Petrology and geochronology of Camas and Ahmetli (Fatsa-Ordu) plutons

Sakarya Zone have a huge magmatic activity during Late cretaceous to Middle-Late Eocene periods. In the region, this research Project aims to explain source characteristics and geodynamic setting of the Camas and Ahmetki plutons having spatial relationships with I-type granitoid from the region. The plutons are made up of syenite, quartz monzonite and monzonite with rarely mafc microgranular enclaves which are more common in their I-type equvalents. The LA-ICP-MS zircon U-Pb age data reveal that the pluton crystallized at 69.5  0.6 Ma before. The samples have elevated Zr+Nb+Ce+Y and low Mg# (usually <42) values. The plutons are of metaluminous to peraluminous (ASI=0.85 to 1.03) and belongs to shoshonitic and ultra-potassic series. The samples are enriched in LREE and exhibit significant negative Eu (Eu/Eu*=0.49 to 0.80), Ba, Nb, Sr and Ti anomalies In spidergrams. Their relatively high Sr-Nd isotopic compositions ISr(69.5 My) = 0.70519 to 0.70607, low Mg# (32-45) and εNd (69.5 Ma) = -1 to -0.3, TDM= 0.81 to 0.93 Ga), revealing that the pluton was formed by lower crustal parental magma with a contribution of lithospheric mantle. we proposed that upwelling of hot asthenosphere triggers melting of chemically enriched mantle and basic magma formed. Then the basic and hot magma underplated to lower part of the lower crust. This results in partial melting of lower crust. All the data combined with regional background, we suggest that the plutons originated in back-arc extensional phase of subduction environment during Latest Cretaceous in the region.