Gümüşhane ÜniversitesiGümüşhane ÜniversitesiAçık Erişim Arşivi · RDL Open

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  • MakaleAçık Erişim2024
    Comparison with carbonate rocks hosted iron skarn in the eastern Sakarya Zone (Gümüşhane, NE Turkey): a geomorphologic, geochemical and stable isotopic approach

    Sipahi, Ferkan; Zeybek, Halil İbrahim; Gücer, Mehmet Ali; Işık, Fatih

    The carbonate rocks in the eastern part of NE Turkey are situated within the Pontide paleo-magmatic arc and are frequently in contact with granitoid formations, often hosting skarn mineralization in the region. These carbonate rocks, typically found on ridges and hillsides exhibit predominant orientations along east–west, northeast-southwest, and northwest-southeast directions. A part of limestone, named as biomicrite, metamorphosed and display a saccharoidal texture. Comprised mainly of calcite, with less secondary quartz and iron oxide minerals, these carbonate rocks are classified as Fe-poor calcio-carbonate and magnesio-carbonate, having higher CaO and LOI contents. Marble and recrystallized limestone with granoblastic texture mainly comprise of calcite, less quartz, magnetite, and hematite. Marble classification diagrams suggest calcic skarn mineralization, indicated by decreasing CaO (or CO2) and increasing MgO from limestone to marble (or skarn). Strontium contents deviate slightly from the lithosphere carbonate average, while low Rb contents, attributed to skarn metamorphism, indicate the absence of K-bearing minerals. The high Al2O3/SiO2 in the carbonate rocks can points out hydrothermal activity and carbonate disengagement can indicate to actualize at temperatures that can affect Ce and Al mobilities. The low authigenic U value, low U/Th and Ni/Co ratios in carbonate rocks have been implied that protolith constituents deposited under oxic conditions. Positive Eu anomalies in limestone and marble suggest the influence of hydrothermal fluids. Carbon and oxygen isotope values in marble are similar with those of metamorphic and skarn marbles, indicating a magmatic origin. Overall, mineralogical and geochemical analyses propose a uniform source and/or geological process for all studied marbles.

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  • MakaleYalnız künye2023
    The Sr, Nd, Pb and Hf isotopes and crystallization conditions of the middle Eocene Daǧdibi Pluton in the eastern Sakarya Zone, Turkey

    Sipahi, Ferkan; Gücer, Mehmet Ali; Dokuz, Abdurrahman; Yi, Keewook; Kaygusuz, Abdullah; Akaryall, Enver; Saydam Eker, Çiǧdem; Doruk, Cüneyt

    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 Daǧdibi 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 μNdi values between -0.96 and +0.52. Pb-Pb isotope ratios are typical for those of the lower continental crust. μHf(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 Daǧdibi Pluton in the middle Eocene.

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  • MakaleYalnız künye2023
    Two-stage bimodal volcanism in a Late Cretaceous arc/back-arc setting, NE Turkey: Constraints from volcano-stratigraphy, zircon U-Pb and 40Ar/39Ar geochronology and whole-rock elemental and Sr-Nd-Pb isotope geochemistry

    Oguz-Saka, Simge; Aydin, Faruk; Karsli, Orhan; Dokuz, Abdurrahman; Aiglsperger, Thomas; Miggins, Daniel P.; Sen, Cuneyt; Kandemir, Raif; Sari, Bilal; Koppers, Anthony A. P.

