The south Cycladic detachment system revisited: the tectonostratigraphic evolution of Keros

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In this study of the Mesozoic-Cenozoic geology of the island of Keros, Greek Cyclades, an attempt was made to reconstruct the tectonostratigraphic evolution of the island, through (i) formally defining the lithostratigraphic units exposed there and, correlating these with the central Aegean tectonostratigraphy, and (ii) identifying the different tectonic events responsible for the juxtaposing and stacking of these rock units into their present relative positions. These results are evaluated in light of tectonics related to the Cenozoic development of the retreating Hellenic Subduction System, which records a prolonged history of subduction, accretion, syn-subduction high-pressure metamorphism (caused by underthrusting of fragments of continental crust during slab retreat) and subsequent large-scale extensional deformation.

Post-orogenic extension in the central Aegean started some 35-30 Ma ago in the back-arc of this retreating subduction system, generating low-angle detachment faults across the entire region. In the northern Cycladic islands – the islands of Andros, Tinos and Mykonos, this phase of lithospheric extension is documented in the North Cycladic Detachment System; whereas in the southern Cycladic islands, on the islands of Kithnos, Serifos, Sifnos and Ios, the extension is documented in the South Cycladic Detachment System. In the northern islands the detachments are top to the N/NNW displacing ; in the central islands (Naxos, Paros, Syros, Amorgos, North Ios) the detachments are also top to the N directed; whereas in the southern islands (South Ios, Sikinos, Serifos, Kithnos) the detachments are top to the S directed. The island of Keros is located at a strategic position in this plate configuration, located between in the north, top-to-the-north detachments, and in the south, top-to-the-south detachments; therefore, the reappraisal of the Keros geology will elucidate on the structural relationships, both spatially and temporally, between the different detachment systems, and as such will help to refine regional tectonic correlations. To date, relatively little information is available on the structure and metamorphism of Keros, and as such, it is absent in regional tectonic reconstructions of the central Cyclades.

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