Fluid and Geochemical Constraints on the Formation and Retrogression of High-Pressure Metamorphic Rocks from Sifnos (Greece)

The Alpine metamorphic evolution of the Cycladic Crystalline Complex of the Aegean aera of Greece is characterized by an Eocene eclogite-to-blueschist facies metamorphism and an Oligocene/ Miocene greenschist-to-amphibolite facies metamorphism. High pressure assemblages are well preserved in the north of Sifnos island (Blueschist Unit), whereas the rest of the island is dominated by greenschist-facies rocks (Greenschist Unit). However, rocks from Sifnos island preserve a complex record of both metamorphic events at all scales. In this paper we combine structural and petrological observations with major and trace geochemistry and stable-isotope data to characterize (a) the fluid involvement during highpressure and greenschist-facies metamorphism and (b) the nature of the retrogression from blueschist to greenschist facies rocks.