Glaucophane schists and associated rocks from Sifnos (Cyclades, Greece): New constraints on the P-T evolution from oxidized systems

Date

2008

Authors

Groppo, Chiara
Forster, Margaret
Lister, Gordon
Compagnoni, Roberto

Journal Title

Journal ISSN

Volume Title

Publisher

Elsevier

Abstract

The island of Sifnos (Cyclades, Greece) is famous for its spectacular blueschist-facies rocks and eclogites. Their very well preserved high-pressure assemblages are characterized by the occurrence of Fe+ 3-rich minerals such as aegirine-rich pyroxene, riebeckite-rich amphibole, magnetite and deerite. Therefore, the common model system NCFMASH (Na2O-CaO-FeO-MgO-Al2O3-SiO2 -H2O), in which all iron is assumed to be ferrous, is not sufficient to completely model these highly oxidized assemblages. We propose new constraints on the P-T evolution of the glaucophane schists and associated rocks from Vroulidia Bay (northern Sifnos) using P-T isochemical diagrams (pseudosections) modelled for the oxidized N(K)CFMASHO system [Na2O-(K2O)-CaO-FeO-Fe2O3-Mg O-Al2O3-SiO2-H2O], and calculated using solid solution models involving Fe+ 3-end-members. The resulting P-T conditions could be fitted by a simple trajectory consisting of a smooth clockwise P-T loop, with two distinct high-pressure events at T = 450-500 °C, P > 2.0 GPa (assemblage A) and T = 525-565 °C, P > 2.1 GPa (assemblage B), respectively, followed by cooling and decompression. Geospeedometry based on40Ar/39Ar data, however, allows constraint as to the duration of individual thermal excursions associated with these events. Should these limits be taken into account, the P-T envelope derived in this paper encompasses a more complex P-T history, with individual excursions that potentially involve relatively short periods of temperature increase ± pressure variation.

Description

Keywords

Keywords: blueschist facies; cooling; glaucophane; oxidation; P-T conditions; source rock; tectonic evolution; ultrahigh pressure metamorphism; Cycladas; Eurasia; Europe; Greece; Sifnos; Southern Aegean; Southern Europe Blueschist- and eclogite-facies; Oxidized system; P-T path; Pseudosection; Sifnos

Citation

Source

Lithos

Type

Journal article

Book Title

Entity type

Access Statement

License Rights

Restricted until

2037-12-31