Geology of Turkey

Turkey's varied landscapes are the product of a wide variety of tectonic processes that have shaped Anatolia 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 in Thrace, extending along rivers that discharge into the Aegean Sea or the Sea of Marmara, and to a few narrow coastal strips along the Black Sea and Mediterranean Sea coasts.Fact|date=May 2007

Nearly 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 of Antalya and Adana, and the valley floors of the Gediz River and the Büyük Menderes River, and some interior high plains in Anatolia, mainly around Tuz Gölü (Salt Lake) and Konya 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, and Iran. 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 oceanic lithosphere 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 the Tertiary Period (about 65 million to 1.6 million B.C.), as the Arabian, African, and Indian continental plates began to collide with the Eurasian Plate. This process is still at work today as the African Plate converges with the Eurasian Plate and the Anatolian Plate escapes towards the west and southwest along strike-slip faults. These are the North Anatolian Fault Zone, which forms the present day plate boundary of Eurasia near the Black Sea coast and, the East 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 2007

Rocks

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 the supercontinents of Gondwana and Laurasia (which lay to the south and north respectively). [Robertson & Dixon, 2006] This large oceanic plate was consumed at subduction zones. 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 or mélange of rocks that include mainly serpentinite, basalt, dolerite, and chert. [Bergougnan, 1975] The Eurasian margin, now preserved in the Pontides (the Pontic Mountains along the Black Sea coast), is thought to have been geologically similar to the Western Pacific region today. [Rice et al., 2006] Volcanic arcs and back-arc basins formed and were emplaced onto Eurasia as ophiolites as they collided with microcontinents (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 2007

During 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 in Erzincan on the night of 1939-12-27; 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 of Kocaeli to the area north of Lake Van on the border with Armenia 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.