Zagros Mountains, Iran
Zagros mountains salt dome: © NASA Earth Science and Remote Sensing Unit, NASA Johnson Space Center
The Zagros Mountains make up a belt of deformed crustal rocks located in south eastern Iran. They extend for over 1500km from eastern Turkey in the northwest through to the Gulf of Oman in the southeast.
The formation of the Zagros Mountain belt is the result of a complex and lengthy orogeny beginning in the Palaeozoic and carrying through to present day. Prior to the onset of subduction in the Late Cretaceous, the Neo-Tethys Ocean was still an actively spreading narrow ocean basin between the Arabian and Eurasian Plates. The Zagros Mountains then formed a passive continental margin on the north eastern flank of the Arabian plate. Thick successions of shallow marine limestones, dolomites, siltstones, shales and salts were deposited on this continental shelf from the Palaeozoic through to the Cenozoic era.
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The Zagros folded zone: © Joshua Doubek |
Subsequent erosion has now removed the softer rocks, such as the mudstones and siltstones leaving more resistant limestone and dolomite rocks. This differential erosion formed the linear ridges and parallel valleys of the Zagros Mountains.
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Fars domain of the Zagros fold-thrust belt: © NASA |
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The continental shelf deposition and tectonic history of the Zagros Mountain sediments were conducive to the formation and trapping of petroleum, today forming a globally significant petroleum reserve. Carbon-rich shales deposited on the Arabian continental shelf were heated as successive sedimentary layers were deposited above, leading to the generation of oil and gas. As folding and thrusting initiated in the region, these hydrocarbons became trapped in the strongly folded anticlines in places where impermeable sedimentary layers overlay porous reservoir rocks. Oil fields in the Zagros mountain chain are therefore elongate and parallel to the northwest-southeast trending folds.
Further reading:
* Berra and Angiolini (2014) The evolution of the Tethys region throughout the Phanerozoic: A brief tectonic reconstruction, in Petroleum systems of the Tethyan region: AAPG Memoir 106, p. 1–27.
* Hessami et al. (2005) Active deformation within the Zagros Mountains deduced from GPS measurements, Journal of the Geological Society, 163, 143-148.
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