Volcanic rocks in western Turkey show age progressive magmatism migrating from northeast to southwest that reflects a southward shift of the Aegean subduction zone during the Miocene. Slab segmentation during this period of trench-roll back is thought to have imposed source region heterogeneity trending northwest to southeast. In this study, we present new Sr, Nd, Pb and 0 isotopic analyses from the Miocene volcanic rocks of the Usak-Gure basin and compare these to previously published data. The data demonstrate a change from subduction-related sources around the Menderes Core Complex to more asthenospheric sources in the Afyon region. Isotopic compositions (Sr-Nd-Pb) of volcanic rocks from the Demirci and Selendi basins to the west and the Afyon volcanic area to the east indicate minimal upper crustal contamination. The most primitive lavas also reveal increasing K contents from west (the NE-SW-trending basins) to east (Afyon region). It is suggested that the composition of the western Anatolian volcanic rocks change from orogenic (with lithospheric mantle sources) associated to denudation of the Menderes Massif Core Complex (MMCC) to anorogenic (with asthenospheric mantle sources) in the vicinity of the Kirka-Afyon-Isparta (KAI) volcanic province with time, from Early Miocene to Quaternary. There is no asthenospheric contribution during the late Miocene onwards in the eastern margin of the MMCC, while the asthenospheric upwelling occurred only in a small area beneath the exhuming core complex. We interpret the U Usak-Gure basin to reflect a structural boundary showing a transition from a subduction-influenced metasomatized mantle source to asthenospheric mantle source volcanism driven by slab-tearing between the Hellenic and Cyprus slab segments. The Usak-Mugla Transfer Zone (UMTZ) most likely corresponds to slab-tear related westernmost faults that were induced by initiation of slab segmentation processes following the late Miocene (circa 11 Ma), and possibly since the Early Miocene. (C) 2014 Elsevier B.V. All rights reserved.