Jurassic metabasic rocks in the Kızılırmak accretionary complex (Kargı region, Central Pontides, Northern Turkey)

Abstract The Kizilirmak accretionary complex near Kargi is tectonically bounded by the Jurassic and Early Cretaceous metamorphic massives of the Central Pontides. It consists mainly of serpentinite, serpentinized peridotite, gabbro, basalt, metabasite and deep-marine sedimentary rocks. The metabasites in the Kizilirmak accretionary complex are tectonically located within a serpentinite, radiolarian chert, spilitized basalt, gabbro association and commonly display a steep contact with serpentinites. Amphiboles from metabasites yielded robust 40 Ar/ 39 Ar plateau ages ranging between 159.4 ± 0.4 Ma and 163.5 ± 0.8 Ma. These are interpreted as cooling ages of the metabasites. The metabasites have 87 Sr/ 86 Sr (i) between 0.7035 and 0.7044 and 206 Pb/ 204 Pb (i) ranging between 18.18 and 18.92. The gabbros have higher 87 Sr/ 86 Sr (i) between 0.7044 and 0.7060 and 206 Pb/ 204 Pb (i) ranging between 17.98 and 18.43. Three basalt samples display 87 Sr/ 86 Sr (i) between 0.7040 and 0.7059. Their 206 Pb/ 204 Pb (i) are unrealistically low (15.42 and 15.62), suggesting, most likely, Pb loss which results in over-corrected values for decay through time. Pb–Sr–Nd isotopic compositions for all samples consistently plot between the fields of MORB or the Depleted MORB Mantle reservoirs and enriched mantle reservoirs (EMII rather than EMI). All the samples (except one dolerite dike) have negative ɛNd DM(t = 160 Ma ) values, suggesting derivation from a reservoir more enriched than the depleted mantle. The protoliths of metabasites correspond to diverse sources (N-MORB, E-MORB, OIB and IAT) based on whole rock major and trace element composition. An IAT-like protolith for the metabasites indicates that the Izmir–Ankara–Erzincan ocean domain was subducting and the tectonic regime was compressional during Late Jurassic and before. The protoliths of these rocks were metamorphosed during the subduction/accretion processes, as observed in the metamorphic rocks located along the Balkan, Northern Turkey and Armenia/Iran ophiolites and/or accretionary complexes. IAT-like geochemistry for the gabbro/dolerites indicates that the non-metamorphosed basaltic rocks occurred in a supra-subduction tectonomagmatic environment and is in agreement with their radiogenic isotope compositions.