Oligocene extension on the south Cyclades shear zone, in the central Cyclades, Ios, Greece

Microstructural analysis with micro-scale based 40 Ar/ 39 Ar geochronology has been used to differentiate between different deformational events in the extensional zone of the central Agean Sea, Greece. North/south directed extension in the central Aegean has been largely accommodated by the South Cyclades Shear Zone. An 40 Ar/ 39 Ar geochronology study shows that extension in the Aegean started much earlier than previously thought, with the pervasive top-to-the-south shear zone operating during the Oligocene, predating the Oligo-Miocene extensional epoch. Furthermore previous work suggests the pervasive top-to-the-south shear zone and the overprinting narrow top-to-the-north shear zone South Cyclades Shear Zone represent conjugate shear zones that operated during Miocene. Results from 40 Ar/ 39 Ar geochronology show that these two shear zones are not conjugate but operated at distinctly different times and that only the narrow top-to-the-north shear zones operated during the Oligo-Miocene epoch.