The Harmancik, Orhaneli and Tavsanli ophiolites of NW Turkey are remnants of oceanic lithosphere formed in the Neo-Tethys during the Mesozoic. These ophiolites constitute part of the Izmir-Ankara suture zone which separates the Pontides to the north from the Anatolides and Taurides to the south. The Harmancik area includes a metamorphic basement, ophiolitic melange, peridotite (dunite, harzburgite), serpentinized peridotite, doleritic dykes and Neogene cover sediments. Metamorphic rocks in the Harmancik area are psammites, pelites and marbles, metamorphosed under blueschist facies conditions. They are overlain tectonically by peridotites cut by basic dykes. The dykes are dolerites, and based on texture and mineralogy, can be divided into three petrographic groups, coarse, medium-grained and porphyritic. These groups have similar chemical compositions with respect to major, trace and REE elements. When plotted on a basalt discrimination diagram the dykes plot in the IAT (Island Arc Tholeiite) field and are considered to have been intruded during subduction zone magmatism. Chondrite-normalized REE patterns for the dykes are Eu-depleted, similar to patterns for the mean dolerite composition of the NE Anatolian ophiolites, and are slightly LREE-enriched. Our results suggest that the Harmancik ophiolite is a supra-subduction zone ophiolite on which a volcanic arc sequence was built, and that the dolefite dykes were formed by the partial melting of the underlying mantle. (C) 2003 Elsevier Ltd. All rights reserved.