Eker, Çiğdem Saydam; Yücel, Cem; Kaygusuz, Abdullah; Aydınçakır, Emre; Jeong, Youn-Joong; Yılmazer, Sinan; Sünnetçi, Kadir

Detrital zircons are crucial stand-ins for the history of continental crust growth and disintegration, as well as the dispersal and assembly of supercontinents. Detrital zircons are effectively used to assess crustal history because sediments transport zircons from source rocks that are no longer at the surface. This study presents detailed Lu-Hf isotopic, U-Pb geochronological analyses of zircon, Sr-Nd isotopic analyses and whole-rock geochemical results from sandstone, volcanically derived sandstone and tuff samples of the Campanian-aged Bozbent Member in the Eastern Pontide Orogen belt of the Sakarya Zone. Sedimentological analyses show that the Bozbent Member was transported and deposited by turbidite currents, while petrographic and geochemical analyses show that the sandstones range from greywacke to litharenite. In this study, U-Pb ages of detrital zircon obtained from Campanian sandstones are presented, along with in situ εHf data. A magmatic origin is indicated by the majority of zircons' oscillatory zoning and by Th/U ratios ranging from 0.2 to 1.5. The ages of detrital zircons range from 2819 to 78 Ma, with most of these zircons being Proterozoic (552–994 Ma). Proterozoic zircons are detrital zircons associated with the Gondwana and the African Craton. The whole-rock geochemical data and Sr-Nd isotope compositions of the sandstones are consistent with local Carboniferous felsic plutons, Jurassic mafic and felsic plutons, Jurassic volcanic rocks, Jurassic clastic rocks and clastic material from Precambrian recycled sediments. It was calculated that more than 90% of the detrital zircons had crystallisation ages older than their depositional ages (CA-DA > 150 Ma, indicative of an extensional basin model). These findings indicate that the Campanian-aged Bozbent Member turbiditic sequence in the Eastern Pontides was deposited in an extensional fore-arc basin and therefore exhibits the petrographic and geochemical characteristics of passive margin sandstones.

Yücel, Cem; Aydınçakır, Emre; Kaygusuz, Abdullah; Arslan, Mehmet; Yi, Keewook; Jeong, Youn-Joong; Cicerali, Derya

The Late Cretaceous magmatic history of the Eastern Pontides Orogenic Belt (NE Turkey) was generally characterized by common I-type and lesser A-type plutons in varying size and composition. Of these, A-type plutons from the Şebinkarahisar (Giresun) area yield SHRIMP zircon U-Pb age of 77.36 ± 0.96 Ma. The rocks of these plutons display a wide range of SiO2 contents (53.63 to 70.96 wt.%) and Mg-numbers (6.2–32.19) with A-type affinities characterized by enrichment in K2O and Na2O, Ga, Zr, and strong negative Eu anomalies. They also show arc-type petrochemical features including enrichment of large-ion lithophile elements (e.g. Cs, K, Rb) and light rare earth elements (LaN/LuN = 6.27–15.61), but depletion in high strength field elements (e.g. Nb, Ta, Ti, and P). The (87Sr/86Sr)i ratios and ɛNd(i) values of the studied rocks are in the range of 0.705129 to 0.0705347 and −3.64 to −3.12, respectively, while bulk rock ɛHf(i) values are between 1.86 and 4.36. They are characterized by positive zircon ɛHf(i) (1.74 to 10.88) plotting between the chondrite and depleted mantle evolutionary line values. Our data combined with the previous studies suggest that the magmas, that formed the Late Cretaceous plutons, were generated in an extensional tectonic environment due to slap roll-back and trench ward migration of the subduction zone to the south. The generation of hybrid magmas forming the studied plutons is in response to the melts derived from a metasomatized lithospheric mantle source, a relatively deeper mantle source, and the juvenile crust along with the heat transfer and decompression. Multi-sourced magmas rise through the continental crust and reach the final composition by predominantly fractional crystallization processes.

