Gümüşhane ÜniversitesiGümüşhane ÜniversitesiAçık Erişim Arşivi · RDL Open

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  • MakaleYalnız künye2016
    Subduction-related Late Carboniferous to Early Permian Magmatism in the Eastern Pontides, the Camlik and Casurluk plutons: Insights from geochemistry, whole-rock Sr–Nd and in situ zircon Lu–Hf isotopes, and U–Pb geochronology

    Karsli, Orhan; Dokuz, Abdurrahman; Kandemir, Raif

    Late Carboniferous to early Permian granitoid rocks represent a volumetrically minor component of the Eastern Pontide lithosphere, but they preserve useful information about the region's tectonomagmatic history. The Casurluk and Camlik plutons primarily consist of gabbro, gabbroic diorite, diorite, monzogabbro, monzodiorite and monzonite, which intrude early to middle Carboniferous granitic basement rocks in the region. In this study, we use in situ zircon U–Pb ages and Lu–Hf isotopic values, whole-rock Sr–Nd isotopic values, and mineral chemistry and geochemistry of these plutons to determine petrogenesis and crustal evolution; we also discuss geodynamic implications. LA–ICP-MS zircon U–Pb dating of magmatic zircons from the rocks suggests that the plutons were emplaced during the late Carboniferous to early Permian (302 Ma). The metaluminous and I-type intrusive rocks belong to the high-K calc-alkaline series. In addition, they are relatively enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs); they are depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs), such as Nb and Ti. All of the samples have homogeneous initial ISr values (0.70675 to 0.70792) and low εNd (t) values (− 5.1 to − 3.3). Zircons from the rocks of both plutons have uniform negative to slightly positive εHf (t) values (− 3.5 to 1.4) and old Hf two-stage model ages (1323 to 1548 Ma), implying that they have the same source, as well as suggesting the involvement of old enriched lithospheric mantle materials during their magma genesis. These results, combined with the εHf (t) values and two-stage model ages, demonstrate that the primary magmas were derived from partial melting of old lithospheric mantle material metasomatized by subduction-related fluids. Considering other regional geological data from the Sakarya Zone where these plutons formed, we conclude that late Carboniferous to early Permian magmatism in the area involved the partial melting of a phlogopite- and spinel-bearing lherzolite under an extensional regime in a subduction-related setting. Such an extension event would have caused hot asthenospheric upwelling and was likely triggered by back-arc rifting during subduction of the Paleo-Tethyan oceanic slab. Thus, the magmas are likely subduction-related products, implying that southward subduction of Paleo-Tethys oceanic lithosphere in the region began during the late Carboniferous to early Permian.

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  • MakaleAçık Erişim2016
    Geochronology and geochemistry of Eocene-aged volcanic rocks around the Bafra (Samsun, N Turkey) area: Constraints for the interaction of lithospheric mantle and crustal melts

    Temizel, Irfan; Arslan, Mehmet; Yücel, Cem; Abdioğlu, Emel; Ruffet, Gilles

    40Ar-39Ar age, whole-rock chemical, and Sr-Nd isotope data are presented for the post-collisional, Eocene (51.3-44.1 Ma)-aged volcanic rocks from the Bafra (Samsun) area in the western part of the Eastern Pontides (N Turkey) aiming to unravel their sources and evolutionary history. The studied Eocene volcanic rocks can be divided into two groups: analcime-bearing (tephritic lava flows and dykes) and analcime-free (basaltic to trachytic lava flows and basaltic dykes). The analcime-bearing volcanic rocks have a fine-grained porphyritic texture with clinopyroxene phenocrysts, whereas analcime-free volcanic rocks show a variety of textures including hyalo-microlitic microgranular porphyritic, intersertal, trachytic, fluidal, and glomeroporphyritic. The volcanic rocks also show evidence of mineral-melt disequilibrium textures such as sieved, rounded, and corroded plagioclases, partially melted and dissolved clinopyroxenes and poikilitic texture. Petrochemically, the parental magmas of the volcanic rocks evolved from alkaline to calc-alkaline lava suites and include high-K and shoshonitic compositions. They display enrichments in light rare earth and large ion lithophile elements such as Sr, K, and Rb, as well as depletions in high field strength elements such as Nb, Ta, Zr, and Ti, resembling subduction-related magmas. The analcime-bearing and -free volcanic rocks share similar incompatible element ratios and chondrite-normalised rare rearth element patterns, indicating that they originated from similar sources. They also have relatively low to moderate initial 87Sr/86Sr (0.7042-0.7051), high positive εNd(t) values (+0.20 to +3.32), and depleted mantle Nd model ages (TDM1 = 0.63-0.93 Ga, TDM2 = 0.58-0.84 Ga). The bulk-rock chemical and Sr-Nd isotope features as well as the high Rb/Y and Th/Zr, but low Nb/Zr and Nb/Y ratios, indicate that the volcanic rocks were derived from a lithospheric mantle source that had been metasomatised by slab-derived fluids. Trace element modelling suggests that the parental magma(s) of the volcanic rocks represent mixtures of melts derived by low-degree (~5-10%) partial melting of spinel-lherzolite (40-85%) and garnet-lherzolite (15-60%) mantle sources. Sr-Nd isotopic modelling also suggests that a 25-35% lower crustal component was added in the parental magmas; AFC modelling additionally indicates minor upper crustal contamination during the evolution of the volcanic rocks. In conclusion, integration of the geochemical, petrologic, and isotopic data with regional geology suggests that the analcime-bearing and -free volcanic rocks evolved from parental magma(s) derived from melts of a subcontinental lithospheric mantle and lower crustal sources.

