An orogeny is an event that leads to both structural deformation and compositional differentiation of the Earth's lithosphere (crust and uppermost mantle) at convergent plate margins. An orogen or orogenic belt develops when a continental plate crumples and is pushed upwards to form one or more mountain ranges; this involves a series of geological processes collectively called orogenesis.
Orogeny is the primary mechanism by which mountains are built on continents. The word "orogeny" comes from Ancient Greek (ὄρος, óros, lit. 'mountain' + γένεσις, génesis, lit. 'creation, origin'). 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.
The formation of an orogen can be accomplished by the tectonic processes such as oceanic subduction (where a continent rides forcefully over an oceanic plate for accretionary orogeny) or continental subduction convergence of two or more continents for collisional orogeny).
Orogeny usually produces long arcuate (from the Latin arcuare, "to bend like a bow") structures, known as orogenic belts. Generally, orogenic belts consist of long parallel strips of rock exhibiting similar characteristics along the length of the belt. Although orogenic belts are associated with subduction zones, subduction tectonism may be ongoing or past processes. The subducting tectonism would consume crust, thicken lithosphere, produce earthquake and volcanoes, and build island arcs in many cases. Geologists attribute the arcuate structure to the rigidity of the descending plate, and island arc cusps relate to tears in the descending lithosphere. These island arcs may be added to a continental margin during an accretionary orogeny. On the other hand, subduction zones may be reworked at a later time due to lithospheric rifting, leading to amphibolite to granulite facies metamorphism of the thinned orogenic crust.
The processes of orogeny can take tens of millions of years and build mountains from plains or from the seabed. The topographic height of orogenic mountains is related to the principle of isostasy, that is, a 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.
Frequently, rock formations that undergo orogeny are severely deformed and undergo metamorphism. Orogenic processes may push deeply buried rocks to the surface. Sea-bottom and near-shore material may cover some or all of the orogenic area. If the orogeny is due to two continents colliding, very high mountains can result (see Himalayas).
An orogenic event may be studied: (a) as a tectonic structural event, (b) as a geographical event, and (c) as a chronological event.
In general, there are two main types of orogens at convergent plate margins: (1) accretionary orogens, which were produced by subduction of one oceanic plate beneath one continental plate to result in either continental arc magmatism or the accretion of island arc terranes to continental margins; (2) collisional orogens, which were produced by collision between two continental blocks, with subduction of one continental block beneath the other continental block.
An orogeny produces an orogen, but a (mountain) range-foreland basin system is only produced on passive plate margins. The 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. 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.
Although orogeny involves plate tectonics, the tectonic forces result in a variety of associated phenomena, including crustal deformation, crustal thickening, crustal thinning and crustal melting as well as magmatism, metamorphism and mineralization. What exactly happens in a specific orogen depends upon the strength and rheology of the continental lithosphere, and how these properties change during orogenesis.
In addition to orogeny, the orogen (once formed) is subject to other processes, such as sedimentation and erosion. The sequence of repeated cycles of sedimentation, deposition and erosion, followed by burial and metamorphism, and then by crustal anatexis to form granitic batholiths and tectonic uplift to form mountain chains, is called the orogenic cycle. For example, the Caledonian Orogeny refers to a series of tectonic events due to the continental collision of Laurentia with Eastern Avalonia and other former fragments of Gondwana in the Early Paleozoic. The Caledonian Orogen resulted from these events and various others that are part of its peculiar orogenic cycle.
In summary, an orogeny is an episode of deformation, metamorphism and magmatism at convergent plate margins, during which many geological processes play a role at convergent plate margins. Every orogeny has its own orogenic cycle, but composite orogenesis is common at convergent plate margins.
Erosion represents a subsequent phase of the orogenic cycle. 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 exhumation 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.
In the 1950s and 1960s the study of orogeny, coupled with biogeography (the study of the distribution and evolution of flora and fauna), geography and mid ocean ridges, contributed greatly to the theory of plate tectonics. Even at a very early stage, life played a significant role in the continued existence of oceans, by affecting the composition of the atmosphere. The existence of oceans is critical to sea-floor spreading and subduction.
Mountain complexes result from irregular successions of tectonic responses due to sea-floor spreading, shifting lithosphere plates, transform faults, and colliding, coupled and uncoupled continental margins.— Peter J Coney
Large modern orogenies often lie on the margins of present-day continents; the Alleghenian (Appalachian), Laramide, and Andean orogenies exemplify this in the Americas. Older inactive orogenies, such as the Algoman, Penokean and Antler, are represented by deformed and metamorphosed rocks with sedimentary basins further inland.
