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{{Short description|The formation of mountain ranges}}{{Use dmy dates|date=March 2021}}{{World geologic provinces}}Orogeny ({{IPAc-en|ɒ|ˈ|r|ɒ|dʒ|ə|n|i}}) is a mountain-building process that takes place at a convergent plate margin when plate motion compresses the margin. An {{em|orogenic belt}} or {{em|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).BOOK, Foundations of Engineering Geology, Tony, Waltham, 20,weblink 978-0-415-46959-3, Taylor & Francis, 2009, 3rd, BOOK, Global Tectonics, Philip, Kearey, Keith A., Klepeis, Frederick J., Vine,weblink 287, Chapter 10: Orogenic belts, 978-1-4051-0777-8, 2009, Wiley-Blackwell, 3rd, A synorogenic (or synkinematic) process or event is one that occurs during an orogeny.BOOK, Allaby, Michael, A dictionary of geology and earth sciences, 2013, Oxford University Press, Oxford, 9780199653065, Fourth, synorogenic, The word orogeny comes {{etymology|grc|{{wiktgrc|ὄρος}} ({{grc-transl|ὄρος}})|mountain||{{wiktgrc|γένεσις}} ({{grc-transl|γένεσις}})|creation, origin}}).ENCYCLOPEDIA, orogeny, Chambers Dictionary, Chambers 21st Century Dictionary, Allied Publishers, 1999, 972, 978-0550106254,weblink 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.BOOK,weblink Pangean Orogenic and Epeirogenic Uplifts and Their Possible Climatic Significance, Pangea: Paleoclimate, Tectonics, and Sedimentation During Accretion, Zenith, and Breakup of a Supercontinent, Klein, G. O., Friedman, G. M., Geological Society of America Special Paper, 288, 1994, 160, 9780813722887, Geological Society of America,

