Quaternary Ceyhan-Osmaniye plain and Hassa graben alkali olivine basalts were erupted along the transtensional depressions of the east Anatolian and Dead Sea left-lateral strike-slip faults in the Adana and Hatay provinces of southern Turkey, respectively. Average values of Ni, Cr, V, Y, Al 2 O 3 , MgO, MnO and SiO 2 in the Ceyhan-Osmaniye (COPB) and Hassa graben basalts (HGB) are similar to those of MORB. However, LILE, HFSE and LREE in these lavas range from 2-10 times MORB values. The COPB and HGB have similar primitive mantle-normalized trace element patterns but different major and trace element concentrations. According to La/Sm n , Gd/Yb n , Th/Yb, Zr/Y, Nb/Ta, Sr/Pr and Y/Ho ratios, geochemical differences between the COPB and HGB can be explained by variable degrees of partial melting of similar mantle sources. Al 2 O 3 contents and Ti/Ti * , Ba/Y, Ce/Y, La/Yb n and La/Sc ratios suggest greater depths of partial melting for the COPB than the HGB. Elevated concentrations of incompatible trace elements and high La/Yb n , Nb/La, Nb/Th and U/Pb ratios suggest that the COPB and HGB were generated from mantle reservoirs resembling OIB sources. Because there is no evidence for a mantle-plume in the region, the COPB and HGB were probably derived from, low degree of partial melting of metasomatically-enriched asthenospheric mantle ascended through the lithospheric fracture formed by the east Anatolian and Dead Sea strike-slip faults in southern Turkey.