Ductile and brittle shortening, extension-parallel folds and maintenance of crustal thickness in the central Aegean (Cyclades, Greece)

In contrast to previous studies that concentrated on the two-dimensional cr ustal strain in the central Aegean region brittle stretching and low-angle detachments was accompanied and/or alternated with horizontal shortening pe rpendicular to the stretching direction since at least the early Miocene. R oughly EW directed ductile shortening produced large-scale overturned and u pright folds having axes parallel or slightly oblique to the stretching lin eation. Upright folding and arching of low-angle normal faults occurred abo ve the brittle-ductile transition and brittle E-W compression culminated wi th vertical axis block rotations, strike-slip faults and minor thrusts. Sin ce at least the early Miocene, the structure of the Cycladic massif evolved through alternating and/or coeval increments of horizontal shortening and vertical thinning associated with an approximately constant NNE-SSW stretch ing. Exact magnitudes of the vertical and horizontal deformational componen ts are difficult to assess. Nevertheless, we note that extensional tectonic s that affected the Cyclades during the last 15-20 m.y. have produced no ne t crustal thinning. We suggest that crustal thickness was maintained by ext ension-parallel folds, which represent true contractional structures, and t hat crust was fed into the extended region from its margins.