Abstract: Quaternary volcanic rocks widespread in Ceyhan, Osmaniye,Yumurtalık and Haruniyeregions are investigated petrologically to interpret the type of crust from which they originated. The rocks are composed mainly of plagioclase, augite andolivine phenoerysts and ground massof similar bult chemistry. They are plateau basalts of tholeiiticcharacter with a weak alkaline affinity. The area lies in a critical region from the point of view of plate tectonics.Thus, detailed petrochemical work: has been carried  out; as a result of attachment of great importance of geochemistryof volcanic rocks to lead to plate tectonic interpretations.  Sedimentary rocks of Cenozoic age are also briefly described.