America occupies the position of a watershed between the expanses of the Atlantic and Pacific Oceans.

From the west, it is bounded by folded mountain structures that rise steeply above the deeply submerged bed of the Pacific Ocean. In the east, the continents have abrasive shores. The continental slope is sharply defined and steep, rising at some distance from the coast above great depths. Atlantic Ocean.

The vast land masses of the Western Hemisphere - North and South America - are independent, historically unrelated continental structures. However, both continents have much in common. Their wedge-shaped outlines are south direction. The extended part of the land is facing north. West Banks The continents are bordered by high mountain ranges; plains predominate in their eastern part. North America in relation to South is located much to the west. The continents are separated by a latitudinal mobile zone, in which the island arcs of the Antilles and the mountain structures of Central America, which have already articulated with the continents, are located. The Antilles-Mexican region, as we noted (Bondarchuk, 1946), is a structural analogue of Indonesia, located between the continents of Asia and Australia.

North American Platform. Most of North America has a crystalline Precambrian basement. Precambrian rocks are found in the area Canadian shield. Separate Precambrian blocks protrude in Colorado, the Rocky Mountains, in the provinces of basins and ranges. Most of the N American Platform is covered by a thick sedimentary platform cover. In the north, in some islands of the Arctic archipelago and Greenland, the crystalline basement lies under a thick ice sheet.

The model of the structure of the North American platform, in the light of the data of K. K. Stockwell (1967) and F. B. King (1967), is characterized by such features. The oldest part of the crystalline basement in the Hudson Bay Basin, the central part of the United States and the Arctic Islands is covered by a platform cover. The Canadian shield has a zonal structure of Precambrian folded zones, gradually increasing its boundaries. Paleozoic and subsequent folded structures, building up the platform in the same way, determined the modern features of the tectoorogeny of the North American continent.

Within the territory under consideration, Precambrian folding is distinguished (King, 1967): Kenoran, Hudson, Elson, and Grenville. They deform thick Precambrian strata with a complex composition. The oldest formations shield are volcanogenic and sedimentary formations located among gneiss fields and other metamorphic rocks. These formations, as well as the gneisses surrounding them, host numerous gabbro and granite intrusions of different ages. Precambrian fold zones characterize individual provinces.

Kenoran folding is located in the southeast of the shield in the provinces of Upper and Slane, as well as in its northwestern part, bordering younger structures. Its age is 2390 million years.

The leveled surface of the Kenoran folding is overlain by undisturbed strata of the platform cover of the Proterozoic age. The Huronian folding includes Proterozoic deposits and older undivided gneisses and granites. It occupies the northeastern part of the shield, where it is adjacent to the Kenoran folding. In the northwestern part of the Canadian Shield, the Huronian folding is located between the areas of Kenoran folding. In Labrador and the southern edge of the Rocky Mountains, Nain Province, but according to F. B. King, these structures are reworked by later, Olson, folding.

The Huronian folding on the Canadian Shield is expressed in the provinces of Churchill, Bor, and South. Its age is determined by the early and middle Proterozoic about 1640 million years ago. The Elson folding is considered to be Middle-Late Proterozoic. It ended 1280 million years ago.

Late Proterozoic deposits lie horizontally on the Huronian folded basement.

In the southeast of the Canadian Shield, there is an area of ​​Grenville folding, concentrated mainly in the Grenville province. In the era of the Grenville folding, older structures were reworked. This folding belongs to the Late Proterozoic. It ended about 800 million years ago. On the Huronian folded basement, in some places, a platform cover of the Late Proterozoic age has been preserved.

An important role in the structure of the Canadian Shield is played by intrusions of mafic rocks, mainly gabbro and anorthosites, as well as alkaline syenites. These rocks are considered older than granites. The latter are of different age and are associated with the corresponding phases of folding. The largest intrusions are concentrated in the strata of the Kenoran structural stage. Among the post-orogenic formations, “circular structures” are distinguished, which are considered cryptovolcanic formations. They are rings of highly deformed rocks of the platform cover, and some of them belong to the Precambrian formations. Separate circular structures cut through the Kenoran and Grenville deposits. They contain igneous rocks and volcanic breccias of post-Ordovician age. Gabbro and diabase dikes are also known among the platform formations. Where the crystalline basement is exposed, all these rocks can be traced in relief.

