Polymetamorphic Evolution of Pre-Alpidic Basement Rocks on the Island of Sikinos (Cyclades, Greece)

On the island of Sikinos, Attic-Cycladic crystalline complex, remnants of a pre-Alpidic basement complex, initially consisting of a sedimentary sequence intruded by granodiorites and diorites are preserved. The basement complex under-went polyphase deformation and metamorphism. Based on textural and mineralogical evidence in the metasediments of the basement complex, three metamorphic events can be distinguished: A pre-Alpidic amphibolite facies metamorphism at peak temperatures of about 570 - 650-degrees-C and poorly constrained pressures of around 5 kbar, an Alpidic high-pressure event under conditions of the epidote-blueschist facies at minimum pressures of 10 kbar in an assumed temperature range of 450 - 500-degrees-C, and a subsequent Barrovian facies overprint under greenschist-facies conditions, at temperatures of 440 - 480-degrees-C and minimum pressures of 5 kbar. Owing to incomplete re-equilibration, these P - T estimates must be regarded with caution, although, they agree well with other estimates in the Attic-Cycladic crystalline complex.