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The geology of the North Sea describes the geological features such as channels, trenches, and ridges today and the geological history, plate tectonics, and geological events that created them. The basement of the North Sea was formed in an intraplate setting during the Precambrian. Rigid blocks were overlaid with various depositions, sands and salts. These rigid blocks were transformed to a metamorphic base due to tectonic processes such as continental collisions which cause horizontal pressure, friction and distortion in the Caledonian plate cycle as well as the Variscan plate cycle. The blocks were also subjected to metamorphic evolution during the Triassic and Jurassic periods when the rock was heated up by the intrusion of hot molten rock called magma from the Earth's interior. The Caledonian (Iapetus) plate cycle saw the formation of the Iapetus suture during the Caledonian orogeny. The Iapetus suture was a major weakness creating a volcanic fault in the central North Sea during the later Jurassic period. The Iapetus ocean was replaced with a suture line and mountain range when Laurentia, Baltica and Avalonia continents collided. This collision formed Laurussia.〔 The Variscan (Rheic) plate cycle resulted in the formation of Pangea when Gondwana and Laurussia collided. The elimination of the Rheic Ocean caused the formation of a massive mountain range through the border countries of the present day North Sea.〔 Triassic and Jurassic volcanic rifting and graben fault systems created highs and lows in the North Sea area. This was followed by late Mesozoic and Cenozoic subsidence creating the intracratonic sedimentary basin of the North Sea. This era experienced higher sea levels because of sea floor spreading, cooler lithosphere temperatures. Plate tectonics and continental orogenies combined to create the continents and the North Sea as we know them today. The final events affecting the North Sea coastline features and submarine topography occurred in the Cenozoic era. ==Tectonic structure== The Mesozoic structures underneath the North Sea can be seen as a failed rift system.〔 〕 After initial crustal extension and the formation of rift basins during the Triassic and Jurassic periods,〔 the extension concentrated on the other side of the British Isles, which would create the northern Atlantic Ocean. The rift basins even saw some inversion during the late Cretaceous and Eocene epochs.〔 〕 From the Oligocene onward, tensions in the European crust caused by the Alpine orogeny to the south cause a new, more modest phase of extension.〔 〕 Some grabens in the area are still active. The subsurface of the North Sea area is dominated by grabens: the north-west south-east oriented Lower Rhine Graben under the southern North Sea and the Netherlands,〔 〕 the north-south oriented North Sea Central Graben that begins north of the Dutch coast and ends in the region east of Scotland, and the Viking Graben along the south-east Norwegian coast.〔〔 The Horn Graben is a smaller graben east of the Central Graben and in front of the Danish coast.〔 Another smaller structure is known as the Terschelling Graben which borders the Central Graben in the West, just North of the Netherlands.〔(Geology of the North Sea ) from (Petroleum Geology )〕 A larger graben is found in the subsurface below the Skagerrak, this north-south structure is called the Bamble-Oslo Graben.〔 Map on page 303 〕 The Viking Graben is separated from the Faeroe Shetland Basin below the Atlantic by the Shetland Platform, the two structures join in the area north-east of the Shetland Islands.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Geology of the North Sea」の詳細全文を読む スポンサード リンク
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