The Precambrian basement of the N American Platform is perfectly aligned. It is strongly dissected by faults into blocks, the different positions of which create a series of depressions and elevations (Nalivkin, Gostintsev, Grossgeim, 1969).

The platform cover of the Canadian Shield is composed of sedimentary and volcanic rocks, their occurrence is horizontal or slightly disturbed. The age of the cover deposits is not the same. In the Upper Lake area, the Keninavan series of platform cover forms a wide syncline. Its layers are broken by normal faults and contain numerous bedded gabbro intrusions. In the western part of the shield and up to the Cordillera, the belt sedimentary series, also of Precambrian age, forms the platform cover. Its anchorage has not been broken.

In the Hudson Bay region, between the shield and the Appalachians, Paleozoic deposits take part in the structure of the shield. They form the lowlands south of the Canadian Shield, the plains of Western Canada, and extend into the Arctic archipelago. Further to the west, the platform cover is composed of Mesozoic and Cenozoic rocks.

In the southwestern part, the N American Platform stretches to the Rocky Mountains. Here it is broken by faults into separate blocks, one of which forms the Colorado Plateau. However, it is possible that this block is an independent island massif, one of the island system of the Cordillera fold zone. The Colorado Plateau is bounded on all sides by the structures of the Rocky Mountains. Only in the southwest does it break off with a steep ledge to the Khila valley.

The surface of the plateau rises to 1800-2600 m above sea level. The highest point - Mount San Francisco (3840 m) - an extinct volcano. The surface of the plateau is strongly denuded. Table ootans mountains and individual laccoliths rise above it. River valleys form grandiose canyons up to 1800 m deep.

The basement of the Colorado Plateau is composed of Precambrian crystalline rocks. They are overlain by a horizontally layered sequence of sedimentary rocks from Paleozoic to Quaternary age.

Intrusions are important igneous rocks and volcanogenic deposits, and on the outskirts of the plateau - lava flows. Extinct volcanoes and laccoliths make up character traits plateau landscapes.

Precambrian Greenlandic crystal shield, according to B. F. King (1967), has much in common with the structure of the Canadian Shield. It composes several islands covered with a common ice cover.

The Precambrian basement of the North American Platform is bordered by fold systems of different ages located between the craton and the oceans surrounding the mainland. The oldest of the Innuit (Caledonian) systems is located along the Arctic Ocean in Northern Greenland and in the north of the Arctic archipelago. The formations of the East Greenland fold zone are considered syntectonic with Innuitic. In the northeast of Greenland, both branches of the Caledonian are articulated. From here, the East Greenland Fold Zone extends south across Scoresby Bay. Deposits of the Cambrian, Ordovician, very thick Silurian and, in places, Devonian age take part in the structure of the Early Naleozoic folded structure. On the leveling surface of the Caledonides lies a platform cover of Carboniferous, Permian and Mesozoic deposits. In some places, the occurrence of these deposits is disturbed by faults.

The southeastern part of the North American Platform is bordered by the Appalachian (Hercynian) folded zone. The formation of this zone was completed in the early Mesozoic. Both sedimentary and igneous formations take part in the structure of the Appalachians. They form a mountainous terrain.

In the southwest, the Ouachita fold region is a continuation of the Appalachians. Its strongly leveled structures are buried over a large area under younger formations. They stretch towards the Pacific Ocean, into Mexico, and can be traced under the Cordillera, lying across the strike of their structures.

From the west, the N American Platform is framed by the Cordillera fold system, stretching from Alaska north to South America, where they are continued by the Andes of Venezuela and Colombia. The Cordilleras were formed on the site of several island arcs, they consist of parts of different ages and structures.

The inner zone of the Cordillera includes older formations, dislocated and penetrated by intrusions in the middle Mesozoic (Nevada orogeny). On the outer margins of the zone, structure formation developed later - in the Late Cretaceous and Paleogene (Laramian folding, orogeny of the Rocky Mountains and British Columbia). In the Tertiary period in the Cordillera mobile zone, folding developed in local basins. At that time, fault tectonics and related volcanism played an important role.

As a result of the outpouring of plateau basalts, large volcanic plateaus arose in the states of Oregon, Washington, British Columbia and Greenland. Their outpouring continued also in the Quaternary period. At this time, volcanic fields were formed in the state of Idaho of southern Mexico, etc., as well as volcanic ridges parallel to the general strike of folding in the Cascade Range, structures stretching along the Pacific coast in Central America from Guatemala to Costa Rica.

