The Pontides orogenic belt (Northern Turkey; Ketin, 1966), which is an integral segment of the Alpine-Himalayan belt, can be divided tectonically into three subzones as the Western Pontides, the Central Pontides and the Eastern Pontides, extending from Rhodopes in the west to Caucasus in the east. The eastern Pontides orogenic belt (Northeastern Turkey) consists of a mountain chain extending along the southeast Black Sea coast with a length of about 500 km and width of 200 km. The term ‘Eastern Pontides’ was coined for this region by Hamilton (1842), and subsequent studies proposed a subdivision into the northern and southern zones (Arni 1939; Gedikoğlu et al. 1979; Özsayar et al. 1981). Bektaş et al. (1995) subdivided it into the Northern, Southern and Axial zones from north to south based on different lithological units, facies changes and tectonic characteristics. Eyuboglu et al. (2006)proposed a modified classification by expanding to include the Amasya region situated in the west, as also supported by geophysical data (Figure).
The Northern Zone is characterized by Mesozoic-Cenozoic volcanic rocks, associated massive-sulfide deposits and calderas, together with granitic and gabbroic intrusions. The Southern Zone has a spectacular lithologic record with numerous rock associations such as the Paleozoic metamorphic-granitic rocks belonging to Hercynian basement of the eastern Pontides orogenic belt (Pulur, Ağvanis and Tokat metamorphic massifs, Kurtoğlu and Karadağ metamorphics, Köse and Gümüshane Granitoids), Triassic-Jurassic Alaskan-type mafic-ultramafic intrusions, late Cretaceous shoshonitic and ultrapotassic magmatic rocks and late Paleocene-early Eocene and also late Miocene adakitic rocks (Eyuboglu et al., 2011a and 2012). Further South (Axial Zone), undated ultramafic-mafic rocks (Kop and Erzincan massifs) and olistostromal ophiolitic mélange of the middle to late Cretaceous are widespread (Eyuboglu et al., 2010 and 2011b). Geological and geophysical studies showed that each zone is separated by E-W-, NE-SW- and NW-SE-trending fault zones that display block-faulting of the eastern Pontides orogenic belt. Trabzon, where workshop will be held, is situated in the Northern Zone of the eastern Pontides orogenic belt.
The Meso-Cenozoic geodynamic evolution of the Pontide belt is controversial due to its complexity and to lack of critical constraints from systematic geological, geophysical, geochemical, and geochronological work. Three interpretations can be found in the literature. The first is that the belt was shaped by southward subduction of Paleotethyan oceanic lithosphere from the Paleozoic onward (Dewey et al., 1973; Bektaş et al., 1999; Chorowicz et al., 1998). In a recent study, Eyuboglu et al. (2012) proposed that the southward subduction of Tethys oceanic lithosphere continued into Oligo-Miocene time when the collision between Eurasia and the eastern Pontides-Lesser Caucasus-Elburz magmatic arc resulted in separation of the Black Sea basin from the Caspian Sea basin, which represent the present-day remnants of the Tethys ocean.
The second interpretation is that the mafic-ultramafic bodies in the south of the Pontide arc are remnants of the Paleotethys oceanic lithosphere (e.g. Adamia et al., 1977, 1981; Ustaömer and Robertson, 1996; Rice et al., 2009; Dilek et al., 2010), and that the orogenic belt was constructed by northward subduction of Paleotethyan oceanic lithosphere from the Paleozoic onward.
A third interpretation by Şengör and Yılmaz (1981) proposed that Palaeotethys was situated north of the Pontides, and hence southward subduction operated from the Palaeozoic until the Dogger, and that northward subduction occurred subsequently from the late Mesozoic until the early Cenozoic. According to their model, the eastern Pontides represent the southern active continental margin of Eurasia while the late Cretaceous arc volcanism developed above the northward subducting Neotethys, which had originally opened in the Liassic as a back-arc basin to the eastern Pontide magmatic arc.
Global tectonic reconstructions (e.g. Golonka, 2004) recognize that numerous microplates are involved in the tectonic evolution of the southern margin of Eurasia, and that subduction polarity along the margins of the microplates may have reversed during closure of Tethys. However, they suggest that southward subduction consistent with present field relations did not begin until ca. 36 Ma.
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