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• MakaleYalnız künye2026/r/gumushane/10500
  Late Cretaceous hybrid melt sources and flare-up magmatism in the eastern Sakarya Zone, NE Türkiye: Zircon Hf-O constraints and implications for VMS fertility

  Aydin, Faruk; Oguz-Saka, Simge; Karsli, Orhan; Dokuz, Abdurrahman; Moghadam, Hadi Shafaii; Zhao, Junxing; Schmitt, Axel K.

  Understanding melt source evolution during arc-back-arc magmatism is essential for resolving crustal growth processes and the development of felsic-hosted volcanogenic massive sulfide (VMS) systems. Here we integrate new zircon HfO isotope data with published geochronological and whole-rock geochemical datasets to reassess the petrogenesis of Late Cretaceous arc and back-arc magmatic flare-ups in the eastern Sakarya Zone (ESZ), NE T & uuml;rkiye. Two high-flux magmatic episodes are recognized: a Turonian-Santonian pulse (similar to 92-86 Ma) forming the lower volcanic sequence (LVS), and a younger Campanian pulse (similar to 84-75 Ma) forming the upper volcanic sequence (UVS), accompanied by contemporaneous arc-related granitoids. Zircons from both LVS and UVS display predominantly positive epsilon Hf(t) values (+2 to +12) coupled with mantle-like delta O-18 (5.0-5.6 parts per thousand), but contain abundant inherited Mesoproterozoic-Paleozoic cores and show variable two-stage model ages (T-DM (c) = 0.4-1.4 Ga). Together with the peraluminous affinity of many felsic units, these features indicate that the dacite-rhyolite suites hosting VMS deposits were generated by melting of compositionally heterogeneous lower crust variably hybridized by juvenile basaltic inputs. Arc granitoids likewise record a transition from dominantly juvenile, I-type magmatism during the Coniacian-Santonian to more evolved, crust-influenced signatures during the Campanian. We propose that both flare-ups reflect repeated episodes of basaltic underplating and deep-crustal heating, producing voluminous felsic magmas capable of sustaining long-lived hydrothermal systems. The spatial and temporal coincidence between felsic-dominated flare-ups and VMS mineralization suggests that hybridized felsic magmas, rather than purely juvenile mantle melts, played a central role in generating the physiochemical conditions required for metal-bearing hydrothermal fluids in the ESZ.

  İncele
• MakaleAçık Erişim2025/r/gumushane/19760
  Geçmişten Günümüze Gümüşhane’de Madencilik

  Sukuroglu, Ebru Emine; Dağ, Serhat; Alemdag, Selcuk; Saylan, Kemal; Nazir, Bayram; Ozer, Ismail; Kurucu, Muhammet; Sipahi, Ferkan; Atalan, Öznur; Zeybek, Halil