Along the Pacific coast and in the western part of the Cordillera, the Pacific Fold Zone stands out. The structures of the Antilles island system are considered to be synchronous to it. Deformations in this zone continue to this day.

The structure of the North American Platform is characterized by the same features as other Precambrian parts of the mainland. earth's crust. Its formation took place around the centers - the constituent parts of the island arcs. The process of structure formation in North America has naturally developed throughout the geological history. Its structures are spatially fixed and do not have drift layers.

The relief of the platform is characterized by a significant smoothness, large territories accumulative plains combined with highland countries. The brilliance of the country's landscapes is enriched by the extremely diverse forms of denudation, represented over large areas and often of enormous size. Their features reflect the influence of climate on the physical geography of the steppe plains, semi-deserts, snow-covered Arctic islands, mountainous countries and forested subtropics.

South American platform. The Precambrian crystalline basement of South America is exposed in the northern half of the mainland. Separate protrusions of it are known in the south in Argentina and Chile. In the northwest and west, the platform is framed by the folded mountain zone of the Andes. The mountains and basement projections are separated by the forward trough. Toward the Atlantic Ocean, the platform forms a steep continental slope and has abrasion shores. The general configuration of the coast of South America fully reflects the configuration of the adjacent part of the Mid-Atlantic Ridge.

In the structure of the South American platform, the Guinean, Central, or West Brazilian, Coastal, or East Brazilian shields are distinguished. Isolated protrusions of the Precambrian in the southern part of the mainland are the Apa, Tebikuari, Uruguayan, Northern Hills of Buenos Aires, the Pampa Blocky Country, the South Mendossa Massif, the Sovero-Patagonian and South Patagonian shields. They are separated by the Amazonian, Parnaibsky, San Franonsky, Paranskaya troughs and the Serra Geral plateau basalts associated with them, the La Plata depressions, or the Chaco-Pampasskaya, Rio Negro, Chubutskaya and Santa Cruz. Thick strata of platform cover occur within their limits.

The Guiana Shield lies in the north of South America between the Orinoco and Amazonian depressions. Its distribution generally corresponds to the Guiana Highlands. The surface of the shield is located within 500-1000 m in the west and 200-500 m above sea level in the east. The highest point - the top of Roranma - 2771 m. The highlands in the south are limited by steep slopes, and in the east - by rocky ridges. At the foot of the slopes is a hilly plain, gradually descending to the Amazonian lowland.

In the structure of the shield, sediments of the Middle and Late Pre-Cambrian age are distinguished. Hornblende and other gneisses, mica schists and granite gneisses are considered the oldest. It is associated with gabbro intrusions, as well as deposits of diabases and andesites. The younger formations of Guiana include ferruginous quartzites, a volcanogenic series of predominantly basaltic and andesitic tuffs. In the British part of Guiana, the volcanic series is composed of layered tuffs, agglomerates, lavas, quartzites, shales, and phyllites. This series is cut through by dolerite and gabbro intrusions. It contains large batholiths of granite.

The most complete Precambrian section has been described in French Guiana (Tugarinov and Voitkevich, 1966). The Cayenne system, composed of amphibolites, quartzites, hornfelses, gneisses, and migmatites with interlayers of crystalline limestones, belongs to the Lower Precambrian. These deposits are highly dislocated. The strike of their structures is variable, most often latitudinal. The Middle Precambrian is represented by the Paramaka system. It includes only intensely metamorphosed strata of chlorite, micaceous and talc schists interbedded with lavas, including peridotites and granite intrusions. Paramak deposits are folded. The Upper Precambrian of French Guiana is divided into two parts: the lower Bonidoro Series and the upper Oranou Series. The first is dominated by detrital rocks, shales, lavas, and volcanic tuffs, including granite intrusions; the second begins with strata of conglomerates, quartzites and shales lie above. It is also cut by granite intrusions, its folded structures extend in a west-north-west direction. The Oranu Series is intruded by rhyolites, on which the sedimentary-volcanogenic Roranma Series of post-Cambrian age overlies.

Three orogenic belts are distinguished in the structure of the coastal part of the Guiana Shield (Shubert, 1956). The oldest - Gilea - covers the Cayenne system. The sedimentary and igneous rocks composing it are highly metamorphosed. The middle belt - the Guianan - includes the strata of the Paramaca system and the youngest Caribbean - deposits of the Bonidoro and Oranu series.

