Zagros Mountains

Zagros Mountains

Overview
The Zagros Mountains are the largest mountain range
Mountain range
A mountain range is a single, large mass consisting of a succession of mountains or narrowly spaced mountain ridges, with or without peaks, closely related in position, direction, formation, and age; a component part of a mountain system or of a mountain chain...

 in Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

 and Iraq
Iraq
Iraq ; officially the Republic of Iraq is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert....

. With a total length of 1,500 km (932 mi), from northwestern Iran, and roughly correlating with Iran's western border, the Zagros range spans the whole length of the western and southwestern Iranian plateau
Iranian plateau
The Iranian plateau, or Iranic plateau, is a geological formation in Southwest Asia. It is the part of the Eurasian Plate wedged between the Arabian and Indian plates, situated between the Zagros mountains to the west, the Caspian Sea and the Kopet Dag to the north, the Hormuz Strait and Persian...

 and ends at the Strait of Hormuz
Strait of Hormuz
The Strait of Hormuz is a narrow, strategically important waterway between the Gulf of Oman in the southeast and the Persian Gulf. On the north coast is Iran and on the south coast is the United Arab Emirates and Musandam, an exclave of Oman....

. The highest points in the Zagros Mountains are Zard Kuh
Zard Kuh
Zard Kuh is a mountain in the central Zagros Range, Iran....

 (4,548 m, 14,921 ft) and Mt. Dena
Dena
Dena is a mountain range within the Zagros Mountains of West/Southwestern Iran.The Dena is a part of the Zagros mountain range, situated on the boundary of the Isfahan, Kohgiluyeh and Boyer-Ahmad and Chaharmahal and Bakhtiari provinces...

 (4,359 m, 14,301 ft).
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Encyclopedia
The Zagros Mountains are the largest mountain range
Mountain range
A mountain range is a single, large mass consisting of a succession of mountains or narrowly spaced mountain ridges, with or without peaks, closely related in position, direction, formation, and age; a component part of a mountain system or of a mountain chain...

 in Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

 and Iraq
Iraq
Iraq ; officially the Republic of Iraq is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert....

. With a total length of 1,500 km (932 mi), from northwestern Iran, and roughly correlating with Iran's western border, the Zagros range spans the whole length of the western and southwestern Iranian plateau
Iranian plateau
The Iranian plateau, or Iranic plateau, is a geological formation in Southwest Asia. It is the part of the Eurasian Plate wedged between the Arabian and Indian plates, situated between the Zagros mountains to the west, the Caspian Sea and the Kopet Dag to the north, the Hormuz Strait and Persian...

 and ends at the Strait of Hormuz
Strait of Hormuz
The Strait of Hormuz is a narrow, strategically important waterway between the Gulf of Oman in the southeast and the Persian Gulf. On the north coast is Iran and on the south coast is the United Arab Emirates and Musandam, an exclave of Oman....

. The highest points in the Zagros Mountains are Zard Kuh
Zard Kuh
Zard Kuh is a mountain in the central Zagros Range, Iran....

 (4,548 m, 14,921 ft) and Mt. Dena
Dena
Dena is a mountain range within the Zagros Mountains of West/Southwestern Iran.The Dena is a part of the Zagros mountain range, situated on the boundary of the Isfahan, Kohgiluyeh and Boyer-Ahmad and Chaharmahal and Bakhtiari provinces...

 (4,359 m, 14,301 ft). The Hazaran
Hazaran
Hazaran is the name of a massif of the Central Iranian Plateau, Kerman province, Iran, an eastern outlier of the Zagros mountains. The Jebal Barez chain is a continuation to the south-east....

 massif in the Kerman province of Iran forms an eastern outlier of the range, the Jebal Barez
Jebal Barez
The Jebal Barez are a mountain chain in the Kerman Province of Iran.They stretch for some 100 km north-west to south-east, parallel to the Halil Rud, to the north-east of Jiroft and to the south-west of Bam, rising to a maximal elevation of 3,400 m....

 reaching into Sistan
Sistan
Sīstān is a border region in eastern Iran , southwestern Afghanistan and northern tip of Southwestern Pakistan .-Etymology:...

.

