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What is Orogeny?

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An event that leads to the compositional differentiation and structural deformation of the lithosphere at the margins of the convergent plate is called orogeny. It is also known as an orogenic belt. When the continental plate is crumpled and uplifted to form one or more mountain ranges then the development of the orogeny takes place. This series of geological processes are called orogenesis. During the development of orogeny, the synergic plate is formed. 


Orogeny is the primary mechanism through which the mountains are built on the continents. The word orogeny was derived from Greek, where oros means mountain, genesis means to create. Orogeny takes place due to the convergence of tectonic plates. This may take the form of subduction. It is the process where a continent rides forcefully over an oceanic plate to form an accretionary orogeny or continental collision where the convergence of two or more continents takes place to form a collisional orogeny.


Physiography of Orogeny

Orogenic belts are typically produced by orogeny, which are elongated regions of bordering continental cratons where the deformation occurs. The process of subduction remains continued during the young orogenic belts and these are characterized by frequent volcanic activity and earthquakes. Older orogenic belts are typically deeply eroded to show displaced and deformed strata. These are often highly metamorphosed and include vast bodies of intrusive rock called batholiths.


Orogenic belts are related to subduction zones, which consume crust, thicken lithosphere, produce earthquakes and volcanoes, and sometimes build island arcs. These island arcs could also be added to a continental margin during an accretionary orogeny. The orogeny may culminate with continental crust from the other side of subducting oceanic plates; these plates arrive at the subduction zone. This ends the subduction and transforms the accretional orogeny into a collisional orogeny. The collisional orogeny may produce extremely high mountains, as has been happening within the Himalayas for the last 65 million years.


The processes of orogeny can take tens of many years and build mountains from what were once sedimentary basins. Activity along an orogenic belt is often extremely long-lived. For example, much of the basement underlying us belongs to the Transcontinental Proterozoic Provinces, which accreted to Laurentia over the course of 200 million years within the Paleoproterozoic. The Yavapai and Mazatzal orogenies were peaks of orogenic activity during this point. An identical sequence of orogenies has taken place on the region of the West Coast of North America. It is the region where it began within the late Devonian with the Antler orogeny. It was then continued with the Sevier orogeny and Sonoma orogeny and these were culminating with the help of Laramide orogeny. The Laramide orogeny alone lasted from 75 million to 35 million years ago for about 40 million years.


The topographic height of orogenic mountains is said to be the principle of isostasy, that's, a balance of the downward gravity upon an upthrust range that is composed of sunshine. The continental crust material and the buoyant upward forces are exerted by the dense underlying mantle. Erosion of overlying strata that is present in the orogenic belts and isostatic adjustment is involved in the removal of this overlying mass of rock, which can bring deeply buried strata to the surface. The erosional process is named unroofing and therefore the resulting exposure of formerly deeply buried strata is named exhumation.


Types of Orogeny

Even though in the process of orogeny the tectonic plates are involved, there are several tectonic forces or sequence of events that occur in the formation of the orogeny. These sequence of events are the deformation of crustal, thickening of crustal, thinning of crustal, and melting of crustal. Along with these events, it includes processes such as magmatism, metamorphism, and the process of mineralization. 

There are two main types of orogeny, and they are:

  1. Accretionary Orogens: These orogens are produced by the subduction of one oceanic plate under the other continental plate. This results in the formation of the accretion of island arc terranes or the continental arc magmatism to the margins of the continent.

  2. Collisional Orogens: When the collision between the two continental blocks takes place then the subduction of one of the continental blocks over the other continental block occurs leading to the formation of the collisional orogens. 

Orogenic events can be studied with the help of tectonic structural events, geographical events, and chronological events. These events can cause the following: 

  • It can cause structural phenomena that are related to the tectonic plates.

  • In particular regions, it can affect rocks and crust.

  • It will happen in a specified period of time.

Alleghanian Orogeny

The Alleghanian orogeny or Appalachian orogeny meaning is one of the geological mountain-forming events that formed the Appalachians and Alleghenies. H.P. Woodward in 1957 originally proposed the term and spelling of Alleghany orogeny. The Alleghanian orogeny occurred approximately 325 million to 260 million years ago over a minimum of five deformation events within the Carboniferous to Permian. When Africa collided with North America then orogeny was caused. 


At the time, these continents didn’t even exist in their current forms: North America was a part of the Euramerica super-continent, while Africa was a part of Gondwana. Super-continent Pangaea formed by this collision, which contained all major continental landmasses. 


The collision provoked the orogeny: it exerted massive stress on what's today the Eastern Seaboard of North America, forming a good and high range. Evidence for the Alleghanian orogeny stretches for several many miles on the surface from Alabama to New Jersey and may be traced further to the southwest. In the north, the Alleghanian deformation extends northeast to Newly found land. 


This subsequent erosion had led to the spread of the sediments to both directions to the east and to the west. The immense region is involved within the continental collision, the vast temporal length of the orogeny and hence the thickness of the pile of sediments and igneous rocks are known to possess been involved are the evidence that at the peak of the building process of the mountain, the Appalachians likely once reached these elevations that are similar to those of the Alps and the Rocky Mountains before they were eroded.


Hercynian Orogeny

The Variscan orogeny or Hercynian orogeny definition is a geologic mountain-building event that is caused by the Late Paleozoic continental collision between Euramerica and Gondwana in order to make the supercontinent of Pangaea. The name Variscan comes from the Medieval Latin name the Varisci. Eduard Suess is a professor of geology at the University of Vienna, coined the term in 1880. 


