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Magmatic activity in the Sakarya Zone, an important segment of the Alpine orogenic belt, continues intermittently from the middle Carboniferous to Miocene. In this study, we provide geochronological and geochemical data from the Dağdibi Pluton in the eastern Sakarya Zone to present some inferences on the source region and petrogenesis of the middle Eocene magmatism. U–Pb zircon geochronology from two granodiorite samples gives middle Eocene ages of 44.75 ± 0.92 and 45.01 ± 0.59 Ma. The pluton is mainly composed of K-feldspar, plagioclase, quartz, Mg-hornblende/actinolite, Fe–Ti oxides and small amounts of biotite, and secondary chlorite and epidote. Parental magma of the intrusive rocks has a high-K calc-alkaline affinity with metaluminous character. The oxygen fugacity values vary between −18 and −17. The rocks show slightly radiogenic 87Sr/86Sr(i) (0.704845–0.705726) ratios and ϵNdi values between −0.96 and +0.52. Pb–Pb isotope ratios are typical for those of the lower continental crust. ϵHf(i) values of the zircons range from 0.14 to 10.26. The geochemical and isotopic features of the pluton point to a parental magma derived from a depleted mantle that was metasomatized by fluids during previous subduction events. The volumetric abundances of the rock types are decreased as the silica content increase, implying that the fractional crystallization is the most important process during the formation of the present compositional range of the pluton. Amphibole, plagioclase and Fe–Ti oxides are the fractionated phases while K-feldspar is largely accumulated. In the light of the data presented above, slab breakoff is regarded as the geodynamic process responsible for the formation of the Dağdibi Pluton in the middle Eocene. [ABSTRACT FROM AUTHOR]

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

The metallogenic belt containing numerous skarn mineralized systems starting from Eastern Europe continues through Turkey and Iran. The study area in the Eastern Pontides is within this metallogenic belt. The 44.39 ± 0.53 Ma Karadağ Intrusion sourced skarn mineralization is located along the granitoid-to-limestone contact. The Karadağ Intrusion is an arc-like pluton with medium–high K calc-alkaline and peraluminous–metaluminous affinity. The Karadağ Fe–Cu skarn mineralization (Gümüşhane, Turkey), an exoskarn, is hosted by Late Cretaceous limestone and consists of early garnet, clinopyroxene, and orthoclase with late epidote and chlorite. Primary ore minerals are magnetite and haematite, accompanied by minor amounts of chalcopyrite and pyrite. Pyroxene comprises mostly diopside and less hedenbergitic diopside and johannsenite. Wollastonite is very rare. Garnet is andradite and grossular–andradite. Thus, all these results imply that the Karadağ Fe–Cu skarn mineralization formed under relatively oxidized and Fe-rich conditions. The homogenization temperatures of the fluid inclusions vary from 189°C to 405°C for quartz and 186°C to 430°C for calcite. The salinity contents in the fluid inclusions are within 0.2–9 wt% NaCl equivalent for quartz and 0.4–14.8 wt% NaCl equivalent for calcite. First melting temperatures between −36.5 and −47.4°C were attained with the presence of NaCl–FeCl2± CaCl2 in the initial phase of fluid inclusions. The first melting in the later stage of fluid inclusions is between −3.8 and −17.2°C, thereby, supporting the existence of NaHCO3-Na2CO3-KCl-type salt composition. The δ18O values of minerals are 1.7–10.3‰ for garnet, 11.1–14.6‰ for quartz, 6.4 to 6.8‰ for epidote, and 2.8–3.8‰ for magnetite in the Karadağ skarn mineralization. The δ18O value of epidote indicates magmatic fluid, whereas those of garnet, magnetite, and quartz suggest magmatic fluids together with less meteoric effect. The δ18O values in limestone (18.7 to 22.3‰), marble (8.7‰), and calcite (10.5 to 12.2‰) were depleted relative to typical δ18O contents of marine carbonates (20 to 30‰). Moreover, the C isotope values of calcite (−5.4 to −1.4‰), marble (−2.1‰), and limestone (1.0 to 1.2‰) reflect those of metamorphic rocks and skarns (−4.0 to 3‰ and −18 to 2‰). Mineral paragenesis, fluid inclusion, and stable isotopic signatures are consistent with ore mineralization caused by the interaction of magmatic fluids with carbonate host rocks. Karadağ Fe-Cu skarn mineralization, associated with Karadağ postcollisional magmatism, is an example of skarn mineralized system in the Eastern Pontides. [ABSTRACT FROM AUTHOR]

