Tectonic uplift: Difference between revisions

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{{shortShort description|The portion of the total geologicGeologic uplift of the mean earthEarth's surface that is not attributableattributed to an isostatic response toplate unloadingtectonics}}

[[File:Raised beach western Crete.jpg|thumb|[[Raised beach]] indicating 9 m of uplift during the [[365 Crete earthquake]], other shorelines identified at this site are at 14 m, 17m, 34m, 55m & 75m elevation, consistent with a long-term uplift rate of 2.5–2.7 mm per year over the last 45,000 years]]

{{technical|date=June 2013}}

[[Image:Kupe's Sail-20070331.jpg|thumb|[[Kupe's Sail]] at [[Palliser Bay]] in [[New Zealand]]{{clarify |date=January 2017 |reason=clarify how the content of this photo is relevant to tectonic uplift}}]]

'''Tectonic uplift''' is the [[orogeny|geologic uplift]] of the [[Earth#Surface|Earth's surface]] that is attributed to [[plate tectonics]]. While [[Isostasy|isostatic]] response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of [[Thrust tectonics|crustal thickening]] (such as [[Mountain formation|mountain building]] events), changes in the density distribution of the crust and underlying [[Mantle (geology)|mantle]], and flexural support due to the bending of rigid [[lithosphere]].

OneTectonic shoulduplift alsoresults take into consideration the effects ofin [[denudation]] (processes that wear away the earth's surface). Within the scope of this topic, uplift relates to denudation in that denudationby bringsraising buried rocks closer to the surface. This process can redistribute large loads from an elevated region to a topographically lower area as well – thus promoting an isostatic response in the region of denudation (which can cause local bedrock uplift). The timing, magnitude, and rate of denudation can be estimated by geologists[[geologist]]s using pressure-temperature studies.

==Crustal thickening==

Crustal thickening has an upward component of motion and often occurs when [[continental crust]] is [[Thrust fault|thrust]] onto continental crust. Basically [[nappe]]s (thrust sheets) from each plate collide and begin to stack one on top of the other; evidence of this process can be seen in preserved [[Ophiolite|ophiolitic]] nappes (preserved in the Himalaya[[Himalayas]]), and in rocks with an inverted [[Metamorphic zone|metamorphic gradient]]. The preserved inverted metamorphic gradient indicates that nappes were actually stacked on top of each other so quickly, that hot rocks did not have time to equilibrate before being thrust on top of cool rocks. The process of nappe stacking can only continue for so long, as gravity will eventually disallow further vertical growth (there is an upper limit to vertical mountain growth).

==Density distribution of the crust and underlying mantle==

{{see also|Continental crust#Density}}

Although the raised surfaces of [[mountain rangesrange]]s mainly result from crustal thickening, there are other forces at play that are responsible for the tectonic activity. All tectonic processes are driven by [[Gravity|gravitational force]] when [[density]] differences are present. A good example of this would be the large-scale circulation of the [[Earth's mantle]]. Lateral density variations near the surface (such as the creation, cooling, and [[subduction]] of [[Oceanic crust|oceanic plateplates]]s) also drive [[TectonicPlate platetectonics|plate]] motion.

The dynamics of mountain ranges are governed by differences in the [[gravitational potential energy]] of entire ''columns'' of the lithosphere (see [[isostasy]]). If a change in surface height represents an isostatically compensated change in crustal thickness, the rate of change of potential energy per unit surface area is proportional to the rate of increase of average surface height. The highest rates of working against gravity are required when the thickness of the [[Crust (geology)|crust]] (not the [[lithosphere]]) changes.<ref name=E&M>England and Molnar, 1990, ''Surface uplift, uplift of rocks, and exhumation of rocks,'' Geology, v. 18 no. 12 p. 1173-1177 [http://geology.gsapubs.org/content/18/12/1173.abstract Abstract]</ref>

==Lithospheric flexure==

[[Lithospheric flexure]] is the process by which the lithosphere bends under the action of forces such as the weight of a growing [[orogeny]] or changes in ice thickness related to glaciation. The lithosphere rests on the [[asthenosphere]], a viscous layer that in geological time scales behaves like a fluid. Thus, when loaded, the lithosphere progressively reaches an isostatic equilibrium. For example, the lithosphere on the oceanward side of an [[oceanic trench]] at a subduction zone will curve upwards due to the [[Elasticity (physics)|elastic properties]] of the Earth's crust.

{{main|Lithospheric flexure}}

{{Expand section|date=June 2014}}

[[Lithosphere]] on the oceanward side of an [[oceanic trench]] at a [[subduction zone]] will curve upwards due to the [[Elasticity (physics)|elastic properties]] of the [[Earth's crust]].

