DETACHMENT FAULT AND SHEAR ZONE OF THE CRETAN-PELOPONNESE RIDGE IN KYTHERA ISLAND

Kythera Island is located on the prominent submarine horst between Crete and the Peloponnese in the southwestern part of the Aegean. The structure of Kythera is characterized by a pile of tectonic slices derived from different paleogeographic zones. The upper unmetamorphosed units comprise pelagic limestones and cherts of Pindos zone emplaced by thrusting in the Eocene on top of Tripolis zone neritic limestones. These units are separated from the lower metamorphosed unit of Phyllite-Quartzite (PQU) exposed in the northern part of Kythera by an extensional detachment fault of Late Miocene age. The lower tectonic unit of PQU was affected by high-pressure/low-temperature blueschist metamorphism during or after the middle Miocene, but the higher non-metamorphic carbonate units were affected only by local recrystallization. Both brittle and ductile structures related to the extensional detachment can be mapped near the contact of the contrasting metamorphic and non-metamorphic units. Brittle extension is expressed in the cover rocks by dominant NW-SE striking normal faults and related veins and breccias. Ductile structures in the metamorphic unit include mylonites and prominent ductile stretching fabrics which have in different places components of NW-SE and NE-SW extension. Pliocene sediments are mostly horizontal and cover the detachment unconformably. Extension was presumably related to rapid subduction rollback, as previously suggested by others. Differential movement of and vertical axis rotation in the Crete-Peloponnese ridge during this process may be linked to cross-ridge strike slip faults. Evidence of NE-SW dextral faulting is seen in northern Kythera outcrops, related to a significant fault of this type between Kythera and the Peloponnese.