Structural evidence for strike-slip deformation in the Izmir-Balikesir transfer zone and consequences for late Cenozoic evolution of western Anatolia (Turkey)

The Izmir-Balikesir transfer zone (IBTZ) is a recently recognized strike-slip dominated shear zone that accommodates the differential deformation between the Cycladic and Menderes core complexes within the Aegean Extensional System. Here, we present new structural and kinematic data obtained from field observations and 1/25,000 scale mapping of Miocene to Recent units within the IBTZ around Izmir Bay. The results point out that the IBTZ is a transtensional brittle shear zone that affects the pre-Neogene basement rock units, the early-middle Miocene volcano-sedimentary units and the Plio-Quaternary continental units.The analysis of large-scale structures and fault kinematic data indicate that three different deformation phases prevailed in the Izmir Bay region during the late Cenozoic. The first phase (Phase 1) is characterized by N-S directed extension and E-W contraction that gave way to the development of strike-slip faults with normal components and likely took place during the early (?) to late Miocene. This transtensional phase, forming the volcano-sedimentary basin of deposition was overprinted by the second phase (Phase 2) which is characterized by variable extension and contraction directions indicating wrench- to extension-dominated transtension. The structures related to Phase 2 are observed all around the Izmir Bay and indicate a distributed nature of the deformation that probably took place during the early Pliocene, coeval with the end of the activity of the Mid-Cycladic Lineament and the last exhumation of the central Menderes Massif. The latest deformation phase (Phase 3) is characterized by an association of NW-SE trending left-lateral and NE-SW trending right-lateral strike-slip faults and E-W trending normal faults forming transtensional deformation. During Phase 3, the IBTZ evolved from a wider shear zone into a relatively narrow discrete fault zone by the late Pliocene, during which the strike-slip and extensional deformation were completely decoupled from each other. The field-based evidence for strike-slip deformation from the region has only recently been recognized, but has very important implications for understanding the deformation styles and coupling of Aegean-West Anatolian extensional deformation system along the IBTZ. We conclude that the Izmir Bay Basin developed during the Plio-Quaternary within the dextral IBTZ.