NEOGENE-QUATERNARY EVOLUTION OF CRETE: FROM LITHOSPHERIC COMPRESSION TO CRUSTAL EXTENSION

Following the introduction of Plate Tectonics theory, the recent to present geodynamics of the southern Aegean Region has been soon associated with the African subduction along the Hellenic Arc, while active volcanism, seismicity and subsidence within the Southern Aegean Sea were interpreted as typical back-arc extension-related phenomena. However, with the increasing collection of data and production of results based on many different methodological approaches and investigation techniques, the last two decades of the 20th century have seen the blooming of publications focusing on the Neogene to Quaternary tectonics and geodynamics of the area. This large amount of papers has certainly increased our general knowledge on the geological evolution of the area, but also raised several questions and left open many scientific problems. Numerous models have been proposed since then attempting to unravel and explain the complex evolution of the Aegean Region. Some of these models focus on the present-day kinematics being mainly based on seismicity, geodetic surveys and other geophysical data, while many others are generally grounded on more geological data and consider much longer time periods.

The Island of Crete represents the southernmost and most external outcrops of the whole Hellenic Arc, therefore providing crucial information on the recent (Neogene-Quaternary) geodynamic evolution of the area. In particular, the island contains the record of both the youngest outcropping synorogenic contractional structures and the diffuse normal faulting that at present affects Crete and its surroundings. This research focuses on the timing of the stress regime change, from compressional to tensional conditions.

During Neogene, the central sector of the Hellenic Arc was mainly affected by frontal to oblique convergence and this caused the activation of both major thrusts and wrench zones. The former structures are generally north-dipping, characterised by an arcuate shape showing an almost independent behaviour, while wrench zone are certainly associated with the oblique reactivation of inherited crustal (or lithospheric) structures.

Geological and tectonic investigations carried out along N-S coast-to-coast transects have documented the occurrence of meso- and macro-scale contractional structures, like reverse faults, duplexes, pitted pebbles and folds, clearly affecting Tortonian to Pliocene (and possibly Lower Pleistocene) deposits and characterized by a NNW-SSE to NNE-SSW shortening direction. This deformational event(s), which affects the upper crust, has been associated with the ongoing Hellenic subduction and caused a southwards migrating out-of-sequence thrust system consisting of both reactivated inherited contrational structures and new ones. This event was likely due to a stronger coupling along the overall subduction system and was juxtaposed to the Early-Middle Miocene exhumation phase. Only during Pleistocene the upper crustal extensional regime was resumed in the island and its surroundings affecting the region with diffuse normal faulting active till present. This latter event was probably related to a sudden southwards jump of the basal detachment along the lithospheric African subduction that caused a general stress release in the uppermost crust.