Geology


The Zagros fold and thrust belt
Zagros fold and thrust belt
The Zagros fold and thrust belt is a ~1800 km long zone of deformed crustal rocks, formed in the foreland of the collision between the Arabian Plate and the Eurasian Plate...

 was formed by collision of two tectonic plates — the Eurasian
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...

 and Arabian Plate
Arabian Plate
The Arabian Plate is one of three tectonic plates which have been moving northward over millions of years and colliding with the Eurasian Plate...

s. Recent GPS measurements in Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

 have shown that this collision is still active and the resulting deformation is distributed non-uniformly in the country, mainly taken up in the major mountain belts like Alborz
Alborz
Alborz , also written as Alburz, Elburz or Elborz, is a mountain range in northern Iran stretching from the borders of Azerbaijan and Armenia in the northwest to the southern end of the Caspian Sea, and ending in the east at the borders of Turkmenistan and Afghanistan...

 and Zagros. A relatively dense GPS network which covered the Zagros in the Iranian part also proves a high rate of deformation within the Zagros. The GPS results show that the current rate of shortening in SE Zagros is ~10 mm/yr and ~5mm/yr in the NW Zagros. The NS strike-slip Kazerun
Kazerun
Kazerun is a city in and the capital of Kazerun County, Fars Province, Iran. At the 2006 census, its population was 84,594, in 20,810 families....

 fault divides the Zagros into two distinct zones of deformation. The GPS results also show different shortening directions along the belt, i.e. normal shortening in the South-East and oblique shortening in the NW Zagros.

The sedimentary cover in the SE Zagros is deforming above a layer of rock salt (acting as a ductile decollement
Decollement
Décollement is a gliding plane between two rock masses. In French, "décoller" means "to detach from" or "to rip off" and was first used by geologists studying the structure of the Swiss Jura Mountains, but is also known as a detachment zone. This is a structure of strata owing to deformation,...

 with a low basal friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

) whereas in the NW Zagros the salt layer is missing or is very thin. This different basal friction partly made different topographies in either sides of Kazerun fault. Higher topography and narrower zone of deformation in the NW Zagros is observed whereas in the SE, deformation was spread more and wider zone of deformation with lower topography was formed. Stresses induced in the Earth's crust by the collision caused extensive folding of the preexisting layered sedimentary rock
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

s. Subsequent erosion removed softer rocks, such as mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...

 (rock formed by consolidated mud) and siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...

 (a slightly coarser-grained mudstone) while leaving harder rocks, such as limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 (calcium-rich rock consisting of the remains of marine organisms) and dolomite
Dolomite
Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....

 (rocks similar to limestone containing calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 and magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

). This differential erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

 formed the linear ridges of the Zagros Mountains.

The depositional environment
Sedimentary depositional environment
In geology, sedimentary depositional environment describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock...

 and tectonic history of the rocks were conducive to the formation and trapping of petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

, and the Zagros region is an important part of Persian Gulf oil production.

Salt dome
Salt dome
A salt dome is a type of structural dome formed when a thick bed of evaporite minerals found at depth intrudes vertically into surrounding rock strata, forming a diapir....

s and salt glacier
Salt glacier
A salt glacier is a flow of salt that is created when a rising diapir in a salt dome breaches the surface. Gravity causes the salt to flow like glaciers into adjacent valleys. Most of the flow occurs during the winter, when the salt is wet, as the strength of salt is critically dependent on its...

s are a common feature of the Zagros Mountains. Salt domes are an important target for oil exploration, as the impermeable salt frequently traps petroleum beneath other rock layers.

Type and age of rock


The mountains are divided into many parallel sub-ranges (up to 10, or 250 km wide), and have the same age as the Alps
Alps
The Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....

. Iran's main oilfields lie in the western central foothills of the Zagros mountain range. The southern ranges of the Fars Province have somewhat lower summits, reaching 4000 metres. They contain some limestone rocks showing abundant marine fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s.

The Kuhrud Mountains form one of the parallel ranges at a distance of approx. 300 km to the east. The area between these two impressive mountain chains is home to a dense human population that lives in the intermediate valleys which are quite high in altitude with a temperate climate. Their rivers, which eventually reach salt lake
Salt lake
A salt lake or saline lake is a landlocked body of water which has a concentration of salts and other dissolved minerals significantly higher than most lakes . In some cases, salt lakes have a higher concentration of salt than sea water, but such lakes would also be termed hypersaline lakes...

s, create fertile environments for agriculture and commerce.

Ecology


The Zagros Mountains contain several ecosystems. Prominent among them are the forest and steppe forest areas (PA0446), which have a semi-arid temperate climate. The annual precipitation there ranges from 400 mm to 800 mm, and falls mostly in the winter and spring. The winters are severe, with winter low temperatures often below −25 degrees C. The summer and autumn are very dry. They are the home to the Zagros Mountains Mouse-like Hamster (Calomyscus bailwardi).

