Abstract: The Upper Eocene Kösedağ pinion, outcropping in the eastern pat of the CE Anatolian alkaline province, intrudes in thetrachybasalts and basalt ic-trachyandcsites of the M.Eocene volcano-sedimentary unity and is unconformably overlain by the LowerMiocene (Aquitanian) lagoonal limestones. The main structural elements are composed of oblique and normal faults with NE-SW direction and some joint systems developed in the pluton. Kösedağ pinton represents an isotropic joint system character, however, some joints with the directions ofEWl 40S and N65EI perpendicular are seen to be dominant. The eastern part of Kösedağ pluton canbe mapped as two mapahle fades such as medium to coarse, and fine-grained fades. The medium to coarse grained fades, constituting the main body, consists mainly of quartz-syenite, syenite and rarely of monzonilic rocks. The fine-grained rocks which are seenas small intrusions within the main body arc syenitic in composition. The major mafic constituents of the syenitic and monzoniticrocks of the eastern part of Kösedağ pluton consist ofamphibole (hornblende,kaersutite), clinopyroxene (augite and scarcely aegirine-augite) and biotite minerals. These rocks show cafemic (CAFEM), metaluminous (Na+K< Al), and silica saturated alkaline(ALKS) character. The RI-R2 parameters indicate a "late orogenic" setting, and also some trace element data such as Y-SiO2, NbSiO2, Rb-SiO2, Nb-Y and Nh+Y-Rb diagrams represent a WPG origin for the Kösedağ pluton. These features are thought to be sourced in a post-coUisional (POST-COLG) environment. This is also supported by some trace element diagrams. On the basis of all tliese data and regional geological setting, the Kösedağ pluton can be considered to be derived from a magma which was generatedfrom the upper mantle by the tensional regime in the passive margine towards the final stages of the crustal thickening just after the collision related to the northward subduct ion of the northern branch of the Neo-Tethys. On the other hand, such a magma source is thought to have been contaminated by some crustal material.