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  • MakaleYalnız künye2015
    A review for genesis of continental arc magmas: U, Th, K and radiogenic heat production data from the Gümüşhane Pluton in the Eastern Pontides (NE Türkiye)

    Maden, Nafiz; Akaryali, Enver

    In this study, in situ radioelemental (238U, 232Th and 40K) measurements and heat production rate evaluation have been conducted at 132 sites in the Gümüşhane Pluton of the Eastern Pontides Orogenic Belt (EPOG) of Northern Türkiye. The average K, U and Th values for granites are 4.35±0.71%, 5.85±2.74ppm, 22.13±5.55ppm, respectively; microgranites 4.33±1.37%, 7.12±2.23ppm, 24.11±9.59ppm; metagranite 3.93±0.68%, 6.24±2.75ppm, 12.87±3.92ppm; andesite/basalt 1.75±0.74%, 3.22±1.07ppm, 9.01±5.14ppm. Based on the abundances of K, U and Th, the radiogenic heat production (RHP) values, which is a reflection of the geological rock types, are estimated as 3.52±1.03μWm-3, 3.86±1.31μWm-3, 2.93±0.89μWm-3, and 1.68±0.63μWm-3 for granites, microgranites, metagranites and andesite/basalt, respectively. The average heat production value for the study area is estimated as 2.83±1.39μWm-3, which is closer to the upper continental crustal value; contrary to the highest heat production value of granitic basement and the lowest heat production values of the sedimentary rocks. The study region is depicted with very high level of Th/U value ranging from 0.11 to 23.19 with mean value of 3.53 ± 2.5, which is comparatively close to the upper continental crustal estimate of 3.8. The numerical results verify that mantle-derived magmas are subjected to contamination with both middle and lower crustal material constituted by fragments of southerly dipping subduction of Tethys Ocean during the late Mesozoic-Cenozoic.

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  • MakaleYalnız künye2015
    Geochronology, geochemistry, and petrogenesis of the Eocene Bayburt intrusions, Eastern Pontides, NE Turkey: Evidence for lithospheric mantle and lower crustal sources in the high-K calc-alkaline magmatism

    Kaygusuz, Abdullah; Öztürk, Mürşit

    Eocene I-type plutons are widespread in the Eastern Pontides, Northeastern Turkey. Geochemical and isotopic results on two Eocene intrusive bodies located in the southern zone of the Eastern Pontides were utilized to achieve a proper reconstruction of their origin. Based on laser ablation ICP-MS U-Pb zircon dating, Kiliçkaya and Kozluk intrusions present similar 206Pb/238U versus 207Pb/235U concordia ages of 46.75±0.79 and 46.9±0.68 Ma, respectively. Both intrusions exhibit similar petrographical, geochemical, and isotopical features, and contain abundant mafic microgranular enclaves (MMEs). The intrusive rocks are composed of diorite, tonalite, and granodiorite, whereas MMEs are composed of diorite. Both the intrusive rocks and the MMEs are I-type, high-K calc-alkaline in composition and display a metaluminous character. They are enriched in large-ion lithophile and light rare-earth elements and are depleted in high-field strength elements. The intrusive rocks show moderate variation in 87Sr/86Sr(i) (0.70531-0.70576), εNd(i) (+0.3 to -0.5), and δ18O values (+6.6 to +6.9), as well as Nd model ages (0.73-0.82Ga). Their Pb isotopic ratios are 206Pb/204Pb=18.67-18.86, 207Pb/204Pb=15.61-15.62, and 208Pb/204Pb=38.62-39.03. Although the isotope signatures of MMEs (87Sr/86Sr(i)=0.70528-0.70561; εNd(i)=+0.7 to -0.3; δ18O=+6.7 to +6.8) are significantly similar to those of the host rocks, the MMEs are characterized by relatively low contents of SiO2 (57-59wt.%), low aluminum saturation index (0.8-0.9), and high Mg numbers (31-36). All of these data suggest magma generation by mixing of enriched lithospheric mantle- and lower crustal-derived melts. Moreover, Sr-Nd isotopic modeling reveals ~17% to 23% lower crustal magma contribution to the mantle component.

