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  • MakaleYalnız künye2017Scopus SJRQ2
    Geochemical and isotopic characteristics of stream and terrace sediments of the harsit stream, NE Turkey

    Eker, Çiğdem Saydam

    The current study compares and contrasts the elemental concentrations and the Nd, Sr and O isotopic compositions of sediments collected from the Harsit Stream bed sediments (HSBS) and terrace sediments (HSTS). There are positive correlations between Al2O3 and SiO2, TiO2, Na2O and Fe2O3, K2O in HSBS and between Al2O3 and Fe2O3, MnO in the HSTS samples. Major element components of HSBS and HSTS are comparable to average upper continental crust. Both types of sediments are generally classified as greywacke, based on chemical composition and O–Sr isotopic compositions. TheɛNd(0) andɛSr(0) values range from −0.6 to −5.7 and from 7.1 to 45, respectively, in HSBS; and from −0.7 to −4.4 and from 20 to 54, respectively, in HSTS. The δ18O values range from 8.8 to 11.8 (average 10.8) in HSBS and from 11.3 to 13.3 (average 12.2) in HSTS, which are generally controlled by detrital or authigenic minerals in the studied samples. The average chemical index of alteration (CIA) and, plagioclase index of alteration (PIA) values are high in HSTS, whereas the index of compositional variability (ICV) and weathering index (WIP) values are high in HSBS. Several minor differences were observed between HSBS and HSTS in terms of geochemistry and isotopic compositions that reflect different processes involved in their sedimentation.

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  • MakaleYalnız künye2016Scopus SJRQ1
    U–Pb zircon chronology and petrogenesis of Carboniferous plutons in the northern part of the Eastern Pontides, NE Turkey: Constraints for Paleozoic magmatism and geodynamic evolution

    Kaygusuz, Abdullah; Arslan, Mehmet; Sipahi, Ferkan; Temizel, İrfan

    Numerous intrusive rocks of varying ages and compositions exist in the Paleozoic to Tertiary periods in the Eastern Pontides. Carboniferous intrusive rocks are commonly observed in the southern part of the Eastern Pontides. The nature of the rocks in the northern part of the region has not been determined because of Upper Cretaceous and Tertiary volcano-sedimentary units. Whole-rock geochemical, isotopic and geochronological data obtained from five different mapped granitoid bodies located in the northern part of the Eastern Pontides allow for the proper reconstruction of Carboniferous magmatism and the geodynamic evolution of the region. According to laser ablation ICP-MS U–Pb zircon dating, the Özdil, Soğuksu, Seslikaya, Kızılağaç and Şahmetlik plutons have similar 206Pb/238U vs. 207Pb/235U concordia ages of 340.7 ± 1.8 Ma and 323.1 ± 1.5 Ma, 348.4 ± 1.6 Ma, 335.4 ± 1.4 Ma, 337.2 ± 0.6 Ma and 334.5 ± 1.4 Ma, respectively. The aluminium saturation index (ASI) values of all of the samples from the plutons are between 1.0 and 1.32, which indicate peraluminous melt compositions. The plutons have SiO2 contents between 59 and 79 wt.% and show low- to high-K calc-alkaline characteristics. The plutons are enriched in large-ion lithophile and light rare earth elements and are depleted in high-field strength elements. Chondrite-normalized rare earth element patterns are characterized by concave-upward shapes and pronounced negative Eu anomalies, with LaCN/YbCN = 1.9–46.8 and EuCN/Eu* = 0.19–1.76. The studied plutons show considerable variations in 87Sr/86Sr(i) (0.70255 to 0.71006) and εNd(i) values (− 4.8 to − 7.1), as well as Nd model ages (1.15 to 2.47 Ga). The Pb-isotopic ratios are 206Pb/204Pb = 17.11–18.60, 207Pb/204Pb = 15.58–15.64 and 208Pb/204Pb = 36.95–38.62. The crystallization temperatures of the melts range from 676 to 993 °C, as determined by zircon and apatite saturation thermometry. These data suggest that the Carboniferous granitic magmas were produced by the partial melting of meta-mafic to meta-felsic lower crustal source rocks, with minor contributions from the mantle. Collectively, these rocks represent a late stage of Hercynian magmatism in the northern part of the Eastern Pontides.