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.
Regions 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 due to abundant magmatism after a delamination of the orogenic root beneath them.
Finally, 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.
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.
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.
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. 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 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 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 (similar to tephrotectonics), or convection within the asthenosphere or mantle.
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.
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 the relationship to granite occurrences. Cawood et al. (2009) categorized orogenic belts into three types: accretionary, collisional, and intracratonic. Notice that 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.
Continental drift and plate tectonics help to explain both the similarities and the differences in the distribution of plants and animals over the continentsand John C Briggs (1987). Biogeography and Plate Tectonics. Elsevier. p. 131. ISBN 978-0-444-42743-4.
It will not be possible to construct a thorough account of the history of the southern hemisphere without the evidence from both the biological and the earth sciences
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.
The Acadian orogeny is a long-lasting mountain building event which began in the Middle Devonian, reaching a climax in the early Late Devonian. It was active for approximately 50 million years, beginning roughly around 375 million years ago, with deformational, plutonic, and metamorphic events extending into the Early Mississippian. The Acadian orogeny is the third of the four orogenies that created the Appalachian orogen and subsequent basin. The preceding orogenies consisted of the Potomac and Taconic orogeny, which followed a rift/drift stage in the Late Neoproterozoic. The Acadian orogeny involved the collision of a series of Avalonian continental fragments with the Laurasian continent. Geographically, the Acadian orogeny extended from the Canadian Maritime provinces migrating in a southwesterly direction toward Alabama. However, the Northern Appalachian region, from New England northeastward into Gaspé region of Canada, was the most greatly affected region by the collision.It was roughly contemporaneous with the Bretonic phase of the Variscan orogeny of Europe, with metamorphic events in southwestern Texas and northern Mexico, and with the Antler orogeny of the Great Basin.Alleghanian orogeny
The Alleghanian orogeny or Appalachian orogeny is one of the geological mountain-forming events that formed the Appalachian Mountains and Allegheny Mountains. The term and spelling Alleghany orogeny was originally proposed by H.P. Woodward in 1957.
The Alleghanian orogeny occurred approximately 325 million to 260 million years ago over at least five deformation events in the Carboniferous to Permian period. The orogeny was caused by Africa colliding with North America. At the time, these continents did not exist in their current forms: North America was part of the Euramerica super-continent, while Africa was part of Gondwana. This collision formed the super-continent Pangaea, which contained all major continental land masses. The collision provoked the orogeny: it exerted massive stress on what is today the Eastern Seaboard of North America, forming a wide and high mountain chain. Evidence for the Alleghanian orogeny stretches for many hundreds of miles on the surface from Alabama to New Jersey and can be traced further subsurface to the southwest. In the north, the Alleghanian deformation extends northeast to Newfoundland. Subsequent erosion wore down the mountain chain and spread sediments both to the east and to the west.Alpine orogeny
The Alpine orogeny or Alpide orogeny is an orogenic phase in the Late Mesozoic (Eoalpine) and the current Cenozoic that has formed the mountain ranges of the Alpide belt. These mountains include (from west to east) the Atlas, the Rif, the Baetic Cordillera, the Cantabrian Mountains, the Pyrenees, the Alps, the Apennine Mountains, the Dinaric Alps, the Pindus (Hellenides), the Carpathians, the Balkanides - Balkan Mountains and Rila-Rhodope massifs, the Pontic Mountains, the Taurus, the Armenian Highlands, the Caucasus, the Alborz, the Zagros, the Hindu Kush, the Pamir, the Karakoram, and the Himalayas. Sometimes other names occur to describe the formation of separate mountain ranges: for example Carpathian orogeny for the Carpathians, Hellenic orogeny for the Pindus, Altai orogeny for Altai Mountains or the Himalayan orogeny for the Himalayas.
