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Thegeology of Turkey is the product of a wide variety oftectonic processes that have shapedAnatolia over millions of years, a process which continues today as evidenced by frequent earthquakes and occasionalvolcanic eruptions.
Except for a relatively small portion of its territory along the Syrian border that is a continuation of the Arabian Platform, Turkey geologically is part of the greatAlpide belt that extends from theAtlantic Ocean to theHimalaya Mountains. This belt was formed during thePaleogene Period, as the Arabian, African, and Indiancontinental plates began to collide with theEurasian 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 alongstrike-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 lies on one of the world'sseismically most active regions.[citation needed]
However, many of the rocks exposed in Turkey were formed long before this process began. Turkey contains outcrops of Precambrian rocks, (more than 520 million years old; Bozkurt et al., 2000). 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 (possiblyterranes) of ancient continental and oceaniclithosphere stuck together by younger igneous, volcanic, and sedimentary rocks.
During theMesozoic era (about 250 to 66 million years ago) a large ocean (Tethys Ocean), floored by oceaniclithosphere existed in-between the supercontinents ofGondwana andLaurasia (which lay to the south and north respectively).[1] This large oceanic plate was consumed at subduction zones (seesubduction zone). At the subduction trenches thesedimentary rock layers that were deposited within the prehistoricTethys Ocean buckled, were folded, faulted, and tectonically mixed with huge blocks of crystalline basement rocks of the oceaniclithosphere. These blocks form a very complex mixture ormélange of rocks that include mainlyserpentinite,basalt,dolerite andchert.[2] The Eurasian margin, now preserved in the Pontides (thePontic Mountains along theBlack Sea coast), is thought to have been geologically similar to the Western Pacific region today.[3] Volcanic arcs (seevolcanic arc) and backarc basins (seeback-arc basin) formed and were emplaced ontoEurasia as ophiolites (seeophiolite) as they collided with microcontinents (literally relatively small plates of continentallithosphere). These microcontinents had been pulled away from the Gondwanan continent further south.[4]
During theCenozoic 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.[1]
Present-day earthquakes range from barely perceptible tremors to major movements measuring five or higher on the open-endedRichter scale. Turkey's most severe earthquake in the twentieth century occurred inErzincan on the night of December 28–29, 1939; it devastated most of the city and caused an estimated 160,000 deaths. 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 andGeorgia.
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. Truelowlands are confined to theErgene Ovası (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.[citation needed]
Nearly 85% of the land is at an elevation of at least 450 meters; the average and median altitude of the country is 1,332 and 1,128 meters, respectively. In Asiatic Turkey, flat or gently sloping land is rare and largely confined to the deltas of theKızıl River, the coastal plains of Antalya and Adana, and the valley floors of the Gediz River and theBüyükmenderes River, and some interior high plains in Anatolia, mainly aroundTuz Gölü (Salt Lake) andKonya Ovası (Konya Plain). 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) – 5,137 meters high – is situated near the point where the boundaries of the four countries meet.
Turkey's terrain is structurally complex. A central massif composed of uplifted blocks and downfoldedtroughs, 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 plain of theErgene river 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.[citation needed]
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 theKızıl 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 aroundTuz 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 withArmenia,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.
The earliest geological history of Turkey is poorly understood, partly because these oldest rocks in the region are involved into younger deformation phases that hindered their evolution. This created problem of reconstructing how the region has been tectonically assembled by plate motions. Turkey can be thought of as a collage of different continental pieces and remnants of oceanic lithospheric rocks amalgamated together by younger tectonic processes that involve accumulation of igneous (both plutonic and volcanic) and sedimentary rocks.