    The eastern Blacksea magmatic arc (EBMA) in the eastern Sakarya Zone (ESZ) provides an excellent opportunity to investigate birth of an extensional intra-arc and back-arc settings in the Late Cretaceous over the Early Cretaceous northern passive margin of the Neotethys Ocean. Volcano-stratigraphy clearly shows that the Late Cretaceous volcanic activity of the EBMA occurred in two major phases. Bimodality, characterized by mafic/ basaltic rocks at the base and felsic/silicic types on top of it, is a typical feature of the lower (LVS) and upper (UVS) volcanic successions in the Giresun region of the ESZ. U-Pb and Ar-Ar ages support the volcanic suc-cession as two-stage (LVS: ca. 92-85 and UVS: ca. 83-67 Ma) bimodal volcanism. Both the volcanic successions are represented by similar rock types consisting of tholeiitic to calc-alkaline basalt-basaltic andesites and calc-alkaline to shoshonitic dacite-rhyolites. Basaltic (M1-and M2-series) and felsic/silicic (F1-and F2-series) sam-ples of the LVS and UVS have an arc-like signature with enriched large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs). Also, the felsic/silicic samples of the F1-and F2-series show prominent negative Sr and Eu anomalies (Eu/Eu* = 0.4 to 0.9), suggesting that plagioclase fractionation played a key role on the evolution of both felsic series. Bimodal rock series in two phases have a wide range of 87Sr/86Sr(i) (0.7048-0.7075) and 143Nd/144Nd(i) (0.5123-0.5127) ratios with var-iable epsilon Nd(i) values of-3.8 to +3.0. 206Pb/204Pb(i), 207Pb/204Pb(i) and 208Pb/204Pb(i) isotope ratios of the Giresun volcanic rocks vary in the range of 17.97-18.52, 15.55-15.65 and 37.53-38.56, respectively. Geochemical and isotopic data suggest that the parental magma of the M1-basaltic rocks were probably derived from a shallow (spinel-bearing) mantle metasomatized by slab/sediment-derived fluids. In contrast, the M2-basalts seem to have been originated from a deeper mantle source (spinel-garnet transition zone) enriched by slab/sediment-derived fluids and hydrous melts (bulk sediment) metasomatism with some contributions of lower/upper crustal materials. The least evolved basaltic samples in two phases are consistent with moderate (-10-15%) to high degree (-20-30%) partial melting of the metasomatized mantle. The silicic melts of the F1 -and F2-rocks series, on the other hand, were likely derived from melting of lower crustal materials consisting of meta-basalts/andesites and lesser amount of meta-sediments. Subsequently, these melts experienced FC +/- AFC and mixing processes during their ascent and emplacement to generate high-silica (rhyolitic) melts. Our data, combined with previous studies, suggest that two-stage bimodal volcanic rocks of the Late Cretaceous in the ESZ were formed in the transition from an extensional continental intra-arc to a back-arc setting during the north-ward subduction of the northern branch of Neotethys Ocean.

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  • MakaleYalnız künye2022
    From Cadomian back-arc basin to Rheic Ocean closure: the geochronological records of the Kurtoglu Massif, eastern Sakarya Zone, Turkey

    Dokuz, Abdurrahman; Gücer, Mehmet Ali; Karsli, Orhan; Yi, Keewook

    New U-Pb zircon data from the Kurtoglu Massif (eastern Sakarya Zone, Turkey) reveal a Cadomian back-arc basin, evolving to closure of the Rheic Ocean. A host metapsammite from the lower tectonic slice of the massif yielded detrital zircon ages ranging from Neoarchean (2.73 Ga) to late Neoproterozoic with a major population between 610 and 553 Ma and a peak at 592 Ma, implying that the basement of the Sakarya Zone has a Cadomian affinity. This metasedimentary sequence was intruded by an orthogneiss in the early Ordovician (481 Ma) probably during the opening of the Rheic Ocean. Zircon grains from the overlying metasedimentary sample yielded concordant ages spreading throughout the Mesoproterozoic (1608-1032 Ma) and early Paleozoic (516-351 Ma), suggesting that they were deposited in the Rheic Ocean likely prior to its final closure. The muscovite metagranite, emplaced into the host rocks of the Kurtoglu Massif at 388 Ma, formed probably during northward closure of the Rheic Ocean. Zircon grains of a metasiltstone from the upper tectonic slice of the massif, represented mainly by phyllites, yielded similar age spectra to that of the host metapsammite of the lower tectonic slice. Such phyllites in the Pulur Massif similar to 35 km to the southeast display a close association with the ophiolitic complexes of the Rheic Ocean. This relationship together with the age spectra mentioned above suggests that sedimentation was on a place away from the Paleozoic igneous sources, in an analogous position to the southern passive margin of the Rheic Ocean.

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  • MakaleYalnız künye2022
    Early Cambrian S-type granites in the Sakarya Zone, NE Turkey: A record for transition from subduction to post-collisional extension deduced from U-Pb zircon age and Nd-Hf isotopes

    Karsli, Orhan; Sengün, Firat; Dokuz, Abdurrahman; Aydin, Faruk; Kandemir, Raif; Kristoffersen, Magnus; Santos, Jose Francisco; Hofmann, Mandy; Duygu, Levent