The Alpine orogeny has also led to the formation of more distant and smaller geological features such as the Weald–Artois Anticline in southern England and northern France, the remains of which can be seen in the chalk ridges of the North and South Downs in southern England. Its effects are particularly visible on the Isle of Wight, where the Chalk Group and overlying Eocene strata are folded to near-vertical, as seen in exposures at Alum Bay and Whitecliff Bay, and on the Dorset coast near Lulworth Cove. Stresses arising from the Alpine orogeny caused the Cenozoic uplift of the Sudetes mountain range and possibly faulted rocks as far away as Öland in southern Sweden during the Paleocene.The Alpine orogeny is caused by the continents Africa and India and the small Cimmerian plate colliding (from the south) with Eurasia in the north. Convergent movements between the tectonic plates (the Indian plate and the African plate from the south, the Eurasian plate from the north, and many smaller plates and microplates) had already begun in the early Cretaceous, but the major phases of mountain building began in the Paleocene to Eocene. The process continues currently in some of the Alpide mountain ranges.
The Alpine orogeny is considered one of the three major phases of orogeny in Europe that define the geology of that continent, along with the Caledonian orogeny that formed the Old Red Sandstone Continent when the continents Baltica and Laurentia collided in the early Paleozoic, and the Hercynian or Variscan orogeny that formed Pangaea when Gondwana and the Old Red Sandstone Continent collided in the middle to late Paleozoic.Andean orogeny
The Andean orogeny (Spanish: Orogenia andina) is an ongoing process of orogeny that began in the Early Jurassic and is responsible for the rise of the Andes mountains. The orogeny is driven by a reactivation of a long-lived subduction system along the western margin of South America. On a continental scale the Cretaceous (90 Ma) and Oligocene (30 Ma) were periods of re-arrangements in the orogeny. Locally the details of the nature of the orogeny varies depending on the segment and the geological period considered.Caledonian orogeny
The Caledonian orogeny was a mountain-building era recorded in the northern parts of Ireland and Britain, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly 490–390 million years ago (Ma). It was caused by the closure of the Iapetus Ocean when the continents and terranes of Laurentia, Baltica and Avalonia collided.
The Caledonian orogeny is named for Caledonia, the Latin name for Scotland. The name was first used in 1885 by Austrian geologist Eduard Suess for an episode of mountain building in northern Europe that predated the Devonian period. Geologists like Émile Haug and Hans Stille saw the Caledonian orogeny as one of several episodic phases of mountain building that had occurred during Earth's history. Current understanding has it that the Caledonian orogeny encompasses a number of tectonic phases that can laterally be diachronous. The name "Caledonian" can therefore not be used for an absolute period of geological time, it applies only to a series of tectonically related events.Carpathian Mountains
The Carpathian Mountains or Carpathians () are a range of mountains forming an arc throughout Central and Eastern Europe. Roughly 1,500 km (932 mi) long, it is the third-longest European mountain range after the Urals with 2,500 km (1,553 mi) and the Scandinavian Mountains with 1,700 km (1,056 mi). The range stretches from the far eastern Czech Republic (3%) in the northwest through Slovakia (17%), Poland (10%), Hungary (4%) and Ukraine (10%) Serbia (5%) and Romania (50%) in the southeast. The highest range within the Carpathians is known as the Tatra mountains in Slovakia, where the highest peaks exceed 2,600 m (8,530 ft). The second-highest range is the Southern Carpathians in Romania, where the highest peaks range between 2,500 m (8,202 ft) and 2,550 m (8,366 ft).
The divisions of the Carpathians are usually in three major sections:
Western Carpathians—Austria, Czech Republic, Poland, Slovakia and Hungary
Eastern Carpathians—southeastern Poland, eastern Slovakia, Ukraine, and Romania
Southern Carpathians—Romania and SerbiaThe term Outer Carpathians is frequently used to describe the northern rim of the Western and Eastern Carpathians.