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  • MakaleYalnız künye2015
    Gamma ray spectrometry for recognition of hydrothermal alteration zones related to a low sulfidation epithermal gold mineralization (eastern Pontides, NE Türkiye)

    Maden, Nafiz; Akaryali, Enver

    This study presents an interpretation of radiospectrometric and magnetic data of Arzular mineralization site, which is one of the best examples for epithermal gold deposits located in the southern zone of the Eastern Pontides (NE Türkiye). Potassium is generally the most useful pathfinder element for gold mineralization zones because of its high level in altered rock surrounding the deposits. Where gold is hosted within quartz veins, typically the vein is low in the radioelements, but the hydrothermally altered host rocks will usually have a distinct radioelement signature useful for exploration. In this study, magnetic, susceptibility and radiospectrometric survey data radiometric signatures associated with the host rocks favorable for the mineralization, enhancing techniques such as the ratio maps as well as potassium (%K), equivalent thorium (eTh ppm) and equivalent uranium (eU ppm) maps were utilized. Our analysis showed that the gold mineralization associated with the alteration is significantly related to increase in potassium, due to adularia, a low T K-feldspar, and decreases in uranium and thorium due to the hydrothermal alteration and magmatic intrusion processes during the regional tectonic activities.

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  • MakaleYalnız künye2014
    The petrogenesis of Early Eocene non-adakitic volcanism in NE Turkey: Constraints on the geodynamic implications

    Aydinçakir, Emre

    Whole-rock geochemistry, mineral chemistry, the 40Ar-39Ar age, and Sr-Nd isotopic data are presented for the Early Eocene non-adakitic volcanic rocks on the eastern corner of the Eastern Pontides orogenic belt (NE Turkey). The tectonic setting of the Eastern Pontides during the Late Mesozoic to Early Cenozoic remains a topic of debate. Here, for the first time, we describe the Early Eocene non-adakitic volcanic rocks from the Eastern Pontides. These rocks contain plagioclase, hornblende phenocrysts, and magnetite/titanomagnetite and apatite microphenocrysts. Geochronology studies based on the 40Ar-39Ar ratio of the amphibole separates reveal that the non-adakitic porphyritic volcanic rocks have a crystallization age of 50.04±0.10 to 50.47±0.22Ma (Ypresian). The volcanic rocks show tholeiitic to calc-alkaline affinities and have low-to-medium K contents. They are also enriched in large-ion lithophile elements (LILE), light rare-earth elements (LREE), and depleted in high field strength elements (HFSE), with a no negative Eu anomaly (Eun/Eu*=1.03-1.08) in mantle-normalized trace element spidergrams. The samples (Lacn/Lucn=2.60-4.28) show low-to-medium enrichment in LREEs relative to HREEs, in chondrite-normalized REE patterns indicating similar sources for the rock suite. These rocks display a range of ISr (50Ma) values from 0.70451 to 0.70485, and E{open}Nd (50Ma) 2.9 and 3.7. The main solidification processes involved in the evolution of these volcanics consist of fractional crystallization, with minor amounts of crustal contamination. All of our evidence supports the conclusion that the parental magma of the rocks probably derived from an enriched mantle, previously metasomatized by fluids derived from the subducted slab, in a post-collisional, geodynamic setting.

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  • MakaleYalnız künye2014
    LA-ICP MS zircon dating, whole-rock and Sr-Nd-Pb-O isotope geochemistry of the Camiboǧazi pluton, Eastern Pontides, NE Turkey: Implications for lithospheric mantle and lower crustal sources in arc-related I-type magmatism

    Kaygusuz, Abdullah; Arslan, Mehmet; Siebel, Wolfgang; Sipahi, Ferkan; Ilbeyli, Nurdane; Temizel, Irfan

    Late Cretaceous I-type plutons are widespread in the Eastern Pontides, NE Turkey. The studied Camiboǧazi pluton is a composite pluton consisting of diorite, tonalite, monzodiorite, monzonite, quartz monzonite, granite, and mafic microgranular enclaves (MMEs). Laser ablation ICP-MS U-Pb dating of zircon yielded crystallization ages of 76.21±0.79Ma, 75.65±0.50Ma, 75.04±0.83Ma, and 74.73±0.86Ma for diorite, monzodiorite, monzonite, and granite, respectively. The rocks of the pluton have I-type, high-K to shoshonitic and metaluminous character, displaying whole-rock geochemical features of arc-related granites. They are enriched in large-ion lithophile and light rare-earth elements, and depleted in high-field-strength elements. Major element variations can be attributed to fractionation of plagioclase, clinopyroxene, hornblende, and Fe-Ti oxides. The rocks show considerable variation in 87Sr/86Sr(i) (0.70498 to 0.70622), εNd(i) (-2.79 to -0.36), δ18O values (+6.3 to +11.4) and Nd model ages (TDM) (0.81Ga to 1.26Ga). Besides, they have (206Pb/204Pb)=18.44-19.09, (207Pb/204Pb)=15.64-15.69, and (208Pb/204Pb)=38.37-38.89. Although isotope signatures of the mafic microgranular enclaves (MMEs) (87Sr/86Sr(i)=0.70551 to 0.70622; εNd(i)=-2.9 to -1.23; δ18O=+8.3 to +9.7) are largely similar to the host rocks, MMEs are characterized by relatively high Mg-numbers (32-36), low contents of SiO2 (52-56wt.%) and low ASI (0.7-0.9). Estimated crystallization temperatures for the rocks of the pluton range from 735±58°C to 844±24°C and a shallow intrusion depth (<10km) is estimated from Al-in-hornblende thermobarometry. Whole-rock geochemical and isotopic data suggest magma generation by dehydration melting of an amphibolite-type lower crustal component with additional input of a subcontinental lithospheric mantle component. Furthermore, Sr-Nd isotope mixing model reveals ~30% to 40% lower crustal magma contribution to the mantle component.

