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    Application of The Titanium-In-Quartz Thermobarometer to Eclogites from The Biga Peninsula, NW Turkey
    (Iop Publishing Ltd, 2016) Sengun, Firat; Zack, Thomas
    Eclogites crop out in the Eamlica metamorphics and beneath the Eetmi melange as a tectonic slice in the Biga Peninsula in northwest Turkey. The Eamlica metamorphics occur in the westernmost part of the Biga Peninsula and are tectonically separated from the Denizgoren ophiolite in the west by the Ovacik fault. The Eetmi melange found on the southern part of the Biga Peninsula is mainly composed of various types of blocks within a detritic matrix. The high-P assemblages in eclogite consist of omphacite + garnet + epidote + glaucophane + quartz + phengite. Typical accessory minerals are rutile, zircon and sphene. Ti-in-quartz thermobarometer (TitaniQ) was applied on eclogites from the Biga Peninsula. The P-T dependencies of Ti-in-quartz solubility can be combined with P-T dependencies of Zr-in-rutile solubility to estimate pressure and temperature of crystallization. Titanium concentrations in quartz from the Eamlica metamorphics range from 0.26 to 0.91 ppm. Zirconium concentrations in rutile range from 26 to 64 ppm. However, Ti contents in quartz from the Eetmi melange vary from 0.47 to 2.19 ppm. Zr contents in rutile range between 50 and 150 ppm. Regional high-P metamorphism with peak conditions of 551 +/- 5 degrees C and 21.5 +/- 0.3 kbar in eclogite from the Eamlica region and 624 +/- 17 degrees C and 22.6 +/- 1.6 kbar in eclogite from the Eetmi region. Tiin- quartz thermobarometer gives precise and comprehensible pressure and temperature values when using the Zr-in-rutile thermobarometer, which could be an advantage over classical methods.
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    In situ Rb-Sr dating of K-bearing minerals from the orogenic Akcaabat gold deposit in the Menderes Massif, Western Anatolia, Turkey
    (Pergamon-Elsevier Science Ltd, 2019) Sengun, Firat; Erlandsson, Viktor Bertrandsson; Hogmalm, Johan; Zack, Thomas
    The Akcaabat gold deposit is mainly composed of massive arsenopyrite veins in strongly foliated augen gneisses of the tine Sub-massif in western Turkey. K-bearing minerals from orogenic gold veins were dated by the in situ Rb-Sr method in order to determine the formation age of the Akcaabat gold deposit. Textural relationships between the vein minerals suggest that arsenopyrite, K-feldspar, quartz, and muscovite formed in one paragenetic stage. Native gold, native bismuth, scorodite, and galena were introduced in a later paragenetic stage. The isochron derived from K-feldspar and muscovite occurring in the veins yielded 31.3 +/- 4.7 Ma. In situ Rb-Sr dating of the same assemblage (K-feldspar and muscovite) in the host rock gave an isochron age of 40.8 +/- 3.8 Ma, 10 Ma older than the vein ages, and corresponding to peak metamorphism of the regional main Menderes metamorphism during the Alpine-Himalayan orogenic event. Biotite from the host rock gave an isochron age of 28.1 +/- 2.2 Ma and probably reflects the cooling age. Homogenization temperatures from fluid inclusions in quartz show that quartz formed at 280-390 degrees C but has a dominant mode in the 350-360 degrees C temperature interval. The age of vein formation was successfully distinguished from the age of the Alpine-Himalayan orogenic event associated with main Menderes metamorphism. This study demonstrates that in situ Rb-Sr isotopic study can be applied to resolve absolute dating of orogenic deposits in metamorphic complexes.
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    Ordovician S-type granites in the western Sakarya Zone, NW Turkey; linkage to a back-arc setting
    (Elsevier B.V., 2023) Karslı, Orhan; Şengün, Fırat; Aydın, Faruk; Moghadam, Hadi S.; Dokuz, Abdurrahman; Griffin, William L.; Saka, Simge Oğuz; 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 (İstanbul-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 Söğüt area (Bilecik, northwest Turkey). Our Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U–Pb analyses on zircons suggest that the Söğüt 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 Söğüt metagranites, with ages of >500 Ma to ∼2.2 Ga. The inherited Cadomian cores give concordant ages of 588 and 572 Ma. The Söğüt 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 εΗf(t) values of +3.6 to −35.4, whereas inherited zircon cores have εΗf(t) values of +33.9 to −26.1. Our data, in conjunction with previous studies, suggest that the Söğüt 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.
