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54-522: This orogeny article is a stub . You can help Misplaced Pages by expanding it . This article related to the Triassic period is a stub . You can help Misplaced Pages by expanding it . This article related to the Jurassic period is a stub . You can help Misplaced Pages by expanding it . Orogeny Orogeny ( / ɒ ˈ r ɒ dʒ ə n i / ) is a mountain - building process that takes place at

108-442: 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

162-410: A deep-sea trench , and a large negative Bouguer anomaly on the convex side of the volcanic arc. The small positive gravity anomaly associated with volcanic arcs has been interpreted by many authors as due to the presence of dense volcanic rocks beneath the arc. Inactive arcs are a chain of islands which contains older volcanic and volcaniclastic rocks . The curved shape of many volcanic chains and

216-732: A collisional orogeny). 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 . 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

270-477: A crust which is either oceanic or intermediate between the normal oceanic crust and that typical of continents; heat flow in the basins is higher than in normal continental or oceanic areas. Some arcs, such as the Aleutians, pass laterally into the continental shelf on the concave side of the arc, while most of the arcs are separated from the continental crust. Movement between two lithospheric plates explains

324-506: A delamination of the orogenic root beneath them. 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

378-589: 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. 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. The collisional orogeny may produce extremely high mountains, as has been taking place in

432-412: A noncollisional orogenic belt, and such belts are sometimes called Andean-type orogens . 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

486-442: 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 . Before

540-404: Is a plane that dips under the overriding plate where intense volcanic activity occurs, which is defined by the location of seismic events below the arc. Earthquakes occur from near surface to ~660 km depth. The dip of Benioff zones ranges from 30° to near vertical. An ocean basin may be formed between the continental margin and the island arcs on the concave side of the arc. These basins have

594-446: 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. Mountain formation in orogens is largely a result of crustal thickening. The compressive forces produced by plate convergence result in pervasive deformation of

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648-412: Is now believed that water acts as the primary agent that drives partial melting beneath arcs. It has been shown that the amount of water present in the down-going slab is related to the melting temperature of the mantle. The greater the amount of water present, the more the melting temperature of the mantle is reduced. This water is released during the transformation of minerals as pressure increases, with

702-404: Is related to the age of the subduction zone and the depth. The tholeiitic magma series is well represented above young subduction zones formed by magma from relative shallow depth. The calc-alkaline and alkaline series are seen in mature subduction zones, and are related to magma of greater depths. Andesite and basaltic andesite are the most abundant volcanic rock in island arc which is indicative of

756-422: Is still in use today, though commonly investigated by geochronology using radiometric dating. Based on available observations from the metamorphic differences in orogenic belts of Europe and North America, H. J. Zwart (1967) 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 in terms of

810-480: Is taking place today in the Southern Alps of New Zealand). Orogens have a characteristic structure, though this shows considerable variation. 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

864-453: 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

918-640: The Himalayas for the last 65 million years. 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

972-691: 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) can create local topographic highs. Eventually, seafloor spreading in

1026-647: 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. Orogens show a great range of characteristics, but they may be broadly divided into collisional orogens and noncollisional orogens (Andean-type orogens). Collisional orogens can be further divided by whether

1080-497: 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

1134-414: 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. 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

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1188-454: The angle of the descending lithosphere are related. If the oceanic part of the plate is represented by the ocean floor on the convex side of the arc, and if the zone of flexing occurs beneath the submarine trench , then the deflected part of the plate coincides approximately with the Benioff zone beneath most arcs. Most modern island arcs are near the continental margins (particularly in

1242-499: The calc-alkaline magmas. Some Island arcs have distributed volcanic series as can be seen in the Japanese island arc system where the volcanic rocks change from tholeiite—calc-alkaline—alkaline with increasing distance from the trench. Several processes are involved in arc magmatism which gives rise to the great spectrum of rock composition encountered. These processes are, but not limited to, magma mixing, fractionation, variations in

1296-635: 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. 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

1350-596: The course of 200 million years in the Paleoproterozoic . 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. A similar sequence of orogenies has taken place on the west coast of North America, beginning in

1404-401: The crust is neither being consumed nor generated. Thus the present location of these inactive island chains is due to the present pattern of lithospheric plates. However, their volcanic history, which indicates that they are fragments of older island arcs, is not necessarily related to the present plate pattern and may be due to differences in position of plate margins in the past. Understanding

1458-427: The crust of the continental margin ( thrust tectonics ). This takes the form of folding of the ductile deeper crust and thrust faulting in the upper brittle crust. Crustal thickening raises mountains through the principle of isostasy . 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

1512-564: The deepest features of ocean basins; the deepest being the Mariana trench (approximately 11,000 m or 36,000 ft). They are formed by flexing of the oceanic lithosphere, developing on the ocean side of island arcs. Back-arc basin : They are also referred to as marginal seas and are formed in the inner, concave side of island arcs bounded by back-arc ridges. They develop in response to tensional tectonics due to rifting of an existing island arc. Benioff zone or Wadati-Benioff zone : This

1566-575: The dense underlying mantle . 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. An example is the Sierra Nevada in California. This range of fault-block mountains experienced renewed uplift and abundant magmatism after

