Constraints on the kinematics of post-orogenic extension imposed by stretching lineations in the Aegean region

Abstract

New kinematic data from shear zones of Tertiary age in the metamorphosed basement of the Aegean region, in combination with published kinematic, lithological and palaeomagnetic data, have enabled us to determine a detailed kinematic evolution of the region during post-orogenic extension in the Aegean. Three distinct stages are recognised. Firstly, extension of both the western and eastern Aegean started in the Late Oligocene–Early Miocene (∼36–25 Ma ago), initially in an ∼023° direction. Stage two started shortly after this with the division of the Aegean crust into the West Aegean Block (a coupled assemblage of small blocks) bound on its northwestern and southeastern margins by the Scutari–Pec Line and Mid-Cycladic Lineament (fracture zones), respectively. Between 25 Ma and ∼3 Ma the West Aegean Block underwent ∼30° clockwise rotation, whilst the eastern Aegean underwent, on average, ∼19° anticlockwise rotation. Rotation of the West Aegean Block as a semi-coherent block was aided by the relative `coolness' of the block compared to the `warmer' eastern Aegean region. As the crust thinned and rotated, the NW–SE-trending faults which characterise the West Aegean Block were cross-cut by E–W-trending faults. In the latest Miocene–Pliocene, the thermal front migrated westwards into the West Aegean Block and the Mid-Cycladic Lineament ceased activity. The final kinematic stage marked the start of the subdivision of the West Aegean Block into two portions in the Pliocene. The southeastern portion (NW Cycladic area) coupled with the SW Cycladic area to form a Central Aegean Block that started to translate southwest. The northern and western portion rotated a further ∼10–15° clockwise whilst the southeastern rim rotated anticlockwise. These data demonstrate that Aegean post-orogenic extension is not dominated by a single block rotation or radial spreading event, but is characterised by the sequential formation and reformation of lithospheric-scale blocks that have developed in response to large-scale partitioning of rotational strain.