İlgi alanları

• MakaleYalnız künye2026/r/gumushane/10581
  Petrogenetic constraints and phase equilibria modelling on amphibole-bearing high-grade metamafic rocks from the Maku ophiolite (NW Iran): implications for metamorphism along the central Neo-Tethyan suture

  Modjarrad, Monir; Uysal, Ibrahim; Yara, Irfan O. M. A.; Sen, Ahmet Dundar; Xin, Guangyao; Müller, Dirk

  We present an integrated petrological, mineral-chemical, whole-rock geochemical, microstructural, and phase-equilibrium study of the West Maku metamafics (WMM), an ophiolite-related mafic unit in NW Iran. The WMM comprises garnet amphibolites and amphibole-bearing high-grade metamafic rocks containing almandine-rich garnet, tschermakite-ferro-tschermakite, andesine, epidote/zoisite, annite, muscovite-phengite, spinel, ilmenite, chlorite, quartz, and K-feldspar. Immobile element systematics indicate a tholeiitic, MORB-like basaltic protolith; LILE and crust-sensitive element enrichment likely reflect inherited crustal/sediment-derived components and metamorphic redistribution during subduction-accretion and/or m & eacute;lange assembly. P-T modelling defines four relative stages: M1, upper greenschist-facies metamorphism at ca. 6.4 kbar and 360 degrees C; M2, prograde heating to 8.0-8.4 kbar and 700-720 degrees C; M3, peak upper-amphibolite- to granulite-facies conditions at 9.0-9.8 kbar and up to 810 degrees C, with localized anatexis; and M4, retrogression at ca. 3.8 kbar and 520 degrees C. The clockwise path records the burial and heating of MORB-derived crust in a subduction-accretionary setting, followed by collision-related thermal relaxation/crustal thickening and subsequent uplift. Regional comparisons indicate thermally heterogeneous evolution along the central Neo-Tethyan suture across Armenia, SE T & uuml;rkiye, NE Iraq and NW Iran.

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• MakaleAçık Erişim2026/r/gumushane/19384
  Yiğitler (tekman/erzurum) yöresindeki jeotermal ve soğuk su kaynaklarının hidrokimyasal özellikleri

  Kaygusuz, Abdullah; Vural, Alaaddin; Kaygusuz, Kamil; Sen, Ahmet Dundar; Çavuş, Dilek

  Bu çalışma, Erzurum-Tekman Yiğitler köyü civarındaki jeotermal, soğuk ve yüzey sularının hidrokimyasal özelliklerini, kökenini ve kullanım olanaklarını belirlemek amacıyla gerçekleştirilmiştir. İnceleme alanında jeotermal sistemin ana hazne kayacını peridotit ve gabro türü kayaçlardan oluşan Şahvelet Ofiyolitleri ile Kösehasan Formasyonu içindeki kireçtaşları, örtü kayacını ise masif yapıdaki Bingöldağı volkanitleri oluşturmaktadır. İncelenen jeotermal suların sıcaklık değerleri 43-49 °C, pH değerleri 7.03-8.33 ve EC değerleri 950-1550 µS/cm arasında değişmektedir. Analizler sonucunda, jeotermal, yeraltı ve yüzey sularının Ca-Mg-HCO₃ fasiyesinde olduğu belirlenmiştir. Piper, Schoeller ve Gibbs diyagramları ile yapılan sınıflandırmalar, aynı kaynaktan beslenen tek bir hidrokimyasal sistemin varlığına işaret etmektedir. (Ca+Mg)-(HCO₃+SO₄) diyagramı, Ca/Mg, HCO₃/SiO₂ ve Ca+Mg/HCO₃ oranları, CAI-I ve CAI-II indeksleri, kaya-su etkileşimine bağlı olarak su kimyasının genelde karbonat daha az oranda da silikat ayrışma süreçlerinden etkilendiğine işaret etmektedir. Hazne kaya sıcaklıkları silis jeotermometreleri ile 52-93°C, entalpi-silis karışım modeli ile 127-141°C hesaplanmıştır. Bu durum, akışkanın sığ seviyelerde %28-46 oranında soğuk yeraltı suları ile karıştığını göstermektedir. İçme suyu standartları açısından; soğuk kaynak suları uygun, yüzey suları ise sulama için elverişli bulunmuştur. Jeotermal sular; yüksek Ca, Fe, Mn, As ve NH4 derişimleri nedeniyle içme amaçlı kullanılamazken, kimyasal değerleri bakımından kaplıca kullanım potansiyeline sahiptir.

