Geography of South America

South America is the fourth largest of the seven continents. It is connected to the north with the Central American land bridge. In the east it is 2900 km from Africa, while the west coast a total of between 7600 km (Patagonia ) and 11,000 km (NW Columbia ) New Zealand away. In the south it is about 900 km from Antarctica, with which it is genetically linked by a chain of islands.

2.2.2.1 Amazon Basin
2.2.2.2 The Paranaiba - Maranhao basin
2.2.2.3 The Paraná Basin

2.3.1 The Northern Andes
2.3.2 The Central Andes 2.3.2.1 The coastal mountain range ( Cordillera Costal )
2.3.2.2 Longitudinal Valley ( Pampa de Tamarugal )
2.3.2.3 Precordillera
2.3.2.4 Hochkordillere / Western Cordillera
2.3.2.5 Puna / Altiplano
2.3.2.6 Eastern Cordillera ( Cordillera Occidental)
2.3.2.7 Cordillera Frontal ( Precordillera )
2.3.2.8 Sierras Pampeanas
2.3.2.9 Sierras Subandinas

2.3.3.1 The coastal mountain range ( Cordillera Costal )
2.3.3.2 The Central Valley (Valle Central)
2.3.3.3 Hochkordillere ( Cordillera Central)

3.1 Climatic conditions
3.2 Vertical differences in climate
3.3 Glacial deposits
3.4 El Niño

Size and relief

South America extends over a size of 17.8 million square kilometers, and thus takes 12 % of the earth's surface. His geological border with Central America forms the Colombian river Río Atrato. The northernmost point is at the Colombian peninsula " La Guajira " just below the 12 ° 30'N near the small community of Áirrainmaru. In the south of the subcontinent enough to Tierra del Fuego, the southernmost point (just north of 56 ° S ), which belongs to Chile uninhabited island Hornos ( Cape Horn ) marks. The distance between these two points is over 7,600 km. Its westernmost expansion reached the South American continent in Cape Pariñas (81 ° 20'W ), near the Peruvian city of Talara. The Eastern counterpart to this is the Brazilian Cape Ponta do Seixas near the city of João Pessoa (approx. 34 ° 45'W ). The east- west distance between these two points is over 5,100 km.

A geological- morphological classification of South America results in three major areas:

The Andes as high mountains on the west side of the continent ( up to 7,000 m high)
The River lowlands in the center and south of the continent (up to 500 m high)
The Bergland as low mountains on the Atlantic side ( up to 3,000 m high)

Geology and Geomorphology

South America as part of the Gondwana continent

South America was up to the Cretaceous part of the old Gondwana continent. This meant that the east coast of present-day South American continent from the height of the Brazilian cities of Fortaleza - Recife until at least the mouth of the Río de la Plata to the West African coast - was connected ( Nigeria / Cameroon South Africa). The area of present-day continental margins must have been a tectonic zone of weakness before the Cretaceous period, which began to break up in the transition from the lower Jurassic to Upper Cretaceous from south to north.

The formation of the South Atlantic was accompanied by a strong volcanism, whose flood basalts yet alike in Africa ( Karru volcanics ), India ( Deccan Traps ) and South America ( Paraná basalt ). The Paraná basalts cover in the countries south of Brazil, Uruguay, Paraguay and northeastern Argentina an area of over 1,200,000 square kilometers. This is the largest lava plateau in the world. One of the most famous manifestations of this Cretaceous basalts ceilings are the Iguazu Falls on the border between Brazil and Argentina. Here overthrow enormous masses of water on the edges of the basalt formation Serra Geral.

The Jurassic - Cretaceous volcanism, which is responsible for the formation of the Paraná Basin, can be divided into three sequences:

Basalts: 150-130 mya
Intermediate volcanic rocks: 130-123 mya
Rhyolites: 125-118 mya

In between, there have always been periods of rest, which can be read at interposed layers of sandstone. Overall, the Paraná basalts reach a maximum thickness of up to 1,800 m with an average thickness of 50 m per shift.

The increasingly acidic volcanism can be explained by intra-and perikratonische processes, which to a melting of the surrounding crustal stone led (a process in geology also called anatexis ).

The final separation and thus also the final end of the supercontinent " Pangaea " took place about 100 million years ago in the mid-Cretaceous time.

