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 Ayıdere 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 Ayıdere group consists of marble and schist lithology sequence at the base and upward amphibolite, metagranite, and metapelitic rocks.
LA – ICP –MS dating of the zircons from samples (A10- A11-A12) of amphibolite of the Kazdag group yielded 206Pb/238U age of 546.0±8.1 Ma and 548 ± 7.3 Ma. The internal structure as revealed from CL images and overall high Th/U (up to 1.16) suggest their magmatic origin. LA – ICP –MS dating of the zircons from two samples (A7 and A27) of amphibolite of the Kazdag group yielded 206Pb/238U age of 73.3±1.7 Ma (A7) and 149±0.87 Ma (A7). The internal structure as revealed from CL images and overall low Th/U (0.02-0.4) suggest their metamorphic origin. These we interpret as late Precambrian - early Cambrian ages of original rock formation (crystallization) its subsequent Jurassic and Cretaceous metamorphism in ages. This Paleozoic oceanic crust might be remnant of the Paleo Tethys Ocean in the region.
Keywords: Kazdağ metamorphic rocks, metaophiolite, the Kazdag group, north-western Turkey