STRUCTURAL ARCHITECTURE AND TECTONIC EVOLUTION OF THE WESTERN GEDIZ GRABEN IN THE AEGEAN EXTENSIONAL PROVINCE, WESTERN TURKEY

The WNW–oriented Gediz Graben (GG) separates the Northern Menderes Massif (MM) from the Central MM, and is bounded by high–angle normal faults along its northern and southern margins. The fault system along its southern margin is seismically active. The graben is nearly 160-km-long and has a wedge-shape, closing in the east and widening to ~60 km in the west. It is segmented into several sub-basins along NNE-SSW oriented cross faults, and the maximum thickness of the supra-basement sedimentary rocks is about 4 km. At its western termination, it is divided into two sub-grabens, separated by the Çaldag High, which consists of the MMM rocks, the Jurassic–Cretaceous carbonates and the Cretaceous ophiolitic units, all unconformably and/or structurally overlain by the Miocene and younger silicaclastic rocks. The Çaldag High with its Mesozoic (and older?) and Cenozoic rock record represents an extensional ‘raft’ within the GG. There is no structural evidence for contractional deformation in the Miocene sequences within the western termination of the GG. Izmir Balikesir Fault Zone(IBFZ) which determine the western termination of the GG, shows major deformation associated with left-lateral strike-slip faulting, and there are both transtensional and transpressional segments. We determined the fault kinematics associated with graben formation and regional extension, and we test the existing tectonic models for graben formation and for the structural nature of the western termination of the GG. We suggest that the development of the fault zone which determine western termination of the GG(Izmir Balikesir Fault Zone(IBFZ)) was coeval with the diachronous opening of the graben, and that it coincided with an oblique-slip accommodation zone around a pole of rotation located right beyond the eastern apex of the GG.