Rare-earth-element. radiogenic and oxygen isotope, and mineral chemical data are presented for tholeiitic and alkaline Quaternary volcanism from Karasu Valley (Hatay. southeastern Turkey). Karasu Valley is the northern segment of the Dead Sea transform fault and is filled with flood-basalt type volcanics of Quaternary age. This valley is an active fault zone that is known as "Karasu fault," extending in a NE-SW direction. The Karasu Valley basaltic volcanics (KVBV) are sub-aphyric to porphyritic. with variable amounts of olivine, clinopyroxene. and plagioclase phenocrysts. Alkali basalts are generally characterized by high contents of olivine, clinopyroxene. and plagioclase phenocrysts. Their groundmass contains olivine, clinopyroxene, plagioclase, and Fe-Ti oxides. Tholeiitic basalts are sub-aphyric to porphyritic (high contents of olivine. clinopyroxene. and plagioclase). Their groundmass is similar to that tb alkali basalts. The range of olivine phenocryst and microlite compositions for all analyzed samples is Fo(81) to Fo(43). Plagioclase compositions in both tholeiitic and alkali basalts range from andesine, An(38) to bytownite, An(72). Clinopyroxene compositions range from diopside to calcic augite. Most of the olivine. plagioclase, and clinopyroxene phenocrysts are normally zoned and/or unzoned. Fe-Ti oxides in both series are titanomagnetite and ilmenite.