Orogenic Events

Pan-African

The Pan-African orogeny is equivalent to Asynitic in other parts of the earth. This event was associated with metamorphism, magmatism, folding, and faulting during Late Precambrian–Early Cambrian in Iran (e.g., south of Zanjan–Mahabad in Azerbaijan, Bafq in Central Iran. This tectonic phase started with tension or extension leading to the formation of rifts and generation of oceanic crust (e.g., in Takab and Anarak) and ended with folding, closure, metamorphism, growth of the continental crust, and development of regional faults.

Caledonian

There was no considerable folding or faulting related to this event in Iran. The Caledonian orogeny in Iran is characterized by facies change in sedimentary basins, hiatuses, and epeirogenic movements (e.g., parts of Alborz, Zagros, and Central Iran). This phase, starting from Late Cambrian, caused the marine facies of Barut and Zaigoon Formations to change into the continental facies of Lalun Formation, and continued on to Late Devonian.

Hercynian

The effects of this orogenic episode in Iran can be traced from the Late Devonian. Due to the scarcity of magmatism, metamorphism, and folding related to this episode, the role of the Hercynian orogeny in Iran is controversial; the Hercynian in Iran is largely represented by extensional rather than compressional tectonics (e.g., Sanandaj–Sirjan). Iranian microplates east and northeast of the Zagros were detached from Gondwana in the Carboniferous during this orogenic phase.

Early Cimmerian

The Early Cimmerian orogeny is one of the most important tectonic events in the geological history of the earth. Many diverse features are associated with this phase, including metamorphism, magmatism, folding, faulting, creation of new basins, and facies change. This event was associated with compressional tectonics in the northern Iran and tensional tectonics in the south. There is evidence that the compressional phase was preceded by tension and rift development. The compressional phase, happening in the Late Triassic, finally led to the closure of the Paleotethys (e.g., southeast to southwest of Caspian Sea). Iranian microplates that had been detached from Gondwana in the Carboniferous and that had been submerged and had moved northwards toward Laurasia finally collided with the Eurasian section of the northern supercontinent Laurasia in the Late Triassic.

Late Cimmerian

The Late Cimmerian orogeny occurred as a significant tectonic event in Iran in Late Jurassic–Early Cretaceous times. This event is represented by folding, facies changes in sedimentary environments, angular unconformity, magmatism, and metamorphism (e.g., Alborz, Sanandaj–Sirjan, and Central Iran). The Jurassic granite of Kolah Ghazi, Shir Kuh, and Shah Kuh was made during this orogenic phase.

Laramide

The Laramide orogeny happened in the Late Cretaceous–Paleocene and played a great role in the geological evolution of Iran. This event started under a compressional regime, followed by an extensional one. The compressional regime, that was associated with significant intrusive magmatic activities, led to the closure of the oceanic basins and Neothetyan rifts. In some areas, slices of the oceanic crust have obducted onto the continental margins producing what could be called ophiolite assemblages or coloured melanges (e.g., mostly seen suture zone between Sanandaj–Sirjan and Zagros, and alongside Nehbandan fault in the east of Iran). The Upper Cretaceous-Paleocene granite of Mount Alvand was formed during the Laramide orogeny.

Alpine (Pyrenean and Styrian)

With regards to the geological evidence, this event was of compressional nature. This tectonic phase is represented by significant changes in the sedimentary environments, plutonism, and metamorphism (e.g., west of Central Iran, south of Central Alborz, Lut). The Sahand-Bazman volcanic arc or belt was mainly formed during the Eocene volcanism of the Alpine orogeny. The northern movement and the final collision of Afro-Arabia (significantly the Arabian Plate) with the Iranian Plate and the clockwise rotation of the Eurasian Plate towards the Iranian Plate caused the Alpine orogeny with the Pyrenean phase in the Late Eocene- Early Oligocene and the Styrian phase in the Middle Miocene respectively. The Zagros, Alborz, and Kopet-Dagh mountains were mainly formed in the Miocene during this orogenic phase.

Pasadenian

This orogenic phase began in the Late Pliocene and continued in the Pleistocene. The Pasadenian orogeny is the most important phase in forging the current shape of Iran. Some younger orogenic events might be the continuation of this orogenic phase (e.g., Alborz–Azerbaijan axis, Zagros, Central Iran). Sahand, Sabalan, Damavand, Bazman and Taftanwere mainly formed during the volcanism of this orogenic phase. With an elevation of 5,610 metres, Mount Damavand is the highest peak in Iran. This volcano first erupted in the Pleistocene about 1.78 million years ago and after several known eruptions around 600,000 and 280,000 years ago, it finally erupted in the Holocene almost 7300 years ago.

References: wikipedia

picture from: The Shanderman eclogites: a Late Carboniferous high-pressure event in the NW Talesh Mountains (NW Iran)

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