High-pressure/low-temperature metamorphism of basalts in Lavrion (Greece): implications for the preservation of peak metamorphic assemblages in blueschists and greenschists

Journal article

Authors / Editors

Proyer, Alexander

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Publication Details

Author list: Baziotis I, Proyer A, Mposkos E

Publisher: Copernicus Publications

Place: STUTTGART

Publication year: 2009

Journal: European Journal of Mineralogy (0935-1221)

Journal acronym: EUR J MINERAL

Volume number: 21

Issue number: 1

Start page: 133

End page: 148

Number of pages: 16

ISSN: 0935-1221

eISSN: 1617-4011

Languages: English-Great Britain (EN-GB)

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Abstract

The Upper Tectonic Unit of the Lavrion area is part of the Attic-Cycladic blueschist belt and was affected by high-pressure, low-temperature metamorphism. Blueschists and greenschists occur in the same outcrop and are believed to have experienced the same pressure-temperature (P-T) history which has been quantified using geothermobarometry and pseudosections for specific bulk-rock compositions. Calculated P-T conditions indicate minimum pressure of similar to 0.9 GPa and temperature of similar to 370 degrees C for the peak of metamorphism. The prograde and retrograde paths followed a very similar low geothermal gradient (10-12 degrees C/km) with cooling during decompression. Pseudosections show that both blueschists and greenschists can exist stably at the metamorphic peak, the dominant amphibole being a function of bulk composition: the blueschists, on average, have lower Mg# than the greenschists, which results in a larger P-T stability field of blue amphibole. A pseudosection analysis of the dehydration behaviour indicates that blueschists and some greenschists can preserve their peak assemblages (no dehydration along the retrograde path), whereas greenschist assemblages, in general, are rather prone to undergo dehydration and hence re-equilibration to lower P-T conditions during exhumation.

Keywords

blueschist, fluid availability, greenschist, Lavrion area, preservation

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