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The Algoman orogeny, known as the Kenoran orogeny in Canada, was an episode of mountain-building (orogeny) during the Late Archean Eon that involved repeated episodes of continental collisions, compressions and subductions. The Superior province and the Minnesota River Valley terrane collided about 2,700 to 2,500 million years ago. The collision folded the Earth's crust and produced enough heat and pressure to metamorphose the rock. Blocks were added to the Superior province along a boundary that stretches from present-day eastern South Dakota into the Lake Huron area. The Algoman orogeny brought the Archaen Eon to a close, about ; it lasted less than 100 million years and marks a major change in the development of the earth’s crust. The Canadian shield contains belts of metavolcanic and metasedimentary rocks formed by the action of metamorphism on volcanic and sedimentary rock. The areas between individual belts consist of granites or granitic gneisses that form fault zones. These two types of belts can be seen in the Wabigoon, Quetico and Wawa subprovinces; the Wabigoon and Wawa are of volcanic origin and the Quetico is of sedimentary origin. These three subprovinces lie linearly in southwestern- to northeastern-oriented belts about wide on the southern portion of the Superior Province. The Slave province and portions of the Nain province were also affected. Between about 2,000 and these combined with the Sask and Wyoming cratons to form the first supercontinent, the Kenorland supercontinent. ==Overview== Through most of the Archean Eon, the Earth had a heat production at least twice that of the present, which caused tectonic processes to be more active. As a result, plates and continents were smaller. No broad blocks as old as 3 Ga are found in Precambrian shields. Toward the end of the Archean, however, some of these blocks or ''terranes'' came together to form larger blocks welded together by greenstone belts. Two such terranes that now form part of the Canadian shield collided about . These were the Superior province and the large Minnesota River Valley terrane, the former composed mainly of granite and the latter of gneiss. This led to the mountain-building episode known as the ''Algoman orogeny'' in the U. S. (named for Algoma, Kewaunee County, Wisconsin), and the ''Kenoran orogeny'' in Canada.〔 Its duration is estimated at 50 to 100 million years.〔 The current boundary between these terranes is known as the Great Lakes tectonic zone (GLTZ). This zone is wide and extends in a line roughly 1,200 kilometers long from the middle of South Dakota, east through the middle of the Upper Peninsula of Michigan, into the Sudbury, Ontario region. The region remains slightly active today. Rifting in the GLTZ began about at the end of the Algoman orogeny. The orogeny affected adjacent regions of northern Minnesota and Ontario in the Superior province〔 as well as the Slave and the eastern part of the Nain province, a far wider region of influence than in subsequent orogenies.〔 It is the earliest datable orogeny in North America〔(【引用サイトリンク】title=Voyageurs National Park, Geologic Features & Processes )〕 and brought the Archean Eon to a close.〔 The end of the Archean Eon marks a major change in the development of the Earth’s crust: the crust was essentially formed and achieved thicknesses of about under the continents. 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「Algoman orogeny」の詳細全文を読む スポンサード リンク
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