Paleomagnetic and structural constraints on the Neogene evolution of the Soma basin as part of the İzmir–Balıkesir Transfer Zone (western Anatolia)

Abstract

The İzmir–Balıkesir Transfer Zone (İBTZ) is a major tectonic feature in western Anatolia since the Neogene, because it accommodates differential extension between the large-scale Menderes (MCC) and Cycladic (CCC) core complexes. However, there is still much discussion whether this extension occurred in a single or in multiple deformation phases. Furthermore, the northern continuation of the İBTZ remains relatively unstudied in this aspect. This part is especially crucial in obtaining a complete picture of the western Anatolian tectonic history, as there could be a relationship between the İBTZ and the North Anatolian Fault Zone (NAFZ). The goal of this study is therefore to constrain the deformation history of the Soma basin, located in the northern part of the İBTZ. To this end, new paleomagnetic, structural and stratigraphic data were acquired there. The new data indicates that the Soma basin evolved as a pull-apart basin as part of the İBTZ during at least two transtensional deformation phases. During the first Early-Middle Miocene phase, deformation was characterized by NE-SW trending dextral strike-slip faulting and rigid-block rotations of on average 29 ± 8° clockwise. This indicates that the İBTZ evolved as a wide dextral shear zone during the first phase, accommodating asymmetric extensional exhumation of the MCC and a differential amount of extension in the CCC. During the second Late Miocene-Pliocene deformation phase, the mode of extension in the Aegean region switched from localized to distributed, related to slab-tearing of the Aegean slab and subsequent acceleration of rollback. In the Soma basin, this is evidenced by a narrowing of the İBTZ, resulting in decoupling of NE-SW trending dextral strike-slip faulting and E-W trending normal faulting. In this context, only the northern part of the Soma basin could have been influenced by the NAFZ, because more intense deformation and incoherent rotations were found there.