Hercynian, on the opposite hand, derives from the Hercynian Forest. Both words were descriptive terms of strike directions observed by geologists within the field, variscan for southwest to northeast, Hercynian for northwest to southeast. The Hercynian direction has reflected the direction of the ancient fold belts that are cropping out throughout Germany and adjacent countries and therefore the meaning shifted from direction to the fold belt. German geologist Franz Kossmat is one of the pioneers in research on the Variscan fold belt, establishing a still valid division of the ecu Variscides in 1927.


The other direction, Variscan, for the direction of the Harz Mountains in Germany, saw a similar shift. Today, Hercynian is usually used as another name for Variscan but is somewhat less used than the latter. It's used just for European orogenies, the existing and genetically linked mountain-building phases within the Appalachians have different names.


Since the 1960s, the regional term Hercynian underwent a further meaning shift. Geologists generally began to use it to characterize late Paleozoic fold-belts and orogenic phases having an age of roughly 380 to 280 Ma. Some publications use the term Variscan for fold belts of even younger age, deviating from the meaning as a term for the North American and European orogeny associated with the Gondwana-Laurasia collision.


Pan African Orogeny

A series of major Neoproterozoic orogenic events had led to the formation of the Pan-African orogeny that is related to the formation of the supercontinents such as Gondwana and Pannotia that are about 600 million years ago. This orogeny is also referred to as the Pan-Gondwanan or Saldanian Orogeny. The most important known systems of orogenies on Earth are Pan-African orogeny and therefore the Grenville orogeny. The sum of the continental crust formed within the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the amount of Earth's history that has produced most continental crust.


Kennedy in 1964 has termed the word Pan-African for a tectonic-thermal event at about 500 Ma when a series of mobile belts in Africa are formed in between much older African cratons. At the time, other terms were used for similar orogenic events on other continents, such as Brasiliano that is present in South America, Adelaidean present in Australia, and Beardmore that is present in Antarctica.


When the tectonics became accepted generally, the term Pan-African was extended to all the supercontinent of Gondwana. Because the formation of Gondwana encompassed several continents and extended from the Neoproterozoic to the first Palaeozoic, Pan-African could not be considered one orogeny, but rather an orogenic cycle that included the opening and shutting off several large oceans and therefore the collisions of several continental blocks. 


Furthermore, the Pan-African events exist with the Caweredomian orogeny that is present in Europe. Therefore, in Asia, the crust from these areas was probably a part of Pannotia during the Precambrian. Attempts to correlate the African Pan-African belts with the South American Brasiliano belts on the opposite side of the Atlantic have in many cases been problematic.


Cordilleran Orogeny

The Cordilleran orogeny meaning is the belt that is present in North America and is formed during the process of an orogeny that had occurred mainly in Cretaceous and Paleocene times. This belt is marked by a zone of thrust faulting and strong folding that extends from the region of Alaska to Guatemala. However, the belt is so obscured in between southern Nevada and northeastern Chihuahua, that some of the geologists doubt its continuity. 


A recent study of a part of the Nevada-Chihuahua interval provides evidence that the belt is continuous, without major interruption; the complications are the results of pre-orogenic and post-orogenic tectonic events. With due in regard to these complicating factors, a structure section through the region of south-eastern Arizona and south-western New Mexico that closely resembles the sections through south-western Canada, regions near Salt Lake City, and Las Vegas in the United States, and northern Mexico. 


In each region, supracrustal rocks were tectonically transported east-northeastward a distance of probably quite 100 km. Those features that vary between the regions are able to reflect the differences that are present in tectonic position within the belt, in anisotropy of preorogenic rocks, or in subsequent geologic history.


Andean Orogeny

The Andean orogeny definition is as follows, it is an ongoing process of orogeny that began within the Early Jurassic and is liable for the increase 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 and Oligocene were periods of re-arrangements within the orogeny. Locally the small print of the character of the orogeny varies counting on the segment and therefore the period considered.


The Paleozoic Pampean, Famatinian, and Gondwanan orogenies are the immediate precursors to the later Andean orogeny. The primary phases of Andean orogeny within the Jurassic and Early Cretaceous were characterized by extensional tectonics, rifting, the event of back-arc basins, and therefore the emplacement of huge batholiths. This development is presumed to have been linked to the subduction of the cold oceanic lithosphere. 


During the mid to Late Cretaceous, the Andean orogeny changed significantly in character. Warmer and younger oceanic lithosphere is believed to have begun to be subducted beneath South America around this point. Such quite subduction is held responsible not just for the extreme contractional deformation that different lithologies were subject to, but also the uplift and erosion that are known to have occurred from the Late Cretaceous onward. Plate tectonic reorganization since the mid-Cretaceous may additionally be linked to the opening of the South Atlantic Ocean.


Conclusion

Orogen is produced by orogeny but in the case of passive plate margins, only a range of foreland basin systems are formed. This foreland basin is formed ahead of that of the orogen because of the resulting flexure of the lithosphere and loading of the developing mountain belt. The continued existence of the oceans had played a significant role in life. 

FAQ (Frequently Asked Questions)

1. What is Orogeny?

Ans: The process through which the mountains are formed on the continents is known as orogeny. It is done by the compositional differentiation and structural deformation at the margin of the convergent plates that occur in the lithosphere. 

2. What is an Orogenic Cycle?

Ans: The formation of orogen takes place by the thrust falling and the folding of the mountain belts this process is called the orogenic cycle. This is done by several processes such as sedimentation, magmatism, deformation, and metamorphism.