Orogeny

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Geologic uplift
)

Geologic provinces of the world (USGS)

Orogeny (/ɒˈrɒdʒəni/) is a mountain-building process that takes place at a convergent plate margin when plate motion compresses the margin. An orogenic belt or orogen develops as the compressed plate crumples and is uplifted to form one or more mountain ranges. This involves a series of geological processes collectively called orogenesis. These include both structural deformation of existing continental crust and the creation of new continental crust through volcanism. Magma rising in the orogen carries less dense material upwards while leaving more dense material behind, resulting in compositional differentiation of Earth's lithosphere (crust and uppermost mantle).[1][2] A synorogenic (or synkinematic) process or event is one that occurs during an orogeny.[3]

The word orogeny comes from

Ancient Greek ὄρος (óros) 'mountain', and γένεσις (génesis) 'creation, origin').[4] Although it was used before him, the term was employed by the American geologist G. K. Gilbert in 1890 to describe the process of mountain-building as distinguished from epeirogeny.[5]

Tectonics

See also: Subduction, Plate tectonics, and Continental collision
oceanic plate beneath a continental plate to form an accretionary orogen (example: the Andes
)
eclogite facies metamorphism, and then exhumed along the same subduction channel. (example: the Himalayas
)

Orogeny takes place on the

oceanic plate to form a noncollisional orogeny) or continental collision (convergence of two or more continents to form a collisional orogeny).[6][7]

Orogeny typically produces orogenic belts or orogens, which are elongated regions of deformation bordering continental

intrusive igneous rock called batholiths.[8]

Subduction zones consume oceanic

Andes Mountains are an example of a noncollisional orogenic belt, and such belts are sometimes called Andean-type orogens.[10]

As subduction continues,

Lachlan Orogen of southeast Australia are examples of accretionary orogens.[11]

The orogeny may culminate with continental crust from the opposite side of the subducting oceanic plate arriving at the subduction zone. This ends subduction and transforms the accretional orogen into a Himalayan-type collisional orogen.[12] The collisional orogeny may produce extremely high mountains, as has been taking place in the Himalayas for the last 65 million years.[13]

The processes of orogeny can take tens of millions of years and build mountains from what were once

late Devonian (about 380 million years ago) with the Antler orogeny and continuing with the Sonoma orogeny and Sevier orogeny and culminating with the Laramide orogeny. The Laramide orogeny alone lasted 40 million years, from 75 million to 35 million years ago.[16]

Orogens

Main article: Orogenic belt
The Foreland Basin System

Orogens show a great range of characteristics,[17][18] but they may be broadly divided into collisional orogens and noncollisional orogens (Andean-type orogens). Collisional orogens can be further divided by whether the collision is with a second continent or a continental fragment or island arc. Repeated collisions of the later type, with no evidence of collision with a major continent or closure of an ocean basin, result in an accretionary orogen. Examples of orogens arising from collision of an island arc with a continent include Taiwan and the collision of Australia with the Banda arc.[19] Orogens arising from continent-continent collisions can be divided into those involving ocean closure (Himalayan-type orogens) and those involving glancing collisions with no ocean basin closure (as is taking place today in the Southern Alps of New Zealand).[7]

Orogens have a characteristic structure, though this shows considerable variation.[7] A foreland basin forms ahead of the orogen due mainly to loading and resulting flexure of the lithosphere by the developing mountain belt. A typical foreland basin is subdivided into a wedge-top basin above the active orogenic wedge, the foredeep immediately beyond the active front, a forebulge high of flexural origin and a back-bulge area beyond, although not all of these are present in all foreland-basin systems.[20] The basin migrates with the orogenic front and early deposited foreland basin sediments become progressively involved in folding and thrusting. Sediments deposited in the foreland basin are mainly derived from the erosion of the actively uplifting rocks of the mountain range, although some sediments derive from the foreland. The fill of many such basins shows a change in time from deepwater marine (flysch-style) through shallow water to continental (molasse-style) sediments.[21]

While active orogens are found on the margins of present-day continents, older inactive orogenies, such as the