==Orogenic uplift==

{{Main|Orogeny}}

Orogenic uplift is the result of tectonic-plate collisions and results in mountain ranges or a more modest uplift over a large region. Perhaps the most extreme form of orogenic uplift is a continental-continental crustal collision. In this process, two continents are sutured together and large mountain ranges are produced. The collision of the Indian and Eurasian plates is a good example of the extent to which orogenic uplift can reach. Heavy thrust faulting (of the Indian plate beneath the Eurasian plate) and folding are responsible for the suturing together of the two plates.<ref>Le Fort, Patrick. "Evolution of the Himalaya." (n.d.): 95-109. Print.</ref> The collision of the Indian and Eurasian plates not only produced the Himalaya but is also responsible for crustal thickening north into [[Siberia]].<ref>Molnar, P., and P. Tapponnier. "Cenozoic Tectonics of Asia: Effects of a Continental Collision: Features of Recent Continental Tectonics in Asia Can Be Interpreted as Results of the India-Eurasia Collision." Science 189.4201 (1975): 419-26. Print.</ref> The [[Pamir Mountains]], [[Tian Shan]], [[Altai Mountains|Altai]], [[Hindu Kush]], and other mountain belts are all examples of mountain ranges formed in response to the collision of the Indian with the Eurasian plate. Deformation of continental lithosphere can take place in several possible modes.

Orogenic uplift is the result of tectonic-plate collisions and results in mountain ranges or a more modest uplift over a large region. Perhaps the most extreme form of orogenic uplift is a continental-continental crustal collision. In this process, two continents are sutured together, and large mountain ranges are produced. The collision of the [[Indian plate|Indian]] and [[Eurasian plate|Eurasian]] plates is a good example of the extent to which orogenic uplift can reach. Heavy thrust faulting (of the Indian plate beneath the Eurasian plate) and [[Fold (geology)|folding]] are responsible for the suturing together of the two plates.<ref>Le Fort, Patrick. "Evolution of the Himalaya." (n.d.): 95-109. Print.</ref> The collision of the Indian and Eurasian plates not only produced the HimalayaHimalayas butand is also responsible for crustal thickening north into [[Siberia]].<ref>Molnar, P., and P. Tapponnier. "Cenozoic Tectonics of Asia: Effects of a Continental Collision: Features of Recent Continental Tectonics in Asia Can Be Interpreted as Results of the India-Eurasia Collision." Science 189.4201 (1975): 419-26. Print.</ref> The [[Pamir Mountains]], [[Tian Shan]], [[Altai Mountains|Altai]], [[Hindu Kush]], and other mountain belts are all examples of mountain ranges formed in response to the collision of the Indian with the Eurasian plate. Deformation of continental lithosphere can take place in several possible modes.

The [[Ozark Plateau]] is a broad uplifted area which resulted from the [[Permian]] [[Ouachita Mountains|Ouachita Orogeny]] to the south in the states of [[Arkansas]], [[Oklahoma]] and [[Texas]]. Another related uplift is the [[Llano Uplift]] in [[Texas]], a geographical ___location named after its uplift features.

The [[Ozarks|Ozark Plateau]] is a broad uplifted area which resulted from the [[Permian]] [[Ouachita Mountains|Ouachita Orogeny]] to the south in the states of [[Arkansas]], [[Oklahoma]], and [[Texas]]. Another related uplift is the [[Llano Uplift]] in Texas, a geographical ___location named after its uplift features. The [[Colorado Plateau]] which includes the [[Grand Canyon]] is also the result of broad tectonic uplift followed by river [[Erosion and tectonics|erosion]].<ref>Karlstrom, K.E., et al., 2012, ''Mantle-driven dynamic uplift of the Rocky Mountains and Colorado Plateau and its surface response: Toward a unified hypothesis,'' Lithosphere, v. 4, p. 3–22 [http://lithosphere.gsapubs.org/content/4/1/3.abstract abstract]</ref>

When mountains rise slowly, either due to orogenic uplift or other processes (e.g., [[Post-glacial rebound|rebound after glaciation]]), an unusual feature known as a [[water gap]] may occur. In these, erosion from a watercourse such as a riverstream occurs faster than mountain uplift, resulting in a [[Canyon|gorge]] or [[valley]] that runs through a mountain range from low-lying country on one side to similar country on the other. Examples of such water gaps include the [[ManawatuManawatū Gorge]] in New Zealand and the [[Cumberland Narrows]] in [[Maryland, United States]].

==Isostatic uplift==

The removal of mass from a region will be [[Isostasy|isostatically compensated]] by crustal rebound. If we take into consideration typical crustal and mantle densities, erosion of an average 100 meters of rock across a broad, uniform surface will cause the crust to isostatically rebound about 85 meters and will cause only a 15-meter loss of mean surface elevation.<ref>Burbank, Douglas W., and Anderson, Robert S. Tectonic Geomorphology. Chichester, West Sussex: J. Wiley & Sons, 2011. Print.</ref> An example of isostatic uplift wouldis be [[post-glacial rebound]] following the melting of [[continental glacier]]s and [[ice sheet]]s. The [[Hudson Bay]] region of [[Canada]], the [[Great Lakes]] of Canada and the [[United States]], and [[Fennoscandia]] are currently undergoing gradual rebound as a result of the melting of ice sheets 10,000 years ago.