The Carpathians provide habitat for the largest European populations of brown bears, wolves, chamois, and lynxes, with the highest concentration in Romania, as well as over one third of all European plant species. The mountains and their foothills also have many thermal and mineral waters, with Romania having one-third of the European total. Romania is likewise home to the second-largest surface of virgin forests in Europe after Russia, totaling 250,000 hectares (65%), most of them in the Carpathians, with the Southern Carpathians constituting Europe's largest unfragmented forest area. Deforestation rates due to illegal logging in the Carpathians are high.The most important cities in or near the Carpathians are: Bratislava and Košice in Slovakia, Kraków in Poland, Cluj-Napoca, Sibiu, and Braşov in Romania, and Uzhhorod in Ukraine.Damara orogeny
The Damara orogeny was part of the Pan-African orogeny. The Damara orogeny occurred late in the creation of Gondwana, at the intersection of the Congo and the Kalahari cratons.The Damara orogeny involved the suturing of the Congo–São Francisco and Río de la Plata cratons at 580–550 Ma (together with India forming northern Gondwana) before the amalgamation of the Kalahari and Mawson cratons in the Kuunga–Damara orogeny at 530 Ma (southern Gondwana).The Adamastor Ocean closed southwards from the Araçuaı́ Belt (São Francisco Craton, now in South America) to the Kaoko Belt (Congo Craton, now in Africa) 580–550 Ma and 545–530 Ma Gariep Belt (Kalahari Craton, now in southern Africa). The Damara orogeny saw a peak in deformation and metamorphism at 530–500 Ma. Thrusting occurred onto the Kalahari Craton until 480 Ma.Río de la Plata docked to Congo before the closure of the Damara Belt oceans (Mozambique and Khomas) which made the Damara orogeny part of the Kuunga orogeny which stretched from Antarctica to India across Africa. All African cratons had been assembled by c. 550 Ma and the last stages of the Damara–Kuunga Orogeny (the final amalgamation of north and South Gondwana) were intra-cratonic.The Damara orogeny created the Naukluft Mountains in central Namibia between 550 Ma and 495 Ma.East African Orogeny
The East African Orogeny (EAO) is the main stage in the Neoproterozoic assembly of East and West Gondwana (Australia–India–Antarctica and Africa–South America) along the Mozambique Belt.Eburnean orogeny
The Eburnean orogeny, or Eburnean cycle was a series of tectonic, metamorphic and plutonic events in what is now West Africa during the Paleoproterozoic era about 2200–2000 million years ago.
During this period the Birimian domain in West Africa was established and structured.Eburnian faults are found in the Eglab shield to the north of the West African craton and in the Man Shield to the south of the craton.
There is evidence of three major Eburnean magmatic events in the Eglab shield.
Between 2210 and 2180 Ma, a metamorphosed batholith was formed in the Lower Reguibat Complex (LRC).
Around 2090 Ma, a syntectonic trondhjemitic pluton intruded into the Archaean reelects of the Chegga series. Around 2070 Ma an asthenospheric upwelling released a large volume of post-orogenic magmas.
Eburnian trends within the Eglab shield were repeatedly reactivated from the Neoproterozoic to the Mesozoic.Famatinian orogeny
The Famatinian orogeny (Spanish: Orogenia de Famatina) is an orogeny that predates the rise of the Andes and that took place in what is now western South America during the Paleozoic, leading to the formation of the Famatinian orogen also known as the Famatinian belt. The Famatinian orogeny lasted from the Late Cambrian to at least the Late Devonian and possibly the Early Carboniferous, with orogenic activity peaking about 490 to 460 million years ago. The orogeny involved metamorphism and deformation in the crust and the eruption and intrusion of magma along a Famatinian magmatic arc that formed a chain of volcanoes. The igneous rocks of the Famatinian magmatic arc are of calc-alkaline character and include gabbros, tonalites and granodiorites. The youngest igneous rocks of the arc are granites.The relationship of the orogeny with the Achala and Cerro Aspero batholiths of central Argentina is not fully understood. These Devonian batholiths are possibly of post-orogenic character.Geologic time scale
The geologic time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history. The table of geologic time spans, presented here, agree with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS).Gondwana
Gondwana ( ) or Gondwanaland was a supercontinent that existed from the Neoproterozoic (about 550 million years ago) until the Jurassic (about 180 million years ago).
It was formed by the accretion of several cratons. Eventually, Gondwana became the largest piece of continental crust of the Paleozoic Era, covering an area of about 100,000,000 km2 (39,000,000 sq mi). During the Carboniferous Period, it merged with Euramerica to form a larger supercontinent called Pangaea. Gondwana (and Pangaea) gradually broke up during the Mesozoic Era. The remnants of Gondwana make up about two thirds of today's continental area, including South America, Africa, Antarctica, Australia, Indian Subcontinent and Arabia.
The formation of Gondwana began c. 800 to 650 Ma with the East African Orogeny, the collision of India and Madagascar with East Africa, and was completed c. 600 to 530 Ma with the overlapping Brasiliano and Kuunga orogenies, the collision of South America with Africa and the addition of Australia and Antarctica, respectively.Gondwanide orogeny
The Gondwanide orogeny was a orogeny active in the Permian that affected parts of Gondwana that are by current geography now located in southern South America, South Africa, Antarctica, Australia and New Guinea. The zone of deformation in Argentina extends as a belt south and west of the cratonic nucleus of Río de la Plata–Pampia.
