Basin and range topography is characterized by alternating parallel mountain ranges and valleys. It is a result ofcrustal extension due tomantle upwelling, gravitational collapse, crustal thickening, or relaxation of confining stresses.[1][2] The extension results in the thinning and deformation of the upper crust, causing it to fracture and create a series of long parallelnormal faults. This results inblock faulting, where the blocks of rock between the normal faults eithersubside,uplift, or tilt. The movement of these blocks results in the alternating valleys and mountains. As the crust thins, it also allows heat from the mantle to more easilymelt rock and form magma, resulting in increased volcanic activity.[3]
Withcrustal extension, a series ofnormal faults which occur in groups, form in close proximity and dipping in opposite directions.[4] As the crust extends it fractures in series offault planes, some blocks sink down due to gravity, creating long linear valleys or basins also known asgrabens, while the blocks remaining up or uplifted produce mountains or ranges, also known ashorsts. Fault scarps are exposed on the horst block and expose thefootwall of the normal fault. This is a type of block faulting known asgrabens and horsts. This basin and range topography is symmetrical having equal slopes on both sides of the valleys and mountain ranges.
Tilted block faulting, also known ashalf-graben or rotational block faulting, can also occur during extension. Large gently dipping normal faults, also known asdetachment faults, act as platforms in which normal faulted blocks tilt or slide along. However, instead of the whole block subsiding only one side, the block may slip along the detachment fault, tilting toward the fault plane, again creating mountains (ranges) and valleys (basins), many tilted slightly in one direction at their tops due to the motion of their bottoms along the main detachment fault. This basin and range topography has one steep side and the other is more gradual.
The Basin and Range Province is the most well known example of basin and range topography.Clarence Dutton compared the many narrow parallel mountain ranges that distinguish the unique topography of the Basin and Range to an "army of caterpillars crawling northward."[5]
Thephysiography of the province is the result oftectonic extension that began around 17 million years ago in the earlyMiocene epoch. Opinions vary regarding the total extension of the region; however, the median estimate is about 100% total lateral extension.[6] The tectonic mechanisms responsible for lithospheric extension in the Basin and Range province are controversial, and several competing hypotheses attempt to explain them.[7][8][9]
The Aegean Sea Plate consists of thinned continental crust. The northern part of the plate is currently a region of crustal extension caused byslab rollback on theHellenic Subduction Zone to the south, causing extensive normal faulting and the formation of horsts and grabens on the seafloor. Many of the islands are the result of peaks reaching above sea level.[10][11]
One of the most studied basin and range topographies is theBasin and Range Province in the western United States, located between theSierra Nevada and theRocky Mountains. The extension of the province was believed to have begun in the lateCenozoic Era, roughly 20Ma.[12] Between 1992 and 1998 scientists conductedGPS surveys to map the deformation of the Basin and Range province.[13] In the study, Thatcher et al. discovered that most deformation was happening in the west, adjacent to the Sierra Nevada block, while less deformation was happening in the east. This coincides with the northwestward movement of theSierra Nevada microplate.[14]
Though the Aegean Sea Plate is more difficult to study because it is underwater, efforts have been made to conduct GPS surveys of the seafloor and surrounding area. Some studies show regions of extension within the plate, while others suggest a four-microplate model to represent the motion.[15] The plate's deformation is thought to be a result ofcrustal collapse (beginningc. 14 Ma) combined with slab rollback on the Hellenic Subduction Zone.[16][17]
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