  Türkiye, madenler bakımından oldukça çeşitli ve zengin bir ülkedir. Ülkede yer alan bazı madenlerin dünya çapında önemli bir yere sahip olduğu bilinmektedir. Türkiye'nin Doğu Karadeniz bölgesinde bulunan Gümüşhane ili de madenler bakımından zengin bir çeşitliliğe sahiptir. Öyle ki, Gümüşhane’de var olan bu çeşitlilik ilk medeniyetlerin bölgeye hâkim olması ile önemli hâle gelmiş, şehirde bulunan madenlerin dışında şehrin İpek Yolu güzergâhında yer alması da bu bölgenin önemini daha da arttırmıştır. Hiç şüphesiz bu önem, Osmanlı Devleti’nin Trabzon’un fethi ile bölgeyi topraklarına katması ile devam etmiştir. Bu dönem ile birlikte şehirde madencilik faaliyetleri artmaya başlamış ve bu yönde yapılan çalışmalar ülkeye maddi anlamda katkı sağlamıştır. Bu açıdan Osmanlı Devleti, 16., 17. ve 18. yüzyıllarda bünyesinde barındırdığı başta gümüş ve altın madenleri olmak üzere diğer madenlerin varlığı nedeniyle ticari olarak canlı bir özellik gösteren Gümüşhane’ye büyük önem vermiştir. Böylece 17. yüzyılda adeta altın çağını yaşayan maden ocakları, 18. yüzyılın sonlarına kadar faaliyetlerini devam ettirmiştir. Bu yüzyıldan sonra da madenlerde yapılan üretim zamanla azalarak bölgedeki maden işletmelerinde çalışan işçiler madenleri terk etmeye başlamıştır. 19. yüzyılın ortalarına gelindiğinde maden ocaklarının işletilmesinde büyük oranda çözülme ortaya çıkmıştır. Yapılan bu çalışma; Gümüşhane şehrinin tarihî çağlar, Osmanlı Dönemi ve Cumhuriyetten günümüze kadar olan maden çalışmalarını ele alarak şehir ekonomisine birinci derecede yön veren madenlerin şehir açısından önemini ortaya koymayı amaçlamıştır. Çalışmada alan ile ilgili yapılmış çalışmalardan ve arşiv vesikalarından istifade edilmiştir.

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  İncele
• MakaleAçık Erişim2025/r/gumushane/19644
  Mescitli Formasyonu’na (Gümüşhane, Türkiye) ait kumtaşlarının endüstriyel hammadde olarak kullanım potansiyelinin incelenmesi

  Aliyazıcıoğlu, Şener; Dağ, Serhat; Zeybek, Halil İbrahim; Çavuşoğlu, İbrahim; Gücer, Mehmet Ali; Sipahi, Ferkan; Dokuz, Abdurrahman

  Doğal zenginliklerin ortaya çıkarılması ve yöresel kayaçların ekonomiye kazandırılarak endüstriyel kullanım alanlarının belirlenmesi günümüzde büyük önem taşımaktadır. Bu çalışmada, Gümüşhane’deki Mescitli Formasyonu kumtaşlarının endüstriyel hammadde olarak kullanım potansiyeli araştırılmıştır. Kumtaşları başlıca monokristalin ve polikristalin kuvars, feldispat, volkanik ve tortul kayaç parçaları, opak mineral, kil matriks ve az oranda bağlayıcı karbonat/silis minerali içermektedir. Grovak (psammit) olarak sınıflandırılan kumtaşlarının kimyasal ayrışma indeksi (CIA) parametresine göre alterasyondan çok fazla etkilenmediği belirlenmiştir. Jeoteknik özellikler açısından, ortalama kuru yoğunluk 2.48 gr/cm3, doygun yoğunluk 2.54 gr/cm3, gözeneklilik %6.63 boşluk oranı %7.11, ultrasonik P-dalga hızı 4793 m/sn, tek eksenli basınç dayanımı 103.09 MPa ve dolaylı çekme dayanımı 5,86 MPa olarak belirlenmiştir. Donma-çözünme deneyi ile don kaybı %1.19 olarak belirlenmiş, 600-800ºC sıcaklıklara kadar ısıtılan kumtaşı numunelerinde ortalama 9.8 gr ve 17.9 gr kütle kaybı gözlenmiştir. Aynı sıcaklık koşullarında kumtaşlarının dayanımının sıra ile %7.64 ve %15.17 oranında azaldığı görülmüştür. Hücre Sitotoksisite analizlerinde toksik etkiye rastlanmamıştır. Sonuçlar, kumtaşlarının günlenmeye maruz kalacak alanlarda kullanım için uygun olmadığı, bina içyapı ve dekoratif amaçlı kaplamalarda kullanılabileceğini göstermiştir. Sıcaklık dayanımı ve hücre sitotoksisite analizleri ise kumtaşlarının ızgara taşı olarak kullanılabileceğini ortaya koymuştur.