Antler, are represented by deformed and metamorphosed rocks with sedimentary basins further inland.[24]

Orogenic cycle

See also: Wilson Cycle

Long before the acceptance of

Tuzo Wilson first put forward a plate tectonic interpretation of orogenic cycles, now known as Wilson cycles. Wilson proposed that orogenic cycles represented the periodic opening and closing of an ocean basin, with each stage of the process leaving its characteristic record on the rocks of the orogen.[25]

Continental rifting

Main article:
Continental rifting

The Wilson cycle begins when previously stable continental crust comes under tension from a shift in

Continental rifting takes place, which thins the crust and creates basins in which sediments accumulate. As the basins deepen, the ocean invades the rift zone, and as the continental crust rifts completely apart, shallow marine sedimentation gives way to deep marine sedimentation on the thinned marginal crust of the two continents.[26][25]

Seafloor spreading

Main article: Seafloor spreading

As the two continents rift apart, seafloor spreading commences along the axis of a new ocean basin. Deep marine sediments continue to accumulate along the thinned continental margins, which are now passive margins.[26][25]

Subduction

Main article: Subduction

At some point, subduction is initiated along one or both of the continental margins of the ocean basin, producing a volcanic arc and possibly an Andean-type orogen along that continental margin. This produces deformation of the continental margins and possibly crustal thickening and mountain building.[26][25]

Mountain building

Madison Limestone
is repeated, with one example in the foreground (that pinches out with distance) and another to the upper right corner and top of the picture.
Sierra Nevada Mountains (a result of delamination) as seen from the International Space Station

Mountain formation in orogens is largely a result of crustal thickening. The compressive forces produced by plate convergence result in pervasive deformation of the crust of the continental margin (thrust tectonics).[27] This takes the form of folding of the ductile deeper crust and thrust faulting in the upper brittle crust.[28]

Crustal thickening raises mountains through the principle of isostasy.[29] Isostacy is the balance of the downward gravitational force upon an upthrust mountain range (composed of light, continental crust material) and the buoyant upward forces exerted by the dense underlying mantle.[30]

Portions of orogens can also experience uplift as a result of

fault-block mountains[32] experienced renewed uplift and abundant magmatism after a delamination of the orogenic root beneath them.[31][33]

Mount Rundle, Banff, Alberta

Mount Rundle on the Trans-Canada Highway between Banff and Canmore provides a classic example of a mountain cut in dipping-layered rocks. Millions of years ago a collision caused an orogeny, forcing horizontal layers of an ancient ocean crust to be thrust up at an angle of 50–60°. That left Rundle with one sweeping, tree-lined smooth face, and one sharp, steep face where the edge of the uplifted layers are exposed.[34]

Although mountain building mostly takes place in orogens, a number of secondary mechanisms are capable of producing substantial mountain ranges.

strike-slip orogens, such as the San Andreas Fault, restraining bends result in regions of localized crustal shortening and mountain building without a plate-margin-wide orogeny. Hotspot volcanism results in the formation of isolated mountains and mountain chains that look as if they are not necessarily on present tectonic-plate boundaries, but they are essentially the product of plate tectonism. Likewise, uplift and erosion related to epeirogenesis (large-scale vertical motions of portions of continents without much associated folding, metamorphism, or deformation)[38]
can create local topographic highs.

Closure of the ocean basin

Eventually, seafloor spreading in the ocean basin comes to a halt, and continued subduction begins to close the ocean basin.[26][25]

Continental collision and orogeny

Main article: Continental collision

The closure of the ocean basin ends with a continental collision and the associated Himalayan-type orogen.

Erosion

metamorphic rocks brought to the surface from a depth of several kilometres). Isostatic movements may help such unroofing by balancing out the buoyancy of the evolving orogen. Scholars debate about the extent to which erosion modifies the patterns of tectonic deformation (see erosion and tectonics
). Thus, the final form of the majority of old orogenic belts is a long arcuate strip of crystalline metamorphic rocks sequentially below younger sediments which are thrust atop them and which dip away from the orogenic core.

