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Petrology of low-grade high-pressure metapelites from the External Hellenides (Crete, Peloponnese); a case study with attention to sodic minerals

Thomas Theye and Eberhard Seidel
Petrology of low-grade high-pressure metapelites from the External Hellenides (Crete, Peloponnese); a case study with attention to sodic minerals
European Journal of Mineralogy (April 1991) 3 (2): 343-366

Abstract

In the Phyllite-Quartzite Unit of the External Hellenides regional differences in the mineralogical compositions of equivalent rocks indicate a gradation in P-T conditions of metamorphism from E-Crete via W-Crete to the Peloponnese. In metasediments of Eastern and Central Crete, sodic minerals appear in rather monotonous assemblages, i.e. albite -I- chlorite and paragonite + chlorite. For this region, the estimated P and T are about 300-350 degrees C, 8-10 kbar, based on parageneses with carpholite, chloritoid or sudoite. Passing to W-Crete (400 + or - 50 degrees C, 10 + or - 3 kbar, using chloritoid-carpholite assemblages), paragonite + chlorite is still present in widespread chloritoid schists, and blue amphiboles (as pseudomorphs) have been observed in paragonite-bearing metasediments. A greater variety of mineral parageneses has been observed in the Peloponnese, where chlorite + paragonite in chloritoid schists and blue amphibole + paragonite in glaucophane schists are widespread. Paragonite-bearing chloritoid-glaucophane schists also occur, which in some cases contain additional sodic pyroxene, or locally garnet. For the Peloponnese, application of thermodynamic data of Holland & Powell (1990) to constrain P and T of metamorphism yields 450 + or - 30 degrees C and 17 + or - 4 kbar. Whole-rock and mineral analyses demonstrate the importance of compositional parameters, besides P and T, on the development of a specific mineral paragenesis. Carpholite is restricted to magnesian rocks ; for intermediate Mg/Fe (super 2+) ratios, the occurrence of assemblages with either chloritoid or glaucophane, with chloritoid and glaucophane, or with Na-pyroxene, is determined by increasing Fe (super 3+) /Al ratio, at given P and T. Garnet occurs in rocks with higher Mn/Fe (super 2+) ratio. Reactions responsible for the prograde changes are identified, and the metamorphic evolution may be connected towards higher grades with the eclogite facies.


ISSN: 0935-1221
Serial Title: European Journal of Mineralogy
Serial Volume: 3
Serial Issue: 2
Title: Petrology of low-grade high-pressure metapelites from the External Hellenides (Crete, Peloponnese); a case study with attention to sodic minerals
Affiliation: Ruhr-Univ. Bochum, Inst. Mineral., D-4630 Bochum, Federal Republic of Germany
Pages: 343-366
Published: 199104
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 2 p.
Accession Number: 1994-002315
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 40 anals., 4 tables, geol. sketch map
N34°55'00" - N35°45'00", E23°15'00" - E26°30'00"
N36°15'00" - N38°19'60", E21°00'00" - E23°30'00"
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe, Hanover, Germany
Update Code: 199402
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