In connection with the further tearing of the South Atlantic, which was probably a result of a "hot spots" or thermal diapir, it arrived in time 90-60 mya back at a basic and effusive volcanism on the northeastern edge of the Paraná Basin. However, this volcanism produced no more flood basalts, intrusive and extrusive but only cone-shaped body of rock. This occurred in relation to these processes niobium deposits in Araxá in Minas Gerais is even world economic importance. The now passive continental margins of South America and Africa experienced in the following years, subsidence and partial grave education.

The außerandine space

The Precambrian shields and cratons

In South America, there are two larger and one smaller Precambrian units. For the two larger one in the north of the Guyana craton (see also chapter " size and relief" ), which is about 1.8 billion years old and the cratons in Brazil, which are only about 600 million years old. A smaller Kraton is found in Uruguay (Rio de la Plata craton ), the oldest series is 2.1 billion years old.

Generally speaking, that the knowledge of the South African Precambrian compared to other shields and cratons on Earth are still very thin. Reasons for this are the partial inaccessibility and held deep weathering.

The Guyana craton

The Guyana Craton is the largest closed old core of the South American continent. It extends between 9 ° N and the equator over the states Colombia, Venezuela, Suriname, Guyana, French Guiana and Brazil to an area of 4.5 million km ².

The last orogeny took place about 1.9 billion years ago in the upper Paleoproterozoic. All subsequent tectonic processes have not affected this region. In the said orogeny and the current strike was generated in WE direction ( in the direction of Venezuela French Guiana ), due to which the Guyana craton differs significantly from the Brazilian cratons, the underscore in NS direction.

The emergence of the Guyana Craton is affected (named after local places ) through four archaic events:

Guriense: 3.4 to 2.7 billion A
Pre- Transamazonico: 2.4 to 2.1 billion A
Transamazonico: 2.1 to 1.7 billion A
Paraguazense: 1.7 to 1.4 billion A

The oldest part of this archaic base are found in a narrow WSW- ENE - band at the edge of the Orinoco. Here you will find hochmetamorphe gneiss, gneiss - granites, granulites or amphibolites. Some of these ancient rocks are very rich in iron, which explains that the greatest metal concentrations occur in South America 's oldest granulite gneisses here in the form of Itabiritserien.

During the pre- Transamazonico it came by regional metamorphism in the formation of greenstone belts, which are typical of cratons.

However, the greenstone belts were during the Transamazonico event, a magmatic phase, repeatedly penetrated by acid ( silicon-rich ) volcanic rocks. In addition there were numerous granitic intrusions from the period 2.1 to 1.9 billion years ago. Then broke the resulting in Guriense Imataca Pastora block and disintegrated into individual basins.

1.6 billion a molasseartigen the terrestrial Roraima layers formed - in these basins were between 1.7. They extend over an area of 1,200,000 million square kilometers and are still tectonically hardly disturbed and not metamorphic. Several sediment packages ( esp. sandstone) today form the terrain mighty plateau. Situated on the border between Venezuela, Guyana and Brazil Cerro Roraima ( 2,772 m) is the Pico da Neblina ( 3,014 m) the highest elevations in the Guyana craton. The undisturbed sedimentation of Roraima layer is a good indication that here the Precambrian deformation history had already been completed.

The Paraguazense event is marked by non-affiliated mountain formations ( anorogene ) granite intrusions, especially in the period 1.6 to 1.3 billion years ago. This formed part of large Batholithe who make particularly in the west, near the border with Colombia, noticeable.

Brazilian shield

If by the Brazilian Shield is mentioned, then you have to say more precisely that the Brazilian Archean is characterized by multiple cores. These old cores were in the Proterozoic ( 2.6 to 0.57 billion) with several folds trains welded, so, in contrary to the Guyana craton will find no rocks with an age of about 3 billion years. The main event for this sign was mentioned Transamazonic orogeny within which all older layers were deformed before about 1.9 billion years. The medium-to jungproterozoischen fold belt, separate the seeds which have been formed in the period 1.5 to 0.5 billion years ago. A final stabilization of the Brazilian shield, therefore, took place only at the beginning of the Paleozoic.

