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.

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