Temporal, geochemical and geodynamic evolution of the Late Cretaceous subduction zone volcanism in the eastern Sakarya Zone, NE Turkey: Implications for mantle-crust interaction in an arc setting

The Late Cretaceous Artvin volcanic rocks (LCAVs) from the eastern Sakarya zone (ESZ) of NE Turkey are composed of mafic/basaltic (S1-Çatak and S2-Çağlayan) and felsic/acidic (S1-Kızılkaya and S2-Tirebolu) rock types that occurred in two successive stages: (i) first stage (S1: Turonian–Early Santonian) and (ii) second stage (S2: Late Santonian–Campanian). Clinopyroxene thermobarometric results point that the S2-Çağlayan basaltic rocks have crystallised at higher temperatures and under deeper crustal conditions than those of the S1-Çatak basaltic rocks. The LCAVs show a wide compositional spectrum, ranging from tholeiite to calc-alkaline/shoshonite and are typically represented by a geochemical composition resembling subduction-related arc rocks although the 87Sr/86Sr(i) (0.7044–0.7071) and ɛNd(i) values (−0.63 to + 3.47) as well as 206Pb/204Pb(i) (18.07–18.56), 207Pb/204Pb(i) (15.57–15.62) and 208Pb/204Pb(i) (37.12–38.55) ratios show very limited variation. The parent magmas of the S1-Çatak and S2-Çağlayan mafic volcanic rocks were derived from underplated basaltic melts that originated by partial melting of metasomatised spinel lherzolite and spinel-garnet lherzolite, respectively. It is proposed that the compositions of the S1-Kızılkaya (mainly dacitic) and S2-Tirebolu (rhyolitic to trachytic) felsic rocks were particularly controlled by metasomatised mantle–crust interaction and MASH zone + shallow crustal fractionation processes. Our data, together with data from previous studies, suggest that the S1- and S2-mafic and felsic rocks of the LCAVs (~95–75 Ma) are the products of two-stage volcanic event that took place during the northward subduction of the northern Neotethys Ocean (NNO).