- Geology of Turkey
Turkey 's varied landscapes are the product of a wide variety of tectonic processes that have shapedAnatolia over millions of years and continue today as evidenced by frequent earthquakes and occasional volcanic eruptions.Background
Turkey's terrain is structurally complex. A central massif composed of uplifted blocks and downfolded troughs, covered by recent deposits and giving the appearance of a plateau with rough terrain, is wedged between two folded mountain ranges that converge in the east. True lowland is confined to the
Ergene Plain inThrace , extending along rivers that discharge into theAegean Sea or theSea of Marmara , and to a few narrow coastal strips along theBlack Sea andMediterranean Sea coasts.Fact|date=May 2007Nearly 85% of the land is at an elevation of at least 450 meters; the median altitude of the country is 1,128 meters. In Asiatic Turkey, flat or gently sloping land is rare and largely confined to the deltas of the
Kızıl River , the coastal plains ofAntalya andAdana , and the valley floors of theGediz River and theBüyük Menderes River , and some interior high plains in Anatolia, mainly around Tuz Gölü (Salt Lake) andKonya Ovası (Konya Basin). Moderately sloping terrain is limited almost entirely outside Thrace to the hills of the Arabian Platform along the border with Syria.More than 80% of the land surface is rough, broken, and mountainous, and therefore is of limited agricultural value. The terrain's ruggedness is accentuated in the eastern part of the country, where the two mountain ranges converge into a lofty region with a median elevation of more than 1,500 meters, which reaches its highest point along the borders with
Armenia ,Azerbaijan , andIran . Turkey's highest peak,Mount Ararat (Ağrı Dağı)—about 5,166 meters high—is situated near the point where the boundaries of the four countries meet.Geological History
The earliest geological history of Turkey is poorly understood, partly because of the problem of reconstructing how the region has been tectonically assembled by plate motions. Turkey can be thought of as a collage of different pieces (possibly
terranes ) of ancient continental and oceaniclithosphere stuck together by younger igneous, volcanic and sedimentary rocks.Plate tectonics Except for a relatively small portion of its territory along the Syrian border that is a continuation of the
Arabian Plate , Turkey geologically is part of the great Alpine belt that extends from the Atlantic Ocean to the Himalaya Mountains. This belt was formed during theTertiary Period (about 65 million to 1.6 million B.C.), as the Arabian, African, and Indiancontinental plate s began to collide with theEurasian Plate . This process is still at work today as the African Plate converges with the Eurasian Plate and theAnatolian Plate escapes towards the west and southwest along strike-slip faults. These are theNorth Anatolian Fault Zone , which forms the present day plate boundary of Eurasia near the Black Sea coast and, theEast Anatolian Fault Zone , which forms part of the boundary of the North Arabian Plate in the southeast. As a result, Turkey is one of the world's more active earthquake and volcano regions.Fact|date=May 2007Rocks
Many of the rocks exposed in Turkey were formed long before this process began. Turkey contains outcrops of
Precambrian rocks, (more than 540 million years old). [Bozkurt et al., 2000]During the
Mesozoic era (about 250 to 65 million years ago) a large ocean (Tethys Ocean ), floored by oceanic lithosphere existed in-between thesupercontinent s ofGondwana andLaurasia (which lay to the south and north respectively). [Robertson & Dixon, 2006] This large oceanic plate was consumed atsubduction zone s. At the subduction trenches the sedimentary rock layers that were deposited within the prehistoric Tethys Ocean buckled, were folded, faulted and tectonically mixed with huge blocks of crystalline basement rocks of the oceanic lithosphere. These blocks form a very complex mixture ormélange of rocks that include mainlyserpentinite ,basalt ,dolerite , andchert . [Bergougnan, 1975] The Eurasian margin, now preserved in the Pontides (thePontic Mountains along the Black Sea coast), is thought to have been geologically similar to the Western Pacific region today. [Rice et al., 2006]Volcanic arc s andback-arc basin s formed and were emplaced onto Eurasia asophiolite s as they collided withmicrocontinent s (literally relatively small plates of continental lithosphere). [ Ustaomer and Robertson, 1997] These microcontinents had been pulled away from the Gondwanan continent further south. Turkey is therefore made up from several different prehistorical microcontinents.Fact|date=May 2007During the
Cenozoic (Tertiary about 65 to 1.6 million years) folding, faulting and uplifting, accompanied by volcanic activity and intrusion of igneous rocks was related to major continental collision between the larger Arabian and Eurasian plates. [ Robertson & Dixon, 1984]Earthquakes
Present-day earthquakes range from barely perceptible tremors to major movements measuring five or higher on the open-ended
Richter scale . Turkey's most severe earthquake in the twentieth century occurred inErzincan on the night of1939-12-27 ; it devastated most of the city and caused an estimated 160,000 deaths.Fact|date=May 2007 Earthquakes of moderate intensity often continue with sporadic aftershocks over periods of several days or even weeks. The most earthquake-prone part of Turkey is an arc-shaped region stretching from the general vicinity ofKocaeli to the area north ofLake Van on the border withArmenia and Georgia.Notes
References:
Bergougnan, H. (1975) Dispositif des ophiolites nord-est anatoliennes, origine des nappes ophiolitiques et sud-pontiques, jeu de la faille nord-anatolienne. Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences, Serie D: Sciences Naturelles, 281: 107-110.
Bozkurt, E. and Satir, M. (2000) The southern Menderes Massif (western Turkey); geochronology and exhumation history. Geological Journal, 35: 285-296.
Rice, S.P., Robertson, A.H.F. and Ustaömer, T. (2006) Late Cretaceous-Early Cenozoic tectonic evolution of the Eurasian active margin in the Central and Eastern Pontides, northern Turkey. In: Robertson, (Editor), Tectonic Development of the Eastern Mediterranean Region. Geological Society, London, Special Publications, 260, London, 413-445.
Robertson, A. and Dixon, J.E.D. (1984) Introduction: aspects of the geological evolution of the Eastern Mediterranean. In: Dixon and Robertson (Editors), The Geological Evolution of the Eastern Mediterranean. Geological Society, London, Special Publications, 17, 1-74.
Ustaömer, T. and Robertson, A. (1997) Tectonic-sedimentary evolution of the north Tethyan margin in the Central Pontides of northern Turkey. In: A.G. Robinson (Editor), Regional and Petroleum Geology of the Black Sea and Surrounding Region. AAPG Memoir, 68, Tulsa, Oklahoma, 255-290.
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