Cooling during the exhumation of a blueschist terrane: Sifnos (Cyclades), Greece

Alpine high-pressure metamorphic rocks exposed in the Cyclades were overprinted during their exhumation. The metamorphic evolution of a pervasively overprinted rock sequence, the Greenschist unit, exposed in the island of Sitnos was studied. The metamorphic evolution in the Greenschist unit is characterized by the progressive transformation of eclogite-facies rocks through albite-bearing epidote blueschists into greenschists. A P-T path for the greenschist unit is presented indicating eclogite-facies conditions of around 480-520°C and 12-15 kbar, followed by overprinting in the albite-bearing epidote-blueschist facies at P-T conditions of 8-10 kbar and ca.480-500°C. The high-pressure metamorphic rocks of Sifnos appears not to follow the thermal evolution path predicted by models which assume whole crust uplift and erosion. On a regional scale the exhumation of the Cycladic blueschist belt is characterized by cooling in the west, but broad clockwise P-T loops with significant heating during decompression are found in the east. -from Authors