  İncele
• MakaleAçık Erişim2025/r/gumushane/14346
  Paleolatitudinal movements of the eastern Sakarya Zone from Jurassic to Eocene

  Kayın, Sercan; Hisarlı, Z. Mümtaz; İşseven, Turgay; Dokuz, Abdurrahman; Algur, Bahadırhan Sefa

  The study area covers a region oriented north-south from the Black Sea coastline in the north to the Kelkit Basin in the south within the eastern Sakarya Zone in northern Türkiye. The objective of this study is to investigate the paleolatitudinal movements of the eastern Sakarya Zone during the Jurassic-Eocene time interval through paleomagnetism. Various volcanic and sedimentary units (e.g., the Şenköy, Berdiga, Mescitli, Çatak, Kızılkaya, and Çağlayan Formations) spanning the time interval from the Early Jurassic to Middle Eocene were identified. A total of 98 locations belonging to Early/Middle Jurassic to Eocene volcanic and sedimentary units were selected for paleomagnetic core sample collection. The samples were subjected to demagnetization through thermal and alternating field methods. Characteristic remanent magnetization directions (ChRM) were obtained. Isothermal remanent magnetization (IRM) and high temperature susceptibility (HTS) measurements were made to identify the minerals responsible for magnetization. To ascertain whether magnetization was acquired through rock formation or as a consequence of subsequent tectonic processes, conglomerate and fold tests were performed. The results showed that magnetization was acquired before folding, i.e., the rocks have primary magnetization. Polarity tests were also conducted using coeval normal and reverse polarity sites. The results indicate that the mean magnetization direction for the Early-Middle Jurassic is 18.1°/55.2° (D/I) and 3.3°/51.5° (D/I) for sedimentary and volcanic rocks, respectively, and 348.7°/46.7° (D/I) for Late Jurassic/Early Cretaceous sedimentary rocks. In the Late Cretaceous period, the mean magnetization direction is 8.0°/49.3° (D/I) and 9.1°/47.0° (D/I) for sedimentary and volcanic rocks, respectively. In the case of the Early/Middle Eocene, the mean magnetization direction is 348.6°/52.7° (D/I) and 5.9°/48.8° (D/I) for sedimentary and volcanic rocks, respectively. In this study, the E/I correction was applied to the Late Jurassic/Early Cretaceous sedimentary rocks, and paleolatitude data obtained from sedimentary rocks were also utilized. Our paleomagnetic results indicate that the eastern Sakarya Zone was situated at latitudes spanning from 27.9° to 35.7° during the Early Jurassic - Middle Eocene time interval. In consequence, the eastern Sakarya Zone constituted a portion of the southern margin of the Eurasian continent during the Late Jurassic and Middle Eocene periods.

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• MakaleYalnız künye2023/r/gumushane/16186
  Post-Variscan autochthonous cover in the eastern Sakarya Zone, Turkey: Evolution of the late Carboniferous back-arc ocean to the Triassic Karakaya Ocean

  Dokuz, Abdurrahman; Alçiçek, Mehmet Cihat; Tunçdemir, Vahdet; Kandemir, Raif; Aydinçakir, Emre

  The processes that caused removal of the upper Carboniferous to Permian sediments in the eastern Sakarya Zone, Turkey, are modeled by using of geochemical data and LA-ICP-MS U-Pb ages from detrital zircons. A felsic provenance and passive margin setting during the deposition of the upper Carboniferous catalcesme sediments are inferred from the geochemistry of sandstones (SiO2 > 85 wt%). Chemical Index of Alteration (CIA) values (75 - 81) indicate warm and humid climatic conditions and tectonic tranquility during deposition. Fifty-three (58%) concordant zircon grains produce a youngest age population in the range of 308.7 +/- 4.4 to 342.1 +/- 6.9 Ma, typical for the Variscan events. The burgundy color and upward-fining in clast size and bed thickness are the most prominent features of the concordantly overlying Hardisi Formation. Geochemistry (SiO2 = 66-81 wt%) and CIA values (58-65) of the clastic rocks point to a subduction-related tectonic setting and increasing rate of erosion in the source area. We highlight that the catalcesme sediments were deposited in a back-arc basin opened to the south of a continental ribbon separated from Gondwana. Approaching of the Paleotethyan mid-ocean ridge to the subduction zone was resulted in flattening in subducting slab, which in turn caused the back-arc basin to migrate into the interior parts of Gondwana and the former back-arc basin to evolve into a lacustrine setting. Increase in the elevation of source areas was resulted in an increase in the rate of physical erosion and trans-portation of burgundy Hardisi clastic sediments into the lacustrine basin.