1620-422: The descent of the lithosphere into the mantle along the subduction zone. They are the principal way by which continental growth is achieved. Island arcs can either be active or inactive based on their seismicity and presence of volcanoes. Active arcs are ridges of recent volcanoes with an associated deep seismic zone. They also possess a distinct curved form, a chain of active or recently extinct volcanoes,

1674-754: 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 . 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

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1728-520: The edge of the uplifted layers are exposed. Although mountain building mostly takes place in orogens, a number of secondary mechanisms are capable of producing substantial mountain ranges. 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

1782-409: 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

1836-471: The major features of active island arcs. The island arc and small ocean basin are situated on the overlying plate which meets the descending plate containing normal oceanic crust along the Benioff zone. The sharp bending of the oceanic plate downward produces a trench. There are generally three volcanic series from which the types of volcanic rock that occur in island arcs are formed: This volcanic series

1890-471: The mantle wedge. If hot material rises quickly enough so that little heat is lost, the reduction in pressure may cause pressure release or decompression partial melting . On the subducting side of the island arc is a deep and narrow oceanic trench, which is the trace at the Earth's surface of the boundary between the down-going and overriding plates. This trench is created by the downward gravitational pull of

1944-533: The margins of continents. Below are some of the generalized features present in most island arcs. Fore-arc : This region comprises the trench, the accretionary prism, and the fore-arc basin. A bump from the trench in the oceanward side of the system is present (Barbados in the Lesser Antilles is an example). The fore-arc basin forms between the fore-arc ridge and the island arc; it is a region of undisturbed flat-bedded sedimentation. Trenches : These are

1998-446: The mineral carrying the most water being serpentinite . These metamorphic mineral reactions cause the dehydration of the upper part of the slab as the hydrated slab sinks. Heat is also transferred to it from the surrounding asthenosphere. As heat is transferred to the slab, temperature gradients are established such that the asthenosphere in the vicinity of the slab becomes cooler and more viscous than surrounding areas, particularly near

2052-543: 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. While active orogens are found on the margins of present-day continents, older inactive orogenies, such as the Algoman , Penokean and Antler , are represented by deformed and metamorphosed rocks with sedimentary basins further inland. Long before

2106-494: The northern and western margins of the Pacific Ocean). However, no direct evidence from within the arcs shows that they have always existed at their present position with respect to the continents, although evidence from some continental margins suggests that some arcs may have migrated toward the continents during the late Mesozoic or early Cenozoic . They are also found at oceanic-oceanic convergence zones, in which case

2160-416: The ocean basin comes to a halt, and continued subduction begins to close the ocean basin. The closure of the ocean basin ends with a continental collision and the associated Himalayan-type orogen. 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

2214-622: The older plate will subduct under the younger one. The movement of the island arcs towards the continent could be possible if, at some point, the ancient Benioff zones dipped toward the present ocean rather than toward the continent, as in most arcs today. This will have resulted in the loss of ocean floor between the arc and the continent, and consequently, in the migration of the arc during spreading episodes. The fracture zones in which some active island arcs terminate may be interpreted in terms of plate tectonics as resulting from movement along transform faults , which are plate margins where

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2268-462: 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 ). A synorogenic (or synkinematic ) process or event is one that occurs during an orogeny. The word orogeny comes from Ancient Greek ὄρος ( óros )  'mountain' and γένεσις ( génesis )  'creation, origin'. Although it

2322-416: 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. 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

2376-688: The relationship to granite occurrences. Cawood et al. (2009) 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. Island arc Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from

2430-458: The relatively dense subducting plate on the leading edge of the plate. Multiple earthquakes occur along this subduction boundary with the seismic hypocenters located at increasing depth under the island arc: these quakes define the Benioff zone . Island arcs can be formed in intra-oceanic settings, or from the fragments of continental crust that have migrated away from an adjacent continental land mass or at subduction-related volcanoes active at

2484-441: 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. 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 . At some point, subduction

2538-491: The sea-floor. 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. 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

2592-429: The source of heat that causes the melting of the mantle was a contentious problem. Researchers believed that the heat was produced through friction at the top of the slab. However, this is unlikely because the viscosity of the asthenosphere decreases with increasing temperature, and at the temperatures required for partial fusion, the asthenosphere would have such a low viscosity that shear melting could not occur. It

2646-414: The squeezing of certain rocks. Eduard Suess (1875) recognised the importance of horizontal movement of rocks. The concept of a precursor geosyncline or initial downward warping of the solid earth (Hall, 1859) prompted James Dwight Dana (1873) to include the concept of compression in the theories surrounding mountain-building. With hindsight, we can discount Dana's conjecture that this contraction

2700-423: 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, 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

2754-460: The surface. The erosional process is called unroofing . 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,

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2808-420: The upper part of the slab. This more viscous asthenosphere is then dragged down with the slab causing less viscous mantle to flow in behind it. It is the interaction of this down-welling mantle with aqueous fluids rising from the sinking slab that is thought to produce partial melting of the mantle as it crosses its wet solidus . In addition, some melts may result from the up-welling of hot mantle material within

2862-399: 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 . Gustav Steinmann (1906) recognised different classes of orogenic belts, including

2916-499: Was used before him, the American geologist G. K. Gilbert used the term in 1890 to mean the process of mountain-building, as distinguished from epeirogeny . Orogeny 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

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