Tectonics

{{See also|Subduction|Plate tectonics|Continental collision}}File:Active Margin.svg|thumb|upright=1.2|Subduction of an oceanic plate beneath a continental plate to form an accretionary orogen (example: the AndesAndesFile:Continental-continental convergence Fig21contcont.gif|thumb|upright=1.2|Continental collision of two continental plates to form a collisional orogen. Typically, continental crust is subducted to lithospheric depths for blueschist to eclogite facies metamorphism, and then exhumed along the same subduction channel. (example: the HimalayasHimalayasOrogeny takes place on the convergent margins of continents. The convergence may take the form of subduction (where a continent rides forcefully over an oceanic plate to form a noncollisional orogeny) or continental collision (convergence of two or more continents to form a collisional orogeny).BOOK, Understanding Earth, Frank Press,weblink 468–69, 978-0-7167-9617-6, 4th, 2003, Macmillan, {{sfn|Kearey|Klepeis|Vine|2009|page=287}}Orogeny typically produces orogenic belts or orogens, which are elongated regions of deformation bordering continental cratons (the stable interiors of continents). Young orogenic belts, in which subduction is still taking place, are characterized by frequent volcanic activity and earthquakes. Older orogenic belts are typically deeply eroded to expose displaced and deformed strata. These are often highly metamorphosed and include vast bodies of intrusive igneous rock called batholiths.BOOK, Levin, Harold L., The earth through time, 2010, J. Wiley, Hoboken, N.J., 978-0470387740, 83, 9th, Subduction zones consume oceanic crust, thicken lithosphere, and produce earthquakes and volcanoes. Not all subduction zones produce orogenic belts; mountain building takes place only when the subduction produces compression in the overriding plate. Whether subduction produces compression depends on such factors as the rate of plate convergence and the degree of coupling between the two plates,{{sfn|Kearey|Klepeis|Vine|2009|page=289}} while the degree of coupling may in turn rely on such factors as the angle of subduction and rate of sedimentation in the oceanic trench associated with the subduction zone. The Andes Mountains are an example of a noncollisional orogenic belt, and such belts are sometimes called Andean-type orogens.{{sfn|Kearey|Klepeis|Vine|2009|pages=287-288, 297-299}}As subduction continues, island arcs, continental fragments, and oceanic material may gradually accrete onto the continental margin. This is one of the main mechanisms by which continents have grown. An orogen built of crustal fragments (terranes) accreted over a long period of time, without any indication of a major continent-continent collision, is called an accretionary orogen. The North American Cordillera and the Lachlan Orogen of southeast Australia are examples of accretionary orogens.{{sfn|Kearey|Klepeis|Vine|2009|page=288}}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.JOURNAL, Accretionary Orogenesis in the Active Continental Margins, S., Yuan, G., Pan, L., Wang, X., Jiang, F., Yin, W., Zhang, J., Zhuo, Earth Science Frontiers, 2009, 16, 3, 31–48, 10.1016/S1872-5791(08)60095-0, 2009ESF....16...31Y, The collisional orogeny may produce extremely high mountains, as has been taking place in the Himalayas for the last 65 million years.JOURNAL, Ding, Lin, Kapp, Paul, Wan, Xiaoqiao, Paleocene-Eocene record of ophiolite obduction and initial India-Asia collision, south central Tibet, Tectonics, June 2005, 24, 3, n/a, 10.1029/2004TC001729, 2005Tecto..24.3001D, free, The processes of orogeny can take tens of millions of years and build mountains from what were once sedimentary basins. Activity along an orogenic belt can be extremely long-lived. For example, much of the basement underlying the United States belongs to the Transcontinental Proterozoic Provinces, which accreted to Laurentia (the ancient heart of North America) over the course of 200 million years in the Paleoproterozoic.JOURNAL, Anderson, J. Lawford, Bender, E. Erik, Anderson, Raymond R., Bauer, Paul W., Robertson, James M., Bowring, Samuel A., Condie, Kent C., Denison, Rodger E., Gilbert, M. Charles, Grambling, Jeffrey A., Mawer, Christopher K., Shearer, C. K., Hinze, William J., Karlstrom, Karl E., Kisvarsanyi, E. B., Lidiak, Edward G., Reed, John C., Sims, Paul K., Tweto, Odgen, Silver, Leon T., Treves, Samuel B., Williams, Michael L., Wooden, Joseph L., Marion E, Bickford, W. Randall Van, Schmus, Transcontinental Proterozoic provinces, Precambrian, 1993, 171–334, 10.1130/DNAG-GNA-C2.171, 0813752183, The Yavapai and Mazatzal orogenies were peaks of orogenic activity during this time. These were part of an extended period of orogenic activity that included the Picuris orogeny and culminated in the Grenville orogeny, lasting at least 600 million years.JOURNAL, Whitmeyer, Steven, Karlstrom, Karl E., Geosphere, 2007, 3, 4, 220, 10.1130/GES00055.1, Tectonic model for the Proterozoic growth of North America, free, A similar sequence of orogenies has taken place on the west coast of North America, beginning in the 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.JOURNAL, Bird, Peter, Kinematic history of the Laramide orogeny in latitudes 35°-49°N, western United States, Tectonics, October 1998, 17, 5, 780–801, 10.1029/98TC02698, 1998Tecto..17..780B, free,

