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    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
    (Elsevier, 2022) Karsli, Orhan; Sengun, Firat; Dokuz, Abdurrahman; Aydin, Faruk; Kandemir, Raif; Kristoffersen, Magnus; Santos, Jose Francisco
    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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    Zircon U-Pb age and Hf isotopic composition of the Carboniferous Gonen granitoid in the western Sakarya Zone of Turkey
    (Tubitak Scientific & Technological Research Council Turkey, 2020) Sengun, Firat; Koralay, Osman Ersin; Kristoffersen, Magnus
    The Gonen granitoid is exposed in the western Sakarya Zone and is overlain unconformably by a Jurassic succession. The medium to coarse-grained Gonen granitoid has mineral assemblage of K-feldspar, plagioclase, quartz, muscovite, and biotite. Accessory phases are apatite and zircon. In this study, zircon U-Pb age is combined with Lu-Hf isotopes, which are presented to reveal the magma source and possible petrogenetic processes that took place during the formation of the parental magma for the Gillen granitoid. U-Pb dating of magmatic zircons yielded a concordia age of 336.3 +/- 2.9 Ma referring to the early Carboniferous crystallization age of the GOnen granitoid. Magmatic zircons have negative epsilon(HT)(t) values (-3.2 to -8.3), indicating that the granitoid magma was derived from the recycling of ancient crustal materials. T-DM model ages vary in the range of 1489-1811 Ma, indicating that the crustal material involved during the early Carboniferous partial melting could be extracted from the mantle or added to the basement of the Sakarya Zone in the Mesoproterozoic/Paleoproterozoic times. Geochronological and Lu-Hf findings point to a collisional setting rather than ongoing subduction during the formation of the early Carboniferous Gonen granitoid.
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    Zircon U-Pb age and Hf isotopic composition of the carboniferous gönen granitoid in the western sakarya zone of Turkey
    (TUBITAK, 2020) Şengün, Fırat; Koralay, Osman Ersin; Kristoffersen, Magnus
    The Gönen granitoid is exposed in the western Sakarya Zone and is overlain unconformably by a Jurassic succession. The medium to coarse-grained Gönen granitoid has mineral assemblage of K-feldspar, plagioclase, quartz, muscovite, and biotite. Accessory phases are apatite and zircon. In this study, zircon U-Pb age is combined with Lu-Hf isotopes, which are presented to reveal the magma source and possible petrogenetic processes that took place during the formation of the parental magma for the Gönen granitoid. U-Pb dating of magmatic zircons yielded a concordia age of 336.3 ± 2.9 Ma referring to the early Carboniferous crystallization age of the Gönen granitoid. Magmatic zircons have negative ?Hf(t) values (–3.2 to –8.3), indicating that the granitoid magma was derived from the recycling of ancient crustal materials. TDM model ages vary in the range of 1489–1811 Ma, indicating that the crustal material involved during the early Carboniferous partial melting could be extracted from the mantle or added to the basement of the Sakarya Zone in the Mesoproterozoic/Paleoproterozoic times. Geochronological and Lu-Hf findings point to a collisional setting rather than ongoing subduction during the formation of the early Carboniferous Gönen granitoid. © TÜBİTAK.