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

摘要

The Late Cretaceous Artvin volcanic rocks (LCAVs) from the eastern Sakarya zone (ESZ) of NE Turkey are composed of mafic/basaltic (S1-catak and S2-caglayan) and felsic/acidic (S1-Kizilkaya 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-caglayan basaltic rocks have crystallised at higher temperatures and under deeper crustal conditions than those of the S1-catak 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 Sr-87/Sr-86(()1) (0.7044-0.7071) and epsilon Nd-(1) values (-0.63 to + 3.47) as well as (206)pb/Pb-204((1)) (18.07-18.56), 207pb (207)pb/Pb-204((1)) (15.57-15.62) and(208)pb/Pb-204((1)) (37.12-38.55) ratios show very limited variation. The parent magmas of the S1-catak and S2-caglayan mafic volcanic rocks were derived from underplated basaltic melts that originated by partial melting of metasomatised spinet Iherzolite and spinel-garnet lherzolite, respectively. It is proposed that the compositions of the S1-Kizilkaya (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 (similar to 95-75 Ma) are the products of two-stage volcanic event that took place during the northward subduction of the northern Neotethys Ocean (NNO).