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  • Derleme MakaleYalnız künye2014
    Mineral chemistry and thermobarometry of Eocene monzogabbroic stocks from the Bafra (Samsun) area in Turkey: Implications for disequilibrium crystallization and emplacement conditions

    Temizel, İrfan; Arslan, Mehmet; Abdioğlu, Emel; Yücel, Cem

    Monzogabbro stocks including felsic enclaves (monzosyenite) around the Bafra (Samsun) area at the western edge of the Eastern Pontides cut Eocene-aged volcanic and sedimentary units. The monzogabbros contain plagioclase, alkali feldspar, clinopyroxene, olivine, hornblende, biotite, apatite, and iron-titanium oxides, whereas the felsic enclaves contain alkali feldspar, plagioclase, hornblende, biotite, clinopyroxene, and iron-titanium oxides. Mineral chemistry data suggest that magmas experienced hydrous and anhydrous crystallization in deep and shallow crustal magma chambers. Several thermobarometers were used to estimate temperatures of crystallization and emplacement for the mafic and felsic magmas. Clinopyroxene thermobarometry yielded 1100-1232 C and 5.9-8.1 kbar for monzogabbros, and 931-1109 C and 1.8-6.9 kbar for felsic enclaves. Hornblende thermobarometry and oxygen fugacity estimates reveal 739-971°C, 7.0-9.2 kbar and 10−9.71 for monzogabbros and 681-928°C, 3.0-6.1 kbar and 10−11.34 for felsic enclaves. Biotite thermobarometry shows elevated oxygen fugacity varying from 10−18.9-10−11.07 at 632-904°C and 1.29-1.89 kbar for monzogabbros, to 10−15.99 -10−11.82 at 719-873°C and 1.41-1.77 kbar for felsic enclaves. The estimated zircon and apatite saturation temperatures are 504-590°C and 693-730°C for monzogabbros and 765-775°C and 641-690°C for felsic enclaves, respectively. These data imply that several phases in the gabbroic and syenitic magmas did not necessarily crystallize simultaneously and further indicate that the mineral compositions may register intervals of disequilibrium crystallization. Besides, thermobarometry contrasts between monzogabbro and felsic enclave may be partly a consequence of extended interactions between the mafic and felsic magmas by mixing/mingling and diffusion. Additionally, the hot felsic magma was close to liquidus conditions (crystallinity < 30%) when injected into cooler mafic magma (crystallinity > 50%), and thus, the monzogabbro stocks reflect hybrid products from the mingling and incomplete mixing of these two magmas.

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  • MakaleYalnız künye2014
    Geochemical fingerprints of Late Triassic calc-alkaline lamprophyres from the Eastern Pontides, NE Turkey: A key to understanding lamprophyre formation in a subduction-related environment

    Karsli, Orhan; Dokuz, Abdurrahman; Kaliwoda, Melanie; Uysal, Ibrahim; Aydin, Faruk; Kandemir, Raif; Fehr, Karl-Thomas

    The Eastern Pontides in NE Turkey is one of the major orogenic belts in Anatolia. In this paper, we report our new 40Ar/39Ar dating, mineral chemistry, major and trace elements and Sr-Nd-Pb isotopic analyses of the lamprophyre intrusions in this region. The lamprophyres are widely scattered and intrude Late Carboniferous granitoid rocks. The lamprophyres exhibit fine-grained textures and are mineralogically uniform. Hornblende 40Ar/39Ar dating yielded a plateau age of 216.01±10.64Ma. Based on their geochemistry, mineral compositions and paragenesis, the lamprophyres are classified as calc-alkaline lamprophyres in general and spessartites in particular, which are rich in large ion lithophile elements (e.g., Rb, Ba, K) but depleted in Nb and Ti. Our samples exhibit moderate fractionation in LREE patterns approximately 100 times that of chondrite but HREE abundances less than 10 times that of chondrite. These calc-alkaline lamprophyres display a range of ISr (216Ma) values from 0.70619 to 0.71291 and εNd (216Ma) values from -1.4 to 4.1, with TDM=1.11 to 2.20Ga. Their Pb isotopic ratios indicate an enriched mantle source. The enrichment process is related to metasomatism of a subcontinental lithospheric mantle source, which is caused by a large quantity of H2O-rich fluids, rather than sediments released from oceanic crust at depth during the closure of the Paleotethys Ocean in Triassic times. All of the geochemical data and the trace element modeling suggest that the primary magma of the calc-alkaline to high-K calc-alkaline spessartites was generated at depth by a low degree of partial melting (~1-10%) of a previously enriched lithospheric mantle wedge consisting of phlogopite-bearing spinel peridotite. The ascendance of a hot asthenosphere triggered by extensional events caused partial melting of mantle material. The rising melts were accompanied by fractional crystallization and crustal contamination en route to the surface. All of the geochemical features combined with regional data suggest that the Eastern Pontides calc-alkaline lamprophyres originated in an extensional environment along an active continental margin throughout the Late Triassic. Such an extensional event, causing upwelling of hot asthenosphere, led to the opening of the northern branch of the Neotethys as a back-arc basin farther south of the Eastern Pontides.