Río de la Plata craton

This little sign is located in the south of Uruguay and separates into two blocks. The older of the two dates from the period between 2.2 to 1.9 billion years ago and is largely hidden under the layers of the Serra Geral Gondwana. Therefore, only very little is known about him. The younger of the two is from an older (900 million years) layer of basaltic lava and in the hanging wall (600 million years) we find granites and granodiorites. The conclusion of the Brazilian cycle means the final consolidation of the außerandinen shields for South America. More Precambrian cores can still be found in the " Sierra de Buenos Aires " and in the " Sierra de Cordoba".

Phanerozoic sedimentary cover

The end of the Precambrian in South America is characterized by the emergence of long-range tanks, which were filled during the Phanerozoic with sediments or remain filled, and who have since experienced virtually no deformation. The sediments themselves are mostly terrestrial - fluviatile. Marine incursions occurred only sporadically. The main phases of sedimentation proceeded mostly in the Devonian and Carboniferous. Here, three large pools can be differentiated:

Amazon Basin ( 1.25 million km ²)
Parnaíba - Maranhao basin ( 650,000 km ²)
Paraná Basin (1,200,000 km ²)

Amazon Basin

The Amazon basin is 3500 km long and 300 to 1000 km wide. It is crossed from west to east through the eponymous Amazon ( see size and relief). The Amazon basin is almost completely covered by rainforest and is divided in its turn into three sections:

The upper Amazon basin is bounded on the west by the Andes and on the east by the confluence between the Rio Negro and Rio Solimoes at the Manaus. This area can only be counted in the Upper Carboniferous to Paleozoic sedimentary basin of the Amazon basin.
The central Amazon basin is a narrow WO- furrow. It ends in the east at the tributary of the Rio Xingu. The tributaries of the Amazon are characterized in this area by rapids and waterfalls, which is related to the spreading of the Paleozoic series in the north and south of the basin.
The lower Amazon basin finally thinks the estuary. The narrow range of the middle section here widens in a funnel shape into different estuaries around the island Marajó.

Structurally, this classification also demonstrated the three thresholds in the Amazon basin. The Iquitos threshold runs to the east of the Peruvian city of Iquitos, the Purus threshold west of Manaus, where it separates the upper from the middle basin. The Gurupa threshold runs to the east of the Rio Xingu and separates the average from the lower pool.

The central Amazon Basin in addition has a grave structure, which can extend up to the Mid-Atlantic Ridge.

The storage Runge layer of the Amazon basin begins in the Ordovician and continues to this day. Particularly powerful deposits have survived from the Carboniferous ( sandstones, shales, limestones, evaporites ). Over almost the entire Mesozoic away, however, was interrupted sedimentation and erosion prevailed. To Continental Series found only in the Upper Cretaceous in the central Amazon basin. Again important for the embankment of the Amazon basin, the Cenozoic sediments, particularly in the river valleys and in the delta. A special feature of the Amazon basin is that the sedimentary filling has undergone tectonic deformation in the west of the basin, close to the Andes, to a certain extent.

Particularly noteworthy is the fact that the Amazon basin drained to the younger Tertiary west of Iquitos in the Pacific. This was prevented by an increase in the Andes in the Miocene.

The Paranaiba - Maranhao basin

The Paranaiba - Maranhao basin extends approximately circular shape in NE Brazil. Its center is located in the state of Maranhão. There it forms a spacious table-land, into which several rivers have incised. The main river, the Rio Paranaiba is not like the Paraná Basin or the Amazon Basin, the central axis. This is related to a young uplift of Ostrands why the hydrographic network in this basin has no center.

The sedimentation of this basin began in the Silurian, from where to permanently diverse layers (sandstone, coal, limestone) were formed. In contrast to the Amazon basin, the sedimentary history of the Paranaiba - Maranhao basin has been completed since the Cretaceous. Today there prevails ablation.

The Paraná Basin

The Paraná Basin sweeps from north to south along the upper and middle reaches of the Río Paraná. Thus, the largest part of this basin in Brazil, a smaller part of the West in Paraguay and in the south in Uruguay and Argentina. Again, the oldest sediments from the Silurian and also found in most parts of the basin are no significant sedimentation more instead. Characteristic of the Paraná Basin, the areal coverage of the basin fill is with flood basalts of the Cretaceous Serra Geral Formation ( see South America as part of the Gondwana continent ).

