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Browsing by Author "Cakir, Uner"

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    Article
    The Ankara Melange: an Indicator of Tethyan Evolution of Anatolia
    (Slovak Acad Sciences Geological inst, 2016) Cakir, Uner; Uner, Tijen
    The Ankara Melange is a complex formed by imbricated slices of limestone block melanges (Karakaya and Hisarlikaya Formations), Neotethyan ophiolites (Eldivan, Ahlat and Edige ophiolites), post-ophiolitic cover units (Mart and Kavak formations) and Tectonic Melange Unit (Hisarkoy Formation or Derekoy Melange). The Karakaya and Hisarlikaya formations are roughly similar and consist mainly of limestone block melange. Nevertheless, they represent some important geological differences indicating different geological evolution. Consequently, the Karakaya and Hisarlikaya formations are interpreted as Eurasian and Gondwanian marginal units formed by fragmentation of the Gondwanian carbonate platform during the continental rifting of the Neotethys in the Middle Triassic time. During the latest Triassic, Neotethyan lithosphere began to subduct beneath the Eurasian continent and caused intense deformation of the marginal units. The Eldivan, Ahlat and Edige ophiolites represent different fragments of the Neotethyan oceanic lithosphere emplaced onto the Gondwanian margin during the Albian-Aptian, middle Turonian and middle Campanian, respectively. The Eldivan Ophiolite is a NE-SW trending and a nearly complete assemblage composed, from bottom to top, of a volcanic-sedimentary unit, a metamorphic unit, peridotite tectonites, cumulates and sheeted dykes. The Eldivan Ophiolite is unconformably covered by Cenomanian-Lower Turonian sedimentary unit. The Eldivan Ophiolite is overthrust by the Ahlat Ophiolite in the north and Edige Ophiolite in the west. The Ahlat ophiolite is an east-west oriented assemblage comprised of volcanic-sedimentary unit, metamorphic unit, peridotite tectonites and cumulates. The Edige Ophiolite consists of a volcanic-sedimentary unit, peridotite tectonites, dunite, wherlite, pyroxenite and gabbro cumulates. The Tectonic Melange Unit is a chaotic formation of various blocks derived from ophiolites, from the Karakaya and Hisarlikaya formations and from post-ophiolitic sedimentary units. It was formed during the collision between Anatolian Promontory and Eurasian Continent in the middle Campanian time.
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    Geochemistry and Origin of Plagiogranites From the Eldivan Ophiolite, Cankiri (Central Anatolia, Turkey)
    (Slovak Acad Sciences Geological inst, 2014) Uner, Tijen; Cakir, Uner; Ozdemir, Yavuz; Arat, Irem
    The Eldivan Ophiolite, exposed around Ankara and Cankiri cities, is located at the central part of the Izmir-Ankara-Erzincan Suture Zone (IAESZ). It represents fragments of the Neotethyan Oceanic Lithosphere emplaced towards the south over the Gondwanian continent during the Albian time. It forms nearly complete series by including tectonites (harzburgites and rare dunites), cumulates (dunites, wherlites, pyroxenites, gabbro and plagiogranites) and sheeted dykes from bottom to top. Imbricated slices of volcanic-sedimentary series and discontinuous tectonic slices of ophiolitic metamorphic rocks are located at the base of tectonites. Plagiogranitic rocks of the Eldivan Ophiolite are mainly exposed at upper levels of cumulates. They are in the form of conformable layers within layered diorites and also dikes with variable thicknesses. Plagiogranites have granular texture and are mainly composed of quartz and plagioclases. The occurrences of chlorite and epidote revealed that these rocks underwent a low grade metamorphism. Eldivan plagiogranites have high SiO2 content (70-75 %) and low K2O content (0.5-1 %) and display flat patterns of REE with variable negative Eu anomalies. LREE/HREE ratio of these rocks varies between 0.2-0.99. All members of the Eldivan rocks have high LILE/HFSE ratios with depletion of Nb, Ti and P similar to subduction related tectonic settings. Geochemical modelling indicates that the Eldivan plagiogranites could have been generated by 50-90 % fractional crystallization and/or 5-25 % partial melting of a hydrous basaltic magma.