Age and Chemistry of Miocene Volcanic. Rocks from the Kiraz Basin of the Küçük Menderes Graben: Its Significance for the Extensional Tectonics of Southwestern Anatolia, Turkey'

Abstract

Neogene volcanic rocks and granitoid plutons are among the most important geological components of western Turkey. Although they are voluminous north of the Gediz Graben, they are very scarce to the south, where volcanic rocks occur as isolated small exposures in a small number of localities. The Kiraz Basin of the Küçük Menderes Graben is a key locality, in which Tertiary volcanic rocks crop out at three locations. These rocks have been chemically analysed and dated (39Ar-40Ar whole rock and biotite analyses) in order to understand their tectonic setting of emplacement and its relation to the wider structure of western Anatolia. Whole rock and biotite 39Ar-40Ar ages vary between 13.9 ± 0.2 Ma and 14.6 ± 0.2 Ma. The Kiraz volcanic rocks are calc-alkaline, with a compositional range from basaltic andesite to dacite. They are strongly enriched in the light ion lithophile elements (LILE) and have chemistries typical of lavas erupted in subduction-related settings. Their close association with rift-bounding faults suggests eruptions via conduits flanking grabens in an extensional environment. The difference in chemical composition and age between the Kiraz volcanic rocks and the slightly older calc-alkaline volcanic rocks north of the Gediz Graben is attributed to their relatively younger ages and greater proximity to the Aegean Arc. Their calc-alkaline chemistry reflects magma generation influenced by the slab descending beneath this arc and eruption/emplacement in an extensional setting.