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  • MakaleYalnız künye2014Scopus SJRQ4
    40Ar-39Ar age, petrography and geochemistry of the Yoncayolu Metamorphic Rocks (NE Turkey): Subduction-related metamorphism under greenschist fades conditions

    Gücer, Mehmet Ali; Aslan, Zafer

    The Yoncayolu Metamorphic Rocks (YMR), exposed in the Sakarya zone (Erzincan, NE Turkey), consists mainly of greenschist rocks which are chlorite schists, muscovite-chlorite schists, metabasic rocks and lesser extent of pyhllites and calc-schists. All YMR are fine-grained, weakly foliated and often cut by quartz veins. The common mineral assemblage is chlorite+albite+epidote+quartz+/-clinozoisite+/-actinolite+/-opaques. Geochemically, protoliths of the YMR resemble calc-alkaline volcanic arc rocks. The YMR have high contents of large ion lithophile elements (LILEs) and low contents of high field strength elements (HFSEs) similar to mid-ocean ridge basalt (MORB). (La/Lu)(CN) values are between 0.26 and 6.16. The REE patterns show slight or no Eu anomalies (Eu-CN/Eu* of 0.48 to 1.13), suggesting minor plagioglase fractionation. 40Ar-39Ar dating on plagioclases from the metabasic samples of the YMR gave ages of 100.8+/-3.4 Ma (Albian) and 94.1+/-3.3 Ma (Cenomanian), suggesting that metamorphism was related to the closure of the Neo-Tethyan Ocean. Metamorphism took place during subduction of the Neo-Tethyan Ocean between similar to 90-70 Ma. Chlorite geothermometry yielded a temperature of 320-350 degrees C and a pressure around 4 kbar. All these findings lend support for greenschist facies metamorphic conditions during the formation of the YMR.

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  • MakaleYalnız künye2014Scopus SJRQ1
    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 künye2014Scopus SJRQ1
    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 künye2011Scopus SJRQ1
    Adakite-like granitoid porphyries in the Eastern Pontides, NE Turkey: Potential parental melts and geodynamic implications

    Karsli, Orhan; Ketenci, Murat; Uysal, Ibrahim; Dokuz, Abdurrahman; Aydin, Faruk; Chen, Bin; Kandemir, Raif; Wijbrans, Jan

    The tectonic setting of the Eastern Pontides during the late Mesozoic to early Cenozoic remains a subject of debate. Petrogenesis of adakite-like granitoid porphyries plays a critical role in determining the nature of the lower continental crust and mantle dynamics during orogenic processes in the region. Here we describe, for the first time, the late Paleocene to early Eocene adakite-like granitoid porphyries from the northern part of the Eastern Pontides although their counterparts in the southern part have recently been found. The adakitic porphyries, which emplaced into the subduction-related Turonian-Santonian volcanics from northern part of the region, consist of I-type calc-alkaline quartz monzonite-tonalite (SiO2 = 62.89-65.07 wt.%) and high-k calc-alkaline granodiorite-granite associations (SiO2 = 69.06-70.43 wt.%). The former displays peraluminous to metaluminous signatures, whereas the latter shows peraluminous geochemical character. The granite-granodiorite porphyries have high K2O (3.32-3.84 wt.%), and low Na2O (3.48-4.61 wt.%) and MgO (0.91-1.04 wt.%) relative to the quartz monzonite-tonalite association (K2O = 1.50-1.92 wt.%; Na2O = 4.08-6.45 wt.%; MgO = 1.44-2.07 wt.%). Ar-Ar geochronology studies on the amphibole separates reveal that the adakite-like porphyries have a crystallization ages of 51.34 +/- 0.27 to 53.55 +/- 0.34 Ma. Here, we contend that these rocks were formed by partial fusion of a mafic lower continental crust in a collisional phase but not in a subduction setting. All the samples exhibit the typical geochemical characteristics of adakite, that is, high Sr (250-1141 ppm), high Sr/Y ratios (16-147), low Y (6.8-14.8 ppm) and low HREE concentrations; they are similar to adakites formed by slab melting associated with the subduction zone. However, the rocks exhibit heterogeneity in isotopic composition, with I-Sr ranging from 0.70554 to 0.70986, epsilon(Nd) (51 Ma) from -8.5 to -0.9 and Nd model ages from 0.72 to 1.26 Ga. The samples are characterized by relatively high Th, Th/U and no significant Eu anomalies, implying that garnet was stable in their source during partial melting. The compositional diversity between rock groups is probably related to partial melting of heterogeneous lower crustal source. All of the features are inconsistent with a slab-melting origin and slab-related petrogenetic model, but instead, they favor an origin by melting of heterogeneous lower continental crust due to a thermal anomaly that was induced by the upwelling of the asthenosphere through a slab break-off in a collisional setting. These interpretations argue against the evidence for the presence of an early Cenozoic arc setting in the Eastern Pontides. Instead, the early Cenozoic time in the region may be attributed to a geodynamic response to a post-collisional uplift phase that occurred along the continent-continent collision between the Pontide and the Anatolide-Tauride blocks. (C) 2011 Elsevier B.V. All rights reserved.

