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A graben is a section of crust that has lowered relative to the blocks on either side, which is a result of its bounding faults dipping towards each other. [2] The plural of graben can be either graben or grabens. Graben form low-lying features such as basins and rift valleys. [1] [2] They can be very long relative to their width.
In physical geography and geology, a horst is a raised fault block bounded by normal faults. [1] Horsts are typically found together with grabens . While a horst is lifted or remains stationary, the grabens on either side subside . [ 2 ]
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.
[3] [4] [5] Tilted type block mountains have one gently sloping side and one steep side with an exposed scarp, and are common in the Basin and Range region of the western United States. An example of a graben is the basin of the Narmada River in India, between the Vindhya and Satpura horsts.
With crustal extension, a series of normal faults which occur in groups, form in close proximity and dipping in opposite directions. [4] As the crust extends it fractures in series of fault planes, some blocks sink down due to gravity, creating long linear valleys or basins also known as grabens, while the blocks remaining up or uplifted produce mountains or ranges, also known as horsts.
Graben – Depressed block of planetary crust bordered by parallel normal faults; Horst – Raised fault block bounded by normal faults; Mid-ocean ridge – Basaltic underwater mountain system formed by plate tectonic spreading; Mud volcano – Landform created by the eruption of mud or slurries, water and gases
This uplift caused massive crustal extension leading to horst and graben structures associated with normal, extensional, faults. The uplift ended in collapse around 25 Mya into the Afar depression covering more than 200,000 km 2 (77,000 sq mi) and spreading at a rate of 6 to 17 millimetres per year (0.24 to 0.67 in/year). [1]
Complex tectonics produced horst and graben features and some lowlands deposited evaporites, such as the Burano Anhydrite—now a significant unit in the Apennine Mountains. Jurassic tectonic conditions differed somewhat from the Triassic, resulting in new basin formation and a carbonate depositional environment akin to the current day Florida ...