Geology and petrogenesis of Orhaneli volcanites, NW Anatolia (Turkey)

Miocene volcanic suites are the most common products of post-collisional magmatism in western Anatolia that is part of the Aegean extensional province. The Orhaneli volcanic field is situated in NW Anatolia and contains mafic and felsic products of post collisional volcanism coexisting rhyolite and basalt lavas and associated pyroclastic rocks. In this region, early pyroclastic products of felsic volcanism were deposited in lacustrine environment and intercalated with sedimentary rocks. Felsic pyroclastic rocks are characterized mainly by pumice-ash and ash-block fall deposits and associated ignimbrites. They interfinger with rhyolitic lava flows at the lower part of the volcanic sequence. Towards the top of the volcanic sequence basalt lavas are dominant. Distribution and K/Ar ages of rhyolite and basalt lavas show that they are closely associated in space and time (19.0-19.4 Ma and 17.5-18.7 Ma, respectively). Orhaneli volcanites are represented by predominantly High-K calcalkaline series displaying a gap in silica concentrations. They are significantly enriched in light ion lithophile elements (LILE) and light rare earth elements (LREE) but depleted in Zr, Nb and Ta. These coexisting mafic and felsic lavas have high 87Sr/86Sr values and and low 143Nd/144Nd values suggesting that their magmas derived from lithospheric mantle source. Basic parental magmas of mafic and intermediate volcanic rocks were generated from EM1-type mantle previously modified by subduction, whereas felsic volcanic rocks were produced by assimilation of silicic crust and combined fractional crystallization (AFC). Major, trace element concentrations, Sr-Nd isotope compositions combined with regional geology of western Anatolia suggest that the Early Miocene continental volcanism in NW Anatolia may have been caused by partial delamination or convective removal of the sub continental lithospheric mantle beneath western Anatolia.