Except for a relatively small portion of its territory along theSyrian border that is a continuation of theArabian plate, Turkey geologically is part of the greatAlpide belt that extends from the Atlantic Ocean to the Himalaya Mountains. This belt was formed during theCenozoic Era (about 66 to 1.6 million years ago), as the Arabian,African, andIndiancontinental plates began to collide with theEurasian plate. This process is still at work today as the African plate converges with the Eurasian plate and theAnatolian sub-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 of thisplate tectonics configuration, Turkey is one of the world's more active earthquake and volcanic regions.[5]
The Anatolian plate, together with theAegean-Peloponnesus block, is located near the centre of a very wide region, including theArabian plate with the adjacentZagros Mountains and centralIran, that moves in a circulatory pattern at a relatively fast rate of 20 mm/yr. The rate of this counter-clockwise motion increases near theHellenic Trench system south of Turkey and decreases away from it (i.e. the Eurasian and African plates move at a rate of 5 mm/yr), resulting in internal deformations in several areas, including central and eastern Anatolia, south-western Aegean-Peloponnesus,Lesser Caucasus, and central Iran. The dominant process in the region is the subduction of the African plate beneath the Hellenic Trench, and the deformation in the entire African-Arabian-Eurasian collision zone is most likely driven by the slab roll-back of the subducting African plate in the East Mediterranean.[6] This process is further fuelled by slab-pull forces in theMakran Trench in theGulf of Oman where the Arabian plate is subducting under Eurasia. A response to this tectonic maelstrom is the rifting in the Red Sea and Gulf of Aden which will separate Arabia from Africa.[7]
Thetomography of the velocity propagation distributions of the P_nseismic waves both in an isotropic andanisotropic conditions, compared with the lateral variations of that velocity has highlighted the physical properties of theuppermost mantle andcrustal thickness of the Earth. A study analyzed 700 earthquakes occurred in Turkey from 1999 to 2010 withmagnitude degree major than 4.0 and the related 50.000 Pn first arrivals recorded by 832 seismic stations at a distance range of 180–1500 km from theepicenter. The tomography highlighted that "Pn velocities are found to be lowest in eastern Turkey (<7.6 km s-1) and highest in the easternMediterranean Sea andZagros Suture (>8.3 km s-1). Large Pn anisotropy is observed in the Aegean, central Anatolia and along the southern coast of Anatolia. [...] Large crustal thicknesses are observed along theDinarides-Hellenides and along the southern coast of Anatolia."[8]
Many of the rocks exposed in Turkey were formed long before this process began. Turkey contains outcrops ofPrecambrian rocks, (more than 540 million years old).[9]
During theMesozoic era (about 250 to 66 million years ago) a large ocean (Tethys Ocean), floored by oceanic lithosphere existed in-between thesupercontinents ofGondwana andLaurasia (which lay to the south and north respectively).[10] This large oceanic plate was consumed atsubduction zones. At the subduction trenches the sedimentary rock layers that were deposited within the prehistoric Tethys Ocean 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.[11] 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.[12]Volcanic arcs andback-arc basins formed and were emplaced onto Eurasia asophiolites as they collided withmicrocontinents (literally relatively small plates of continental lithosphere).[4] These microcontinents had been pulled away from the Gondwanan continent further south. Turkey is therefore made up from several different prehistorical microcontinents.[citation needed]
During theCenozoic (Tertiary about 66 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.[1]Pamukkale terraces are made oftravertine, a sedimentary rock deposited by mineral water fromhot springs. The area is famous for a carbonate mineral left by the flowing of thermal spring water.[13][14]
Turkey's most severe earthquake in the twentieth century occurred inErzincan on the night of 1939-12-27; it devastated most of the city and caused an estimated 30,000 deaths. Earthquakes of moderate intensity often continue with sporadic aftershocks over periods of several days or even weeks. Seismicity in Turkey is more likely to happen in the North Anatolian Fault Zone, East Anatolian Fault Zone and in the subduction region of the Aegean Plate between the Anatolian plate.
This article incorporates text from this source, which is in thepublic domain. Country Studies.Federal Research Division. This article incorporatespublic domain material fromThe World Factbook.CIA.
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