EARLY MIOCENE MILDLY-ALKALINE VOLCANISM IN THE KARACADAG AREA (CENTRAL ANATOLIA, TURKIYE)

In the Karacadag area (Central Anatolia, Turkiye), small volumes of mildly-alkaline lavas associated with large volumes of calcalkaline lavas crop out. 40Ar/39Ar age data indicate that the mildly-alkaline lavas were erupted during Early Miocene (ca. 18 Ma). The lavas are composed of alkali basalt, hawaiite, mugearite, benmoreite and trachydacite, and include olivine, ortho/clinopyroxene, amphibole, plagioclase, opaque and rare anorthoclase. The mildly-alkaline lavas have a sodic tendency (Na2O/K2O = 1.5-3.2) and resemble those of within-plate lavas. Alkali basalts of the suite were derived from a heterogeneous mantle source which is lithospheric mantle previously enriched by small degree melts from the astenosphere, plus possibly a depleted asthenospheric mantle. Melting modeling based on REE indicates that alkali basalts formed by 1-5 % partial melting of a spinet lherzolithic mantle source. Also, petrologic modeling based on trace element and isotopic data shows that fractional crystallisation played an important role in the evolution of the mildly-alkaline suite than AFC (assimilation and fractional crystallisation).