Rift (geology)
Horst_graben.jpg
In geology, a rift is a place where the Earth's [[crust] and lithosphere are being pulled apart. Typical features are a central linear downdropped fault segment, called a graben, with parallel normal faulting and rift-flank uplifts on either side. 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 coninues, eventually a mid-ocean ridge may form, marking a divergent boundary between two tectonic plates. Failed rifts are ancient to modern features where continental rifting began, but then failed to continue. Typically the transition from rifting to spreading develops as three converging rifts over a hotspot. Two of these evolve to the point of seafloor spreadung, while the third ultimately fails, becoming an aulacogen.
Examples of rifts include:
- Great Rift Valley in Africa
- Red Sea
- throughout the Basin and Range Province in North America
- the Rio Grande Rift in the southwestern US
- the rift in the middle of 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 Taupo Volcanic Zone in the north east North Island of New Zealand