Crustal thickening, which for example is currently occurring in the [[Himalaya]]Himalayas due to the continental collision between the [[Indian Plate|Indian]] and the [[Eurasian Plate|Eurasian]] plates, can also lead to surface uplift; but due to the isostatic sinking of thickened crust, the magnitude of surface uplift will only be about one-sixth of the amount of crustal thickening. Therefore, in most [[Convergent plate boundary|convergent settingsboundaries]], isostatic uplift plays a relatively small role, and high peak formation can be more attributed to tectonic processes.<ref>Gilchrist, A. R., M. A. Summerfield, and H. A. P. Cockburn. "Landscape Dissection, Isostatic Uplift, and the Morphologic Development of Orogens." Geology 22.11 (1994): 963-966. Print.</ref> Direct measures of the elevation change of the land surface can only be used to estimate erosion or bedrock uplift rates when other controls (such as changes in mean surface elevation, volume of eroded material, timescales and lags of isostatic response, variations in crustal density) are known.

==Coral islands==

In a few cases, tectonic uplift can be seen in the cases of [[coral island]]s. This is evidenced by the presence of various oceanic islands composed entirely of [[coral]], which otherwise appear to be [[highvolcanic island]]s (''i.e.'', islands of [[volcanic]] origin). Examples of such islands are found in the [[Pacific Islands|Pacific]], notably the three [[phosphate]] [[islet]]s, of [[Nauru]], [[Makatea]], and [[Banaba Island|Banaba]], as well as [[Maré Island|Maré]] and [[Lifou]] in [[New- Caledonia]],; [[Fatu Huku]] in the [[Marquesas Islands]]; and [[Henderson Island (Pitcairn Islands)|Henderson Island]] in the [[Pitcairn Islands]]. The uplift of these islands is the result of the movement of oceanic tectonic plates. Sunken islands or [[guyot]]s with their coral reefs are the result of crustal subsidence as the oceanic plate carries the islands to deeper or lower oceanic crust areas.

==Uplift vs. exhumation==

The word "uplift" refers to displacement contrary to the direction of the gravity vector, and displacement is only defined when the object being displaced and the frame of reference is specified. Molnar and England,<ref name=E&M/> identify three kinds of displacement to which the term “uplift”"uplift" is applied:

# Displacement of the Earth's surface with respect to the [[geoid]]. This is what we refer to as "surface uplift"; and surface uplift can be defined by averaging elevation and changes in elevation over surface areas of a specified size.

# The "uplift of rocks" refers to the displacement of rocks with respect to the geoid.

# The displacement of rocks with respect to the surface is called [[Exhumation (geology)|exhumation]].

This simple equation relates the three kinds of displacement:

::''Surface uplift = uplift of rock -– exhumation''

The term geoid is used above to mean ''[[Sea level|mean sea level]]'', and makes a good frame of reference. A given displacement within this frame of reference allows one to quantify the amount of work being done against gravity.

Measuring uplift and exhumation can be tricky. Measuring the uplift of a point requires measuring its elevation change – usually geoscientists are not trying to determine the uplift of a singular point, but rather the uplift over a specified area. Accordingly, the change in elevation of all points on the surface of that area must be measured, and the rate of erosion must be zero or minimal. Also, sequences of rocks deposited during that uplift must be preserved. Needless to say, in mountain ranges where elevations are far above sea level these criteria are not always easily met. [[Paleoclimatology|Paleoclimatic restorations]] though can be very valuable; these studies involve inferring changes in climate in an area of interest from changes with time of flora/fauna that is known to be sensitive to temperature and rainfall.<ref>Burbank, Douglas West., and Robert S. Anderson. Tectonic Geomorphology. Malden, MA: Blackwell Science, 2000. {{ISBN|978-0632043866}}</ref> The magnitude of the exhumation a rock has been subjected to may be inferred from [[Geothermobarometry|geobarometrygeothermobarometry]] (measuring previous pressure and temperature history of a rock or assemblage). Knowing the pressure and temperature history of a region can yield an estimate of the ambient [[geothermal gradient]] and bounds on the exhumation process; however, geobarometric/geothermometric studies do not produce a rate of exhumation (or any other information on time). OneExhumation rates can inferbe exhumation ratesinferred from [[Fission track dating|fission tracks]] and from [[Radiometric dating|radiometric ages]] as long as onea hasthermal anprofile estimatedcan thermalbe profileestimated.

==Gallery==

<gallery>

File:Cliffs of Moher (1542448559).jpg|[[Cliffs of Moher]]

File:Blue Mountains National Park Uplift.jpg|Tectonic uplifting in the [[Blue Mountains National Park]]

File:Tasmania Tasman National Park 5.jpg|Cliffs of the [[Tasman National Park]]

File:Horseshoe Bend 13 February 2023.jpg|[[Incised meander]] caused by downcutting of [[Colorado River]] during uplift of [[Colorado Plateau]]

File:2018 07 12 Schottland (171) Duncansby Stacks.jpg|[[Duncansby Stacks]]

File:Aerial view of 12 Apostles, Victoria, Australia (Ank Kumar) 03.jpg|[[The Twelve Apostles]]

File:Paracas National Reserve. Ica, Peru.jpg|Coast and cliffs of [[Paracas National Reserve]]

</gallery>

==References==

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[[Category:Geomorphology]]