Ab~tract-Turkey forms one of the most actively deforming regions in the world and has a long hi story of devastating earthquakes. The better understanding of its neotectonic features and acti ve tectonics would provide insight, not only for the country but also for the entire Eastern Mediterranean region. Active tectonics of Turkey is the manifestation of collisional intracontinental convergenceand tectonic escape-related deformation since the Ear_ ly Pli ocene (-5 Ma). Three major structures govern the neotectomcs of Turkey; they are dextral North Anatol ian Fault Zone (NAFZ), sinistral East Anatoli an Fault Zone (EAFZ) and the ~egean-cyprean Arc. Also, sinistral Dead Sea Fault Zone has an Important role. The Anatolian wedge between the NAFZ and EAFZ moves westward away from the eastern Anatoli a, the collision zone between the Arabian and the Eurasian pl ates. Ongoing deformation ~l ong, and mutual interaction among them has resulted in four di stmct neotectonic provinces, namely the East Anatolian contracti onal, the North Anatolian, the Central Anatoli an ' Ova' and the West Anatoli an extensional provinces. Each province is characterIzed by its unique structural elements, and forms an excellent laboratory to study active strike-sli p, normal and reverse fau lting and the ~ssoc iated basin formation. © 200 I Editions scientifiques et mect1cales Elsevier SAS

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Western Turkey is one of the most spectacular regions of widespread active continental extension in the world. The most prominent structures of this region are E–W-trending grabens (e.g. Gediz and Büyük Menderes grabens) and intervening horsts, exposing the Menderes Massif. This paper documents the result of a recent field campaign (field geological mapping and structural analysis) along the southern margin of the modern Gediz Graben of Pliocene (∼ 5 Ma) age. This work provides field evidence that the presently low-angle ductile-brittle detachment fault is cut and displaced by the high-angle graben-bounding normal faults with total displacement exceeding 2.0 km. The evolution of the N–S extension along the Gediz Graben occurred during two episodes, each characterized by a distinct structural styles: (1) rapid exhumation of Menderes Massif in the footwall of low-angle normal fault (core-complex mode) during the Miocene; (2) late stretching of crust producing E–W grabens along high-angle normal faults (rift mode) during Pliocene–Quaternary times, separated by a short-time gap. The later phase is characterized by the deposition of now nearly horizontal sediments of Pliocene age in the hanging walls of the high-angle normal faults and present-day graben floor sediments. The evolution of extension is at variance with orogenic collapse and/or back-arc extension followed by the combined effect of tectonic escape and subduction rollback processes along the Aegean-Cyprean subduction zone. Consequently, it is misleading to describe the Miocene sediments exhumed on shoulders of the Gediz Graben as simple graben fill.

The Menderes Massif covers large areas in western Turkey. The better understanding of its tectono-metamorphic history would provide insight for the Alpine evolution of western Turkey and the entire eastern Mediterranean region. This paper summarizes the available literature on the metamorphic rocks of western Turkey and that of the Menderes Massif with special reference and emphasis to the papers presented in the special issue.

The Büyük Menderes Graben is one of the most prominent structures of western Anatolia (Turkey) and borders the Aegean. New structural and stratigraphic evidence demonstrates that the (?)Miocene fluvio-lacustrine, coal-bearing red clastic sediments exposed along the northern margin of the graben are northward back-tilted, locally folded and overlain unconformably by horizontal terraced Pliocene-Pleistocene sediments. Also, there is no evidence that these red clastics at the base of the Neogene sequence were deposited during neotectonic extension. It is suggested here that these sediments cannot be regarded as passive neotectonic graben-fill deposits.This new evidence further indicates that the age of the modern Büyük Menderes Graben is Pliocene, younger than previously considered (Early-Middle Miocene) and that initiation of north-south neotectonic extensional tectonics in the graben, and thus in western Anatolia, is unlikely to have resulted from orogenic collapse. The Pliocene estimate of the start of extension is in close agreement with the start of slip on the North Anatolian Fault Zone. The north-south extensional tectonics, and associated east-west faulting and basin formation, commenced during the Pliocene due to the effect of westward tectonic escape of the Anatolian block along the North and East Anatolian Faults. New mammal evidence also constrains the start of slip on the younger faults which bound the present-day graben floor to c. 1 Ma.The Büyük Menderes Graben has experienced a two-stage extension. An initial extension (latest Oligocene-Early Miocene) along initially moderately, steeply dipping normal faults was superseded by movement on steeper normal faults during the (?)Pliocene. The two phases of deformation appear to reflect significant changes in the tectonic setting of western Anatolia and are attributed to orogenic collapse followed by tectonic escape.

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