An orogen may be almost completely eroded away, and only recognizable by studying (old) rocks that bear traces of orogenesis. Orogens are usually long, thin, arcuate tracts of rock that have a pronounced linear structure resulting in

tectonic plates) from the core of the shortening orogen out toward the margins, and are intimately associated with folds and the development of metamorphism.[40]

History of the concept

Before the development of geologic concepts during the 19th century, the presence of marine

Neoplatonic thought, which influenced early Christian writers.[41]

The 13th-century

Elie de Beaumont (1852) used the evocative "Jaws of a Vise" theory to explain orogeny, but was more concerned with the height rather than the implicit structures created by and contained in orogenic belts. His theory essentially held that mountains were created by the squeezing of certain rocks.[44] Eduard Suess (1875) recognised the importance of horizontal movement of rocks.[45] The concept of a precursor geosyncline or initial downward warping of the solid earth (Hall, 1859)[46] prompted James Dwight Dana (1873) to include the concept of compression in the theories surrounding mountain-building.[47] With hindsight, we can discount Dana's conjecture that this contraction was due to the cooling of the Earth (aka the cooling Earth theory). The cooling Earth theory was the chief paradigm for most geologists until the 1960s. It was, in the context of orogeny, fiercely contested by proponents of vertical movements in the crust, or convection within the asthenosphere or mantle.[48]

tholeiitic basalts, and a nappe
style fold structure.

In terms of recognising orogeny as an event,

Leopold von Buch (1855) recognised that orogenies could be placed in time by bracketing between the youngest deformed rock and the oldest undeformed rock, a principle which is still in use today, though commonly investigated by geochronology using radiometric dating.[49]

Based on available observations from the metamorphic differences in orogenic belts of Europe and North America, H. J. Zwart (1967)[50] proposed three types of orogens in relationship to tectonic setting and style: Cordillerotype, Alpinotype, and Hercynotype. His proposal was revised by W. S. Pitcher in 1979[51] in terms of the relationship to granite occurrences. Cawood et al. (2009)[52] categorized orogenic belts into three types: accretionary, collisional, and intracratonic. Both accretionary and collisional orogens developed in converging plate margins. In contrast, Hercynotype orogens generally show similar features to intracratonic, intracontinental, extensional, and ultrahot orogens, all of which developed in continental detachment systems at converged plate margins.

  1. Accretionary orogens, which were produced by subduction of one oceanic plate beneath one continental plate for arc volcanism. They are dominated by calc-alkaline igneous rocks and high-T/low-P metamorphic facies series at high thermal gradients of >30 °C/km. There is a general lack of ophiolites, migmatites and abyssal sediments. Typical examples are all circum-Pacific orogens containing continental arcs.
  2. Collisional orogens, which were produced by subduction of one continental block beneath the other continental block with the absence of arc volcanism. They are typified by the occurrence of blueschist to eclogite facies metamorphic zones, indicating high-P/low-T metamorphism at low thermal gradients of <10 °C/km. Orogenic peridotites are present but volumetrically minor, and syn-collisional granites and migmatites are also rare or of only minor extent. Typical examples are the Alps-Himalaya orogens in the southern margin of Eurasian continent and the Dabie-Sulu orogens in east-central China.

See also

  • Biogeography – Study of the distribution of species and ecosystems in geographic space and through geological time
  • Epeirogenic movement – Upheavals or depressions of land exhibiting long wavelengths and little folding
  • Fault mechanics – Field of study that investigates the behavior of geologic faults
  • Fold mountains – Mountains formed by compressive crumpling of the layers of rock
  • Guyot – Isolated, flat-topped underwater volcano mountain
  • List of orogenies – Known mountain building events of the Earth's history
  • Mantle convection – Gradual movement of the planet's mantle
  • Tectonic uplift – Geologic uplift of Earth's surface that is attributed to plate tectonics