  İncele
• MakaleAçık Erişim2023/r/gumushane/10639
  Ordovician S-type granites in the western Sakarya Zone, NW Turkey; linkage to a back-arc setting

  Karsli, Orhan; Sengun, Firat; Aydin, Faruk; Moghadam, Hadi S.; Dokuz, Abdurrahman; Griffin, William L.; Saka, Simge Oguz; Zack, Thomas

  Turkey's Early Paleozoic tectonic evolution has received much attention in recent years. Early Paleozoic intrusive rocks are mainly distributed across Europe, Turkey (Istanbul-Zonguldak Zone, Strandja Zone, and Tauride Block), and Iran. However, the Early Paleozoic rocks have not yet been identified in north Turkey's Sakarya Zone, and thus the Early Paleozoic paleogeography of the Sakarya Zone remains enigmatic. Here, we provide new field observations, petrography, geochemistry, and geochronology of the western Sakarya Zone to identify the nature, origin, and tectonic setting of the Ordovician magmatic rocks cropping out in the So center dot gut area (Bilecik, northwest Turkey). Our Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb analyses on zircons suggest that the So center dot gut metagranites were emplaced at-484-461 Ma (except two zircons with ages of 490 and 494 Ma). There are abundant inherited zircon cores in the So center dot gut metagranites, with ages of >500 Ma to-2.2 Ga. The inherited Cadomian cores give concordant ages of 588 and 572 Ma. The So center dot gut metagranites are felsic and have high SiO2 (72-76 wt%) and K2O (4.1-5.3 wt%) contents, with high K2O/Na2O ratios (1.2-1.9), and low Mg# (17-35) values. The samples are Ca-poor (CaO = 0.52-0.68 wt%) and show peraluminous [A/CNK = molar Al2O3/(K2O + CaO + Na2O) = 1.15-1.28] and high-K calc-alkaline geochemical characters, with high modal content of muscovite (-10%), consistent with S-type compositions. The samples have low REE concentrations, with negative Eu anomalies. Ordovician zircon rims show epsilon Hf(t) values of +3.6 to-35.4, whereas inherited zircon cores have epsilon Hf(t) values of +33.9 to-26.1. Our data, in conjunction with previous studies, suggest that the So center dot gut metagranites were generated by fluid-absent muscovite-dehydration melting of metasediments accumulated in a back-arc setting. This back-arc basin was characterized by a denuded continental crust with abundant pelite-dominated sediments and minor input of juvenile mafic melts. Our results, combined with previously published data and paleogeographic reconstructions, allow us to conclude that the Ordovician S-type granites were formed by progressive back-arc extension and crustal thinning prompted by the rollback of the southward subducting oceanic-lithosphere slab. This led to the opening of the Rheic Ocean on the northern side of Gondwana in response to the final closure and termination of the Tornquist Ocean as a branch of the Iapetus Ocean. We argue that the Ordovician S-type granites from the northern side of Gondwana could signal significant crustal reworking away from any clear continental collision zone.

  İncele
• MakaleYalnız künye2023/r/gumushane/10557
  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.

  İncele
• MakaleYalnız künye2023/r/gumushane/12805
  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.

  İncele
• MakaleYalnız künye2022/r/gumushane/10645
  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.

  İncele
• MakaleYalnız künye2022/r/gumushane/15856
  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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