    Cadomian realms have recently received much attention in the Alpine-Mediterranean orogenic belts, with discontinuous outcrops extending from the Alps to the Istanbul Zone, Menderes Massif, Taurides in Turkey and Iran as well. However, they have not been identified in the Sakarya Zone, northern Turkey to date. Here, we present, for the first time, zircon U-Pb geochronology, zircon Hf-isotopes and trace elements as well as whole-rock geochemistry and Nd-isotopes from the Karamese metagranitoid in the Yusufeli (Artvin) area, NE Turkey. The zircon U-Pb age data demonstrate that the Karamese metagranitoid intruded into the Precambrian basement units in the Early Cambrian (ca. 534-530 Ma). Zircon overgrowths in the Karamese metagranitoid interpreted as a result of metamorphic overprint yielded ages of 328 Ma. This age indicates that the Sakarya Zone experienced the Variscan metamorphic events at 328 Ma. The Early Cambrian metagranitoid shows that some rocks in the basement of the Sakarya Zone date back to Precambrian in age. The Karamese metagranitoid is an S-type granite, with high modal content of muscovite (similar to 10%). The samples show highly peraluminous [A/CNK = molar Al2O3/(CaO + K2O + Na2O) = 1.34-1.58] and medium-K calc-alkaline geochemical affinities. The Karamese metagranitoid displays low REE concentrations and a slight positive Eu anomaly and show slightly light REEs and LILEs enrichments, and HFSEs depletions. The samples have negative epsilon(Nd)(t) of -4.76 to -2.90 and epsilon(Hf) (t) of -4.75 to -1.08 values. These geochemical-isotopic characteristics reveal that the Karamase metagranitoid originated through fluid-absent muscovite dehydration melting of heterogeneous metasedimentary source rocks (mostly greywacke), with a minor input of juvenile mafic melt. We argue that the Early Paleozoic metagranitoids along the eastern Sakarya Zone is an expression of crustal thinning in the Cadomian orogenic belt in northern Gondwana, with the tectonic turnover from convergent margin to crustal extension possibly induced by break-off of Tornquist oceanic lithosphere which is a branch of Iapetus Ocean during Early Cambrian.

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  • MakaleYalnız künye2020
    Temporal, geochemical and geodynamic evolution of the Late Cretaceous subduction zone volcanism in the eastern Sakarya Zone, NE Turkey: Implications for mantle-crust interaction in an arc setting

    Aydin, Faruk; Oğuz Saka, Simge; Şen, Cüneyt; Dokuz, Abdurrahman; Aiglsperger, Thomas; Uysal, İbrahim; Kandemir, Raif; Karslı, Orhan; Sarı, Bilal; Başer, Rasim

    The Late Cretaceous Artvin volcanic rocks (LCAVs) from the eastern Sakarya zone (ESZ) of NE Turkey are composed of mafic/basaltic (S1-Çatak and S2-Çağlayan) and felsic/acidic (S1-Kızılkaya and S2-Tirebolu) rock types that occurred in two successive stages: (i) first stage (S1: Turonian–Early Santonian) and (ii) second stage (S2: Late Santonian–Campanian). Clinopyroxene thermobarometric results point that the S2-Çağlayan basaltic rocks have crystallised at higher temperatures and under deeper crustal conditions than those of the S1-Çatak basaltic rocks. The LCAVs show a wide compositional spectrum, ranging from tholeiite to calc-alkaline/shoshonite and are typically represented by a geochemical composition resembling subduction-related arc rocks although the 87Sr/86Sr(i) (0.7044–0.7071) and ɛNd(i) values (−0.63 to + 3.47) as well as 206Pb/204Pb(i) (18.07–18.56), 207Pb/204Pb(i) (15.57–15.62) and 208Pb/204Pb(i) (37.12–38.55) ratios show very limited variation. The parent magmas of the S1-Çatak and S2-Çağlayan mafic volcanic rocks were derived from underplated basaltic melts that originated by partial melting of metasomatised spinel lherzolite and spinel-garnet lherzolite, respectively. It is proposed that the compositions of the S1-Kızılkaya (mainly dacitic) and S2-Tirebolu (rhyolitic to trachytic) felsic rocks were particularly controlled by metasomatised mantle–crust interaction and MASH zone + shallow crustal fractionation processes. Our data, together with data from previous studies, suggest that the S1- and S2-mafic and felsic rocks of the LCAVs (~95–75 Ma) are the products of two-stage volcanic event that took place during the northward subduction of the northern Neotethys Ocean (NNO).

