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    Metamorphic evolution of the Karakaya Complex in northern Turkey based on phyllosilicate mineralogy
    (SPRINGER WIEN, 2015) Tetiker, Sema; Yalcin, Huseyin; Bozkaya, Omer; Goncuoglu, M. Cemal
    The Triassic Karakaya Complex (KC) of the Sakarya Composite Terrane in northern Turkey is traditionally subdivided into two units. The Lower Karakaya Complex (LKC) consists of a tectonic m,lange with blocks of metabasic rocks, metacarbonates, meta-arenites and metapelites that have been affected by high pressure/low temperature metamorphism. It is followed by a low pressure/low temperature metamorphic overprint; the latter is the only metamorphic event in some tectonic slivers of the LKC. The Upper Karakaya Complex (UKC) units are primarily composed of diagenetic to low-grade metamorphic rocks, comprising Late Permian and Triassic cherts and blocks of OIB-type volcanic rocks interfingering with Anisian limestones. LKC slide-blocks of variable sizes are frequently observed within the UKC. Phyllosilicates of LKC and UKC were examined for their abundance, crystallinity, polytype and b cell dimension. Trioctahedral chamositic chlorites have IIb polytype and phengites 2 M (1) polytypes in the LKC units and 2 M (1) + 1 M + 1M (d) polytypes of phengitic dioctahedral illites in the UKC units. Kubler index data correspond to the low anchizone and epizone for the LKC units, and to the high diagenesis-low anchizone, and in part to the epizone for the UKC units. The b values of illites are consistent with a high-pressure facies series for the LKC, but only intermediate-pressure facies for the UKC. According to textural features, mineral paragenesis, clay transformations, index minerals, and b values, the lower-middle parts of the LKC represent an accretional tectonic setting, whereas the UKC units reflect pressure temperature conditions of an extensional basin affected by high heat flow.
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    Pre-Alpine illitization ages from the Palaeozoic sequences of the Tauride Belt, Southern Turkiye: new data for a Late Palaeozoic event in northern Gondwana
    (Taylor & Francis Inc, 2025) Bozkaya, Omer; Uysal, I. Tonguc; Todd, Andrew; Yalcin, Huseyin; Mahlmann, Rafael Ferreiro; Okuyucu, Cengiz; Goncuoglu, M. Cemal
    Due to the effects of the Alpine orogeny, it is extremely difficult to obtain age data for pre-Alpine geological events for northern Gondwana. This study aims to study the metamorphism in Precambrian (Ediacaran) metaclastic rocks of the Geyik Dagi unit and re-evaluate the geodynamic models of the northern Gondwana-margin based on the geochronology of illite diagenesis in the Late Silurian to Carboniferous shales of the Aladag and Geyik Dagi units of the Taurides, in southern Turkiye. The average illitization (diagenesis) ages of similar to 275 Ma and similar to 165 Ma correspond to the periods of main unconformities between the Middle Carboniferous and the Late Permian and the Triassic and the Late Jurassic. The fossil records from below and above the unconformity plane between the Middle Carboniferous and the Late Permian indicate a gap of > 70 Ma. Mineralogical and organic matter reflectance data indicate a temperature difference of similar to 50 degrees C between Permian and Carboniferous units indicating different thermal gradients below and above the hiatus. This thermal event coincides with the maximum burial depth resulting from the Palaeozoic subsidence curve of the Geyik Dagi Unit. Mineral and organic petrography-based thermal indicators indicate a pre-Alpine (Variscan) regional tectonic event, confirmed here for the first time by combined mineralogical, organic-petrographic, and isotopic age data. The new data may have the potential to re-evaluate geodynamic models of the northern Gondwana-margin during the Late Palaeozoic. The illitization ages associated with the Alpine metamorphism are ascribed to ophiolite emplacement during the Cretaceous and to tectonic events during the Eocene compressional period, which led to the present nappe structure of the Taurides.