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• MakaleYalnız künye2025/r/gumushane/10405
  Subduction initiation of the Neotethyan Ocean recorded in chromite deposits: A case study of the Kızıldag ophiolite, southern Turkiye

  Uysal, Ibrahim; Akmaz, Recep Melih; Su, Ben-Xun; Demir, Yilmaz; Sen, Ahmet Dundar

  The chromitites of the K & imath;z & imath;lda & gbreve; ophiolite (KO) are primarily characterized by massive and disseminated textures within refractory mantle peridotites, predominantly harzburgite and dunite, with occasional occurrences of banded and nodular chromitites. Based on chromite composition, these chromitites can be classified into two groups exhibiting a broad compositional range: intermediate (0.55 <= Cr# < 0.70, TiO2 = 0.08-0.51 wt%) and high-Cr (0.70 <= Cr# <= 0.77, TiO2 = 0.05-0.28 wt%). The compositions of minor and trace elements align consistently with variations in Cr#. Total PGE (Os, Ir, Ru, Rh, Pt, Pd) contents in these chromitites are generally less than 500 ppb, with many samples showing enrichment of IPGE (Os, Ir, Ru) relative to PPGE (Rh, Pt, Pd). However, certain samples from both groups display elevated PGE concentrations (Sigma PGE(intermediate) = 718 ppb, Sigma PGE(High-Cr) = 866 ppb) compared to other samples. The dominant platinum group mineral inclusions in chromite are Ru-rich laurite [(Ru, Os)S-2], with a single osmiridium (Os-Ir alloy) grain also observed suggesting formation under high-temperature and low & fnof;S-2 conditions. Primary base metal mineral inclusions include millerite and pentlandite. Additionally, some chromite crystals contain single or multi-phase silicate inclusions, such as clinopyroxene, orthopyroxene, olivine, and amphibole. Parental melt compositions, calculated from Al2O3 and TiO2 contents of chromites, indicate that most high-Cr chromitites originated from boninitic melts, whereas intermediate chromitites and some high-Cr samples derived from melts with intermediate compositions. Trace element compositions of amphibole and clinopyroxene inclusions in the chromite crystals from the intermediate group further support crystallization from hydrous intermediate melts. It is proposed that the intermediate chromitite group formed from partial melts influenced by fluids from the subducted oceanic crust during the early stages of subduction initiation, while high-Cr chromitites originated from hydrous melts derived from a more depleted mantle wedge in later stages.

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• MakaleYalnız künye2025/r/gumushane/10643
  Compositional variability and alteration dynamics of chromitites under greenschist metamorphism in the Kizildag ophiolite, southern Turkiye

  Akmaz, Recep Melih; Uysal, Ibrahim; Su, Ben-Xun; Sen, Ahmet D.; Hu, Wen-Jun; Seitz, Hans-Michael; Mueller, Dirk; Eslami, Alireza