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  • MakaleAçık Erişim2020
    Tracking the timing of Neotethyan oceanic slab break-off: Geochronology and geochemistry of the quartz diorite porphyries, NE Turkey

    Karsli, Orhan; Dokuz, Abdurrahman; Aydin, Faruk; Uysal, Ibrahim; Sengün, Firat; Kandemir, Raif; Santos, Jose Francisco; Andersen, Tom

    The initiation of the break-off of the northern branch of the Neotethyan oceanic lithosphere is an important but poorly understood event in the geology of the Sakarya Zone (SZ) in northeastern Turkey. Although it is wellknown that Latest Cretaceous intrusives (-70 Ma) and early Eocene adakitic magmatic rocks are present in the eastern SZ, the outcrops of the early Eocene non-adakitic rocks are very limited, and their tectono-magmatic evolution has not been studied. We describe a small outcrop of non-adakitic quartz diorite porphyry in the Kov area of the Gumushane region in northeastern Turkey. The genesis of these porphyries is significant in evaluating the syn-to post-collision-related magmatism. The LA-ICP-MS zircon U-Pb dating revealed that the Kov quartz diorite porphyries (KQDP) formed at ca. 50 Ma, coeval with adakitic rocks, and-20 Myr later than the slab rollback-related intrusive rocks. The KQDPs are calc-alkaline in composition and enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti), with significant negative anomalies of Nb, Ta, and Ti but positive anomalies of Th, U, and Pb. Isotopic compositions of the samples show limited range of variation and slight enrichment of 87Sr/86Sr(t) (0.70489 to 0.70555), epsilon Nd(t) (-1.4 to -1.2) with TDM of 1.11 to 1.61 Ga. Pb isotopic ratios of the samples point to an enriched mantle source. They were likely crystallized from the melt that originated from an EM2-type spinel-facies subcontinental lithospheric mantle (SCLM), followed by the fractionation with insignificant crustal assimilation. The SCLM was metasomatically enriched, and the metasomatic agent was likely H2O-rich fluids rather than sediments released from subducting oceanic crust during the Late Cretaceous closure of the Neotethyan oceanic lithosphere. In conjunction with the geological background and previous data, we propose that the generation of the KQDPs resulted from a slab break-off event that caused ascending or infiltration of hot asthenosphere, triggering mantle melting. Such sporadic occurrences of the KQDPs, with coeval adakitic rocks in the SZ, are likely associated with the onset of extensional tectonics due to the earlier stage of slab break-off along the region during the early Eocene period.

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  • MakaleYalnız künye2019
    Adakite-like parental melt generation by partial fusion of juvenile lower crust, Sakarya Zone, NE Turkey: A far-field response to break-off of the southern Neotethyan oceanic lithosphere

    Karsli, Orhan; Dokuz, Abdurrahman; Kandemir, Raif; Aydin, Faruk; Schmitt, Axel K.; Ersoy, E. Yalçın; Alyıldız, Cihangir

    The timing of major tectonic events and the driving mechanisms for magma generation during Late Cenozoic convergence and collision between Arabia and Eurasia still remain unknown. The Sakarya Zone (SZ) in northern Turkey is a critical member of this collisional assemblage. In the easternmost part of the SZ, we have recognized a Late Miocene volcanic suite termed the Çağirankaya volcanics which displays characteristic post-collisional geochemical features. Here, we report a new data set of zircon U–Pb ages, whole-rock major and trace element, as well as Sr–Nd isotope analyses for dacite and andesite samples from the Çağirankaya volcanics. Zircon U–Pb ages for a selected dacitic sample average 5.16 ± 0.11 Ma (mean square of weighted deviates, MSWD = 0.45, n = 35), confirming a late Miocene age of this volcanic episode. The high-K calc-alkaline andesites and dacites exhibit an adakite-like geochemical signature, and are characterized by high Sr (424 to 552 ppm), Sr/Y ratios (31–43), and low Mg# (42 to 46) values, along with low Y (12–14 ppm) and heavy rare earth element (HREE) concentrations, that resemble those in adakites formed by partial melting of hot oceanic slab during subduction. Isotopic compositions are near bulk Earth (87Sr/86Sr(t) = 0.70482 to 0.70489, εNd(t) = +1.08 to +1.33), which rules out a solely asthenospheric origin. Elevated Nb/Ta (14 to 17) and K2O/Na2O (0.6–1.0) imply a juvenile mafic lower crustal source composed of ~20% garnet-bearing amphibolite. Geochemical modeling suggests that adakite-like parental melts were generated in the absence of subduction and without large-scale delamination of lower continental crust. Instead, our findings suggest that Late Miocene adakite-like volcanic rocks in the SZ formed in a post-collisional intra-continental setting, which experienced far-field extension after the subducted slab of the southern Neotethyan branch became detached in the collision zone. Asthenospheric upwelling and underplating of basaltic magma provided the heat for partial melting of lower crustal amphibolite, forming minor amounts of adakite-like melts in the SZ.