The debate about whether Eocene magmatism is considered to be post-collisional or subduction-related or not still continues. Here we offer new 40Ar-39Ar ad U-Pb zircon geochronology, mineral chemistry, bulk rock and Sr-Nd-Pb isotope geochemistry data obtained from the southern dike (SD) suite, in comparison with the northern dike (ND) suite, from the Eastern Pontides. The geochronological data indicate that the SD suite erupted between 45.89 and 45.10 Ma corresponding to the Lutetian (Middle Eocene). The magmas of the ND suite are characterised by slightly more alkaline affinity compared to the SD suite. The trace and rare earth element (REEs) content of the SD suite is characterised by large ion lithophile element (LILEs; Sr, K 2 O, Ba, Rb) enrichment and depletion of Nb, Ta, and TiO 2 elements to different degree with high Th/Yb ratios, which indicate that the magmas forming the SD and ND suites were derived from lithospheric mantle sources enriched by mostly slab-derived fluids in the spinel stability field. The Sr, Nd and Pb radiogenic isotope ratios of the dikes support the view that the magma for the hydrous group (H-SD) was derived from a relatively more enriched mantle source than the other SD and ND suites. The ND suite and the anhydrous group (A-SD) display similar geochemical features characterised by moderate light earth element (LREE)/heavy rare earth element (HREE) ratios, while the H-SD group has respectively lower LREE/HREE ratios indicating higher melting degree. Detailed considerations of the alkalinity, enrichment and partial melting degree for the source of the studied volcanic rocks indicate that the magmas of the northern dike suite are characterised by slightly more alkaline affinity, whereas the magmas throughout the southern dike suite show increments in the enrichment rate and melting degree. In light of the obtained data and comparative interpretations, the geodynamic evolution and differences in petrogenetic character of the Lutetian magmas from both the northern and southern parts of the Eastern Pontides may be explained by different degrees of melting of a net veined mantle source initially metasomatized by mostly subduction fluids during asthenospheric upwelling due to fragmented asymmetric delamination in a post-collisional extensional tectonic environment. [ABSTRACT FROM AUTHOR]

Early Cenozoic magmatism in the eastern Sakarya Zone (NE Turkey) provides an important constraint on the regional tectono-magmatic evolution of the region. Early Eocene syn-collisional adakitic rocks are observed as small stocks with outcropping areas commonly less than 10 km2. This study presents petrography, whole-rock geochemistry and Sr-Nd-Pb isotope data, as well as in-situ 40Ar/39Ar age constraints on one of these adakitic andesites in the Altınpınar area of Gümüşhane, and discusses source region, petrological processes and geodynamic setting prevailed during their genesis. Andesites commonly show microlitic porphyric and vitrophyric porphyric textures, and include significant amounts of mafic microgranular enclaves (MMEs). Plagioclase, hornblende, Fe-Ti oxides and minor pyroxene are the main mineral phases. In-situ 40Ar-39Ar amphibole dating constrains the cooling age of andesites into a time span from 52.8 ± 1.3–48.8 ± 1.9 Ma. Andesites are medium to high-K calc-alkaline and display most of the signatures typical of those of the adakites. They are characterized by moderate MgO (1.7–4.1 wt%), low Y (9−14 ppm), Yb (0.9–1.5 ppm), and HREE and high Sr (325−964 ppm) contents, and high Sr/Y (36–76) ratios. 87Sr/86Sr (t) (0.704948−0.705100) and 143Nd/144Nd (t) (0.512588−0.512628) ratios are in the isotopic range of the adakites. All these geochemical and isotopic data suggest that the parental magma of adakitic andesites has been produced by partial melting of oceanic basalts under amphibole-eclogite facies conditions during the breakoff of the northern Neotethyan oceanic slab. [ABSTRACT FROM AUTHOR]