page_title: Zagros Mountains
section_title: Geology
hierarchical_section_title: Zagros Mountains / Geology
caption_attribution_description: English: The Zagros Mountains in Iran offer a visually stunning topographic display of geologic structure in layered sedimentary rocks. This scene is nearly 100 kilometers (62 miles) wide but is only a small part of similar terrain that covers much of southern Iran. This area is actively undergoing crustal shortening, as global tectonics moves Arabia toward Asia. Consequently, layers of sedimentary rock are folding much like a carpet will fold if pushed. The convex upward folds create structures called anticlines, which are prominently seen here. The convex downward folds (between the anticlines) create structures called synclines, which are mostly buried and hidden by sediments eroding off the anticlines. Layers having differing erosional resistance create distinctive patterns, often sawtooth triangular facets, that encircle the anticlines. Local relief between the higher mountain ridges and their intervening valleys is about 1,200 meters (about 4,000 feet).
context_page_description: The Zagros Mountains are a long mountain range in Iran, Iraq and southeastern Turkey. This mountain range has a total length of 1,600 km. The Zagros mountain range begins in northwestern Iran and roughly follows Iran's western border, while covering much of southeastern Turkey and northeastern Iraq. From this border region, the range roughly follows Iran's coast on the Persian Gulf. It spans the whole length of the western and southwestern Iranian plateau, ending at the Strait of Hormuz. The highest point is Mount Dena, at 4,409 metres.
context_section_description: The Zagros fold and thrust belt was mainly formed by the collision of two tectonic plates, the Eurasian Plate and the Arabian Plate. This collision mainly happened during the Miocene (about 25–5 million years ago or mya) and folded the entirety of the rocks that had been deposited from the Paleozoic (541–242 mya) to the Cenozoic (66 mya – present) in the passive continental margin on the Arabian Plate. However, the obduction of Neotethys oceanic crust during the Cretaceous (145–66 mya), and the continental arc collision in the Eocene (56–34 mya) both had major effects on uplifts in the northeastern parts of the belt.
  The process of collision continues to the present, and as the Arabian Plate is being pushed against the Eurasian Plate, the Zagros Mountains and the Iranian Plateau are getting higher and higher. Recent GPS measurements in Iran 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 and Zagros. A relatively dense GPS network which covered the Iranian Zagros also proves a high rate of deformation within the Zagros. The GPS results show that the current rate of shortening in the southeast Zagros is ~10 mm/a (0.39 in/year), dropping to ~5 mm/a (0.20 in/year) in the northwest Zagros. The north-south Kazerun strike-slip fault divides the Zagros into two distinct zones of deformation. The GPS results also show different shortening directions along the belt, normal shortening in the southeast, and oblique shortening in the northwest Zagros. The Zagros mountains were created around the time of the second ice age, which caused the tectonic collision, leading to its uniqueness.
  The sedimentary cover in the SE Zagros is deforming above a layer of rock salt (acting as a ductile decollement with a low basal friction), whereas in the NW Zagros the salt layer is missing or is very thin. This different basal friction is partly responsible for the different topographies on either side of the Kazerun fault. Higher topography and narrower zone of deformation in the NW Zagros is observed whereas in the SE, deformation was spread more and a 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 rocks. Subsequent erosion removed softer rocks, such as mudstone (rock formed by consolidated mud) and siltstone (a slightly coarser-grained mudstone) while leaving harder rocks, such as limestone (calcium-rich rock consisting of the remains of marine organisms) and dolomite (rocks similar to limestone containing calcium and magnesium). This differential erosion formed the linear ridges of the Zagros Mountains.
  The depositional environment and tectonic history of the rocks were conducive to the formation and trapping of petroleum, and the Zagros region is an important area for oil production. Salt domes and salt glaciers are a common feature of the Zagros Mountains. Salt domes are an important target for petroleum exploration, as the impermeable salt frequently traps petroleum beneath other rock layers. There is also much water-soluble gypsum in the region.
caption: SRTM Shaded Relief Anaglyph of Zagros Mountains
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