Zircon geochronology and petrology of cretaceous volcanics in the Tirebolu-Doğankent-Çanakçı area (Giresun, NE-Turkey)

The Late Cretaceous time in the Eastern Sakarya Zone (NE, Turkey) is represented by intensive volkanic activities that occured in two different periods, which generally consist of alternation of mafic (basaltic to andesitic) and felsic rocks series (dacitic and rhyolitic) within each period. Although there is no geochronological data for the mafic rock series of the first volkanic period, their each is know as Turonian in terms of paleontological data U-Pb zircon dating from the fisrt cycle of felsic rocks of the volkanic sequence yielded ages ranging from Coniaciyan to Early Santonian. U-Pb zircon dating for the second cycle of mafic and felsic rocks of the volkanic sequence yielded ages variying from Early to Middle Campanian. The studied mafic and felsic volcanic rocks have mostly transitional geochemical character changing from tholeiitic to calc-alkaline with typical arc signatures. Sr-Nd-Pb isotopic compositions of the studied mafic (87Sr/86Sr = 0.7051-0.7075, 143Nd/144Nd = 0.5125-0.5128, 206Pb/204Pb = 18.54-18.64, 207Pb/204Pb = 15.57-15.66 and 208Pb/204Pb = 38.42-38.75) and felsic volcanites (87Sr/86Sr = 0.7048-0.7074, 143Nd/144Nd = 0.5122-0.5129, 206Pb/204Pb = 18.59-18.85, 207Pb/204Pb = 15.37-15.66 and 208Pb/204Pb = 38.67-39.94) are different from those of subduction related I-type calc-alkaline granitoids of the same age in the region. Formerly depleted and than metasomatized mantle which was enriched by fluids and lower crust-derived differantiated mafic-intermediate mantle which experienced considerable fractional crystalization and low degree of crustal assimilation are suggested to be the parent melt of the felsic rocks.