Rift

USGS image
Plates in the crust of the earth, according to the plate tectonics theory

In geology, a rift is a place where the Earth's crust and lithosphere are being pulled apart[1] and is an example of extensional tectonics.[2]

Typical rift 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.

Most rifts occur along the central axis of a mid-ocean ridge, where new oceanic crust and lithosphere is created along a divergent boundary between two tectonic plates.

Failed rifts are where continental rifting began, but then failed to continue to the point of break-up. Typically the transition from rifting to spreading develops at a triple junction where three converging rifts meet over a hotspot. Two of these evolve to the point of seafloor spreading, while the third ultimately fails, becoming an aulacogen.

Examples

References

  1. http://www.mantleplumes.org/VM_DecompressMelt.html Decompressional Melting During Extension of Continental Lithosphere
  2. http://www.le.ac.uk/geology/art/gl209/lecture4/lecture4.html Plate Tectonics: Lecture 2