URALIAN OROGENIC BELT

a 3,500-kilometre- (2,175-mile-) long elongate mountain system that extends from the Aral Sea to the islands of Novaya Zemlya. It is 500 km wide in the south but only 100150 km wide in the north. The belt formed as a result of the closure of the Uralian Sea by eastward subduction, and by collision of island arcs and small continental blocks to the east with an east European continent. During collision, a major thrust transported westward many slabs of Uralian ocean floor in the form of ophiolites, which host chromite deposits, and it led to formation of oil-bearing foreland basins along the western side of the Ural Mountains. Final compression took place in the Permian Period (286 to 245 million years ago) and the Early Triassic Epoch (245 to 240 million years ago). Post-orogenic extensional collapse helped the uplift and unroofing of high-pressure rocks such as eclogites and glaucophane schists in the west and to the formation in the northeast of a series of graben infilled with clastic sediments and lavas in the Triassic Period (245 to 208 million years ago). On the western side of the Urals near the city of Perm, red sandstones and thick evaporites containing economic potash deposits accumulated in the Permian. Sir Roderick Murchison named the Permian Period after the city in 1841. Brian Frederick Windley