Turkish Journal of Earth Sciences




Alkali basalts occur as small lava flows associated with the andesitic lava flows and pyroclastics of Early to Middle Miocene age which are the main constituents of the Galatia volcanic complex. The northern margin of the complex is bordered by the North Anatolian Fault wher eas the southern margin is surrounded by a continental sedimentary sequence which interfingers with the volcanics. New K-Ar age determinations of the basalts reveal that alkali basalts erupted at two differ ent periods of time: Early Miocene and Late Miocene. The Lower Miocene basalts are contemporaneous with the major phase of the andesitic volcanism in the area. Eruption of the Upper Miocene basalts was preceded by 10 Ma period of quiescence of eruptive activity . All the basalts, regardless of their age, display alkaline geochemical characteristics and have very similar REE and multieleme nt patterns corresponding to rift-type intra-plate basalts. Primitive mantle normalised trace element diagrams demonstrate Rb, Ba, K, Th and U (LILE) enrichment indicating a weak island arc signature. The geochemical, geochronological and field relations suggest that the Lower Miocene alkali basalts, being in the same age range as the major phase (andesitic) volcanics of the complex, erupted contemparaneously with the development of the sedimentary basins, whereas Upper Miocene alkali basalts might have erupted in local extensional zones which developed subsequent to the closure of the northern branch of Neo-T ethys.

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