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From Wikipedia, the free encyclopedia

Diagram illustrating the structural relationship between grabens and horsts
Diagram illustrating the structural relationship between grabens and horsts
Infrared-enhanced satellite image of a graben in the Afar Depression
Infrared-enhanced satellite image of a graben in the Afar Depression

In geology, a graben (/ˈɡrɑːbən/) is a depressed block of the crust of a planet or moon, bordered by parallel normal faults.

Etymology

Graben is German for ditch or trench. The plural form is either graben[1] or grabens.[2] The German plural is Gräben. (IPA: [ˈɡʁɛːbən])

Formation

A graben is a valley with a distinct escarpment on each side caused by the displacement of a block of land downward. Graben often occur side-by-side with horsts. Horst and graben structures indicate tensional forces and crustal stretching.

Graben are produced from parallel normal faults, where the displacement of the hanging wall is downward, while that of the footwall is upward. The faults typically dip toward the center of the graben from both sides. Horsts are parallel blocks that remain between graben; the bounding faults of a horst typically dip away from the center line of the horst. Single or multiple graben can produce a rift valley.

Half-graben

The Newark Basin, an early Mesozoic half-graben
The Newark Basin, an early Mesozoic half-graben

In many rifts, the graben are asymmetric, with a major fault along only one of the boundaries, and these are known as half-graben. The polarity (throw direction) of the main bounding faults typically alternates along the length of the rift. The asymmetry of a half-graben strongly affects syntectonic deposition. Comparatively little sediment enters the half-graben across the main bounding fault because of footwall uplift on the drainage systems. The exception is at any major offset in the bounding fault, where a relay ramp may provide an important sediment input point. Most of the sediment will enter the half-graben down the unfaulted hanging wall side (e.g. Lake Baikal).[3]

Rima Ariadaeus on the Moon is thought to be a graben. The lack of erosion on the Moon makes its structure with two parallel faults and the sunken block in between particularly obvious.
Rima Ariadaeus on the Moon is thought to be a graben. The lack of erosion on the Moon makes its structure with two parallel faults and the sunken block in between particularly obvious.

Notable examples

Africa

Antarctica

Asia

Europe

North America

Canada

Guatemala

United States

Multi-national

Oceania

South America

See also

Notes

  1. ^ Schlumberger Oilfield Glossary
  2. ^ horst and graben. Encyclopædia Britannica. Retrieved 2012-11-15.
  3. ^ Hans Nelson, C.; Karabanov, Evgeny B.; Colman, Steven M.; Escutia, Carlota (1999). "Tectonic and sediment supply control of deep rift lake turbidite systems: Lake Baikal, Russia". Geology. 27 (2): 163–166. doi:10.1130/0091-7613(1999)027<0163:TASSCO>2.3.CO;2.
  4. ^ Hochstein, M. P., and Nixon, I. M., (1979). "Geophysical study of the Hauraki Depression, North Island, New Zealand," New Zealand Joumal of Geology and Geophysics, 22 (1): 1-19.
  5. ^ Sprigg, R.C. (1961). "The Oil and Gas Prospects of the St. Vincents Gulf Graben". The APPEA Journal. 1 (1): 71–88. doi:10.1071/AJ60011.
  6. ^ Stacey, A. R., and Berry, R. F., (2004). "The Structural history of Tasmania: a review for petroleum explorers," PESA Eastern Australasian Basins Symposium II

References

This page was last edited on 4 October 2021, at 21:59
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