About IRAN Iran covers an area of 1 648 000km², situated between latitudes 25؛ and 39؛ N and longitudes 45؛ and 61؛ E.It is bounded by Turkey, Iraq and the Persian Gulf tothe West and Southwest. The Gulf of Oman to the Southeast. Pakistan and Afghanistan to the East.And Turkmenistan and the Caspian Sea, Azerbaijan and Armenia to the North .Itscapital, Tehran, are also the headquarters of the Geological Survey of Iran.This issues national and regional maps and reports
Morphology The major part of Iran is occupied by a moderately elevated interior basin bounded by highmountain systems along its N and SW margins .Along its E border, lower but rugged mountains provide a link between the N and S mountain systems. Within the interior basin of Iran. Several lesser chains enclose extensive deserts. Plains and playas .The N chain, the Alborz (Elburz), represents a N branch of the Alpine-Himalayan orogenic system and runs for a distance of 960 km .separating the Caspian Lowland from the Central Iran Plateau .Ranging in width from 70 to 130km. with many summits from 3600 to 4800 m in altitude, the Alborz culminates in the 5670 m volcano Mount Damavand.
The South branch of the Alpine- Himalayan orogenic belt is occupied by the Zagros and Makran ranges extending from the Turkish border to the SE for 1600 km to the Strait of Hormoz at the month of the Persian Gulf The South branch continues in the E with the Makran ranges. The Zagros belt comprises a classical series of parallel ridges and valleys .They Culminate in Zard –Kuh (4548m). Deep dissection, tight folding and overthrust structures have created a very rugged topography in High Zagros (Zagros Thrust Zone).
Closed to the East margin of Iran , a N-S trending range provides a link between the Alborz and Zagros ranges; it extends from South of Mashhad through Zahedan and joins the Zagros-Makran trend East of Iranshahr. These mountains are narrowest and lowest in the center, where they are only 80 km wide and the ridge crests do not exceed 2000 m. South of Zahedan, Mount Taftan, a volcanic cone, reaches 4061 m (krinsley, 1970)
Between the bounding ranges, the central high plateau is a major feature of Iran. It is a territory of depressions, low rises ,playas ,dune fields ,broad alluvial fans, and isolated mountain chains .The drainage in internal ,feeding several large basins ,including the Lake Urumiyeh (NW Iran), Darya –ye- Namak (130 km s of Tehran), kavkhuni (SE of Esfahan) ,and Jaz Murain (SE Iran) depressions .
The Persian Gulf, a main artery of commerce with more than 60% of the world oil trade, is a shallow epicontinental sea, which covers the Arabian shelf platform with water depths of less than 100 m (mainly 60 m) .the smaller offshore islands E of 54؛ E meridian are Infracambrain –Cambrian Hormoz salt plugs, partly fringed by Neogene clastic and marine deposits and by recent coral reefs .The larger islands near the coast , Lavan ,Hendurabi ,kish and Qeshm ,are gentle anticlines of the folded belt of the zagros system .The strait of Hormoz ,40 to 50 km wide ,links the Persian Gulf with the deeper water of the Gulf of Oman
The climate of NW Iran is more humid and cooler than of the rest of the country. Total precipitation is sufficient for dry-farming wheat agriculture in Azarbaijan .The Alborz Range forms the hydrological and climatic divide between the Caspian Depression and the Central Iranian plateau .The central Iranian Plateau has a continental desert climate with hot summers and moderately cold winters .In the interior basin, annual rainfall is less than 100 mm. SE Iran has a hot and dry climate ,locally modified by the higher mountains and by the sea .Annual precipitation is below 100 mm in the Sistan and Juz Murian depressions and less than 50 mm in the Lut Depression .The Lut desert is swept by hot ,desiccating winds in spring and summer which originate from the surrounding mountain range and are heated by adiabatic compression .This leads to probably the world's highest summer temperatures in the Central Lut Desert (above 50؛C). Mean annual temperature differences are above 40؛C and extremes are as low as 10؛C in winter and as high as 60؛C in summer .The climate of SW Iran is determined by the position in the global N dry belt and modified by the W wind drift from the Mediterranean area in late winter and spring .during which the main precipitation occurs.
History of exploration Geological investigation in the vast Iranian region lying E of the Zagros Thrust began in the first half of the 19th century ,but until about four decades ago were mostly based on road reconnaissance or else were focused on a few areas of particular geological or economic interest and relatively easy access.
This situation changed in 1950 , when the newly created National Iranian Oil company began a more systematic approach by reconnaissance geological fieldwork through large parts of central, N and E Iran , as well as detailed exploration in a number of selected regions such as the Qom area and the Kavir Basin in the central Iran, the Caspian region and Kopetdag Range in the N Iran .An important result of these was the publication of the first geological Map of Iran on a scale of 1: 2 500 000 (National Iranian Oil Co.. 1959).
In 1959 a law promulgating the Geological Survey of Iran was passed. and in 1962 the Survey began to operate .One of the main task of this young organization was the preparation and publication of a quadrangle map series on a scale of 1:250 000, a task which naturally called for a systematic geological study in all parts of the country. Fieldwork for these maps have been completed and a total of 121 maps have already been published .Detailed geological mapping on the 1:100000 scale have also been carried out. This work is now well advanced .The Geological Survey has also been engaged in the production of a series of thematic maps such as tectonics, seismotectonics, metamorphic, metallogenic, etc. In the field of geophysics, the total intensity map, (1:1.000.000) and aeromagnetic maps on a 1: 250.000 scale covering entire Iranian territory have been published. At the same time, important contributions have been made by several foreign organizations in cooperation with the Geological Survey of Iran.
