To better understand the driving mechanisms behind the transition from collision to extension in a convergent orogen, data from multiple low-temperature thermochronometers were obtained from the Simav detachment fault (SDF), the earliest developed major extensional structure recognized in the western Anatolide orogen of western Turkey. Twenty-two zircon fission track (FT), 26 apatite FT, 12 apatite (U-Th)/He ages, and 26 apatite FT track length analyses are presented. The data establish that the SDF was a major extensional fault active between ~25 and ~19 Ma. The coincidence in timing of magmatism with cessation of SDF activity implies the detachment became locked owing to doming induced by magma emplacement. Zircon FT ages away from the influence of Miocene magmatism record rapid footwall cooling between ~25 and ~21 Ma at a slip rate of up to ~15 km/Myr and demonstrate that active ductile deformation along the SDF migrated northward with time. Apatite FT ages from the footwall of the SDF are spatially invariant over >100 km and consistently ~2--3 Myr younger than the zircon fission track ages from the same samples. These data are consistent with a regional, but relatively rapid erosion-linked cooling phase that removed ~2--3 km of overburden following cessation of SDF activity but before deposition of sedimentary rocks on the detachment surface at 16.4 Ma. Postcollision extension of the Anatolide orogen with development of the SDF can be best explained as the result of postcollision magmatism and thermal weakening of the crust inducing the extensional reactivation of an earlier major out-of-sequence thrust.