It is proposed that north-south crustal extension and related sedimentary basin formation commenced in the early Miocene. This extension is believed to be related to a spreading of a thickened crust as a result of Palaeogene compression. That such spreading commenced virtually immediately after the cessation of this compression is considered to be due to the high thermal profile of the crust in that area at the end of the Palaeogene.

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.

This paper expands the K-Ar dating and palynologically controlled stratigraphical data base reported in earlier papers to the north trending Selendi and Uşak-Güre basins located to the north of east-west trending Alaşehir graben in western Turkey. These north trending basins began to form during Early Miocene times and most of their basin fills accumulated before 14 Ma, except for the youngest Asartepe formation. Recent studies of both east-west grabens and north trending basins show that they started to develop simultaneously during Early Miocene times under the north-south extensional regime, and the classification of the structures as 'replacement' and 'revolutionary' has no meaning for the Alaşehir graben and the basins located to its north.

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.

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