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  • MakaleYalnız künye2010Scopus SJRQ1
    Generation of the Early Cenozoic adakitic volcanism by partial melting of mafic lower crust, Eastern Turkey: Implications for crustal thickening to delamination

    Karsli, Orhan; Dokuz, Abdurrahman; Uysal, Ibrahim; Aydin, Faruk; Kandemir, Raif; Wijbrans, Jan

    Early Cenozoic (48-50 Ma) adakitic volcanic rocks from the Eastern Pontides, NE Turkey, consist of calc-alkaline and high-K calc-alkaline andesite and dacite, with SiO2 contents ranging from 56.01 to 65.44 wt.%. This is the first time that Early Eocene volcanism and adakites have been reported from the region. The rocks are composed of plagioclase, amphibole, quartz, and Mg-rich biotite. They have high and low-Mg# values ranging from 55 to 62 and 13 to 42, respectively. High-Mg# rocks have higher Ni and Co contents than low-Mg# samples. The rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements, depletions in Nb, Ta and Ti and have high La/Yb and Sr/Y ratios. Their relative high ISr (0.70474-0.70640) and low εNd (50 Ma) values (- 2.3 to 0.8) are inconsistent with an origin as partial melts of a subducted oceanic slab. Combined major- and trace element and Sr-Nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region, where a transition from a collision to an extension stage has created thickening and delamination of the Pontide mafic lower crust at 50 Ma. The high-Mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle, and its subsequent interaction with the mantle peridotite during upward transport, leaving garnet as the residual phase, elevates the MgO content and Mg# of the magmas, whereas low-Mg# magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling, which supplies heat flux to the lower crust. The data also suggest that the mafic lower continental crust beneath the region was thickened between the Late Cretaceous and the Late Paleocene and delaminated during Late Paleocene to Early Eocene time, which coincides with the initial stage of crustal thinning caused by crustal extensional events in the Eastern Pontides and rules out the possibility of an extensional regime before ~ 50 Ma in the region during the Late Mesozoic to Early Cenozoic.

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  • MakaleYalnız künye2009Scopus SJRQ1
    C2/c pyroxene phenocrysts from three potassic series in the Neogene alkaline volcanics, NE Turkey: Their crystal chemistry with petrogenetic significance as an indicator of P -T conditions

    Aydin, Faruk; Thompson, Richard M.; Karsli, Orhan; Uchida, Hinako; Burt, Jason B.; Downs, Robert T.

    Chemical and structural data are reported for C2/c pyroxene phenocrysts collected from three potassic series (Group A: basanite-tephrite, Group B: tephrite-phonolitic tephrite, Group C: alkaline basalt-trachybasalt) of the Neogene alkaline volcanics (NAVs) in northeastern Turkey, in order to investigate the evolution of the magmatic plumbing system and the location of magma chamber(s) with crystallization conditions. The rock series hosting the clinopyroxene phenocrysts show generally porphyritic texture and have a variable phenocryst-rich nature (20-58%), with phenocryst assemblages characterized by cpx ± ol ± plag ± foid ± amp ± bio. The clinopyroxene phenocrysts can be chemically classified as Ti- and Fe3-rich Al-diopsides for Groups A and B (ABcpxs) and Ti- and Fe3-poor Al-diopsides for Group C (Ccpxs). They have poorly variable composition, clustering in the diopside field. Structurally, the diopside groups have nearly similar a (ranging from 9.73 to 9.75 Å), Vcell (437.2-440.9 Å3), and hbetai angle values (106.01°-106.23°), but some differences in polyhedral parameters and geometries of the AB-cpxs and C-cpxs have been observed. For example, the AB-cpxs are characterized by. larger c (5.27-5.30 vs. 5.25-5.28 Å), VT (2.27-2.30 vs. 2.23-2.28 Å3), and VM2 (25.53-25.72 vs. 25.41-25.59 Å3) values and smaller b (8.87-8.88 vs. 8.88-8.91 Å) and VM1(11.49-1.63 vs. 11.64-11.83 Å3) values with respect to the C-cpxs. In addition, the AB-cpxs show higher values of VM2/VM1 (2.20-2.23) due to large VM2 and small VM1 compared to the VM2/ VM1 ratios of the C-cpxs (<2.19). Such differences in the crystal structure of the AB-cpxs and C-cpxs from the NAVs are partly related to different crystallization pressures, but mostly related to variation in melt composition and, possibly, the influence of other crystallizing mineral phases. In particular, R(M2-O1) and R(M1-O2) (i.e. bond lengths) differences in the clinopyroxenes of different groups support the presence of evolved host rocks with different alkaline character (i.e. silicaundersaturated Groups A-B and silica-saturated Group C). Based on the cpx-geothermobarometry, the crystallization pressures for the C-cpxs are lower than 4.5 kbars, but the AB-cpxs have relatively high-pressure values (5.6- 10.6 kbars), suggesting that the AB-cpxs crystallized in higher pressure environments. The relatively higher crystallization temperatures of the AB-cpxs also indicate higher cooling rates. The P-T estimates suggest that the source regions of the clinopyroxene phenocrysts from the NAVs were crustal magma chambers in a closed plumbing system at a moderate- to low-pressure regime.

