Rift

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In geology, a rift is a place where the Earth's crust and lithosphere are being pulled apart, an example of extensional tectonics. Typical features are a central linear downdropped fault segment, called a graben, with parallel normal faulting and rift-flank uplifts on either side forming a rift valley, where the rift remains above sea level. The axis of the rift area commonly contains volcanic rocks and active volcanism is a part of many but not all active rift systems. Rifts are distinct from Mid-ocean ridges, where new oceanic crust and lithosphere is created by seafloor spreading. In rifts, no crust or lithosphere is produced. If rifting continues, eventually a mid-ocean ridge may form, marking a divergent boundary between two tectonic plates. Failed rifts, which may be ancient or modern, are where continental rifting began, but then failed to continue to the point of break-up. Typically the transition from rifting to spreading develops as three converging rifts over a hotspot. Two of these evolve to the point of seafloor spreading, while the third ultimately fails, becoming an aulacogen.

[edit] Examples

• The East African Rift
• The Red Sea Rift
• The Baikal Rift Zone, the bottom of Lake Baikal is the deepest continental rift on the earth.
• The Gulf of Suez Rift
• Lake Timiskaming in Temiskaming Shores, Ontario
• Throughout the Basin and Range Province in North America
• The Rio Grande Rift in the southwestern US
• The rift zone that contains the Gulf of Corinth in Greece
• The Reelfoot Rift, an ancient buried failed rift underlying the New Madrid Seismic Zone in the Mississippi embayment
• The Rhine Rift, in south western Germany, known as the Upper Rhine valley
• The Taupo Volcanic Zone in the north east North Island of New Zealand
• The Oslo Graben in Norway
• The Ottawa-Bonnechere Graben in Ontario and Quebec
• The Northern Cordilleran Volcanic Province in British Columbia, Yukon and Alaska
• The West Antarctic Rift in Antarctica
• The Midcontinent Rift System, a late Precambrian rift in central North America