Orogens

(File:ForelandBasinSystem.png|thumb|upright=1.75|right|The Foreland Basin System)Orogens show a great range of characteristics,JOURNAL, Simandjuntak, T. O., Barber, A. J., Contrasting tectonic styles in the Neogene orogenic belts of Indonesia, Geological Society, London, Special Publications, 1996, 106, 1, 185–201, 10.1144/GSL.SP.1996.106.01.12, 1996GSLSP.106..185S, 140546624, en, 0305-8719, JOURNAL, Garzanti, Eduardo, Doglioni, Carlo, Vezzoli, Giovanni, Andò, Sergio, Orogenic Belts and Orogenic Sediment Provenance, The Journal of Geology, May 2007, 115, 3, 315–334, 10.1086/512755, 2007JG....115..315G, 67843559, 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.{{sfn|Kearey|Klepeis|Vine|2009|pages=330-332}} 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).{{sfn|Kearey|Klepeis|Vine|2009|page=287}}Orogens have a characteristic structure, though this shows considerable variation.{{sfn|Kearey|Klepeis|Vine|2009|page=287}} 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.{{sfn|Kearey|Klepeis|Vine|2009|pages=302-303}} 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.JOURNAL,weblink Foreland basin systems, DeCelles P.G. & Giles K.A., Basin Research, 1996, 8, 2, 105–23, 10.1046/j.1365-2117.1996.01491.x, 1996BasR....8..105D, 30 March 2015,weblink" title="web.archive.org/web/20150402091232weblink">weblink 2 April 2015, dead, While active orogens are found on the margins of present-day continents, older inactive orogenies, such as the Algoman,BOOK, Billions of Years in Minnesota, The Geological Story of the State, Bray, Edmund C, 1977, Library of Congress Card Number: 77:80265, PenokeanJOURNAL

Orogenic cycle

{{see also|Wilson Cycle}}Long before the acceptance of plate tectonics, geologists had found evidence within many orogens of repeated cycles of deposition, deformation, crustal thickening and mountain building, and crustal thinning to form new depositional basins. These were named orogenic cycles, and various theories were proposed to explain them. Canadian geologist 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.BOOK, Robert J. Twiss, Eldridge M. Moores, Structural Geology,weblink 493, Plate tectonic models of orogenic core zones, 978-0-7167-2252-6, Macmillan, 2nd, 1992, registration,weblink

Continental rifting

The Wilson cycle begins when previously stable continental crust comes under tension from a shift in mantle convection. 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.{{sfn|Kearey|Klepeis|Vine|2009|pages=208-209}}

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.{{sfn|Kearey|Klepeis|Vine|2009|pages=208-209}}

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.{{sfn|Kearey|Klepeis|Vine|2009|pages=208-209}}