Thus the Guiana Shield can be seen as independent center formation of the continental crust in the Precambrian. As on other shields, the expansion of the land occurred here sequentially, joining the core, composed of sedimentary-volcanogenic strata of new structural floors of folded zones.

After consolidation, the surface of the Guiana Shield was completely leveled. In the late Mesozoic, mainly in the Cretaceous, a cover of sandstones of continental origin formed on it. The remnants of this sandstone, which survived from denudation, form table uplands and play a significant role in the landscapes of the Guiana Highlands.

In the south, the Guianan shield separates the Amazonian trough from the Brazilian one. It stretches in a latitudinal direction from the Atlantic to the Pacific Ocean, from which it is separated by the folded zone of the Andes. Along the trough flows the greatest rock of the world, the Amazon, which has a tectonic valley (a very convincing example of the unity of the structure and topography of the earth's crust). The Amazonian trough is filled with Paleozoic and younger sediments. This is an inter-island accumulation basin. Its development continues in modern conditions.

The Brazilian shield is the central part of the mainland of South America south of the Amazonian trough. The Paramba-San Francisco meridional depression divides the shield into western, central and eastern, Atlantic, parts. Opies are considered as independent shields. The Paramba-San Frapsis Basin separating them is a relic of the interisland basin. The tectonic valleys of Paramba, San Francisco and the upper Parana are associated with it. In the south, the Parana and Chaco-Pampas depressions adjoin the Brazilian Shield.

The surface of the shield is very uneven and considerably raised. Throughout the shield corresponds to the Brazilian Highlands. This is an undulating plain, located on average at an altitude of 600-800 m above sea level. The crystalline foundation of the shield is broken by numerous faults into blocks that are significantly displaced relative to each other. The position of the blocks creates the orographic appearance of the highlands.

The most elevated part of the Brazilian Highlands is made up of blocky massifs of Pico di Bandeira - 2884 m and the city of Itatnaya - 2821 m above sea level. In the central part of Brazil, the watershed of the Paranaiba - Tacantins rivers rises to 1678 m. In the east, the highlands form the Great Ledge - 1000-1500 m above sea level and break off as a fault ledge to the Atlantic Ocean. Along the right bank of São Francisco, blocky ridges of the Serra do Espinhaço (up to 1800 m) stretch from the northeast to the southwest. In the south of the highlands lies the vast Serra Geral lava plateau, rising to a height of up to 1018 m.

The structure of the Brazilian shield is very complex and has not yet been sufficiently studied. The stratigraphic subdivision of the sedimentary-metamorphic complexes composing it includes an extremely large number of series and systems, the relationship of which is not unified. Conditionally, in the structure of the crystalline basement, the Precambrian is lower, middle and upper. The most ancient are the Bakoa gneisses, whose age is 2400-2500 million years. Younger formations of the Middle and Upper Precambrian are distinguished in the Minae and Itakolomi series.

The composition of the Minae series is quite variable. In the Barbacena region, it is represented by strata of gneisses and shales; north of Lafayette, the Middle Precambrian includes conglomerates, quartzites, dolomites, iron formations, graphite phyllites, lava flows, and volcanic tuffs. The thickness of the series exceeds 3000 m. It includes intrusions of ultramafic rocks and diorites. The ultramafic rocks are locally transformed into serpentinite and talc schists. The entire sequence has a northeast strike. In its southern part, isoclinal folding is well expressed. Numerous faults are known. The formation of this series is correlated with the Grenville formations of North America.

The Itacolomi Series of the Upper Precambrian of Brazil is composed of sedimentary-metamorphic strata, which include phyllites, itabirites (thin-layered, flyschoid, ferruginous quartzites), dolomites, detrital rocks, talc schists, etc. The thickness of the series is about 3000 m.

The general section of the ancient deposits of the Brazilian Shield ends with clastic sedimentary rocks of the Lavras and Bambum series, the age of which is considered Late Precambrian - Early Paleozoic. Some deposits of the Lavras Series are considered as tillites.