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    Provenance of detrital rutiles from the Jurassic sandstones in the Central Sakarya Zone, NW Turkey: U-Pb ages and trace element geochemistry
    (Elsevier Gmbh, 2020) Sengun, Firat; Zack, Thomas; Dunkl, Istvan
    This provenance study focuses on detrital rutile grains from Jurassic sandstones of the Bayirkoy Formation in the central Sakarya Zone. Cr and Nb concentrations of detrital rutile grains in the Jurassic sandstones vary from 18 to 6855 mu g/g and 70-13440 mu g/g, respectively. Source area discrimination based on the Cr-Nb concentrations shows that 79 % of the detrital rutile grains originated from metapelitic and 21 % from metamafic rocks. The calculated rutile formation temperatures vary from 471 to 798 degrees C with an average temperature of 635 degrees C at P=10 kbar. Zr-in-rutile thermometer gives overlapping temperatures for all detrital rutile grains from both the metapelitic and metamafic sources. This demonstrates that most of the detrital rutiles sourced from metapelitic and metamafic rocks underwent similar metamorphic conditions and have similar metamorphic history. The U-Pb rutile dating yielded ages for the detrital rutiles in the time range of 346 to 319 Ma, which gives the age of metamorphism for the potential source rocks. Trace element compositions, Zr-in-rutile thermometer and U-Pb rutile geochronology show that detrital rutile grains were predominantly derived from early Carboniferous rocks that underwent metamorphism in amphibolite-facies conditions. Amphibolite-facies rocks of the Saricakaya Massif in the central Sakarya Zone seem to be the primary source lithologies for the detrital rutiles in the Jurassic Bayirkoy Formation as it comprises previously-mentioned source lithologies and has a close geographic position to the area studied. Carboniferous Variscan metamorphism was followed by emplacement of numerous post-collisional granitoids in the central Sakarya Zone.
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    Rutile geochemistry and thermometry of eclogites and associated garnet-mica schists in the Biga Peninsula, NW Turkey
    (Elsevier Gmbh, 2017) Sengun, Firat; Zack, Thomas; Topuz, Gultekin
    In northwest Turkey, high-pressure metamorphic rocks occur as exotic blocks within the cetmi m lange located on the south of the Biga Peninsula. Rutile chemistry and rutile thermometry obtained from the eclogite and associated garnet-mica schist in the cetmi m lange indicate significant trace element behaviour of subducted oceanic crust and source-rock lithology of detrital rutiles. Cr and Nb contents in detrital rutile from garnet-mica schist vary from 355 to 1026 pzig and 323 and 3319 g/g, respectively. According to the Cr-Nb discrimination diagram, the results show that 85% of the detrital rutiles derived from metapelitic and 15% from metamafic rocks. Temperatures calculated for detrital rutiles and rutiles in eclogite range from 540 degrees C to 624 degrees C with an average of 586 degrees C and 611 degrees C to 659 degrees C with an average of 630 degrees C at P = 2.3 GPa, respectively. The calculated formation temperatures suggest that detrital rutiles are derived from amphibolite- and eclogite-facies metamorphic rocks. Amphibolite-facies rocks of the Kazdag Massif could be the primary source rocks for the rutiles in the garnet-mica schist from the cetmi m lange. Nb/Ta ratios of metapelitic and metamafic rutiles fall between 7-24 and 11-25, respectively. Nb/Ta characteristics in detrital rutiles may reflect a change in source-rock lithology. However, Nb/Ta ratios of rutiles in eclogite vary from 9 to 22. The rutile grains from eclogites are dominated by subchondritic Nb/Ta ratios. It can be noted that subchondritic Nb/Ta may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration. (C) 2017 Elsevier GmbH. All rights reserved.
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    Trace element composition of rutile and Zr-in-rutile thermometry in meta-ophiolitic rocks from the Kazdag Massif, NW Turkey
    (Springer Wien, 2016) Sengun, Firat; Zack, Thomas
    In northwest Turkey, ophiolitic meta-gabbros are exposed on the Kazdag Massif located in the southern part of the Biga Peninsula. Trace element composition of rutile and Zr-in-rutile temperatures were determined for meta-gabbros from the Kazdag Massif. The Zr content of all rutiles range from 176 to 428 ppm and rutile grains usually have a homogeneous Zr distribution. The rutile grains from studied samples in the Kazdag Massif are dominated by subchondritic Nb/Ta (11-19) and Zr/Hf ratios (20-33). Nb/Ta and Zr/Hf show positive correlation, which is probably produced by silicate fractionation. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents. The core of rutile grains are generally characterized by low Nb/Ta ratios of 17-18 whereas the rims exhibit relatively high Nb/Ta ratios of 19-23. Trace element analyses in rutile suggest that these rutile grains were grown from metamorphic fluids. The P-T conditions of meta-gabbros were estimated by both Fe-Mg exchange and Zr-in-rutile thermometers, as well as by the Grt-Hb-Plg-Q geothermobarometer. The temperature range of 639 to 662 A degrees C calculated at 9 kbar using the Zr-in-rutile thermometer is comparable with temperature estimates of the Fe-Mg exchange thermometer, which records amphibolite-facies metamorphism of intermediate P-T conditions. The P-T conditions of meta-ophiolitic rocks suggest that they occur as a different separate higher-pressure tectonic slice in the Kazdag metamorphic sequence. Amphibolite-facies metamorphism resulted from northward subduction of the A degrees zmir-Ankara branch of the Neo-Tethyan Ocean under the Sakarya Zone. Metamorphism was followed by internal imbrication of the Kazdag metamorphic sequence resulting from southerly directed compression during the collision.