ACCEL - Aegean Core Complexes along an Extended Lithosphere

The Aegean region together with the surrounding mainland areas exhibit by far the highest present-day seismic activity in Europe. This is the active tectonic expression of the escape of Anatolia, active subduction of African lithosphere beneath the Aegean plate and extension of the Aegean region. The geodynamics community has been galvanised by a plethora of new geophysical data for the Aegean region, leading to a range of different models to explain the mechanisms and timing of Cenozoic kinematics. Almost all models seeking to explain Cenozoic geodynamic history of the Aegean are based upon knowledge from detailed investigations in the eastern Cyclades providing the primary geological database for models that make differing predictions regarding spatial migration of the active geodynamic focus over time. While only selected western Cycladic islands have enjoyed modern study, the absence of comprehensive geological data for the whole western Cyclades prevents discrimination amongst these models. Capitalizing on our pilot studies from Serifos that indicate the presence of a hitherto unrecognised metamorphic core complex, project ACCEL (Aegean Core Complexes along an Extended Lithosphere) uses the techniques of 3D spatial analysis, low to high temperature thermogeochronometry/geochronology and fault/flow analysis to quantify the largely unknown geodynamic history of Serifos, Kea, Kithnos (western Cyclades). This will dramatically improve discrimination between plate tectonic models that are presently tested largely from the much better investigated sections in the eastern Cyclades.

The Aegean region in Greece records currently by far the most intense seismic activity in Europe. This tectonic activity is the result of the down going African plate beneath the European plate, which forces extension in the Aegean region. The geodynamics community has been galvanized by a plethora of new geophysical data for the Aegean region, leading to a range of different models to explain the mechanisms and timing of recent tectonic activities. Almost all models seeking to explain geodynamic history of the Aegean are based upon knowledge from detailed investigations in the Eastern Cyclades where Miocene ( 23-5 Ma) crustal scale extension along faults are considered as a proxy for recent tectonic deformation. Investigation of these fault systems provided the primary geological database for models that make differing predictions regarding spatial migration of the active geodynamic focus over time. The Western Cyclades, where both basic field studies and a modern geodynamic database did not exist, were excluded from recent geodynamic models of crustal extension in the Aegean region. In the frame of the project ACCEL (Aegean Core Complexes along an Extended Lithosphere Western Cyclades, Greece), we discovered a new, more than 100 kilometer long fault system (i.e. the Western Cycladic Detachment System), which strikes from the island of Sifnos in the southeast, over the islands Serifos, Kithnos and Kea, to Attica, close to Athens, in the northeast. Based on new geological maps of the island Serifos and Kea our new geochronological data prove that this fault system was active throughout the Miocene offsetting several tens of kilometers of different crustal sections. Around 10 Ma two magmatic plutons intruded at Serifos and Attica respectively into the extensional faults. Microtectonic investigations of fault rocks demonstrated ductile creeping processes but also frictional deformation associated with strong seismic activities. The most spectacular result of the project ACCEL is the geometry and the sense of movements along the Western Cycladic Detachment System. Whereas all known fault systems in the Western and Northern Cyclades are low- angle normal faults with a hanging wall movement towards the north, the normal faults in the Western Cyclades have a clear south directed sense of displacement. This important observation documents a symmetric extension of the Aegean tectonic plate in the Miocene claiming a major modification of existing plate tectonic models for the Eastern Mediterranean region.