Deciphering subduction from exhumation in the segmented Cycladic Blueschist Unit (Central Aegean, Greece)

The Cycladic Blueschist Unit (CBU) represents the northern passive margin of the Adria continental block and ophiolites that are the remnants of the Pindos Ocean, which were affected by high pressure–low temperature metamorphism in the blueschist and eclogite facies during the Eocene. Prior to the Lutetian, the ophiolitic and margin units were thrust towards the SW inside a NE-dipping subduction zone. Two subsequent exhumation stages are characterized by top-to-the-NE senses of shear: i) from mantle depths to lower crustal levels, before 37 Ma, which was accommodated by an extensional inversion of the Vardar suture zone, and ii) from deep crustal levels to the near-surface, between 30 and 20 Ma, which was accommodated by the North Cycladic Detachment. It is during this late stage of ductile exhumation that the central Cyclades Core Complex was exhumed. Segmentation of the CBU by normal faults started at 12 Ma, as recorded by the low temperature thermochronometers, and was coeval with block rotation and folding with NS-trending axes, which were predominantly controlled by the Myrthes–Ikaria strike-slip fault in the centre of the Cyclades. A map restoration of the CBU geometry, prior to segmentation, has been carried out using available structural and paleomagnetic data. The restoration shows that, following the CBU exhumation from mantle depths to crustal levels, a single core complex was exhumed along a single NE dipping detachment.

► We present a synthesis, at the scale of the whole Cyclades, of available structural, petrological and geochronological data.
► We restore the deformation subsequent to the late segmentation of the Cyclades.
► For the first time at a regional-scale, a distinction between deformations related to subduction and exhumation is made.
► A single detachment was active and exhumed the Cycladic blueschist from the lower crust up to the brittle-ductile transition.
► We propose a new tectonic model for the exhumation of the Cycladic blueschist, in the framework of the Hellenic subduction.