GEOCHEMISTRY OF QUATERNARY BASALTS ERUPTED ALONG THE EAST ANATOLIAN AND DEAD-SEA FAULT ZONES OF SOUTHERN TURKEY - IMPLICATIONS FOR MANTLE SOURCES

Quaternary Ceyhan-Osmaniye plain and Hassa graben alkali olivine basal ts were erupted along the transtensional depressions of the east Anato lian and Dead Sea left-lateral strike-slip faults in the Adana and Hat ay provinces of southern Turkey, respectively. Average values of Ni, C r, V, Y, Al2O3, MgO, MnO and SiO2 in the Ceyhan-Osmaniye (COPE) and Ha ssa graben basalts (HGB) are similar to those of MORE. However, LILE, HFSE and LREE in these lavas range from 2-10 times MORE values. The CO PE and HGB have similar primitive mantle-normalized trace element patt erns but different major and trace element concentrations. According t o La/Sm-n, Gd/Yb-n, Th/Yb, Zr/Y, Nb/Ta, Sr/Pr and Y/Ho ratios, geochem ical differences between the COPE and HGB can be explained by variable degrees of partial melting of similar mantle sources. Al2O3 contents and Ti/Ti, Ba/Y, Ce/Y, La/Yb-n and La/Sc ratios suggest greater depth s of partial melting for the COPE than the HGB. Elevated concentration s of incompatible trace elements and high La/Yb-n, Nb/La, Nb/Th and U/ Pb ratios suggest that the COPE and HGB were generated from mantle res ervoirs resembling OIB sources. Because there is no evidence for a man tle-plume in the region, the COPE and HGB were probably derived from, low degree of partial melting of metasomatically-enriched asthenospher ic mantle ascended through the lithospheric fracture formed by the eas t Anatolian and Dead Sea strike-slip faults in southern Turkey.