The Andes

The Andes are in stark contrast to the außerandinen areas of Atlantic South America. They belong as part of the circumpacific Fire Ring to the most troubled areas of the world. They are a young mountain range, which distinguishes them from the Paleozoic sedimentation and the even older archaic cores.

Although they do morphologically very uniform impression, they can be divided into three categories: South Andes (up to Valparaiso / Mendoza), Central Andes ( to limit Peru / Ecuador) and Northern Andes (up to the Sierra Nevada de Santa Marta and the Cordillera de Mérida ). According to present knowledge, it is increasingly clear that there was no common geosyncline as output for the orogeny, nor a fold, which had affected all parts of the Andes alike.

The Northern Andes

The northern Andes are divided into Ecuador in two mountain trains, while they fan out in Colombia in three moves.

The northern foothills of the Andes form the Sierra Nevada de Santa Marta and the Caribbean coastal mountains of Venezuela. The Caribbean coastal mountains, which reached south of Caracas heights of 2,800 m, is a highly complex orogenic belt of metamorphic rocks and deep-sea sediments. It is believed that oceanic crustal components were postponed by the collision between the Caribbean and the South American plate. The whole area here is characterized by numerous faults that have been active since the Tertiary, and which explain the high risk of earthquakes in north-eastern Venezuela.

The Caribbean Coast Mountains is geologically an extension of the Cordillera de Mérida, which in turn is the Ostausläufer the Eastern Cordillera of Colombia. The western foothills of the Eastern Cordillera, the Sierra de Perijá in Colombia. Both branches together frame the Maracaibo Bay. In contrast to the southern Andes volcanic rocks no more were mined here since the Paleozoic. The uplift of these two branches took place in the Eocene.

In Colombia, the differentiation into three branches ( Western, Central and Eastern Cordillera ) is clearly distinguishable. The Western Cordillera is overlain by basaltic rocks. The Central Range is clearly lifted her over (and also the Eastern Cordillera opposite). She was probably a high area in the Mesozoic. From the Miocene there was in this room to excessive volcanism accompanied by the formation of stratovolcanoes. In the Eastern Cordillera of the Precambrian base is locally disrupted, which is tectonically strongly verfaltet. They are based on powerful Cretaceous sediments, which were recognized even by no more orogeny. The Sierra Nevada de Santa Marta is surrounded by young depression from all sides. Therefore stands as an isolated block rugged over the Caribbean.

In the south of the northern Andes, in Ecuador, the Andes differentiate clearly into two strands: the Western Cordillera (Sierra ) and the Eastern Cordillera. The Western Cordillera consists of an alternation between basaltic rocks and Cretaceous deposits, which were, however, strongly verfaltet in the Tertiary. Between the two Andean chains is accumulated during the Tertiary grave valley of Quito. This is an approximate height 2500-3000 m and is characterized by pyroclastic and glaciogenic deposits. During the Tertiary were forming other volcanoes, both in the Valley of Quito as well as on the flanks of the Western and Eastern Cordillera. The Eastern Cordillera is, however, almost exclusively of metamorphic rocks.

The Central Andes

The coastal mountain range ( Cordillera Costal )

The coastal mountain range extends south of Lima starting over the entire length of the Andes down to the extreme south of South America. It extends partly as a cliff and reaching the Sierra Vicuña Mackenna in Antofagasta with over 3,000 m their highest elevations. It was built more than an old metamorphic base, which is still open in some places (eg in Mollendo and Arequipa in Peru). Between Jurassic and Cretaceous, there was already in the formation of basaltic and andesitic volcanic rocks as a result of an active continental margin. Both during the Late Palaeozoic, as well as during the Jurassic and the Cretaceous came the rise of plutons. Thus, the entire overburden the Coastal Cordillera is very strongly influenced by interference.

Central Valley ( Pampa de Tamarugal )

In northern Chile between Arica and Copiapó closes behind the Coast Range to the grave -like collapse of the Pampa de Tamarugal. Its internal structure is still unknown to a large extent.

