Cordillera Occidental (Central Andes)
The border goes through the innominated point located at two thirds of elevation of Licancaburs northeastern slope at the southwestermost point of Bolivia at 22°4941 south and 67°5235 west. The climate of the region is cold and inadequate for animal and its main feature is its ground, in which are large quantities of metallic minerals including gold, silver and others. The range consists of three sections, The northern section, in which you can find the highest peaks in Bolivia, Sajama is perennially covered in snow. It contains the volcanoes Pomerape and Parinacota the latter being a dormant volcano with a cone of snow similar to Mount Fuji in Japan, the central section, situated between Uyuni and Coipasa. Its most prominent summit is the Ollagüe volcano on the border with Chile, the southern section, characterized by volcanic activity and by having sandstorms and fog, taking into account the most active volcano in the world, which is 5,920 meters high. The lakes Laguna Colorada and Laguna Verde can be found on Licancabur, Cordillera Central Cordillera Oriental Cordillera Occidental Licancabur
An Orogeny is an event that leads to a large structural deformation of the Earths lithosphere due to the interaction between tectonic plates. Orogens or orogenic belts develop when a plate is crumpled and is pushed upwards to form mountain ranges. Orogeny is the mechanism by which mountains are built on continents. The word orogeny comes from Ancient Greek, though 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. Formation of an orogen is accomplished in part by the processes of subduction or convergence of two or more continents. Orogeny usually produces long arcuate structures, known as orogenic belts, orogenic belts consist of long parallel strips of rock exhibiting similar characteristics along the length of the belt. Orogenic belts are associated with zones, which consume crust, produce volcanoes. Geologists attribute the arcuate structure to the rigidity of the descending plate and these island arcs may be added to a continent during an orogenic event.
The processes of orogeny can take tens of millions of years, 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, an orogenic event may be studied, as a tectonic structural event, as a geographical event, and as a chronological event. The foreland basin forms ahead of the orogen due mainly to loading and resulting flexure of the lithosphere by the mountain belt. The basin migrates with the front and early deposited foreland basin sediments become progressively involved in folding and thrusting. Sediments deposited in the basin are mainly derived from the erosion of the actively uplifting rocks of the mountain range. The fill of many such shows an change in time from deepwater marine through shallow water to continental sediments. Although orogeny involves plate tectonics, the tectonic forces result in a variety of associated phenomena, including magmatism, crustal melting, 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 is subject to other processes, for example, the Caledonian Orogeny refers to the Silurian and Devonian events that resulted from the collision of Laurentia with Eastern Avalonia and other former fragments of Gondwana. The Caledonian Orogen resulted from events and various others that are part of its peculiar orogenic cycle
As a result of pressure and plate material melting in the mantle and volcanoes are common near convergent boundaries. When two plates move towards one another, they form either a subduction zone or a continental collision and this depends on the nature of the plates involved. In a subduction zone, the plate, which is normally a plate with oceanic crust, moves beneath the other plate. During collisions between two plates, large mountain ranges, such as the Himalayas are formed. The nature of a convergent boundary depends on the type of plates that are colliding, at an oceanic-continental convergent boundary, the oceanic lithosphere will always subduct below the continental lithosphere. This is caused by the density difference between the oceanic and continental lithosphere. This type of boundary is called a subduction zone. At the surface, the expression is commonly an oceanic trench which forms on the oceanic side. On the continental side, a chain of volcanoes forms above the location of the subducting plate, an example of a continental-oceanic subduction zone is the area along the western coast of South America where the oceanic Nazca Plate is being subducted beneath the continental South American Plate. A volcanic arc is formed on the plate, above the location of the downgoing oceanic slab.
