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50-701: The Capricorn orogeny was an orogenic event in what is now Western Australia , following the collision of the Pilbara Craton and the Glenburgh Terrane with the Yilgarn Craton during the Glenburgh orogeny . Spanning one billion years, the Capricorn orogeny is marked by widespread deformation and intracratonal reworking. The Leake Springs Metamorphics are a group of siliclastic metasedimentary rocks covering

100-732: 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

150-497: 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

200-582: 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

250-412: 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

300-442: 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

350-420: 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

400-410: Is continuously being created at mid-ocean ridges. As continental plates diverge at these ridges, magma rises into the upper mantle and crust. As the continental plates move away from the ridge, the newly formed rocks cool and start to erode with sediment gradually building up on top of them. The youngest oceanic rocks are at the oceanic ridges, and they get progressively older away from the ridges. As

450-449: Is in the west Pacific and north-west Atlantic  — both are about up to 180-200 million years old. However, parts of the eastern Mediterranean Sea could be remnants of the much older Tethys Ocean , at about 270 and up to 340 million years old. The oceanic crust displays a pattern of magnetic lines, parallel to the ocean ridges, frozen in the basalt . A symmetrical pattern of positive and negative magnetic lines emanates from

500-446: 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

550-399: Is primarily composed of mafic rocks, or sima , which is rich in iron and magnesium. It is thinner than continental crust , or sial , generally less than 10 kilometers thick; however, it is denser, having a mean density of about 3.0 grams per cubic centimeter as opposed to continental crust which has a density of about 2.7 grams per cubic centimeter. The crust uppermost is the result of

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600-422: 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

650-473: 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

700-449: 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

750-544: The Azores and Iceland . Prior to the Neoproterozoic Era 1000 Ma ago the world's oceanic crust was more mafic than present-days'. The more mafic nature of the crust meant that higher amounts of water molecules ( OH ) could be stored the altered parts of the crust. At subduction zones this mafic crust was prone to metamorphose into greenschist instead of blueschist at ordinary blueschist facies . Oceanic crust

800-613: 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

850-683: 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

900-634: 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

950-404: The lower oceanic crust . There, newly intruded magma can mix and react with pre-existing crystal mush and rocks. Although a complete section of oceanic crust has not yet been drilled, geologists have several pieces of evidence that help them understand the ocean floor. Estimations of composition are based on analyses of ophiolites (sections of oceanic crust that are thrust onto and preserved on

1000-497: 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

1050-414: 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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1100-631: 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

1150-504: The continents), comparisons of the seismic structure of the oceanic crust with laboratory determinations of seismic velocities in known rock types, and samples recovered from the ocean floor by submersibles , dredging (especially from ridge crests and fracture zones ) and drilling. Oceanic crust is significantly simpler than continental crust and generally can be divided in three layers. According to mineral physics experiments, at lower mantle pressures, oceanic crust becomes denser than

1200-602: The cooling of magma derived from mantle material below the plate. The magma is injected into the spreading center, which consists mainly of a partly solidified crystal mush derived from earlier injections, forming magma lenses that are the source of the sheeted dikes that feed the overlying pillow lavas. As the lavas cool they are, in most instances, modified chemically by seawater. These eruptions occur mostly at mid-ocean ridges, but also at scattered hotspots, and also in rare but powerful occurrences known as flood basalt eruptions. But most magma crystallises at depth, within

1250-578: 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

1300-539: 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 ). 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

1350-427: 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

1400-562: 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

1450-738: 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

1500-512: 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

1550-409: 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

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1600-406: The mantle rises it cools and melts, as the pressure decreases and it crosses the solidus . The amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness (7±1 km). Very slow spreading ridges (<1 cm·yr half-rate) produce thinner crust (4–5 km thick) as the mantle has a chance to cool on upwelling and so it crosses

1650-538: 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

1700-635: The northern two-thirds of the Gascoyne Province and grading into low-grade metasedimentary rocks of the Wyloo Group in the north. During the Capricorn orogeny, these rocks were intruded by the tonalite , monzogranite , quartz diorite and syenogranite of the Moorarie Supersuite (including the Minnie Creek batholith ). Throughout the orogeny, numerous phases of metamorphism took place, such as

1750-416: 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

1800-508: The oceanic crust can be used to estimate the (thermal) thickness of the lithosphere, where young oceanic crust has not had enough time to cool the mantle beneath it, while older oceanic crust has thicker mantle lithosphere beneath it. The oceanic lithosphere subducts at what are known as convergent boundaries . These boundaries can exist between oceanic lithosphere on one plate and oceanic lithosphere on another, or between oceanic lithosphere on one plate and continental lithosphere on another. In

1850-528: The orogeny resulted from the collision of the Yilgarn and Pilbara cratons. Later, the Geological Survey of Western Australia proposed that the event was mid-continent deformation due to distant, continent-edge collision events. This article about a specific Australian geological feature is a stub . You can help Misplaced Pages by expanding it . Orogeny Orogeny ( / ɒ ˈ r ɒ dʒ ə n i / )

1900-416: 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

1950-494: 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. Oceanic plate Oceanic crust

2000-648: The reworking of older Archean granite and gneiss in the Paradise Zone and Mooloo Zone between 1.805 and 1.80 billion years ago. During a second phase, the Yarlarwheelor Gneiss Complex and Errabiddy Shear Zone saw reactivation of faults and the transformation of psammite schist to chlorite - sericite schist. A third event, preserved in the Limejuice Zone produced high-grade gneiss rock fabrics. Between 1990 and 2004, some geologists proposed that

2050-441: 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

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2100-491: 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

2150-479: The second situation, the oceanic lithosphere always subducts because the continental lithosphere is less dense. The subduction process consumes older oceanic lithosphere, so oceanic crust is seldom more than 200 million years old. The process of super-continent formation and destruction via repeated cycles of creation and destruction of oceanic crust is known as the Wilson Cycle . The oldest large-scale oceanic crust

2200-526: The solidus and melts at lesser depth, thereby producing less melt and thinner crust. An example of this is the Gakkel Ridge under the Arctic Ocean . Thicker than average crust is found above plumes as the mantle is hotter and hence it crosses the solidus and melts at a greater depth, creating more melt and a thicker crust. An example of this is Iceland which has crust of thickness ~20 km. The age of

2250-414: 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

2300-423: 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

2350-460: 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,

2400-525: The surrounding mantle. The most voluminous volcanic rocks of the ocean floor are the mid-oceanic ridge basalts, which are derived from low- potassium tholeiitic magmas . These rocks have low concentrations of large ion lithophile elements (LILE), light rare earth elements (LREE), volatile elements and other highly incompatible elements . There can be found basalts enriched with incompatible elements, but they are rare and associated with mid-ocean ridge hot spots such as surroundings of Galapagos Islands ,

2450-447: 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

2500-494: 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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