The deformation of the orogeny is visible in the Sierra de la Ventana mountains in Argentina and the Cape Fold Belt in South Africa. The Gondwanide orogeny might have been linked with the roughly contemporary San Rafael orogeny of western Argentina.The Gondwanide orogeny is the successor to the Neoproterozoic-Paleozoic Terra Australis orogeny in Gondwana.Following the Gondwanide orogeny southwestern Gondwana entered a period of extensional tectonics and crustal thinning leading to formation of various rift basins (e.g. Cuyo Basin) in the Triassic.Grenville orogeny
The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, from Labrador to Mexico, as well as to Scotland.
Grenville orogenic crust of mid-late Mesoproterozoic age (c. 1250–980 Ma) is found worldwide, but generally only events which occurred on the southern and eastern margins of Laurentia are recognized under the "Grenville" name.These orogenic events are also known as the Kibaran orogeny in Africa and the Dalslandian orogeny in Western Europe.Laramide orogeny
The Laramide orogeny was a period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the orogeny are in dispute. The Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The major feature that was created by this orogeny was deep-seated, thick-skinned deformation, with evidence of this orogeny found from Canada to northern Mexico, with the easternmost extent of the mountain-building represented by the Black Hills of South Dakota. The phenomenon is named for the Laramie Mountains of eastern Wyoming. The Laramide orogeny is sometimes confused with the Sevier orogeny, which partially overlapped in time and space.
The orogeny is commonly attributed to events off the west coast of North America, where the Kula and Farallon Plates were sliding under the North American plate. Most hypotheses propose that oceanic crust was undergoing flat-slab subduction, i.e., with a shallow subduction angle, and as a consequence, no magmatism occurred in the central west of the continent, and the underlying oceanic lithosphere actually caused drag on the root of the overlying continental lithosphere. One cause for shallow subduction may have been an increased rate of plate convergence. Another proposed cause was subduction of thickened oceanic crust.
Magmatism associated with subduction occurred not near the plate edges (as in the volcanic arc of the Andes, for example), but far to the east, called the Coast Range Arc. Geologists call such a lack of volcanic activity near a subduction zone a magmatic gap. This particular gap may have occurred because the subducted slab was in contact with relatively cool continental lithosphere, not hotter asthenosphere. One result of shallow angle of subduction and the drag that it caused was a broad belt of mountains, some of which were the progenitors of the Rocky Mountains. Part of the proto-Rocky Mountains would be later modified by extension to become the Basin and Range Province.Pan-African orogeny
The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago. This orogeny is also known as the Pan-Gondwanan or Saldanian Orogeny. The Pan-African orogeny and the Grenville orogeny are the largest known systems of orogenies on Earth. The sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.Svecofennian orogeny
The Svecofennian orogeny is a series of related orogenies that resulted in the formation of much of the continental crust in what is today Sweden and Finland plus some minor parts of Russia. The orogenies lasted from about 2000 to 1800 million years ago during the Paleoproterozoic Era. The resulting orogen is known as the Svecofennian orogen or Svecofennides. To the west and southwest the Svecofennian orogen limits with the generally younger Transscandinavian Igneous Belt. It is assumed that the westernmost fringes of the Svecofennian orogen have been reworked by the Sveconorwegian orogeny just as the western parts of the Transscandinavian Igneous Belt has. The Svecofennian orogeny involved the accretion of numerous island arcs in such manner that the pre-existing craton grew with this new material from what is today northeast to the southwest. The accretion of the island arcs was also related to two other processes that occurred in the same period; the formation of magma that then cooled to form igneous rocks and the metamorphism of rocks.Tertiary
Tertiary is a widely used, but obsolete term for the geologic period from 66 million to 2.6 million years ago.
The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start of the Cenozoic Era, and extended to the beginning of the Quaternary glaciation at the end of the Pliocene Epoch. The time span covered by the Tertiary has no exact equivalent in the current geologic time system, but it is essentially the merged Paleogene and Neogene periods, which are informally called the Lower Tertiary and the Upper Tertiary, respectively.Variscan orogeny
The Variscan or Hercynian orogeny is a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea.
|Foliation and Lineation|