Ignimbrites of Cappadocia (Central Anatolia, Turkey): petrology and geochemistry

In Cappadocia (Central Anatolia, Turkey), high-K calc-alkaline volcanic rocks have a volume of at least 1000 km3 and cover an area of about 40,000 km2. Rhyolitic to dacitic ignimbrites and two andesitic lava flows were erupted from Upper Miocene (11.2 Ma) to Quaternary times, in relation to the collision of the Arabian and Eurasian plates. K-rich rhyolitic and locally Na-rich dacitic ignimbrites are commonly intercalated with lacustrine sediments and, more rarely, with andesitic lava flows. Each ignimbrite exhibits its own mineralogical association and trace-element chemistry that enable stratigraphic correlations (i.e., Rb and Sr or Fe, Mg, Mn and Ti contents of biotite). Geochemical data (major, trace elements and Sr–Nd isotopes) show that the origin of the studied volcanic units can be related to fractional crystallisation of a mantle-derived magma. However, crustal contamination is also thought to be a major process that evolved through time. From Miocene (11.2 Ma) to Quaternary times, the ignimbritic rocks exhibit a drastic decrease of 87Sr/86Sr ratio which may be linked with the transition from collisional to extensional tectonics.