Age and petrology of Eocene-Oligocene calc-alkaline volcanism in Biga Peninsula (NW Turkey): Implications for magma origin and geodynamic evolution

In NW Anatolia, Eocene-Oligocene post-collisional volcanism is represented by K-rich volcanic rocks, including high K calc-alkaline products. Magmatic rocks in the Dededag area (Biga Peninsula, NW Turkey) can be classified into 6 different groups with lithostratigraphic and chronostratigraphic data using 40Ar/39Ar methods (Eoceneearly Oligocene, 42.08 +/- 0.09 to 29.02 +/- 0.29 Ma). From the Eocene period, there are calc-alkaline Laledag granodiorite, Beycayir volcanics with andesite and dacite composition, and also Kizildam volcanics with alkaline and basic character (basaltic trachyandesite, trachybasalt). Furthermore, in the Oligocene period, calc-alkaline volcanism started with Dededag volcanics with dacite and rhyolite intermediate-acidic composition, continued with Kircalar volcanics consisting of basalt and basaltic andesite, and Harmancik volcanics ranging from basalt to rhyolite. The calc-alkaline camyayla pluton with quartz monzonite composition intruded into Oligocene Dededag and Harmancik volcanics in the region. Alkaline lavas in the region are classified as high-K and shoshonitic, and calc-alkaline lavas are medium-high-K. On N-type mid-ocean ridge basalt and chondritenormalized trace element diagrams, enrichment was observed for all volcanic units with regard to large ion lithophile elements and light rare earth elements. High field strength elements and heavy rare earth elements were depleted in all volcanic units. These compositions reveal the participation of a mantle source that was enriched by subduction components. Using geochemical data, all the volcanic rocks differentiated as a result of magma mixing/replenishment and contamination/assimilation processes. Consequently, the source of volcanism is thought to derive from the compressional regime associated with collision during the Eocene-Oligocene, and from a previously-enriched lithospheric mantle source with subsequent effects of the extensional regime.