Temporal constraints on magmatic evolution of Acıgöl Bimodal Volcanic Field (Nevşehir, Türkiye)

Neogene to Quaternary post-collisional Central Anatolian volcanism is associated with complex tectonic transition from collisional to extensional regime starting from Miocene. Upper Miocene – Pliocene volcanism is characterized by calc-alkaline effusive products and 10 major ignimbrite sheets. Quaternary represents an evident change in both eruptive styles and the geochemical characteristics of the volcanic products. Pleistocene Acıgöl Bimodal Volcanic Field (ABVF) represents one of the youngest volcanism in Cappadocian Volcanic Province (CPV) and comprises coeval basic and acidic rocks with a Daly Gap between ∼60 % and 72 % SiO₂. Pleistocene basaltic volcanism in ABVF is represented by fissural lavas and monogenetic scoria cones, whereas rhyolitic activity is observed as dome/dome flows and pyroclastics including plinian falls and Kumtepe ignimbrite. Basalts of Lower and Middle Pleistocene are silica-undersaturated being nepheline-normative, on the other hand, Upper Pleistocene basic rocks are hypersthene/quartz-normative. Similarly, Lower and Middle Pleistocene rhyolites have higher Sr, Ba, La, than Upper Pleistocene rhyolites which are represented by elevated Y, Th, Nb, Ta and Rb.

Petrological data and performed geochemical models show that Lower – Middle Pleistocene primitive basalts can be generated by the partial fusion of an EM-II type spinel peridotite containing amphibole, phlogopite and accessory rutile. Slightly evolved Upper Pleistocene basalts can be formed by crystal fractionation dominated differentiation of earlier basaltic parents. Fractional crystallization of basaltic magmas in high-level segregated chambers with varying amounts of crustal contribution can produce rhyolitic compositions. Furthermore, the amount of crustal contribution diminishes in Upper Pleistocene.