Evolution of a passive crustal-scale detachment (Syros, Aegean region): Insights from structural and petrofabric analyses in the hanging-wall

New detailed (micro-)structural investigations, quartz petrofabric analyses and geological/structural mapping in southeast Syros (Cycladic massif, Aegean region) allow us to place new constraints on the tectonic evolution of the Uppermost unit, which occupies the immediate hanging-wall of the crustal scale Van Detachment. We show that the Eocene Oligocene deformation history in the hanging-wall of this detachment is associated with SW-directed ductile shearing. This history includes an early distributed constrictional deformation expressed by transport-parallel upright folds, L-tectonites and cleft-girdles quartz c-axis fabrics that were formed at temperatures 500 degrees C. Ductile deformation progre-ssively localized at the bottom of the Uppermost unit leading to the formation of a greenschist-facies mylonitic zone under plane strain conditions inferred from Type-I cross-girdles quartz c-axis fabrics. The ongoing mylonitization was also associated with temporally increasing pure shear component of deformation coupled with cooling from 500 degrees C to 400 degrees C. We suggest that the Van Detachment represents a passive normal-sense roof fault resulted from the NE-directed ductile extrusion of the Blueschist unit (footwall) at middle Eocene Oligocene times. In the middle Miocene, the activation of the brittle SSW-directed Late Van Detachment enhanced the brittle exhumation of both the Blueschist unit and the Van Detachment. (C) 2017 Elsevier Ltd. All rights reserved.