Mountain building

File:Sierra Nevada Mountains.JPG|thumb|250px|Sierra Nevada Mountains (a result of delamination) as seen from the International Space StationInternational Space StationMountain 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).JOURNAL, Faccenna, Claudio, Becker, Thorsten W., Holt, Adam F., Brun, Jean Pierre, Mountain building, mantle convection, and supercontinents: revisited, Earth and Planetary Science Letters, June 2021, 564, 116905, 10.1016/j.epsl.2021.116905, 234818905, free, This takes the form of folding of the ductile deeper crust and thrust faulting in the upper brittle crust.BOOK, Howell, David G., Tectonics of Suspect Terranes, Mountain building and the shaping of continents, 1989, 157–199, 10.1007/978-94-009-0827-7_6, 978-94-010-6858-1, Crustal thickening raises mountains through the principle of isostasy.BOOK, Earth Surface Processes, PA Allen,weblink 36 ff, Isostasy in zones of convergence, 978-0-632-03507-6, 1997, Wiley-Blackwell, 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.BOOK, Mechanics in the Earth and Environmental Sciences, §5.5 Isostasy, 170,weblink Gerard V. Middleton, Peter R. Wilcock, 978-0-521-44669-3, 1994, Cambridge University Press, 2nd, Portions of orogens can also experience uplift as a result of delamination of the orogenic lithosphere, in which an unstable portion of cold lithospheric root drips down into the asthenospheric mantle, decreasing the density of the lithosphere and causing buoyant uplift.JOURNAL, 10.1126/science.289.5486.1912, 10988067, Osmium Isotopic Evidence for Mesozoic Removal of Lithospheric Mantle Beneath the Sierra Nevada, California, SB, Jacobsen, JT, Chesley, RL, Rudnick, Q, 2000, Yin, Lee, C.-T., Science, 289, 5486, 1912–16,weblink 2000Sci...289.1912L, dead,weblink" title="web.archive.org/web/20110615170551weblink">weblink 15 June 2011, An example is the Sierra Nevada in California. This range of fault-block mountainsBOOK, Mountain Environments: An Examination of the Physical Geography of Mountains, John Gerrard, 9,weblink 978-0-262-07128-4, 1990, MIT Press, experienced renewed uplift and abundant magmatism after a delamination of the orogenic root beneath them.JOURNAL, 10.1130/0091-7613(2000)282.0.CO;2, 2000, 28, 811, Timing of Volcanism in the Sierra Nevada of California: Evidence for Pliocene Delamination of the Batholithic Root?, G. Lang, Farmer, Allen F., Glazner, Manley, Curtis R., Geology, 9, 2000Geo....28..811M, File:Mount Rundle, Banff, Canada (200544945).jpg|thumb|Mount Rundle, Banff, AlbertaBanff, AlbertaMount 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.WEB,weblink The Formation of the Rocky Mountains, Mountains in Nature, n.d., 29 January 2014, 23 July 2014,weblink" title="web.archive.org/web/20140723230042weblink">weblink dead, Although mountain building mostly takes place in orogens, a number of secondary mechanisms are capable of producing substantial mountain ranges.BOOK, Fundamentals of Geomorphology, Richard J. Huggett,weblink 104, 978-0-415-39084-2, 2007, Routledge, 2nd, BOOK, Sedimentary Basins: Evolution, Facies, and Sediment Budget,weblink 453, 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., Gerhard Einsele, 978-3-540-66193-1, 2000, 2nd, Springer, BOOK, Companion Encyclopedia of Geography: The Environment and Humankind,weblink 33, Ian Douglas, Richard John Huggett, Mike Robinson, 978-0-415-27750-1, 2002, Taylor & Francis, Areas that are rifting apart, such as mid-ocean ridges and the East African Rift, have mountains due to thermal buoyancy related to the hot mantle underneath them; this thermal buoyancy is known as dynamic topography. In 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)BOOK, Holmes Principles of Physical Geology, Arthur Holmes, Arthur Holmes, Doris L. Holmes, Doris L. Holmes,weblink 92, 978-0-7487-4381-0, 4th, Taylor & Francis, 2004, 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.{{sfn|Kearey|Klepeis|Vine|2009|pages=208-209}}

Continental collision and orogeny

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

Erosion

Erosion represents the final phase of the orogenic cycle. Erosion of overlying strata in orogenic belts, and isostatic adjustment to the removal of this overlying mass of rock, can bring deeply buried strata to the surface. The erosional process is called unroofing.JOURNAL, Sagripanti, Lucía, Bottesi, Germán, Kietzmann, Diego, Folguera, Andrés, Ramos, Víctor A., Mountain building processes at the orogenic front. A study of the unroofing in Neogene foreland sequence (37ºS), Andean Geology, May 2012, 39, 2, 201–219, 10.5027/andgeoV39n2-a01, free, 11336/68522, free, Erosion inevitably removes much of the mountains, exposing the core or mountain roots (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 terranes or blocks of deformed rocks, separated generally by suture zones or dipping thrust faults. These thrust faults carry relatively thin slices of rock (which are called nappes or thrust sheets, and differ from tectonic plates) from the core of the shortening orogen out toward the margins, and are intimately associated with folds and the development of metamorphism.BOOK, Emplacement Mechanisms of Nappes and Thrust Sheets, 9, Petrology and Structural Geology, Olivier Merle, §1.1 Nappes, overthrusts and fold-nappes, 1 ff,weblink 978-0-7923-4879-5, Springer, 1998,

