Petrogenesis of the Neogene bimodal magmatism of the Galatean Volcanic Province, Central Anatolia, Turkey

A series of geochemical analyses and radiometric age determinations are undertaken on rock samples collected from the Çamlıdere region in the Galatean Volcanic Province of NW Turkey, to better understand the characteristics of the bimodal Early-Middle Miocene volcanism developed near the Late Cretaceous Tethyan Suture Zone. Çamlıdere volcanic rocks consist of large volumes of older (> 20 Ma) calc-alkaline andesites, dacites and rhyolites and pyroclastites, and small volumes of slightly younger (~ 19 Ma) alkaline trachybasalts and basaltic trachyandesites, cropping out as dykes or small lava flows. The older rocks exhibit elevated LILE, LREE and depleted HFSE contents, carrying geochemical characteristics suggesting earlier subduction process. Some samples of the younger mildly alkaline lavas display geochemical characteristics of intraplate magmatism with enrichment of LILE contents with little or no HFSE depletion. Knowing that the Galatean volcanic rocks experienced syn-volcanic extensional tectonics during the Miocene, we think that the reactivation of the old suture zone produced first calc-alkaline series originated from a subduction-modified subcontinental lithospheric mantle, followed by more alkaline products. However, some volcanic rocks suggest penetration of small amounts of asthenospheric melts to this lithospheric mantle source. The regionally known last volcanic phase produced small amounts of alkaline basaltic rocks in Güvem area at about 10 Ma. Volcanic activities ended possibly with, or just after the Güvem event, when the extensional tectonic regime switched to strike-slip faulting in the region, with the inception of one of the major faults of Turkey, the North Anatolian Fault Zone.