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  • MakaleYalnız künye2019
    Jurassic acidic magmatism in a back-arc setting, eastern Sakarya Zone, Turkey: Geochemical constraints and an evolutionary model

    Dokuz, Abdurrahman; Sünnetçi, Kadir

    The Early Jurassic in the Sakarya Zone, Turkey, was dominated by basic magmatism. The products of this magmatic episode are found as basaltic lavas and pyroclastic rocks in the Şenköy Formation, which was deposited in an extensional basin, or as intrusives cutting Variscan crystalline basement rocks. The Olur (Erzurum) region in the easternmost part of the Sakarya Zone is one of the few locations where contemporaneous acidic rocks crop out, exposed in an area of ~50 km 2 . The acidic rocks in the eastern Sakarya Zone consist of dacitic lavas, rare pyroclastic rocks, and very rare pebble dikes. Porphyries and trondhjemites are their intrusive equivalents and crop out as dikes and small stocks within the underlying Variscan basement. These Early Jurassic rocks have modal K-feldspar contents of <10% and are trondhjemitic in character. Laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating of zircons from two samples yielded formation ages for these rocks of 185.3 ± 1.0 and 184.1 ± 1.1 Ma (±2σ). Geochemically, the rocks are strongly peraluminous and display a medium- to low-K affinity and sodic compositions (K 2 O/Na 2 O = 0.03–0.49). Enrichment in large-ion lithophile elements and depletion in Nb, Ta, P, and Ti are regarded as signatures of a subduction-related setting. Moderately radiogenic I Sr ratios (0.70508–0.70877) and depleted mantle-like Ɛ Nd (t) values (−0.6 to +3.0) and Pb(t) isotopes suggest that the acidic rocks were derived from juvenile lower crust. Geochemical and isotope data imply that the partial melting of juvenile mafic lithologies of the lower crust produced K-poor tonalitic melts that later fractionated to trondhjemitic melts while ascending to the surface. Considering the available data, we suggest that the Early Jurassic bimodal magmatic rocks of the eastern Sakarya Zone were formed in a back-arc setting during the southward subduction of the Paleotethys oceanic lithosphere. These rocks are a prime example of the formation of shallow subduction products following Late Triassic ridge subduction.

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  • MakaleAçık Erişim2011
    Early abyssal- and late SSZ-type vestiges of the Rheic oceanic mantle in the Variscan basement of the Sakarya Zone, NE Turkey: Implications for the sense of subduction and opening of the Paleotethys

    Dokuz, Abdurrahman; Uysal, Ibrahim; Kaliwoda, Melanie; Karsli, Orhan; Ottley, Chris J.; Kandemir, Raif

    The boundary between the Gondwana and Laurussia, or a terrane separated from it, is traced by a suture recording the closure of the Rheic ocean in the Pulur, Beyçam and Kurtoǧlu areas of the eastern Sakarya Zone of Turkey. Pulur lherzolite has a lower Cr# [100Cr/(Cr+Al)=5-37] of the spinel and slightly enriched flat medium-heavy rare earth element (M-HREE) whole-rock pattern typical for those of the fertile abyssal-type lherzolite. By contrast, the Beyçam harzburgite displays the mineralogical and geochemical features of a moderately depleted residue at a supra subduction zone (SSZ). Some of spinels from the Beyçam peridotites show TiO2 contents (0.15-0.48wt.%) identical to a later interaction with a melt of island-arc tholeiite (IAT) composition. Meta-basalt from the Beyçam area is the representative of such a melt and displays the whole-rock M-HREE pattern of a complementary product of the Beyçam harzburgite. Data presented in this study support the primarily northward directed closure of the Rheic ocean, but suggest that the Variscan basement in the eastern part of the Sakarya Zone consists of mantle peridotites formed in a south-vergent SSZ. This dual polarity of subduction in the Rheic ocean, at least in the second half of its closure, is also favored by the geological structure and lithological diversity of the Variscan rocks. These are: (1) spatial distribution of the peridotites, e.g., SSZ-type harzburgites to the north and abyssal-type lherzolites to the south, (2) lack of high-pressure metamorphic rocks, (3) decrease in the degree of Variscan metamorphism toward the north, and (4) emplacement of Variscan syn-collisional magmatism into the low grade metamorphic rocks to the north. Paleotethys was the other ocean of the region created in the Late Paleozoic. Northward subduction of the Rheic ocean from Early Devonian to Early Carboniferous appears to be the most plausible mechanism responsible for the opening of Paleotethys. In this scenario the Paleotethys is envisaged as a back-arc basin opened to the north in the wake of separated terranes from Laurussia. Onset of trench-Rheic mid-ocean ridge collision in the Early Devonian along the northern margin of Laurussia has been proposed to account for the initiation of SSZ-type subduction to the south. The short duration of this subduction appears insufficient to open a fully developed back-arc basin to the south because the elimination of Rheic mid-ocean ridge to the north accelerated the oceanic closure.

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