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  • MakaleYalnız künye2014
    Origin of analcimes in the Tertiary volcanic rocks from the Eastern Pontides (NE Turkey): A textural, mineralogical and geochemical approach

    Yücel, Cem; Temizel, Irfan; Abdioʇlu, Emel; Arslan, Mehmet; Yaʇcioʇlu, Ufuk Celal

    Silica-undersaturated mafic volcanic rocks of Tertiary age in form of lava flows, dikes and sills of tephritic compositions extend along the northern part of the Eastern Pontides. These rocks typically contain Ca-clinopyroxene (Wo32-53En26-54Fs8-24), analcime, Fe-Ti oxides, apatite and minor olivine, plagioclase (An49 - 94), K-feldspar (Or29 - 66), hornblende and phlogopite in microgranular porphyritic, hyalo-microlitic porphyritic and glomeroporphyritic textures. Petrochemical features of the studied rocks, such as enrichment in LILE, depletion in Nb, Ta and Ti and moderate or high LREE/HREE ratios, provide strong evidence for melt production from a subduction-metasomatized lithospheric mantle. Besides, the rocks are characterized by their low K2O contents and low K2O/Na2O ratios as a result of analcimization. Analcime detected in these rocks appears to have formed by pseudomorphic mineral replacement reactions. Euhedral or anhedral analcime crystals, 100 - 600 um in diameter, are set in groundmass and display six-sided polygon or rounded shape and irregular cracks. The analcime pseudomorphs are colourless, milky white to grey and occur in clinopyroxene or in the groundmass. Based on the electron microprobe results, analcimes contain a minor amount of cations other than Na and probably represent the remnants of leucite as marked by K-zoning. X-ray diffraction studies of the analcime-bearing samples confirm the presence of cubic and tetragonal analcime crystals in addition to tetragonal leucite. The presence of Ca-clinopyroxene and plagioclase rather than their sodic equivalents, presence of anhydrous mineral phases and lack of Na differentiation trend as well as partial alteration of the rocks likely supports the secondary growth of analcime either during cooling or after magma solidification.

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  • MakaleYalnız künye2014
    The Eastern Black Sea-type volcanogenic massive sulfide deposits: Geochemistry, zircon U-Pb geochronology and an overview of the geodynamics of ore genesis

    Eyuboglu, Yener; Santosh, M.; Yi, Keewook; Tuysuz, Necati; Korkmaz, Sadettin; Akaryali, Enver; Dudas, Francis O.; Bektas, Osman

    The Meso-Cenozoic geodynamic evolution of the eastern Pontides orogenic belt provides a key to evaluate the volcanogenic massive sulfide (VMS) deposits associated with convergent margin tectonics in a Cordilleran-type orogenic belt. Here we present new geological, geochemical and zircon U-Pb geochronological data, and attempt to characterize the metallogeny through a comprehensive overview of the important VMS mineralizations in the belt. The VMS deposits in the northern part of the eastern Pontides orogenic belt occur in two different stratigraphic horizons consisting mainly of felsic volcanic rocks within the late Cretaceous sequence. SHRIMP zircon U-Pb analyses from ore-bearing dacites yield weighted mean Pb-206/U-238 ages ranging between 91.1 +/- 1.3 and 82.6 +/- 1 Ma. The felsic rocks of first and second horizons reveal geochemical characteristics of subduction-related calc-alkaline and shoshonitic magmas, respectively, in continental arcs and represent the immature and mature stages of a late Cretaceous magmatic arc. The nature of the late Cretaceous magmatism in the northern part of the eastern Pontides orogenic belt and the various lithological associations including volcaniclastics, mudstones and sedimentary facies indicate a rift-related environment where dacitic volcanism was predominant. The eastern Pontides VMS deposits are located within the caldera-like depressions and are closely associated with dome-like structures of felsic magmas, with their distribution controlled by fracture systems. Based on a detailed analyses of the geological, geophysical and geodynamic information, we propose that the VMS deposits were generated either in intra arc or near arc region of the eastern Pontides orogenic belt during the southward subduction of the Tethys oceanic lithosphere. (C) 2013 Elsevier B.V. All rights reserved.