The volcanic arc is the expression of the magma that is generated by hydrous melting of the mantle above the downgoing slab. The buoyant fluids rise into the asthenosphere, where they lower the temperature of the mantle. Either action will create extensive mountain ranges and it may have pushed nearby parts of the Asian continent aside to the east. When two plates with oceanic crust converge, they create an island arc as one plate is subducted below the other. The arc is formed from volcanoes which erupt through the plate as the descending plate melts below it. The arc shape occurs because of the surface of the earth. A deep oceanic trench is located in front of such arcs where the descending slab dips downward, plates may collide at an oblique angle rather than head-on to each other, and this may cause strike-slip faulting along the collision zone, in addition to subduction or compression. Not all plate boundaries are easily defined, some are broad belts whose movements are unclear to scientists
The continental crust is the layer of igneous and metamorphic rocks that forms the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its composition is more felsic compared to the oceanic crust. The continental crust consists of layers, with a bulk composition that is intermediate to felsic. The average density of continental crust is about 2.7 g/cm3, less dense than the material that makes up the mantle. Continental crust is less dense than oceanic crust, whose density is about 2.9 g/cm3. At 25 to 70 km, continental crust is thicker than oceanic crust. About 40% of Earths surface is occupied by continental crust. It makes up about 70% of the volume of Earths crust, because the surface of continental crust mainly lies above sea level, its existence allowed land life to evolve from marine life. There is little evidence of continental crust prior to 3.5 Ga, all continental crust ultimately derives from the fractional differentiation of oceanic crust over many eons.
This process has been and continues today primarily as a result of the associated with subduction. In contrast to the persistence of continental crust, the size, different tracts rift apart and recoalesce as part of a grand supercontinent cycle. There are currently about 7 billion cubic kilometers of continental crust, the relative permanence of continental crust contrasts with the short life of oceanic crust. Because continental crust is less dense oceanic crust, when active margins of the two meet in subduction zones, the oceanic crust is typically subducted back into the mantle. Continental crust is rarely subducted.01 Ga, whereas the oldest oceanic crust is from the Jurassic, Continental crust and the rock layers that lie on and within it are thus the best archive of Earths history. The height of mountain ranges is usually related to the thickness of crust and this results from the isostasy associated with orogeny. The crust is thickened by the compressive forces related to subduction or continental collision, the buoyancy of the crust forces it upwards, the forces of the collisional stress balanced by gravity and erosion.
This forms a keel or mountain root beneath the mountain range, the thinnest continental crust is found in rift zones, where the crust is thinned by detachment faulting and eventually severed, replaced by oceanic crust. The edges of continental fragments formed this way are termed passive margins, igneous rock may be underplated to the underside of the crust, i. e. adding to the crust by forming a layer immediately beneath it
Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. The crust overlies the solidified and uppermost layer of the mantle, the crust and the solid mantle layer together constitute oceanic lithosphere. Oceanic crust is the result of erupted mantle material originating from below the plate, cooled and in most instances and this occurs mostly at mid-ocean ridges, but at scattered hotspots, and in rare but powerful occurrences known as flood basalt eruptions. It is primarily composed of rocks, or sima, which is rich in iron. Although a complete section of oceanic crust has not yet been drilled, Oceanic crust is significantly simpler than continental crust and generally can be divided in three layers. Layer 1 is on an average 0.4 km thick and it consists of unconsolidated or semiconsolidated sediments, usually thin or even not present near the mid-ocean ridges but thickens farther away from the ridge. Layer 3 is formed by slow cooling of magma beneath the surface and consists of coarse grained gabbros and it constitutes over two-thirds of oceanic crust volume with almost 5 km thickness.
The most voluminous volcanic rocks of the floor are the mid-oceanic ridge basalts. These rocks have low concentrations of large ion lithophile elements, light rare earth elements, volatile 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, the Azores and Iceland. Oceanic crust is continuously being created at mid-ocean ridges, as plates diverge at these ridges, magma rises into the upper mantle and crust. As it moves away from the ridge, the lithosphere becomes cooler and denser, the youngest oceanic lithosphere is at the oceanic ridges, and it gets progressively older away from the ridges. As the mantle rises it cools and melts, as the pressure decreases, the amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness, 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 depth, creating more melt.
An example of this is Iceland which has crust of thickness ~20 km, 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 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 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 is in the west Pacific and north-west Atlantic - both are about up to 180-200 million years old
An island arc is a type of archipelago, often composed of a chain of volcanoes, with arc-shaped alignment, situated parallel and close to a boundary between two converging tectonic plates. Most of these island arcs are formed as one oceanic plate subducts another one and. For example, large parts of the Andes/Central American/Canadian mountain chain may be known as a volcanic arc, on the other hand, the Aegean or Hellenic arc in the Mediterranean area, composed of numerous islands such as Crete, is an island arc, but is not volcanic. Parallel to it is the South Aegean Volcanic Arc, which is the island arc of the same tectonic system. There is some debate about the usefulness of the distinction between island arcs and volcanic arcs, the term volcanic island arc is merely a sub-classification of island arc. Island arcs are tectonically created arc-shaped mountain belts that are partly below sea level, they represent a specific geographic-topographic situation in which a mountain belt is partly submerged in ocean.