History


Signs of early agriculture date back as far as 9000 BC to the foothills of the Zagros Mountains, in cities later named Anshan
Anshan (Persia)
Anshan - History :Before 1973, when it was identified as Tall-i Malyan, Anshan had been assumed by scholars to be somewhere in the central Zagros mountain range....

 and Susa
Susa
Susa was an ancient city of the Elamite, Persian and Parthian empires of Iran. It is located in the lower Zagros Mountains about east of the Tigris River, between the Karkheh and Dez Rivers....

. Jarmo
Jarmo
Jarmo is an archeological site located in northern Iraq on the foothills of Zagros Mountains east of Kirkuk city. It is known as the oldest agricultural community in the world, dating back to 7000 BCE. Jarmo is broadly contemporary with such other important Neolithic sites such as Jericho in the...

  is one archaeological site in this area. Shanidar
Shanidar
Shanidar Cave is an archaeological site in the Zagros Mountains in Erbil Governorate, Kurdistan Region, Iraq. The site is located in the valley of the Great Zab...

, where the ancient skeletal remains of Neanderthal
Neanderthal
The Neanderthal is an extinct member of the Homo genus known from Pleistocene specimens found in Europe and parts of western and central Asia...

s have been found, is another.

Some of the earliest evidence of production has been discovered in the Zagros Mountains; both the settlements of Hajji Firuz Tepe
Hajji Firuz Tepe
Hajji Firuz Tepe is an archaeological site located in West Azarbaijan province in northwestern Iran. The site was excavated between 1958 and 1968 by archaeologists from the University of Pennsylvania Museum of Archaeology and Anthropology...

 and Godin Tepe
Godin Tepe
Godin Tepe is an archaeological site in western Iran, situated in the valley of Kangavar in Kermanshah Province. Discovered in 1961, the site was excavated from 1965 to 1973 by a Canadian expedition headed by T. Cuyler Young Jr...

 have given evidence of wine storage dating between 3500 and 5400 BC.

During early ancient times, the Zagros was the home of peoples such as the Kassites
Kassites
The Kassites were an ancient Near Eastern people who gained control of Babylonia after the fall of the Old Babylonian Empire after ca. 1531 BC to ca. 1155 BC...

, Guti, Assyria
Assyria
Assyria was a Semitic Akkadian kingdom, extant as a nation state from the mid–23rd century BC to 608 BC centred on the Upper Tigris river, in northern Mesopotamia , that came to rule regional empires a number of times through history. It was named for its original capital, the ancient city of Assur...

ns, Elamites and Mitanni
Mitanni
Mitanni or Hanigalbat was a loosely organized Hurrian-speaking state in northern Syria and south-east Anatolia from ca. 1500 BC–1300 BC...

, who periodically invaded the Sumer
Sumer
Sumer was a civilization and historical region in southern Mesopotamia, modern Iraq during the Chalcolithic and Early Bronze Age....

ian and/or Akkad
Akkad
The Akkadian Empire was an empire centered in the city of Akkad and its surrounding region in Mesopotamia....

ian cities of Mesopotamia
Mesopotamia
Mesopotamia is a toponym for the area of the Tigris–Euphrates river system, largely corresponding to modern-day Iraq, northeastern Syria, southeastern Turkey and southwestern Iran.Widely considered to be the cradle of civilization, Bronze Age Mesopotamia included Sumer and the...

. The mountains create a geographic barrier between the flatlands of Mesopotamia, which is in Iraq, and the Iranian plateau. A small archive of clay tablet
Clay tablet
In the Ancient Near East, clay tablets were used as a writing medium, especially for writing in cuneiform, throughout the Bronze Age and well into the Iron Age....

s detailing the complex interactions of these groups in the early second millennium BC has been found at Tell Shemshara
Tell Shemshara
Tell Shemshara is an archaeological site located along the Little Zab in Sulaymaniyah Governorate, northeastern Iraq. The site was excavated between 1957 and 1959 by Danish and Iraqi archaeologists and is now inundated by Lake Dukan. The excavations showed that the site was occupied, although not...

 along the Little Zab
Little Zab
The Little Zab , , ) originates in Iran and joins the Tigris in Iraq. The river is approximately long and drains an area of c. . The river is fed by rainfall and snowmelt, resulting in a peak discharge in spring and low water in summer and early fall...

. Tell Bazmusian
Tell Bazmusian
Tell Bazmusian is an archaeological site on the right bank of the Little Zab in the Ranya Plain . The site was excavated between 1956 and 1958 by Iraqi archaeologists as part of a salvage operation to document cultural remains that would be flooded by Lake Dukan, the reservoir created by the Dukan...

, near Shemshara, was occupied between the sixth millennium BCE and the ninth century CE, although not continuously.

External links