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  • MakaleYalnız künye2008Scopus SJRQ1
    An application of the interaction matrices method for slope failure susceptibility zoning: Dogankent settlement area (Giresun, NE Turkey)

    Ceryan, Nurcihan; Ceryan, Sener

    Large-scale instability phenomena frequently occur in slopes in such geologically complex areas as Dogankent in NE Turkey. This study presents an application of the interaction matrices (IM) methodology, as a semi-qualitative method sensitive to large-scale slope instability. For both rock and soil slopes, the main interactive factors were distance from faults, degree of weathering and slope angle. Using IM, a slope failure susceptibility map was created for the Dogankent area and checked again field evidence. The results indicated that IM could be a useful method for slope stability assessment.

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  • MakaleYalnız künye2008Scopus SJRQ1
    Influence of weathering on the engineering properties of Harsit granitic rocks (NE Turkey)

    Ceryan, Sener; Tudes, Sule; Ceryan, Nurcihan

    Weathering and hydrothermal alteration of the granitic rocks in the Eastern Black Sea Region (NE Turkey) are important phenomena affecting the engineering projects in the region. The study investigated the probable paths of rock-forming mineral transformations due to weathering in the Harsit granitoid rocks, the changes of the major oxides as a consequence of weathering and the effects of weathering on the engineering properties. To identify the changes in the major oxides, the volume concentrations were considered in relation to the dry density. Chemical leaching during weathering was shown to be significant in changing the minerals. It was concluded that the engineering properties of the weathered granitic rocks can be most reliably predicted by P-wave velocity.

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  • MakaleYalnız künye2006Scopus SJRQ2
    Sedimentary records of the extensional tectonic regime with temporal cessation: Gümüşhane Mesozoic Basin (NE Turkey)

    Yilmaz, Cemil; Kandemir, Raif

    The Gümüşhane Mesozoic Basin is characterized by Lower-Middle Jurassic volcanic-siliciclastic sediments (Şenköy Formation), Upper Jurassic-Cenomanian platform carbonates (Berdiga Formation) and Upper Cretaceous turbidites (Kermutdere Formation). Four extensional periods (Lias-Dogger, Turonian-Coniacian, Late Campanian (?) and Early (?) Maastrichtian) separated by two quiet tectonic periods (early Malm-Cenomanian and Santonian-Campanian) have been defined in this sequence. The previous studies suggested that Mesozoic basins only formed by extensional movements in the middle Cretaceous. Three extensional periods seperated by two quiet periods from the Cenomanian to the end of the Maastrichtian in Gümüşhane and NE Turkey were firstly proved by sedimentological findings in this study. The definition of these periods depends on features such as (1) neptunian dykes in different levels, (2) shallow marine limestone, (3) thinning-and-fining-upward sequences, (4) mixed faunal assemblages, (5) micro-turbiditic structures, (6) syn-sedimentary fault, (7) grabens, half-grabens, (8) pelagic limestone, (9) calciturbidites, (10) laterally and vertically rapid changes of the thickness and facies, (11) platform-to-basin transition and (12) monogenic breccias.

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