Many of these are composed of volcanoes, and can thus be classified as volcanic island arcs. This process, called flux melting, generates low-density calc-alkaline magma that rises to intrude. The resulting volcano chain has the shape of an arc parallel to the convergent plate boundary, 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 downgoing and overriding plates. This trench is created by the pull of the relatively dense subducting plate pulling the leading edge of the plate downward. Multiple earthquakes occur along this boundary with the seismic hypocenters located at increasing depth under the island arc. Ocean basins that are being reduced by subduction are called remnant oceans as they will slowly be shrunken out of existence and this process has happened repeatedly in the geological history of the Earth. Insular Islands Intermontane Islands Back-arc basin High island Volcanic arc
The oceanic trenches are linear oceanographic features which are topographic depressions of the sea floor, relatively narrow in width, but hemispheric-scale in length. They are the deepest parts of the ocean floor, a trench marks the position at which the flexed, subducting slab begins to descend beneath another lithospheric slab. Trenches are generally parallel to an island arc, and about 200 km from a volcanic arc. Oceanic trenches typically extend 3 to 4 km below the level of the surrounding oceanic floor, the greatest ocean depth to be sounded is in the Challenger Deep of the Mariana Trench, at a depth of 11,034 m below sea level. Oceanic lithosphere moves into trenches at a rate of about 3 km2/yr. Globally, there are over 50 major ocean trenches covering an area of 1.9 million km2 or about 0. 5% of the oceans and this applies to Cascadia, southern Lesser Antilles, and Calabrian trenches. Trenches are related to but distinguished from continental collision zones, where continental crust enters the subduction zone, when buoyant continental crust enters a trench, subduction eventually stops and the convergent plate margin becomes a collision zone.
Trenches were not clearly defined until the late 1940s and 1950s, the bathymetry of the ocean was of no real interest until the late 19th and early 20th centuries, with the initial laying of Transatlantic telegraph cables on the seafloor between the continents. Even the elongated bathymetric expression of trenches was not recognized until well into the 20th century, the term “trench” does not appear in Murray and Hjort’s classic oceanography book. Instead they applied the term “deep“ for the deepest parts of the ocean, the term was first used in a geologic context by Scofield two years after the war ended to describe a structurally controlled depression in the Rocky Mountains. Johnstone, in his 1923 textbook An Introduction to Oceanography, first used the term in its sense for any marked. His measurements revealed that trenches are sites of downwelling in the solid Earth, the concept of downwelling at trenches was characterized by Griggs in 1939 as the tectogene hypothesis, for which he developed an analogue model using a pair of rotating drums.
World War II in the Pacific led to improvements of bathymetry in especially the western and northern Pacific. The rapid growth of deep sea research efforts, especially the use of echosounders in the 1950s and 1960s confirmed the morphological utility of the term. The important trenches were identified and their greatest depths sonically plumbed, the heroic phase of trench exploration culminated in the 1960 descent of the Bathyscaphe Trieste, which set an unbeatable world record by diving to the bottom of the Challenger Deep. This has been termed trench rollback or hinge retreat and this is one explanation for the existence of back-arc basins. Slab rollback is a process which occurs during the subduction of two tectonic plates resulting in the motion of the trench. Forces acting perpendicular to the slab at depth are responsible for the migration of the slab in the mantle and ultimately the movement of the hinge
A geological fold occurs when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of material before it is lithified. Folds in rocks vary in size from microscopic crinkles to mountain-sized folds and they occur singly as isolated folds and in extensive fold trains of different sizes, on a variety of scales. A set of folds distributed on a regional scale constitutes a fold belt, Folds are classified by their size, fold shape and dip of the axial plane. A fold surface seen in profile can be divided into hinge, the limbs are the flanks of the fold and the hinge is where the flanks join together. The hinge point is the point of minimum radius of curvature for a fold, the crest of the fold is the highest point of the fold surface, and the trough is the lowest point. The inflection point of a fold is the point on a limb at which the concavity reverses, on regular folds, the hinge points along an entire folded surface form a hinge line, which can be either a crest line or a trough line.
