Robin Lacassin

Several crustal and lithospheric mechanisms lead to deformation and vertical motion of the upper plate during subduction, but their relative contribution is often enigmatic. Multiple areas of the Hellenic Forearc have been uplifting since Plio‐Quaternary times, yet spatiotemporal characteristics and sources of this uplift are poorly resolved. The remarkable geology and geomorphology of Kythira Island, in the southwestern Hellenic forearc, allow for a detailed tectonic reconstruction since the Late Miocene. We present a morphotectonic map of the island, together with new biostratigraphic dating and detailed analyses of active fault strikes and marine terraces. We find that the Tortonian‐Pliocene stratigraphy in Kythira records ∼100 m of subsidence, and a wide coastal rasa marks the ∼2.8–2.4 Ma maximum transgression. Subsequent marine regression of ∼300–400 m and minor E‐W tilt are recorded in ∼12 marine terrace levels for which we estimate uplift rates of ∼0.2–0.4 mm/yr. Guided by simple landscape evolution models, we interpret the coastal morphology as the result of initial stability or of slow, gradual sea‐level drop since ∼2.8–2.4 Ma, followed by faster uplift since ∼1.5–0.7 Ma. Our findings on‐ and offshore suggest that E‐W extension is the dominant mode of regional active upper crustal deformation, and N‐S normal faults accommodate most, if not all of the uplift on Kythira. We interpret the initiation of E‐W extension as the result of a change in plate boundary conditions, in response to either propagation of the North Anatolian Fault, incipient collision with the African plate, mantle dynamics or a combination thereof.