Kaygusuz, Abdullah; Güloğlu, Zikrullah Samet; Aydınçakır, Emre; Yücel, Cem; Vural, Alaaddin; Siebel, Wolfgang; Jeong, Youn-Joong

The Eastern Pontide Orogenic Belt (EPOB) hosts numerous plutonic bodies with different dimensions, compositions and ages ranging from Paleozoic to Late Eocene in NE Turkey. U-Pb zircon dating suggests that the Arslandede pluton crystallized at 44.50 ± 0.29 Ma, corresponding to the Lutetian (Middle Eocene) period. Rocks of this pluton have monzonitic character, with compositions ranging from monzodiorite to granite (SiO2 = 49˗71 wt%). The studied monzonitic rocks have I-type, metaluminous and shoshonitic character and are enriched in large-ion lithophile elements (LILEs). The rare earth elements (REEs) have concave up shape (LaN/YbN = 6.64–11.57) and show negative to slightly positive Eu anomalies (EuN/Eu* = 0.37–1.24). 87Sr/86Sr(i) values of 0.704801–0.705102 and εNd(i) values of 1.01–1.34 correspond to the mantle series on isotope ratio diagrams. Positive εHf(i) values (5.01–14.91) plot between the depleted mantle and the chondritic evolution lines. The petrological features of the rocks from the Arslandede pluton show that fractional crystallization with low rates of assimilation and/or magma mixing were effective during crystallization. All data show that the magma source of the pluton derived from an enriched lithospheric mantle and emplaced into the crust after differentiation in a deep seated magma chamber contaminated by relatively small proportions of crustal rocks.

Aydınçakır, Emre; Yücel, Cem; Kaygusuz, Abdullah; Bilici, Özgür; Yi, Keewook; Jeong, Youn-Joong; Güloğlu, Z. Samet

The Eastern Pontides in NE Turkey hosts a very limited number of plutonic rocks from the Jurassic period. Here we submit new geochemical, Sr-Nd-Pb and zircon Lu-Hf isotope data, and zircon U-Pb ages for plutonic rocks in this region. Zircon U-Pb dating for the Alemdar and Işıkdere plutons yielded an age of 175–170 Ma (Middle Jurassic). The Alemdar and Işıkdere plutons have I-type, medium to high-K calc-alkaline series, and metaluminous to slightly peraluminous characteristics. On PM-normalized diagrams, the plutons are enriched in large-ion lithophile elements (LILEs) with pronounced depletion of high field strength elements (HFSEs, Ta, Nb, Ti). Chondrite-normalized plots for the plutons show variable enrichment in light rare earth elements (LREEs) with depletion of heavy rare earth elements (HREEs). The rocks of the Alemdar Pluton have homogeneous ISr values (0.70585 to 0.70673), low εNd(i) values (−3.9 to −1.6), pozitif εHf(i) values (+3.3 to +9.1), and Hf single-stage model ages (563–712 Ma), whereas those of Işıkdere have high ISr values (0.70666 to 0.70673), low εNd(i) values (−3.9 to −3.8), εHf(i) values (−3.1 to +1.1), and Hf single-stage model ages (791–969 Ma). These values imply that they have different sources. These results suggest that the magma of the Alemdar was formed by the partial melting of a relatively depleted lithospheric mantle wedge interaction of the OIB-like melts, while those of Işıkdere have derived from the partial melting of an enriched mantle metasomatized by slab-derived sediments and then modified by fractional crystallization and crustal contamination in crustal magma chambers. Considering the available data, we conclude that the studied plutons were related to extensional tectonic events during the Middle Jurassic in response to the roll-back of the Paleotethys oceanic slab in the final stage of oceanic closure. These rocks are an example of the formation of deep subduction products following Early Jurassic subduction.

Kaygusuz, Abdullah; Yücel, Cem; Arslan, Mehmet; Temizel, İrfan; Yi, Keewook; Jeong, Youn-Joong; Siebel, Wolfgang; Sipahi, Ferkan

