The Zagros are a system of folded mountains in western and southern Iran, extending about 1,100 miles (177 km) from the Turkish-Russian-Iranian border, to Zendam fault north of the Strait of Hormuz. The Makran Mountains extend east from the Zagros, through the Baluchistan region of Iran, Pakistan, and Afghanistan. The mountains form the southern and western borders of the Iranian Plateau and Dasgt-e Kavir and Lut Deserts. The northwestern Zagros are forested and snow-capped, and include many volcanic cones, whereas the central Zagros are characterized by many cylindrical folded ridges and interridge basins. The southwest Zagros and Makran ranges are characterized by more subdued topography with bare rock, sand dunes, and lowland salt marshes. Many major oil fields are located in the western foothills of the central Zagros, where many salt domes have punctured through overlying strata creating many oil traps.
southwestern central Iran has been an active continental margin since the Mesozoic, with at least three main phases of magmatic activity related to
subduction of Tethyan oceanic crust beneath the mountain ranges. Late Cretaceous magmatism in the Makran formed above subducting oceanic crust related to the Oman ophiolite preserved on the Arabian continental margin. In the late Eocene the axis of active magmatism shifted inland away from the Mesozoic magmatic belt, but then shifted back during the oligocene-Miocene. The oligocene-Miocene magmas are also related to subduction of oceanic crust, suggesting that the Arabian-Iranian collision did not begin until the Miocene. Most of the southern Zagros consists of folded continental margin sediments of the Arabian platform, deformed since the Miocene and mostly since the Pliocene. In contrast, the Makran is an oceanic accretionary wedge consisting of folded Cretaceous to Eocene flysch-and ribbon-chert-bearing mélange resting above the subducting oceanic crust of the Gulf of Oman. A large ophiolitic sheet is thrust over the ophiolitic mélange and flysch and is part of a large ophiolitic belt that stretches the length of the Makran-Zagros ranges, falling between the Cenozoic volcanics and accretionary wedge/folded platform rocks of the Makran and Zagros. The main differences between the Zagros and the Makran exist because continent/ continent collision has begun in the Zagros, but has not yet begun in the Makran.
Iran is seismically active, as shown by the devastating magnitude 6.7 earthquake that destroyed the ancient walled fortress city of Bam on December 26, 2003, killing an estimated 50,000 people. The Zagros belt is extremely active, where thrust-style earthquakes occur beneath a relatively ductile layer of folded sedimentary rocks on the surface. The Makran accretionary wedge is also seismically active, especially along the boundary where the subduction zone and upper-plate accretionary wedge meet. The boundary between the Makran and Zagros is a structurally complex region where many strike-slip faults, including the Zendan fault and related structures, rupture to the surface. The Bam earthquake was a strike-slip earthquake, related to this system of structures. The central Iranian plateau is also seismically active, and experiences large-magnitude earthquakes that rupture to the surface.
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