Precordillera

Following the Central Valley ( Pampa de Tamarugal ) is likewise limited to that portion Precordillera, which runs to the west of Hochkordillere. It is composed in the substructure of highly folded Palaeozoic series and also of Mesozoic marine and volcanic deposits. In some places, all Jurassic deposits are formed marin.

Hochkordillere / Western Cordillera

From Lima to about the height Copiapós the Western Cordillera is covered by Cenozoic volcanic rocks. The volcanic activity began here 25 million years ago and continues to this day, what the existence of hundreds of peaks between 5,000 m - 7,000 m occupied. Between Copiapo and Iquique is located between the Precordillera and the Hochkordillere another sunken crust piece, at an altitude between 2,500 m - 3,500 m forms a plateau with numerous large salt lakes. In the southern part of the Hochkordillere the structural design of the Hochkordillere by the rise of plutons is characterized. On the Argentine Hochkordillere is also the Aconcagua ( 6,958 m ), the highest mountain in the Americas.

Puna / Altiplano

(Referred to in Argentina as Puna ) The Altiplano extends as a broad depression area of NW Argentina on Bolivia to Peru. This grave piece was greatly reduced in the Cenozoic compared to the surrounding Cordillera. The average heights of the Altiplano are 3500-4000 m; its surface is characterized mainly in the central and southern part by the appearance of extensive salt pans ( Salare ). It also appeared in the Miocene a strong volcanic activity that led to the formation of stratovolcanoes that tower over the Altiplano ( Queva ( 6,130 m), Antofalla ( 6,100 m) or Sajama ( 6,520 m))

Eastern Cordillera ( Cordillera Occidental)

The Eastern Cordillera starts in parallel with the Altiplano in NW- Argentina and Bolivia extends over almost to the height of Lima. In each section here proterozoisches rock is even open. However, the main material of the Eastern Cordillera are Paleozoic sediments, which were usually highly verfaltet. Here, too, on plutons that are partially exposed. The most impressive examples of this are the mountains Illampu and Illimani in La Paz

Cordillera Frontal ( Precordillera )

The Cordillera Frontal is a mountain range that runs exclusively in Argentina. It begins at the height of San Miguel de Tucumán and is characterized by Mesozoic Cenozoic volcanism and continental sediments. Your upstream is located as a separate mountain range the Precordillera of La Rioja on San Juan to Mendoza. Characteristic of this mountain chain are the Cambrian marine deposits.

Sierras Pampeanas

The Sierras Pampeanas, which lie south of the Puna, run exclusively in Argentina ( 24 ° S - 36 ° S). In them the highly folded and metamorphosed Proterozoic basement is open. Between the Pliocene and Pleistocene individual blocks and clumps were lifted.

Sierras Subandinas

The Andean foreland again comprises the entire transition region between the Cordillera and the lowlands between Peru and Argentina. The western part still consists of rolling hills, which then fall off but always flat to the east, until they finally merge into the plains.

The Southern Andes

The coastal mountain range ( Cordillera Costal )

The Coastal Cordillera consists of a horst -like upper torso, which was eroded in Cenozoic and covered by young sediments. From Tierra del Fuego to the south of the island of Chiloé plutons are also yet penetrated into the subsoil. The coastal mountain range loses its manifestation as a mountain range south of the island of Chiloe, but appeared 100 km further south in the form of numerous small islands, which are upstream of the southern Chilean coast, on. The Coastal Cordillera is thus a relic of the Gondwana - time, which was indeed incorporated from the Andes, but these 'foreign' faces.

The Central Valley (Valle Central)

The Chilean Central Valley already formed from 47 ° S in the local channels and runs from clearly identifiable to Santiago de Chile. This is probably a grave breach of experienced different degrees of reduction moves from north to south. One indication of this could be the Cenozoic sediments that reach Puerto Montt at a thickness of 4,000 m, while in the vicinity of Santiago, 500 meters could be detected. The Central Valley is of course with a variety of vertical disorders.

Hochkordillere ( Cordillera Central)

South of Santiago then reported at the 6,800 m high volcano Tupungato again an elongated volcanic chain. It consists of a variety of high explosive stratovolcanoes, which in turn were formed from andesitic to basaltic lavas. This 1000 km long volcanic chain loses quickly to the south in height and extends approximately up to 42 ° S south of Puerto Montt. From 42 ° S to play Mesozoic and Tertiary sedimentary overburden, the rest of the metamorphic basement rocks against the Cenozoic volcanism a greater role. In this zone there are only a few isolated volcanoes and the height of 3,000 m is rarely exceeded. Shaping the relief affects here Pleistocene glaciation with numerous glacial lakes, Karen and fjords.

