 0.9 wt%) and XMg=0.49-0.62, from enderbites; and orthopyroxenes with very low Al2O3 (less than 0.4 wt%) and XMg=0.70, from two-pyroxene mafic granulites. These differences do not reflect metamorphic conditions, but are due to local mineral assemblages. Zoning occurs in few orthopyroxenes from garnet-cordierite and mafic granulites, in both cases due to a retrograde evolution. The crystal chemistry and site populations of two Al-rich and one Al-poor specimen were determined by X-ray single crystal diffraction. The most relevant structural differences are the decrease in M1 and M2 polyhedral dimensions, and an increase in TB, both induced by Al. The high degree of Fe2+ -Mg order (kD between 0.017 and 0.023) is coherent with slow cooling. Closure temperatures of the ordering process are between 214 and 243 C, with cooling rates in the range expected for a regional metamorphic terrane. (Auth.)


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 4
Serial Issue: 3
Title: Orthopyroxenes from granulite rocks of the Wilson Terrane (Victoria Land, Antarctica); crystal chemistry and cooling history
Affiliation: Universita di Torino, Dipartimento di Scienze Mineralogiche e Petrologiche, Turin, Italy
Pages: 453-463
Published: 199206
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 30
Accession Number: 1995-056307
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: 4 tables
Secondary Affiliation: Universita di Siena, ITA, Italy
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from the Antarctic Bibliography, United States
Update Code: 199520
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