Reconstructing the deformation of the North Anatolian Fault Zone through restoring the Oligo-Miocene exhumation pattern of the Almacik Block (northwestern Turkey) based on the apatite (U-Th)/He ages

The Almacik Block is an approximately 73 km long and 21 km wide tectonic sliver formed by the North Anatolian Fault Zone in northwestern Turkey. Morphologically, it is one of the most pronounced structures along the North Anatolian Fault Zone. All the segments bounding the Almacik Block were ruptured during the second half of the 20th century. The fifty-four apatite (U-Th)/He ages we obtained showed that the region including the Almacik Block was exhumed during the Oligo-Miocene interval and then original exhumation pattern was distorted by the North Anatolian Fault Zone during the Miocene to recent. To interpret this distortion and to reconstruct it to the original state, we modelled "Lambda"-shaped mountain fronts in the most probable deformation scenarios. The block has been tilted southward about an approximately east-west-trending horizontal (slightly dipping to the east) axis. As a result of this rotation, the northern part of the block has been uplifted about 2800 m, whereas the southern part has subsided about 430 m, likely during the last 2.5 Myr. The exhumation in the studied region started at around 34 Ma and lasted until 16 Ma with a mean exhumation rate of about 60 m/Myr.