Temporal and chemical changes during the Late Cretaceous arc magmatism in the Western Pontides (Turkey)

During the Late Cretaceous, a 2700 km long magmatic arc extended from the Lesser Caucasus through the Pontides into Srednogorie, Timok, Banat, and Apuseni (ABTS) in the Balkans. We studied the arc volcanic rocks in three regions of the Western Pontides, and compared them to the other arc magmatic rocks from the Lesser Caucasus, Eastern Pontides and Balkans. Prior to the onset of the arc magmatism, the region underwent uplift and erosion. New and published geochronologic and biostratigraphic data indicate that magmatism in the Lesser Caucasus, Pontides and Balkans started during the Turonian (ca. 93 Ma), peaked in the middle Campanian (80–78 Ma), and subsequently became rare and sporadic after the late Campanian (ca. 75 Ma). The arc magmatism, characterized by typical subduction signatures, was mainly of middle to high-K calc-alkaline affinity. Late Cretaceous volcanism occurred in a submarine and extensional environment. Along the whole belt, the arc volcanic rocks are overlain by Maastrichtian to Paleocene marine limestones and sandstones, marking the end of the main phase of arc magmatism. However, in the Western Pontides, Maastrichtian limestone sequence includes a volcanic horizon with a U-Pb zircon age of ca. 71 Ma. The geochemistry of the Maastrichtian volcanic rocks is more diverse compared to the older arc volcanic rocks, including alkaline and calc-alkaline basalts, as well as adakitic dacites. The coeval initiation of arc magmatism along the 2700-km-long magmatic arc is associated with the acceleration of Africa-Eurasia convergence at ca. 96 Ma, which is also independently indicated by the beginning of intra-oceanic subduction, inferred from the ages of suprasubduction-zone ophiolites and sub-ophiolite metamorphic rocks in Anatolia. The end of the magmatic activity in the arc is associated with a marked decrease in the convergence rate during the Campanian.