The trend and plunge of a hinge line gives you information about the orientation of the fold. To more completely describe the orientation of a fold, one must describe the axial surface, the axial surface is the surface defined by connecting all the hinge lines of stacked folding surfaces. If the axial surface is a surface it is called the axial plane and can be described by the strike. An axial trace is the line of intersection of the surface with any other surface. Finally, folds can have, but dont necessarily have a fold axis, a fold axis, “is the closest approximation to a straight line that when moved parallel to itself, generates the form of the fold. ”. A fold that can be generated by an axis is called a cylindrical fold. This term has broadened to include near-cylindrical folds. Often, the axis is the same as the hinge line. A fold can be shaped as a chevron, with planar limbs meeting at an axis, as cuspate with curved limbs, as circular with a curved axis. Fold tightness is defined by the size of the angle between the limbs, called the interlimb angle.
Gentle folds have an angle of between 180° and 120°, open folds range from 120° to 70°, close folds from 70° to 30°
Magnitogorsk is an industrial city in Chelyabinsk Oblast, located on the eastern side of the extreme southern extent of the Ural Mountains by the Ural River. It was named after the Magnitnaya Mountain and it is the second largest city in Russia that is not the administrative center of any federal subject or district. Here the largest iron and steel works in the country is situated, Magnitnaya was founded in 1743 as part of the Orenburg Line of forts built during the reign of the Empress Elizabeth. By 1747, the settlement had been large enough to guide the building of a small wooden chapel named subsequently The Church of the Holy Trinity. Iron ore mining in this region back to 1752, when two entrepreneurs named Tverdysh and Myasnikov decided to check on the feasibility of mining in the area that became famous later. They managed to take advantage of the fact that the Magnitnaya mountain did not belong to anyone at that time. So, they secured it for themselves by way of petition to Empress Elizabeth, in 1759, the petition was eventually accepted, and they launched iron ore production.
At this time, hundreds of foreign experts kept coming here in order to implement and direct the work. In 1928, a Soviet delegation arrived in Cleveland, Ohio to discuss with American consulting company Arthur G. McKee a plan to set up in Magnitogorsk a copy of the US Steel steel mill in Gary. The contract was four times increased and eventually the new plant had a capacity of four million tons annually. It was a showpiece of Soviet achievement, huge reserves of iron ore in the area made it a prime location to build a steel plant capable of challenging its Western rivals. However, a proportion of the workforce, as ex-peasants, typically had few industrial skills. To solve these issues, several hundred foreign specialists arrived to direct the work, however, by the time that May completed his plans for Magnitogorsk construction of both factory and housing had already started. The sprawling factory and enormous cleansing lakes had left little room available for development and this modification resulted in a city being more rope-like than linear.
The book Behind the Urals, by John Scott, documents the development of Magnitogorsk during the 1930s. Scott discusses the fast-paced industrial and social developments during Stalins first five-year plan, in 1937, foreigners were told to exit and Magnitogorsk was declared a closed city. There is not much information about events and development of the city during the closed period. During perestroika the closed city status was removed and foreigners were allowed to visit the city again, with the depletion of the substantial local iron-ore reserves, Magnitogorsk has to import raw materials from Sokolvsko-Sarbaisky deposit in northern Kazakhstan
A continental arc is a type of volcanic arc occurring as an arc-shape topographic high region along a continental margin. The continental arc is formed at a continental margin where two tectonic plates meet and a subduction zone develops. The magmatism and petrogenesis of continental crust are complicated, in essence, continental arcs reflect a mixture of oceanic crust materials, mantle wedge, when two tectonic plates collide, relatively denser oceanic crust will be subducted under relatively lighter continental crust. Under such conditions, the downgoing plate releases volatiles such as H2O and CO2 and this process can create relatively buoyant magma, which subsequently forms a series of volcanoes at the surface along the subduction zone. There are some researchers who argue that refertilization of arc lithospheric mantle may be an important process associated with arc magmatism, because the subduction zone is generally an arc-shape, geologists named those volcanoes volcanic arcs. A volcanic arc built on continental crust is called a continental arc, the origin of igneous rock, or petrogenesis, in continental arcs is more complicated than that in oceanic arcs.