Fundamental differences in crustal character and in age of basementconsolidation allow three major structural units to be distinguished, separated from each other by an ophiolite –bearing suture.Other criteria such as structural style
age and intensity of deformation, age and nature of magmatism, are used to subdivide these major zones into smaller elements. The three major units and their main constituents are as follows. (1) A S unit with a crystalline basement consolidated in Precambrian time and a platform –type Paleozoic development. This unit comprises the Zagros folded belt. (2) The central unit is interpreted as an assemblage of marginal Gondwana fragments that were united with the mother-continent and separated from the N (Eurasian) continent in the Paleozoic, but detached from Gondwana and attached to Eurasia in the Mesozoic, and finally rejoined by Gondwanic Afro-Arabia in the Late Cretaceous. It comprises central Iran and the Alborz. (3) The northern unit sharply separated from the central unit by the North Iran Suture .It is characterized by continental crust including remnants of more or lees cratonized former (Paleozoic) oceanic crust that seems to reflect a Paleotethys. The N unit represents a marginal strip of the Hercynian realm of Central Asia- broadly overlapped by the Alpine realm. It was deformed and largely consolidated by strong early kimmerian folding and a Late Alpine folding (stِocklin, 1977). The N unit comprises the South Caspian Depression and the kopet Dagh Range.
Zagros In the simply folded belt of the Zagros Mountians, a sequence of Precambrian to Pliocene shelf sediments about 8-10 km thick has undergone folding from Miocene to Recent time. The Zagros Mountains trend SE through NE Iraq an SW Iran. They are the topographic expression of an orogenic continues to the present .The sediments have been folded into a series of huge anticlines and synclines. The folding has taken place since the Miocene and is reflected in the topography, which is dominated by anticlinal mountains and synclines valleys .The anticlinal oil traps of Iran and NE Iraq are in this belt.
The Zagros orogenic belt is bounded to the SW by the stable platform of Arabia, where shelf sediments laterally equivalent to those in the simply folded belt are virtually underformed and overlie the metamorphic rocks of the Arabian Shield.
Zagros Thrust Zone The folded belt passes northeastward without a sharp boundary into a narrow zone of thrusting bounded on the NE by the main zagros Thrust line. In this zone older Meosozoic rocks and the Paleozoic platform cover were thrust southwestward in several schuppen-like slices on the younger Mesozoic and Tertiary rocks of the folded belt. The thrust zone represent the deepest part of the Zagros Basin in Mesozoic and early Tertiary time.
Sanandaj –Sirjan metamorphic belt
The Sanandaj –Sirjan Zone was first recognized as a separate linear structural element by stِcklin (1968).the zone lies between the main Zagros Thrust in the SW and the Urumiyeh-Bazman volcanic belt in the NE. It joins the Taurus orogenic belt in Turkey. The ranges occupy a NW –trending belt in which the Zagros structural grain is overprinted on the typical Central Iran structural framework. Characteristic features include the consistent Zagros trend of the zone as a whole, the nearly complete lack of Tertiary volcanics and the poor development of Tertiary formations in general. Part of the zone is characterized by Paleozoic volcanism and Hercynian and or Early Kimmerian metamorphism.
Urumiyeh –Bazman volcanic belt This volcanic belt runs parallel to the Sanandaj –Sirjan Zone on its NE side, and owes its existence to the widespread and intensive volcanic activity which developed on the Iranian plate from the Upper Cretaceous to Recent time .the Urumiyeh-Bazman volcanic belt is supposed to have resulted from the collision of the Arabian and Central Iranian continental plate margins. It is represented by sub- alkaline volcanics that vary in composition from basaltic through andesitic to rhyolitic composition.
Central –East Iran microplate Central Iran in a broad sense, comprising the whole area between the North and South Iranian ranges .Within the Iranian plate the Central-East Iran microplate is bordered by the Great Kavir Fault in the N .by the Nain –Baft Fault in the W and SW and by the Harirud Fault in the E .It is surrounded by the Upper Cretaceous to Lower Eocene ophiolite and ophiolitic mélange. The microplate consists of different structural components; the Lut Block, Kerman-Tabas Block, Yazd Block and Anarak-Khur Block.
Makran and Zabol –Baluch Zone, SE Iran Makran and Zabol –Baluch in SE Iran are post–Cretaceous flysch –molasse belts which join together in SE Iran and continue to the Pakistan Baluchistan Range. The fiysch sediments were deposited on the Upper Cretaceous ophiolites.
Alborz The Alborz Mountains, forming gently sinuous E-W range across N Iran. S of the Caspian Sea, constitute a N part of the Alpine-Himalayan Orogeny in W Asia (Figs 323,324).The Alborz Range in N Iran is stratigraphically and structurally related to Central Iran. The similarities are particularly evident on its flank .However; some distinctions can be made .In contrast to Central Iran the Late Cimmerian and early Alpine tectonic movements did not cause angular unconformities in the Alborz.
Kopet Dagh The NE active fold belt of Iran, the Kopet Dagh, is formed on the Hercynian metamorphosed basement at the SW margin of the Turan Platform .The belt is composed of about 10 km of Mesozoic and Tertiary sediments (mostly carbonates) and, like the Zagros, was folded into long linear NW-SE trending folds during the last phase of the Alpine Oregon, in the Plio- Pleistocene time. No magmatic rocks are exposed in Kopet Dagh except for those in the basement in the Aghdarband Window and some Triassic basic dikes.