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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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    Thermal histories of Cenozoic southern Marmara granitoids from emplacement to exhumation: Implications for tectono-thermal evolution of NW Anatolia (Türkiye)
    (Pergamon-Elsevier Science Ltd, 2026) Altunkaynak, Safak; Unal, Alp; Kamaci, Omer; Guraslan, Isil Nur; Sunal, Gursel; Yigitbas, Erdinc; Dunkl, Istvan
    We investigated the thermal history of the southern Marmara granitoids (Northern Kap & imath;dag, Southern Kap & imath;dag and Avs,a Plutons), from the crystallization cooling to exhumation cooling, by using multiple geothermochronology methods that included zircon U-Pb, biotite 40Ar/39Ar, apatite and zircon (U-Th)/He dating as well as geothermobarometry calculations. The geothermobarometry calculations and zircon U-Pb dating indicate that they were emplaced into mid-crustal levels (13.5 to 8.8 km) during the middle to late Eocene (48-37 Ma). The integrated multiple geo-thermochronological dataset yields similar t-T paths for each pluton, which were divided into three distinct intervals: Interval I: high to mid temperatures (800-350 degrees C), Interval II: mid to mid-low temperatures (350-180 degrees C), and Interval III: mid-low to low temperatures (180-60 degrees C). Interval I is characterized by steep t-T paths showing that the plutons reached mid-temperature levels by rapid cooling during the middle to late Eocene (48-35 Ma). Interval II, on the other hand, is distinguished by skewed t-T paths along the mid- to low temperatures, implying a deceleration in the cooling rates. Finally, in Interval III, the t-T paths steepen again, indicating rapid exhumation in the early Oligocene (32-28 Ma). We infer that the Eocene rapid cooling was most likely induced by bottom-up extension (slab break-off or convective removal of the lithosphere) while the early Oligocene rapid exhumation of NW Anatolia was triggered by the back-arc extension resulting from the rollback of the subducting African slab along the Hellenic trench system, which has migrated southward in time.