References

  1. ISBN 978-0-415-46959-3
    .
  2. ISBN 978-1-4051-0777-8
    .
  3. ISBN 9780199653065
    .
  4. ISBN 978-0550106254
    .
  5. ISBN 9780813722887
    .
  6. ISBN 978-0-7167-9617-6
    .
  7. ^ a b c Kearey, Klepeis & Vine 2009, p. 287.
  8. ^
    ISBN 978-0470387740
    .
  9. ^ Kearey, Klepeis & Vine 2009, p. 289.
  10. ^ Kearey, Klepeis & Vine 2009, pp. 287–288, 297–299.
  11. ^ Kearey, Klepeis & Vine 2009, p. 288.
  12. doi:10.1016/S1872-5791(08)60095-0
    .
  13. doi:10.1029/2004TC001729
    .
  14. ISBN 0813752183
    .
  15. doi:10.1130/GES00055.1
    .
  16. doi:10.1029/98TC02698
    .
  17. S2CID 140546624
    .
  18. S2CID 67843559
    .
  19. ^ Kearey, Klepeis & Vine 2009, pp. 330–332.
  20. ^ Kearey, Klepeis & Vine 2009, pp. 302–303.
  21. doi:10.1046/j.1365-2117.1996.01491.x. Archived from the original
    (PDF) on 2 April 2015. Retrieved 30 March 2015.
  22. ^ Bray, Edmund C (1977). Billions of Years in Minnesota, The Geological Story of the State. Library of Congress Card Number: 77:80265.
  23. doi:10.1016/j.precamres.2007.02.022
    . Retrieved 6 March 2016.
  24. ^ Poole, F.G. (1974). "Flysch deposits of the foreland basin, western United States" (PDF). In Dickinson, W.R. (ed.). Tectonics and Sedimentation. Society of Economic Paleontologists and Mineralogists. pp. 58–82. Special Publication 22.
  25. ^
    ISBN 978-0-7167-2252-6
    .
  26. ^ a b c d Kearey, Klepeis & Vine 2009, pp. 208–209.
  27. S2CID 234818905
    .
  28. ISBN 978-94-010-6858-1
    .
  29. ISBN 978-0-632-03507-6
    .
  30. ISBN 978-0-521-44669-3
    .
  31. ^
    PMID 10988067. Archived from the original
    (PDF) on 15 June 2011.
  32. ISBN 978-0-262-07128-4
    .
  33. doi:10.1130/0091-7613(2000)28<811:TOVITS>2.0.CO;2
    .
  34. ^ "The Formation of the Rocky Mountains". Mountains in Nature. n.d. Archived from the original on 23 July 2014. Retrieved 29 January 2014.
  35. ISBN 978-0-415-39084-2
    .
  36. ISBN 978-3-540-66193-1
    . Without denudation, even relatively low uplift rates as characteristic of epeirogenetic movements (e.g. 20m/MA) would generate highly elevated regions in geological time periods.
  37. ISBN 978-0-415-27750-1
    .
  38. ISBN 978-0-7487-4381-0
    .
  39. hdl:11336/68522
    .
  40. ISBN 978-0-7923-4879-5
    .
  41. ISBN 9780813712031
    . Retrieved 17 April 2022.
  42. ISBN 9780813516660
    . Retrieved 17 April 2022.
  43. S2CID 244188689
    .
  44. ISBN 978-0-87933-394-2
    .
  45. ^ Suess, Eduard (1875). Die Entstehung Der Alpen [The Origin of the Alps]. Vienna: Braumüller.
  46. ^ Hall, J (1859). "Palaeontology of New York". New York National Survey. 3 (1).
  47. S2CID 131423196
    .
  48. ISBN 0-471-103764
    .
  49. ^ Buch, L. Von (1902). Gesammelte Schriften (in German). Berlin: Roth & Eck.
  50. ^ Zwart, HJ (1967). "The duality of orogenic belts". Geol. Mijnbouw. 46: 283–309.
  51. S2CID 128935736
    .
  52. ^ Cawood, PA; Kroner, A; Collins, WJ; Kusky, TM; Mooney, WD; Windley, BF (2009). Accretionary orogens through Earth history. Geological Society. pp. 1–36. Special Publication 318.

Further reading

External links

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