Post-5 Ma rock deformation on Alonnisos (Greece) constrains the propagation of the North Anatolian Fault

The localization of the North Anatolian Fault in the northern Aegean Sea (North Aegean Trough) is an intriguing example of continental transform fault propagation. Understanding this process critically depends on quantifying the amount of strike-slip displacement and the superposition of normal and strike-slip faulting in the region, which is the aim of this study. In particular, we unravel and quantify normal and dextral faulting along the Alonnisos fault system, at the south-western margin of the North Aegean Trough (Sporades Basin), in order to constrain the spatial and temporal evolution of the basin and the North Anatolian Fault. We present detailed structural data collected from Messinian strata of Alonnisos to infer the amount of tilting and shortening and to constrain normal and dextral faulting along the Alonnisos fault system through simple analytical half-space models of dislocations. The Messinian rocks of Alonnisos record significant tilting and gentle folding close to the termination zone of the main fault segment. The tilting of the Messinian rocks implies footwall uplift in the order of 6-7 km (vertical displacement) during normal faulting on the boundary fault system, which lead to post 5 Ma substantial deepening of the Sporades Basin. The post-Messinian folding accommodated ~ 1 km shortening at the footwall termination zone of the Alonnisos fault, which implies a dextral slip of 3-4 km. Our results support the models of currently distributed dextral strain in the North Aegean in response to the propagation of the North Anatolian Fault. However, similarities with the evolution of the Sea of Marmara might suggest that dextral shear could yet become fully localized in the NAT in the next few Myrs.