The Eastern Pontides orogenic belt in NE Turkey hosts numerous I-type plutons of Eocene epoch. Here, we report new U–Pb SHRIMP zircon ages and in situ zircon Lu-Hf isotopes along with bulk-rock geochemical and Sr-Nd-Pb-O isotope data from the Kemerlikdağı, Aydıntepe and Pelitli plutons and mafic microgranular enclaves (MMEs) to constrain their parental melt source(s) and evolutionary processes. U-Pb SHRIMP zircon dating yielded crystallization ages between 45 and 44 Ma for the studied plutons and their MMEs. The plutons range from gabbro to granite and have I-type, medium to high-K calc-alkaline, and metaluminous to slightly peraluminous characteristics. On the primitive mantle-normalized multi-trace-element variations, the plutons and their MMEs are characterized by significant enrichment in LILE/HFSE. Chondrite-normalized REE patterns of the plutons and their MMEs are close to each other and show moderate enrichment with variable negative Eu anomalies. The studied plutons have fairly homogeneous isotope composition (87Sr/86Sr(i) = 0.70502 to 0.70560; εNd(i) = +0.9 to–1.4; δ18O = +5.0 to +8.7‰, εHf(i) =–2.2 to +13.5). The MMEs show medium to high-K calc-alkaline and metaluminous character. Although the isotope signatures of the MMEs (87Sr/86Sr(i) = 0.70508 to 0.70542; εNd(i) = +0.9 to −1.1; δ18O = +5.8 to +8.0, εHf(i) = +4.3 to +10.4) are very similar to those of the host rocks. Fractionation of plagioclase, amphibole, pyroxene and Fe-Ti oxides played an important role in the evolution of the plutons. The isotopic composition of the studied plutons and MMEs are similar to I-type plutons derived from mantle sources. The MMEs show incomplete magma mixing/mingling, representing small bodies of mafic parental magma. The parental magma(s) of the studied plutons were generated from the enriched lithospheric mantle and then modified by fractional crystallisation, and lesser assimilation and mixing/mingling in the crustal magma chambers.

Eyuboglu, Yener; Dudas, Francis O.; Santosh, M.; Zhu, Di-Cheng; Yi, Keewook; Chatterjee, Nilanjan; Jeong, Youn-Joong; Akaryali, Enver; Liu, Ze

The Eastern Pontides Orogenic Belt represents one of the best examples of fossil convergent margins in the eastern Mediterranean region. However, the origin and geodynamic setting of the late Mesozoic-Cenozoic magmatism in this belt remain controversial due to lack of systematic geological, geochemical and chronological data. The general consensus is that the late Mesozoic-Cenozoic igneous activity is related to northward subduction of oceanic lithosphere in the late Mesozoic and following collision between Tauride and Pontide blocks in the early Cenozoic Here we present a comprehensive study focusing on the origin and geodynamic setting of gabbro bodies exposed along a narrow zone, parallel to the southeastern coast of the eastern Black Sea basin, in the Northern Zone of the Eastern Pontides Orogenic Belt. The studied gabbro bodies are hosted within late Cretaceous basaltic, andesitic, and dacitic volcanics including pyroclastic rocks and interbedded sedimentary rocks. The gabbro bodies range in size from 0.1 km(2) to 1.5 km(2), and outcrop patterns vary from round or elliptical to markedly elongate with sharp and discordant contact with the host rocks. Their mineral assemblage includes mainly clinopyroxene, plagioclase, minor olivine, amphibole, magnetite and rarely orthopyroxene, biotite, zircon and titanite. The occurrence of sutured grain boundaries on clinopyroxene and plagioclase, and the presence of reverse compositional zoning in clinopyroxene and olivine suggest mixing between magmas of contrasting compositions during mineral growth. Thermobarometric computations indicate that the temperature at the beginning of crystallization was similar to 1250 degrees C and crystallization was polybaric Zircon and titanite U-Pb ages indicate that these small intrusions were emplaced into crustal rocks of the Eastern Pontides Orogenic Belt during Lutetian (45 +/- 2 Ma). The depletion of HFSE is consistent with the involvement of an arc-related source in the petrogenesis of these rocks, and low to moderate enrichment Ce, Rb, Ba, K, Pb, Sr and Th suggests that involvement of subducted oceanic sediment was modest. The low Th content and low Th/Yb indicate that the role of sediment addition was nevertheless limited. The Nd, Sr and Pb isotopic data are consistent with the interpretation that the dominant source component in these gabbros is a depleted, peridotitic mantle, and that crustal contamination is relatively unimportant. We suggest that mafic magmas that produced the gabbroic intrusions were derived from melting of a depleted mantle source under the forearc region of the Eastern Pontides Orogenic Belt during southward subduction of two oceanic plates separated by a mid-ocean ridge, leading to the formation of a slab window. We also infer fractional crystallization and assimilation during both magma storage in the crust-mantle transition zone and transfer into the overlying arc crust. (C) 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.