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  • MakaleYalnız künye2013
    Petrogenesis of the post-collisional volcanic rocks from the Borçka (Artvin) area: Implications for the evolution of the Eocene magmatism in the Eastern Pontides (NE Turkey)

    Aydinçakir, Emre; Sen, Cüneyt

    Whole-rock geochemistry, 40Ar-39Ar data, and Sr-Nd isotopes are presented for the Eocene Borçka volcanic rocks on the eastern corner of the eastern Pontide orogenic belt (NE Turkey). Borçka (Artvin) volcanic rocks are divided into three suites-basic dyke, Borçka basalt, and Civanköy suite. These rocks contain plagioclase (An49-88), clinopyroxene (Wo38-49En38-54Fs8-25), hornblende (Mg#=0.57-0.74) phenocrysts, and magnetite/titanomagnetite and apatite microphenocrysts. 40Ar-39Ar ages on hornblendes, ranging from 46.9±0.1 to 39.9±0.5Ma, within the middle Eocene. The volcanic rocks show tholeiitic-calc-alkaline affinities and have low-to-medium K contents. They are enriched in large ion lithophile (LILE) and light rare earth elements (LREE), with pronounced depleted high field strength elements (HFSE). The chondrite-normalized REE patterns (Lacn/Lucn=1-19) show low-to-medium enrichment, indicating similar sources for the rock suite. Initial 87Sr/86Sr values [(87Sr/86Sr)46Ma] vary between 0.70423 and 0.70495, while initial 143Nd/144Nd values [(143Nd/144Nd)46Ma] lie between 0.51263 and 0.51285. The main solidification processes involved in the evolution of the volcanics consist of fractional crystallization, with minor amounts of crustal contamination. All our evidences support the conclusion that the parental magma of the rocks probably derived from an enriched mantle, previously metasomatized by fluids derived from subducted slab, in a post-collisional, extension-related geodynamic setting.

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  • MakaleAçık Erişim2013
    Geothermal structure of the eastern Black Sea basin and the eastern Pontides orogenic belt: Implications for subduction polarity of Tethys oceanic lithosphere

    Maden, Nafiz

    The numerical results of thermal modeling studies indicate that the lithosphere is cold and strong beneath the Black Sea basin. The thermal lithospheric thickness increases southward from the eastern Pontides orogenic belt (49.4 km) to Black Sea basin (152.2 km). The Moho temperature increases from 367 C in the trench to 978 C in the arc region. The heat flow values for the Moho surface change between 16.4 mW m-2 in the Black Sea basin and 56.9 mW m-2 in the eastern Pontides orogenic belt. Along the southern Black Sea coast, the trench region has a relatively low geothermal potential with respect to the arc and back-arc region. The numerical studies support the existence of southward subduction beneath the Pontides during the late Mesozoic-Cenozoic.

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  • MakaleAçık Erişim2013
    Petrogenesis of the late Cretaceous Turnagöl intrusion in the eastern Pontides: Implications for magma genesis in the arc setting

    Kaygusuz, Abdullah; Sipahi, Ferkan; Ilbeyli, Nurdane; Arslan, Mehmet; Chen, Bin; Aydinçakir, Emre

    A series of Cretaceous plutons is present in the eastern Pontides of northeastern Turkey. The Turnagöl intrusion is the least studied and, thus, the least understood plutons in the orogen. This intrusion consists of hornblende-biotite granodiorites emplaced at 78 Ma based on LA-ICP-MS U-Pb zircon dating. It is of sub-alkaline affinity, belongs to the medium- to high-K calc-alkaline series, and displays features typical of I-type granites. The rocks of the intrusion are enriched in large-ion lithophile elements and light rare earth-elements with negative Eu anomalies (Eu/Eu* = 0.69-0.82), but are deficient in high-field-strength elements. They have a small range of ( 87Sr/86Sr)i (0.7060-0.7063), ÉNdi(-2.6 to -3.1), and δ18O (+8.1 to +9.1) values. Their Pb isotopic ratios are 206Pb/204Pb = 18.63-18.65, 207Pb/ 204Pb = 15.62-15.63, and 208Pb/204Pb = 38.53-38.55. The fractionation of plagioclase, hornblende, and Fe-Ti oxides had key functions in the evolution of the Turnagöl intrusion. The crystallization temperatures of the melts ranged from 758 to 885 C as determined by zircon and apatite saturation thermometry. All these characteristics, combined with the low values of K2O/Na2O and (Na 2O + K2O)/(FeOt + MgO + TiO2), as well as the high values of (CaO + FeOt + MgO + TiO2), suggest an origin by dehydration melting from a metabasaltic lower crustal source.

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  • MakaleAçık Erişim2013
    The nature of transition from adakitic to non-adakitic magmatism in a slab window setting: A synthesis from the eastern Pontides, NE Turkey

    Eyuboglu, Yener; Santosh, M.; Dudas, Francis O.; Akaryali, Enver; Chung, Sun-Lin; Akdaǧ, Kemal; Bektaş, Osman

    The eastern Pontides orogenic belt provides a window into continental arc magmatism in the Alpine-Himalayan belt. The late Mesozoic-Cenozoic geodynamic evolution of this belt remains controversial. Here we focus on the nature of the transition from the adakitic to non-adakitic magmatism in the Kale area of Gumushane region in NE Turkey where this transition is best preserved. The adakitic lithologies comprise porphyries and hyaloclastites. The porphyries are represented by biotite-rich andesites, hornblende-rich andesite and dacite. The hayaloclastites represent the final stage of adakitic activity and they were generated by eruption/intrusion of adakitic andesitic magma into soft carbonate mud. The non-adakitic lithologies include basaltic-andesitic volcanic and associated pyroclastic rocks. Both rock groups are cutting by basaltic dikes representing the final stage of the Cenozoic magmatism in the study area. We report zircon U-Pb ages of 48.71 ± 0.74 Ma for the adakitic rocks, and 44.68 ± 0.84 Ma for the non-adakitic type, suggesting that there is no significant time gap during the transition from adakitic to non-adakitic magmatism. We evaluate the origin, magma processes and tectonic setting of the magmatism in the southern part of the eastern Pontides orogenic belt. Our results have important bearing on the late Mesozoic-Cenozoic geodynamic evolution of the eastern Mediterranean region.

