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

Western Turkey falls within a wide belt of NNE–SSW-directed, active continental extension, generally similar to the Basin and Range Province of the USA. It comprises a zone of WNW–ESE-trending major grabens. Detailed study of the Gediz graben reveals two contrasting infills that represent two distinct extensional stages, separated by a short phase of compression. The older infill consists of an 800 m thick, folded and exhumed continental sedimentary sequence with intercalated calc-alkaline volcanics. It accumulated in a basin formed in the northern hanging wall of a detachment fault during Miocene–early Pliocene times. The younger infill rests on the older infill with angular unconformity and consists of about 170 m of undeformed, terraced continental sediments and basaltic lavas. It accumulated during Plio-Quaternary times in an asymmetric graben bounded by step-like normal faults. This later extension was probably triggered by the commencement of sea-floor spreading along the Red Sea in early Pliocene times and has persisted to the present. Almost all the grabens in western Turkey are best explained by this episodic, two-stage graben model with an intervening phase of short-term compression, which differs from the progressive evolution inferred for the Basin and Range Province of the USA.

In the southern sector of the Menderes Massif, north of Selimiye (Milas) augen gneisses interpreted as a deformed peraluminous granite have been dynamothermally metamorphosed and are surrounded by and intrude a regionally metamorphosed Palaeozoic ‘envelope’. The granitic rocks exhibit a moderately-dipping mylonitic foliation and NNE-SSW- trending mineral elongation lineation. The progressive deformation of the granitic rocks produces a structural sequence typical of an extensional shear zone marked, from bottom to top, by a very thick extensive zone of mylonites followed in turn by brecciated mylonite and cataclasite. The kinematic indicators exhibit a top-to-the south, down-dip sense of shear. These structures are attributed to exhumation of the granitic rocks of the massif along a major, south-dipping, normal-sense shear zone that accommodated crustal extension during Late Oligocene collapse of the orogen in western Turkey. Thus, the southern Menderes Massif may be interpreted as the exhumed footwall of a major extensional shear zone, and possibly as an incipient core complex.

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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.