GEOCHRONOLOGY, PETROGRAPHY, AND GEOCHEMISTRY, OF THE KAZDAG METAMORPHIC ROCS IN THE BIGA PENINSULA – NW TURKEY
The Kazdag group consists of gneisses with marble and amphibolite intercalations at the base upwards metaophiolitic rocks tectonically lay on the basement. Metaophiolitic rocks are mainly represented by metadunite, metapyroxenite, layered metagabbro and serpentinite. The mineral assemblage in the amphibolite consists of hornblende+ plagioclase+ quartz+ clinopyroxene± biotite ± garnet ± epidote, whereas the mineral assemblage in the metaophiolitic rocks is comprised by olivine (Fo) + serpentine + orthopyroxene ± amphibole; olivine (Fo) + serpentinite ± talc ; orthopyroxene + garnet. These rocks underwent amphibolite – granulite facies metamorphism. Hornblende and plagioclase 40Ar/39Ar ages in amphibolites from the Kazdag group yield an age of 29.5 ± 4 Ma (late Oligocene) for the amphibolite – granulite facies metamorphic event. In additional to that, Rb – Sr dating ages in amphibolites of the basement of the Kazdag group present the age of 917±31 Ma indicate the age of the basement that is the oldest age to get in this region. The Kazdag metaophiolite sequence tectonically overlain on the Precambrian basement in the Kazdag region.
Geochemical data reveal that the metaophiolitic rocks of the Kazdag group are sub alkaline in nature and display tholeiitic affinity. The Kazdag metamorphics are characterized by relatively high Zr/Y (1.23 – 5.95), Th/Ta (0.67 – 16.77) and Th/ Yb (0.103 – 3.852) ratios. They show marked negative Nb and Ti anomalies, implying a subduction - related chemistry.REE patterns display enrichment of LREE fairly comparable with N- MORB. The Kazdag metaophiolitic rocks might be derived from highly depleted mantle in an arc related setting in the light of the trace and REE geochemistry.