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  • MakaleYalnız künye2012
    Geochronological evidence and tectonic significance of Carboniferous magmatism in the southwest Trabzon area, eastern Pontides, Turkey

    Kaygusuz, Abdullah; Arslan, Mehmet; Siebel, Wolfgang; Sipahi, Ferkan; Ilbeyli, Nurdane

    The northern and southern zones of the eastern Pontides (northeast Turkey) contain numerous plutons of varying ages and compositions. Geochemical and isotopic results on two Hercynian granitoid bodies located in the northern zone of the eastern Pontides allow a proper reconstruction of their origin for the first time. The intrusive rocks comprise four distinct bodies, two of which we investigated in detail. Based on LA-ICP-MS U-Pb zircon dating, the Derinoba and Kayadibi granites have similar 206Pb/ 238U versus 207Pb/ 235U Concordia ages of 311.1 2.0 and 317.2 3.5 million years for the former and 303.8 1.5 million years for the latter. Aluminium saturation index values of both granites are between 0.95 and 1.35, indicating dominant peraluminous melt compositions. Both intrusions have high SiO 2 (74-77 wt.%) contents and show high-K calc-alkaline and I-to S-type characteristics. Primitive mantle-normalized element diagrams display enrichment in K, Rb, Th, and U, and depletion in Ba, Nb, Ta, Sr, P, and Ti. Chondrite-normalized rare earth element patterns are characterized by concave-upward shapes and pronounced negative Eu anomalies with L acn/Y bcn=4.6-9.7 and E ucn/Eu*=0.11-0.59 (Derinoba), and L acn/Y bcn=2.7-5.5 and E ucn/Eu*=0.31-0.37 (Kayadibi). These features imply crystal-melt fractionation of plagioclase and K-feldspar without significant involvement of garnet. The Derinoba samples have initial Nd values between-6.1 and-7.1 with Nd model ages and T DM between 1.56 and 2.15 thousand million years. The Kayadibi samples show higher initial Nd (I) values,-4.5 to-6.2, with Nd model ages between 1.50 and 1.72 thousand million years. This study demonstrates that the Sr isotope ratios generally display negative correlation with Nd isotopes; Sr isotope ratios were lowered in some samples by hydrothermal interaction or alteration. Isotopic and petrological data suggest that both granites were produced by the partial melting of early Palaeozoic lower crustal rocks, with minor contribution from the mantle. Collectively, these rocks represent a late stage of Hercynian magmatism in the eastern Pontides.

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  • MakaleYalnız künye2012
    One-dimensional thermal modeling of the eastern pontides orogenic belt (NE Turkey)

    Maden, Nafiz

    The eastern Pontides orogenic belt is one of the most complex geodynamic settings in the Alpine-Himalayan belt due to the lack of systematical geological and geophysical data. In this study, 1D crustal structure and P-wave velocity distribution obtained from gravity modeling and seismological data in the area has been used for the development of the thermal model of the eastern Pontides orogenic belt. The computed temperature-depth profiles suggest a temperature of 590 ± 60°C at a Moho depth of 35 km indicates the presence of a brittle-ductile transition zone. This temperature value might be related to water in the subducted crust of the Tethys oceanic lithosphere. The Curie temperature depth value of 29 km, which may correspond to the crustal magma chambers, is found 5-7 km below the Moho depth. Surface heat flow density values vary from 66.5 and 104.7 mW m -2. High mantle heat flow density value of 48 mW m -2 is obtained for the area should be related to melting of the lithospheric mantle caused by upwelling of asthenosphere.

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  • MakaleYalnız künye2012
    Petrography and geochemistry of Eocene sandstones from eastern Pontides (NE TURKEY): Implications for source area weathering, provenance and tectonic setting

    Eker, Cigdem Saydam

    Subaerial weathering level, source area and tectonic environments were interpreted by using petrographic and geochemical characteristics of Eocene age sandstones found in the eastern Pontides. The thickness of Eocene age clastic rocks in the eastern Pontides ranges from 195 to 400 m. Mineralogical components of sandstones were mainly quartz, feldspar, rock fragments, and opaque and accessory minerals. Depending on their matrix and mineralogical content, Eocene age sandstones are identified as arkosic arenite-lithic arenite and feldspathic wacke-lithic wacke. CIA (Chemical Index of Alteration) values observed in the Eocene age sandstones (43-55) suggest that the source terrain of the sandstones was not affected by intense chemical weathering. Low CIW/CIA (Chemical Index of Weathering/Chemical Index of Alteration) values of the sandstones studied here suggest only slightly decomposed material and having undergone little transport until final deposition. Zr/Hf, Th/Sc, La/Sc and CIA ratios are low and demonstrate a mafic source; on the other hand, high LREE/HREE ratios and a slightly negative Eu anomaly indicate a subordinate fclsic source. Modal mineralogical and SiO 2/Al 2O 3 and K 2O/Na 2O and Th, Zr, Co, Sc of Eocene age sandstone contents indicate that they are probably magmatic arc originated and deposited in the back arc basin.

