40Ar–39 Ar dating, whole-rock and Sr-Nd isotope geochemistry of the Middle Eocene calc-alkaline volcanic rocks in the Bayburt area, Eastern Pontides (NE Turkey): Implications for magma evolution in an extension-related setting

Discussions continue about whether Middle Eocene magmatism in the Eastern Pontides is associated with collision or subduction. This paper presents new whole-rock geochemistry, Sr-Nd isotopic and 40Ar-39Ar age data for volcanic rocks from Bayburt area of (NE Turkey) to investigate their sources evolutionary history. The 40Ar–39Ar ages reveal that these erupted between 44.6 ± 0.1 Ma 43.5 Ma, within Lutetian (Middle Eocene). studied are composed basalt, andesite, basaltic andesite minor dacite lava pyroclastic rocks. These consist plagioclase, amphibole, pyroxene, olivine, biotite, sanidine quartz phenocrysts Fe-Ti oxides. They have microlithic, hyalo-microlithic, porphyritic rarely glomeroporphyritic textures. low high-K calc-alkaline affinities. display enrichment large-ion lithophile elements depletion high-field strength high Th/Yb ratios, which indicate magmas forming were derived lithospheric mantle enriched by mostly slab-derived fluids spinel stability field. 87Sr/86Sr(i) values vary 0.70485 0.70551 143Nd/144Nd(i) 0.51255 0.51267. correspond array on isotope ratio diagram. main solidification processes fractional crystallization assimilation. In light obtained this study together previous studies, petrogenetic character southern parts may be explained melting an source initially metasomatized subduction a post-collisional extensional-related tectonic setting.