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Pressure–temperature evolution of blueschist facies rocks from Sifnos, Greece, and implications for the exhumation of high‐pressure rocks in the Central Aegean
Author(s) -
Schmädicke E.,
Will T. M.
Publication year - 2003
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1046/j.1525-1314.2003.00482.x
Subject(s) - blueschist , geology , greenschist , geothermobarometry , cyclades , metamorphism , metamorphic rock , geochemistry , eclogite , metamorphic facies , phengite , petrology , subduction , seismology , facies , tectonics , geomorphology , structural basin
The blueschist and greenschist units on the island of Sifnos, Cyclades were affected by Eocene high‐pressure (H P ) metamorphism. Using conventional geothermobarometry, the H P peak metamorphic stage was determined at 550–600 °C and 20 kbar, close to the blueschist and the eclogite facies transition. The retrograde P–T paths are inferred with phase diagrams. Pseudosections based on a quantitative petrogenetic grid in the model system Na 2 O–CaO–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O reveal coeval decompression and cooling for both the blueschist and the greenschist unit. The conditions of the metamorphic peak and those of the retrograde stages conform to a similar metamorphic gradient of 10–12 °C km −1 for both units. The retrograde overprint can be assigned to low‐pressure blueschist to H P greenschist facies conditions. This result cannot be reconciled with the (prograde) Barrovian‐type event, which affected parts of the Cyclades during the Oligocene to Miocene. Instead, the retrograde overprint is interpreted in terms of exhumation, directly after the H P stage, without a separate metamorphic event. Constraints on the exhumation mechanism are given by decompression‐cooling paths, which can be explained by exhumation in a fore‐arc setting during on‐going subduction and associated crustal shortening. Back‐arc extension is only responsible for the final stage of exhumation of the H P units.