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The Alaşehir graben is a well-defined prominent extensional structure in western Turkey, generally trending E–W and containing four sedimentary units. At the beginning of graben formation during Early–Middle Miocene times, the first fault system was active and responsible for the accumulation of the first and second sedimentary units. In Pliocene times, a second fault system developed in the hanging wall of the first system and a third sedimentary unit was deposited. The recently active third fault system separates older graben fill and a fourth sedimentary unit. Activity on each fault system caused the rotation and uplift of previous systems, similar to the ‘flexural rotation/rolling hinge’ model, but our field observations indicate that the rotated first fault system is also active, allowing exhumation of larger amounts of rock units. This paper documents that graben formation in western Turkey is a sequential process. Its different periods are represented by three fault systems and associated sedimentation. Consequently, recent claims using age data from only the second and/or third sedimentary units to determine the timing of graben formation are misleading.

The main exhumation of the Menderes massif, western Turkey, occurred along an originally N‐dipping Datça–Kale main breakaway fault that controlled depositions in the Kale and the Gökova basins during the Oligocene – Early Miocene interval. The isostatically controlled upward bending of the main breakaway fault brings the lower plate rocks to the surface. In the Early Miocene, E–W‐trending N‐ and S‐dipping graben‐bounding faults fragmented the exhumed, dome‐shaped massif. The development of half grabens by rolling master fault hinges has allowed further exhumation of the central Menderes massif. After the Pliocene, high‐angle normal faults cut all of the previous structures. This model suggests that the Menderes massif is a single large metamorphic core complex that has experienced a two‐stage exhumation process.

The Simav metamorphic core complex of the northern Menderes massif, western Turkey, consists of a plutonic (Tertiary) and metamorphic (Precambrian) core (footwall) separated from an allochthonous cover sequence (hanging wall) by a low-angle, ductile-to-brittle, extensional fault zone (i.e. detachment fault). The core rocks below the detachment fault are converted into mylonites with a thickness of a few hundred metres. Two main deformation events have affected the core rocks. The first deformational event (D 1 ) was developed within the Precambrian metamorphic rocks. The second event (D 2 ), associated with the Tertiary crustal extension, includes two distinct stages. Stage one is the formation of a variably developed ductile (mylonitic) deformation (D 2d ) in metamorphic and granitic core rocks under greenschist facies conditions. The majority of the mylonites in the study area have foliations that strike NNW to NNE and dip SW to SE. Stretched quartz and feldspar grains define the mineral lineation trending SW-NE direction and plunging gently to SW. The kinematic indicators indicate a top-to-NE sense of shear. Stage two formation of brittle deformation (D 2b ) that affected all core and cover rocks. D 2b involves the development of cataclasites and high-angle normal faults. An overall top towards the north sense of shear for the ductile (mylonitic) fabrics in the core rocks is consistent with the N-S regional extension in western Turkey.

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