Western Anatolia (Turkey) has experienced discrete pulses of widespread volcanism since the collision of the Sakarya and Tauride continental blocks in the early Eocene. Underplating of the leading edge of the Tauride platform at a north-dipping subduction zone beneath the Sakarya continent resulted in crustal thickening and detachment of the Neo-Tethyan oceanic lithosphere from continental lithosphere, causing slab break-off and the development of an asthenospheric window. Thermal perturbation caused by this asthenospheric upwelling led to melting of the meta-somatized overriding mantle lithosphere that produced volcanism and granitic plutonism across the suture zone and the Sakarya continent. The products of this first episode of postcollisional volcanism in western Anatolia were subalkaline in character, with rocks ranging in composition from basalt, basaltic andesite, and andesite to dacite; they show enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE) relative to the high field strength elements and display the highest (87)Sr/(86)Sr (i) (0.7087 to 0.7071) and the lowest epsilon Nd (i) (-6.5 to -3.5) values in comparison to the rocks of the following volcanic episodes. Geochemical features and compositional variations of this subalkaline volcanic group indicate increasing amounts of crustal contamination and a decreasing subduction signature during their evolution from the Eocene through the Oligo-Miocene.