We provide new isotopic data from the Kazdag Massif which is the metamorphic basement of the Sakarya Zone, a micro continental fragment in NW Anatolia, which substantiate the presence of a Precambrian basement tectonically overlain by a Palaeozoic oceanic crust assemblage consisting of meta - ultramafic rocks. The Kazdag metamorphic rocks are divided into two groups: the Kazdag group (the lower unit) and the Ayidere group (the upper unit). The Kazdag group consists of gneisses with marble and amphibolite intercalations, overlain tectonically by metaophiolitic rocks. Metaophiolitic rocks are mainly represented by metadunite, metapyroxenite, layered metagabbro, serpentinite and amphibolite. The Ayidere group consists of marble and schist lithology sequence at the base and upward amphibolite, metagranite, and metapelitic rocks.