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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 crustal strain in the central Aegean region (Cyclades), it is shown that NNE‐SSW extension via ductile and brittle stretching and low‐angle detachments was accompanied and/or alternated with horizontal shortening perpendicular to the stretching direction since at least the early Miocene. Roughly E‐W directed ductile shortening produced large‐scale overturned and upright folds having axes parallel or slightly oblique to the stretching lineation. Upright folding and arching of low‐angle normal faults occurred above the brittle‐ductile transition and brittle E‐W compression culminated with vertical axis block rotations, strike‐slip faults and minor thrusts. Since 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 stretching. Exact magnitudes of the vertical and horizontal deformational components are difficult to assess. Nevertheless, we note that extensional tectonics that affected the Cyclades during the last 15–20 m.y. have produced no net crustal thinning. We suggest that crustal thickness was maintained by extension‐parallel folds, which represent true contractional structures, and that crust was fed into the extended region from its margins.