  This study presents a complete alteration sequence in chromitites from the Kizildag ophiolite (southern T & uuml;rkiye), documenting three distinct chromite types that record processes related to Neotethyan subduction. Chromitites exhibit predominantly lenticular forms and occasionally banded textures, embedded within mantle peridotites and the mantle-crust transition zone, specifically harzburgite and dunite. Our analysis categorizes chromite grains into three groups: fresh, altered, and porous. Fresh chromites are characterized by high contents of Cr2O3 ranging from 42.69 to 57.08 wt% and Al2O3 from 12.46 to 25.34 wt%. In contrast, altered chromites, typically located along fractures or at the edges of fresh grains, show significant variability in chemical composition, with Cr2O3 content between 43.34 and 63.94 wt% and Al2O3 between 2.91 and 14.84 wt%. Porous chromites, distinguished by their porous structure, present Cr2O3 contents from 44.58 to 52.66 wt% and Al2O3 from 3.00 to 8.38 wt%. Notably, altered and porous chromites demonstrate substantial enrichments in Fe and trace elements such as Mn, Ni, Zn, Co, and Ga, indicating a shift due to metamorphic processes. The observed high Cr# (0.68-0.93) and low Mg# (0.25-0.65) values in rims of the altered and porous chromite further illustrate the metamorphic influence on chromite, with greenschist-facies conditions indicated by the Cr-Al-Fe3+ diagram at temperatures below 450 degrees C. The alteration dynamics reflect a progression that initiates with the olivine matrix and advances through reactions involving fresh chromites. This progression results in mass loss, the formation of chlorite, and the porous structures. Our findings contribute to the understanding of metamorphic alteration processes in chromitites and provide a detailed account of the geochemical trends (such as Fe/Mg exchange and trace element enrichment) that reflect greenschist-facies metamorphism. The evidence of chlorite formation and the prevalence of porous textures highlight the influence of metamorphic fluids over serpentinization, offering a model for chromite alteration in supra-subduction zones. This research elucidates the metamorphic history of chromitites in the Kizildag ophiolite.

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• MakaleAçık Erişim2025/r/gumushane/10560
  Multiple Mantle Melting and Metasomatism during the Initial Stages of Subduction: Multi-Geochemical and Os-Isotope Evidence from Well-Preserved Kızıldağ Ophiolite, southern Türkiye

  Uysal, Ibrahim; Sen, Ahmet D.; Su, Ben-Xun; Ersoy, Yalcin; Demir, Yilmaz; Pan, Qi-Qi; Hu, Wen-Jun; Bagci, Utku; Godard, Marguerite

  The processes governing ophiolite formation and evolution remain incompletely understood. The K & imath;z & imath;lda & gbreve; ophiolite, a well-preserved remnant of the Neo-Tethyan oceanic lithosphere in the Anatolian region, southern T & uuml;rkiye, offers critical insights into subduction-related processes and geodynamics. This study presents new element data for mineral and whole-rock samples, combined with Re-Os isotopic compositions of mantle peridotites and associated crustal rocks and extrusives. Petrographic observations identify two distinct groups of peridotites: (1) those with very low modal clinopyroxene, interpreted as highly depleted harzburgites and preserving primary mineral assemblages, and (2) depleted harzburgites containing secondary clinopyroxene with elevated trace element contents, inferred to have crystallized from percolating melts and thus reflecting metasomatic modification. Spinel and orthopyroxene compositions indicate 17-25% degrees of partial melting, with evidence for melting in both garnet and spinel stability fields. However, mineral and whole-rock compositions also record subsequent cryptic and modal metasomatism. Crustal rocks and extrusives exhibit geochemical signatures transitional between fore-arc basalts and boninites, consistent with subduction initiation settings. Variations in Os isotope ratios (187Os/188Os) in crustal rocks further reveal melt-rock interactions and the incorporation of radiogenic Os from subducted oceanic crust. The integration of petrographic, geochemical, and isotopic data supports a four-stage tectonic model for subduction initiation and mantle wedge evolution, consistent with global models proposed for supra-subduction zone (SSZ) ophiolites, particularly those of the Tethyan domain. These findings provide new constraints on mantle melting, metasomatism, and subduction initiation processes and contribute to a broader understanding of SSZ mantle evolution in both regional and global contexts.