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  • MakaleYalnız künye2011
    A slab detachment and delamination model for the generation of Carboniferous high-potassium I-type magmatism in the Eastern Pontides, NE Turkey: The Kose composite pluton

    Dokuz, Abdurrahman

    The Hercynian Kose composite pluton (KCP) is located in the Eastern Pontides, Turkey, and consists of two units of high-K calc-alkaline, primarily peraluminous granites: (i) the internal body, and (ii) the external body. The internal body, which was emplaced at 322-318 Ma ((40)Ar/(39)Ar ages on biotite and hornblende, respectively), displays a wide compositional range (49-71 wt.% SiO(2)) and contains several lithologies: hybrid equigranular rocks, microgranular magmatic enclaves, mafic dikes, porphyry dikes and mylonites. The external body, which was emplaced at 306.7 Ma ((40)Ar/(39)Ar age on K-feldspar), consists exclusively of monzogranite (> 71 wt.% SiO(2)). Field relationships, mineralogy, major- and trace element geochemistry, and initial Sr-Nd isotope values (I(sr)= 0.70821 to 0.71002, e(Nd)(t) = -6.6 to -8.0) show that the internal body was differentiated and evolved by crystal fractionation and magma mixing processes. The end-members of the mixing process were a mafic rock and a felsic rock. Mafic magma was derived from a relatively deep-seated (25-30 km) crustal storage reservoir, not directly from the mantle, and underwent significant differentiation by fractional crystallization and crustal contamination before mixing. In addition, these magma storages probably supplied the additional heat necessary to initiate crustal melting. Some of the additional heat may have also been released by the radiogenic decay of heat producing elements. Eventually, the existing felsic magma from the melting of K-bearing meta-greywackes was raised to its emplacement level at a depth of similar to 10-16 km. After partial crystallization, it was sporadically intruded by modified mafic magma from the deeper crustal reservoir to generate hybrid rocks. The hybrid rocks were then elevated to a shallower depth by normal faults during the collapse of the orogen and erosion. Mylonites that were later overprinted by pseudotachylites are typically constrained to the internal body and are regarded as markers of this event. The external body is characterized by a significantly less radiogenic and limited range of Sr-Nd isotope values (I(sr)= 0.70639 to 0. 70792, e(Nd)(t) = -4.4 to -6.5) than those of the internal body and a lack of rocks documenting the open system differentiation processes. Fractional crystallization is the exclusive process responsible for the elemental range within the body. The rocks also contain less biotite relative to those of the internal body. All these involve less K-bearing mid-crustal rocks (orthogneisses) in their source, which was probably located at depths near the lower crust. The absence of purely lower crustal-derived melts can be explained by the removal of this type of material during the formation of the parental melt. This melt later ascended to its emplacement level at a depth of around similar to 5-10 km and cut the hybrid rocks of the internal body and regional metamorphic rocks that had been raised previously due to ongoing erosion. The melt that injected into the cracks of the internal body crystallized into porphyries because there was not enough time for the entire crystallization of magma. The data presented here indicate that late Early Carboniferous and Late Carboniferous magmatism occurred in a collisional setting. Slab detachment and subsequent delamination seem to be the most plausible mechanisms for the generation of the Hercynian high-K calc-alkaline magmatism in the Eastern Pontides, Turkey. (C) 2010 International Associatio for Gondwana Research. Published by Elsevier B.V. All rights reserved.

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  • MakaleAçık Erişim2011
    First Report of a Trilobite in the Carboniferous of Eastern Pontides, NE Turkey

    Kandemir, Raif; Lerosey-Aubril, Rudy

    The pre-Mesozoic basement of the Eastern Pontides consists of a Permo-Carboniferous sedimentary sequence including the Catalcesme and Hardisi formations. The Catalcesme Formation has yielded rich assemblages of fusulinids, corals, gastropods, brachiopods, bryozoans, algae, conodonts and plants. Hitherto trilobites were unknown from this formation; here we report the discovery of a pygidium from a dark grey limestone bed near the top. Trilobites are a minor component of benthic marine communities during the Late Pennsylvanian, and to our knowledge, the discovery of this pygidium constitutes the first report of their occurrence in deposits of this age in Turkey. The morphological characteristics of the specimen, especially the number of axial rings and pleural ribs and the well-defined border (Owens 1983), suggest that it probably belongs to an undescribed species of Ditomopyge Newell, 1931 (Ditomopyginae). It also exhibits a distortion of the posterior part of the axis, and a shortening (right side) or a fusion (left side) of some pleural ribs, which is tentatively interpreted as repaired injuries or the results of a developmental dysfunction.

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