History of the concept

Before the development of geologic concepts during the 19th century, the presence of marine fossils in mountains was explained in Christian contexts as a result of the Biblical Deluge. This was an extension of Neoplatonic thought, which influenced early Christian writers.JOURNAL, Vai, G.B., 2009, The scientific revolution and Nicholas Steno's twofold conversion, Geol Soc Am Mem, 203, 187–208, 9780813712031,weblink 17 April 2022, The 13th-century Dominican scholar Albert the Great posited that, as erosion was known to occur, there must be some process whereby new mountains and other land-forms were thrust up, or else there would eventually be no land; he suggested that marine fossils in mountainsides must once have been at the sea-floor.BOOK, Gohau, Gabriel, A history of geology, 1990, Rutgers University Press, New Brunwick, 9780813516660, 26–27,weblink 17 April 2022, Orogeny was used by Amanz Gressly (1840) and Jules Thurmann (1854) as orogenic in terms of the creation of mountain elevations, as the term mountain building was still used to describe the processes.JOURNAL, François, Camille, Pubellier, Manuel, Robert, Christian, Bulois, Cédric, Jamaludin, Siti Nur Fathiyah, Oberhänsli, Roland, Faure, Michel, St-Onge, Marc R., Temporal and spatial evolution of orogens: a guide for geological mapping, Episodes, 1 October 2021, 45, 3, 265–283, 10.18814/epiiugs/2021/021025, 244188689, free, 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.BOOK, Élie de Beaumont, JB, Jean-Baptiste Élie de Beaumont, 1852, Notice sur les Systèmes de Montagnes, Note on Mountain Systems, Bertrand, Paris, fr, English synopsis in BOOK, Dennis, John G., 1982, Orogeny, Benchmark Papers in Geology, 62, Hutchinson Ross Publishing Company, New York, 978-0-87933-394-2, Eduard Suess (1875) recognised the importance of horizontal movement of rocks.BOOK, Suess, Eduard, 1875, Die Entstehung Der Alpen,weblink The Origin of the Alps, Braumüller, Vienna, The concept of a precursor geosyncline or initial downward warping of the solid earth (Hall, 1859)JOURNAL, Hall, J, 1859, Palaeontology of New York, New York National Survey, 3, 1, prompted James Dwight Dana (1873) to include the concept of compression in the theories surrounding mountain-building.JOURNAL, Dana, James D., 1873, On Some Results of the Earth's Contraction From Cooling, Including a Discussion of the Origins of Mountains, and the Nature of the Earth's Interior, American Journal of Science, 5, 30, 423–43, 1873AmJS....5..423D, 10.2475/ajs.s3-5.30.423, 131423196,weblink 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.BOOK, Şengör, Celâl, Celâl Şengör, 1982, Classical theories of orogenesis, Miyashiro, Akiho, Akiho Miyashiro, Aki, Keiiti, Şengör, Celâl, Orogeny, John Wiley & Sons, 0-471-103764, Sengor1982, Gustav Steinmann (1906) recognised different classes of orogenic belts, including the Alpine type orogenic belt, typified by a flysch and molasse geometry to the sediments; ophiolite sequences, 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.BOOK, Buch, L. Von, 1902, Gesammelte Schriften, Roth & Eck, Berlin, de, Based on available observations from the metamorphic differences in orogenic belts of Europe and North America, H. J. Zwart (1967)JOURNAL, Zwart, HJ, 1967, The duality of orogenic belts, Geol. Mijnbouw, 46, 283–309, 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 1979JOURNAL, WS, Pitcher, The nature, ascent and emplacement of granitic magmas, Journal of the Geological Society, 1979, 136, 6, 627–62, 10.1144/gsjgs.136.6.0627, 1979JGSoc.136..627P, 128935736, in terms of the relationship to granite occurrences. Cawood et al. (2009)BOOK, Cawood, PA, Kroner, A, Collins, WJ, Kusky, TM, Mooney, WD, Windley, BF, 2009, Accretionary orogens through Earth history, Geological Society, Special Publication 318, 1–36, 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 Â°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