Climate

Climatic conditions

The climate of South America is very complex. Year-round climatic influences are the cold Humboldt current along the west coast of Peru, the intertropical convergence zone ITCZ, the cyclone formation at the edge of the subtropical high pressure area and the trade winds.

The cold Humboldt ocean current causes a cooling of the sea surface off the coast of Peru and northern Chile, which leads to the formation of coastal deserts. This phenomenon is due to the fact that the cooled air to a constant inversion, thus resulting in a stable high pressure system that does not allow convection and thus no precipitation. The effects are vast desert regions on the coasts and fog near the sea surface.

The equatorial tropical location causes the formation of a southern winter Intertropical convection over the central Amazon region, which leads to heavy rainfall. In the austral summer she shifted further south, thus the inner tropics are characterized by year-round rainfall. Also in the austral summer continental thermal low forms of which ( in the austral summer ) is also rainy. The southern edge of the tropics were dominated by ( southern) summer precipitation.

The northern edge of the tropics are characterized by trade jam in the east (all year high precipitation) and by cool sea water on the coast in the north ( very low rainfall). The Südpassatwinde on the east coast lead to increased rainfall in the coastal regions. In the austral summer marked by the formation monsunaler easterlies and the southern winter by ram rainfall in the coastal regions.

The stable high-pressure system on the western edge of South America in conjunction with the cold air masses in the southern polar regions leads to the formation of cyclones off the coast Westpatagoniens. The cyclonic fronts vary in their location in the austral summer and southern winter. The shift to the north in the southern winter leads to periodic winter rainfall in southern Chile, as well as sporadic winter rainfall in central Chile. In turn, the shift of the cyclonic fronts in the austral summer results ( influenced by the changed position of the ITCZ ) to a pronounced summer drought in all of Central and Southern Chile and Patagonia.

The cyclonic fronts form at the Andenluvseite the Patagonian mountains violent congestion rainfall which can be referred to as hyper- maritime and occur throughout the year. The Chilean part of Patagonia thus has very high, year-round rainfall. The Andenleeseite Patagonia (Argentina ) is characterized by dryness. (see finite 2005).

Vertical differences in climate

The Andes themselves have a more climatic division in the vertical dimension. Thus, they can be divided into 5 levels. The Tierra Caliente ( Warm Earth, up to 1000 m ), the Tierra Templada ( moderate earth, up to 2000 m ), the Tierra Fria ( cold earth, to 3500 m, cultivation limit and frost line ), the Tierra Helada ( icy ground, up to 4500 m, snowline ) and the Tierra Glacial ( glacial earth until 6000 m, Anökumene ).

Glacial deposits

Furthermore, available in the Andes glaciations. In Peru, the largest Intertropical glaciation of the world are to be found. In Patagonia there is an extensive continental glaciation and down reaching down to sea level glacier tongue. Glaciers are found in the areas where there are plenty of year-round low temperatures and correspondingly high rainfall in height.

El Niño

One significant for South America climate phenomenon is the El Niño phenomenon (El Niño, the Christ Child ). This is not how often incorrectly used to a climatic, but a purely oceanic phenomenon. The cold water currents off South America and tear from it collects hot water off the South American coast. As a result, climatic thus abolishes the normally predominant stable high- pressure situation and there is a reversal of the Walker circulation ( between South America and Indonesia, length circular parallel). This reversal has serious consequences, as the hot water off the coast comes to a dramatic death of the normal kaltwassergewöhnten sea creatures and occur on land heavy precipitation. Otherwise, the drought characteristics of the landscape can be severely damaged in such heavy precipitation events ( slides, mudslides, etc.).

Hornos Island Cordillera Blanca Amazon River Gran Chaco Brazilian Highlands Gran Sabana Mya (unit) Shield (geology) Tectonics Basement (geology) Magmatism Mount Roraima Nevado Sajama San Juan, Argentina

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