The partial melting of the oceanic slab generates primary magma. The dehydration of the slab and the partial melting of asthenosphere together generate the primary magma of continental arcs. Primary magma is composed of tholeiitic basalt because of mixture of peridotites from the mantle wedge and large ion lithophile enriched fluids from the dehydrating subducting plate. Because the larger thickness and lower density, the continental crust is likely to prevent the rising of primary magma. Ascending primary magma is likely to pond at the bottom of continental crust, in this chamber an underplating process will take place, the assimilation and fractional crystallization of primary magma and lower crustal rocks forms underplate at the bottom of crust. Through those procedure the olivine tholeiitic primary magma would change to calc-alkaline magmas, a further enriched source may be provided by the tectonic erosion process that causes scraping and dragging of lower continental lithosphere into the melting zone.
Thus, a high concentrations of Rb, Cs, Ba, K, Th, the geothermal structure in a subduction zone determines the melting rate of subduction slab and asthenosphere. The change in structure may have significant impact on the intensity of magmatism. Calc-alkaline phenocryst-rich dacite and rhyolite rocks are abundant in continental arc and these rocks contain hydrous minerals biotite and hornblende partially resorbed in magmatic process. Strongly-zoned plagioclase with sieve texture occurs in those rocks, granodiorite and diorite are most common intrusive rocks found in continental arcs. The erosion of continental arcs is a part of the process of global lithosphere circulation. According to relative study, the contribution of continental arc erosion in total continental crust loss is nearly 25%, a process called tectonic erosion happens when friction force during convergence scrapes off huge amount of rocks from the base of continental arcs
Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced or sinks due to gravity into the mantle. Regions where this occurs are known as subduction zones. Rates of subduction are typically in centimeters per year, with the rate of convergence being approximately two to eight centimeters per year along most plate boundaries. Plates include both oceanic crust and continental crust, stable subduction zones involve the oceanic lithosphere of one plate sliding beneath the continental or oceanic lithosphere of another plate due to the higher density of the oceanic lithosphere. That is, the lithosphere is always oceanic while the overriding lithosphere may or may not be oceanic. Subduction zones are sites that have a rate of volcanism, earthquakes. Subduction zones are sites of convective downwelling of Earths lithosphere, subduction zones exist at convergent plate boundaries where one plate of oceanic lithosphere converges with another plate.
The descending slab, the plate, is over-ridden by the leading edge of the other plate. The slab sinks at an angle of approximately twenty-five to forty-five degrees to Earths surface and this sinking is driven by the temperature difference between the subducting oceanic lithosphere and the surrounding mantle asthenosphere, as the colder oceanic lithosphere is, on average, denser. At a depth of approximately 80–120 kilometers, the basalt of the oceanic crust is converted to a rock called eclogite. At that point, the density of the oceanic crust increases and provides additional negative buoyancy and it is at subduction zones that Earths lithosphere, oceanic crust, sedimentary layers and some trapped water are recycled into the deep mantle. Earth is so far the only planet where subduction is known to occur, subduction is the driving force behind plate tectonics, and without it, plate tectonics could not occur. Subduction zones dive down into the mantle beneath 55,000 kilometers of convergent plate margins, subduction zones burrow deeply but are imperfectly camouflaged, and geophysics and geochemistry can be used to study them.
Not surprisingly, the shallowest portions of subduction zones are known best, subduction zones are strongly asymmetric for the first several hundred kilometers of their descent. They start to go down at oceanic trenches and their descents are marked by inclined zones of earthquakes that dip away from the trench beneath the volcanoes and extend down to the 660-kilometer discontinuity. Subduction zones are defined by the array of earthquakes known as the Wadati–Benioff zone after the two scientists who first identified this distinctive aspect. Subduction zone earthquakes occur at greater depths than elsewhere on Earth, such deep earthquakes may be driven by deep phase transformations, thermal runaway, the subducting basalt and sediment are normally rich in hydrous minerals and clays. Additionally, large quantities of water are introduced into cracks and fractures created as the slab bends downward