Contemporaneous subduction-related and intraplate Quaternary magmatism in Cappadocia (central Anatolia)

Widespread volcanism occurred in central Anatolia during the Quaternary in response to continental collision among Eurasia, Africa and Arabia plates. As a result of this event, the southern part of Eurasian plate was dismembered and, subsequently, the Anatolian block began to be expelled westward along the North and East Anatolian faults. In this scenario, the petrochemical evolution of the volcanism is strictly related with the tectonic evolution of the area. The Cappadocia region, confined by the Tuz Golu and Ecemis strike-slip fault systems (also known as Central Anatolia Fault System), is characterized during the Quaternary by volcanic products with bimodal petrological and geochemical features. Indeed calc-alkaline and Na-alkaline volcanic rocks, with subduction-related and within plate characters, respectively, do occur intimately associate in space and slightly differentiated in time. Calc-alkaline volcanic rocks range in composition from basalts to rhyolites. They are found around the Acigol caldera, the Gollu Dag dome and around the Hasan Dag and Ercyies Dag stratovolcanoes. Within-plate related Na-alkaline volcanic rocks range in composition from basanites to alkali basalts. They are found as monogenetic centres in Karapinar, along the WSW flank of Hasan Dag and near the Kizilirmak river, north-west of Nevsehir. No clear evidence for a time-related shift from calc-alkaline to Na-alkaline volcanism is observed, differently from what occurring in the western and eastern Anatolia regions where calc-alkaline volcanic rocks are distinctly older than Na-alkaline ones. In Cappadocia, calc-alkaline and alkaline rocks mostly have similar age range (1.98-0.018 Ma) and sometimes a complete time overlapping between subduction related and within-plate volcanic rocks is observed, as in the case of the Acigol-Nevsehir Complex. In addition, there is a limited variation in the radiogenic isotopic compositions of subduction-related and within-plate volcanic rocks with 87Sr/86Sr within the ranges from 0.70395 to 0.70458 and from 0.70334 to 0.70553, respectively and 143Nd/144Nd, 0.51268-0.51287 and 0.51268-0.51293, respectively. The genesis and ascent of the different type of magmas is clearly related with the complex tectonic setting of the area in which strike-slip faults are associated to the formation of local extensional pull-apart basins. In this frame, the geochemical features of the calc-alkaline magmatism of this region are consistent with derivation of magmas from a mantle modified by a subduction component, whereas Na-alkaline activity may derive from a deeper asthenospheric mantle source not affected by this metasomatic event.