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• MakaleAçık Erişim2024/r/gumushane/20069
  Kızıldağ (Hatay) ofiyolitine ait manto peridotitlerinin petrografisi, tüm-kayaç jeokimyası ve erigiyik-kayaç etkileşim izleri

  Sen, Ahmet Dundar

  Kızıldağ ofiyoliti (G-Türkiye) Neotetis okyanusunun güney kolunda oluşmuş okyanusal litosfer kalıntısı kayaçlar topluluğu olarak bilinmektedir. Ofiyolit istifi tabandan tavana doğru manto peridotitleri, ultramafik-mafik kümülatlar, izotrop gabrolar, levha dayk kompleksi ve yastık şekilli bazaltik örtü kayaçları şeklindedir. Manto peridotitleri harzburjit bileşimindedir ve değişen oranlarda serpantinleşme gözlenmektedir. Manto peridotitlerinin tüm kayaç ana oksit-iz element ve Lantanit Grubu Element (LGE) içerikleri harzburjitlerin değişen derecelerde kısmi ergime kalıntısı kayaçlar olduğuna işaret etmektedir. Harzburjitler düşük tüm-kayaç Al ve Ca kompozisyonlarına sahiptir ve SSZ peridotitlerin tüketilmiş karakterini yansıtmaktadır. Tüketilmiş manto harzburjitleri, bazı büyük iyon yarıçaplı elementler (LILE) ve hafif lantanit grubu elementler (HLGE) bakımından zenginleşme gösterdiği tespit edilmiştir ve bu durum yitim sırasında meydana gelen ergiyik manto etkileşimine işaret etmektedir. Harzburjitlerin tüm kayaç MgO içerikleri ile CaO ve Al2O3 içerikleri kıyaslandığında bu kayaçların %20-30 arası kısmi ergime kalıntısı kayaçlar olduğu görülmektedir. Ayrıca kısmi ergime sırasında uyumsuz davrandığı bilinen Ti ve Yb içeriklerindeki zenginleşmeler ergiyik-kayaç etkileşimine işaret etmektedir.

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• MakaleAçık Erişim2014/r/gumushane/15678
  Geochemical make-up of oceanic peridotites from NW Turkey and the multi-stage melting history of the Tethyan upper mantle

  Uysal, Ibrahim; Şen, A. Dündar; Ersoy, E. Yalçin; Dilek, Yildirim; Saka, Samet; Zaccarini, Federica; Escayola, Monica; Karsli, Orhan

  We present the whole-rock and the mineral chemical data for upper mantle peridotites from the Harmanci{dotless}k region in NW Turkey and discuss their petrogenetic-tectonic origin. These peridotites are part of a Tethyan ophiolite belt occurring along the İzmir-Ankara-Ercincan suture zone in northern Turkey, and include depleted lherzolites and refractory harzburgites. The Al2O3 contents in orthopyroxene and clinopyroxene from the depleted lherzolite are high, and the Cr-number in the coexisting spinel is low falling within the abyssal field. However, the orthopyroxene and clinopyroxene in the harzburgites have lower Al2O3 contents for a given Cr-number of spinel, and plot within the lower end of the abyssal field. The whole-rock geochemical and the mineral chemistry data imply that the Harmanci{dotless}k peridotites formed by different degrees of partial melting (~%10-27) of the mantle. The depleted lherzolite samples have higher MREE and HREE abundances than the harzburgitic peridotites, showing convex-downward patterns. These peridotites represent up to ~16 % melting residue that formed during the initial seafloor spreading stage of the Northern Neotethys. On the other hand, the more refractory harzburgites represent residues after ~4-11 % hydrous partial melting of the previously depleted MOR mantle, which was metasomatized by slab-derived fluids during the early stages of subduction. The Harmanci{dotless}k peridotites, hence, represent the fragments of upper mantle rocks that formed during different stages of the tectonic evolution of the Tethyan oceanic lithosphere in Northern Neotethys. We infer that the multi-stage melting history of the Harmanci{dotless}k peridotites reflect the geochemically heterogeneous character of the Tethyan oceanic lithosphere currently exposed along the İzmir-Ankara-Erzincan suture zone.

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