The structure of the Brazilian Shield is not well understood. So far, there are four stages in the history of its structure formation: 2400–2510, 1000–1100, 720–760, and 460–600 Ma (Tugarinov and Voitkevich, 1966). Structural relationships of parts of the shield of different ages are most fully displayed in the state of Mipas Gerais. The central part of the massif here is made up of Bakao gneisses (2400, 2510 million years), they are bordered by formations aged 1350 million years, further - sedimentary-metamorphic strata of Rio das Veyjas. From the east and west they are bordered by the formations of the Minae series, and from the south by the massifs of the Itakolomi series.

Thus, the general plan of the structure of the Brazilian Shield is a consistent expansion of the ancient structural centers due to the attachment of folded regions, which is also characteristic of the South American platform. The consolidation of the Brazilian Shield ended in the Late Precambrian. Subsequently, its surface was leveled for a long time and was the arena for the formation of a platform cover. The submeridional depression separating the shield is filled with Paleozoic and Mesozoic deposits. In places, the platform cover on the shield is composed of Triassic continental formations, marine layers of the Turonian and Paleocene age in the northern part and in the center - continental horizontally occurring Eocene strata.

The relief of the Brazilian Shield, as well as other Precambrian massifs, is characterized primarily by the position of the leveling surface deformed by faults and the position of blocks. In exposed places, the surface of the Precambrian basement has the appearance of a hilly or undulating plain, the features of which vary significantly depending on the composition of the exposed rocks. The surface dissected by erosion is characterized by rocky relief. The rivers here are rapids, mountainous.

In places covered by platform cover, the Brazilian Shield has a two-story structure. The lower floor is a crystalline plinth, the upper one is a platform cover. It is characterized by a flat surface of plateaus and plateaus, mesas, remnant elevations, limited steep or gentle slopes, the features of which in each individual case are due to the nature of the deposits exposed by depudation and many climatic factors.

In the southern part of the mainland of South America, the Precambrian formations act as separate, unrelated massifs, which in the past were independent islands. Their structure has been studied very little.

In the structure of the Uruguay crystalline shield, the Lower, Middle, and Upper Precambrian are distinguished. The Lower Precambrian deposits are extended along the La Plata valley and have a sublatitudinal strike. Their composition includes various gneisses and mica schists hosting granite intrusions. The Middle Precambrian - the Minae Formation of Uruguay - includes massive quartzites, lenses of crystalline limestones, talc schists and volcanogenic deposits. The intrusions are represented by alkaline rocks and granitoids. Upper Precambrian rocks are combined into the Otgua series. The latter includes volcanic breccias and folded quartzites. Their structures extend in the meridional and northeast directions.

Between Uruguay and the Brazilian Shield, a vast territory is occupied by the Serra Geral volcanic plateau, structurally connected with the La Plata depression. The plateau has a flat, slightly dissected surface.

Crystalline massifs in the central part of South America stand out along Paraguay - the Ana and Tebikuari horsts. In the south of the mainland, the Precambrian protrusions are concentrated in the west and are adjacent to the mobile Pacific zone. In Patagonia, they form separate shields separated by large depressions. In the Precambrian of the central part of Argentina, phyllites and greywackes are known, crumpled into folds. Their age is considered late Precambrian. In the ridges of Catamarca, La Rioya, San Luis, metamorphic strata contain granite batholiths. The gneisses of the hills of Buenos Aires host diorite intrusions.

There is still very little data on the features of the relief of the Precambrian massifs in the southern part of the South American Platform.

From the west, South America is bordered by a grandiose shaft of the South American Cordillera, which separates the platform from the Pacific Ocean. Between the platform and the folded mountain system, a foothill trough is stretched, made mainly by Cenozoic deposits. The structure of the Cordillera is complex and combines parts of different ages. The model of the cross section of the Cordillera folded zone from east to west consists of the following structural elements:

1) a platform steeply plunging to the west;

2) the forward trough of the Andes;

3) Eastern Cordillera, composed of sedimentary deposits of Paleozoic age, crumpled into folds. At the outer edge, this fold system contains isolated massifs of Precambrian schist, including granite intrusions;

4) Western Cordillera, composed of marine sediments of the Mesozoic age and younger volcanogenic formations. Their volcanic cones form the highest peaks - Chimborazo 6310 m, Cotopaxi 5943 m. In the structure of the mountains, a batholith elongated along the strike of the mountains stands out;

5) remains, or, more precisely, islands, mainly of Hercynian structures. The entire mountain range rises steeply above the adjacent deep depressions of the Pacific Ocean floor.

There are four phases in the formation of the structure of the South American Cordillera. The main folds and faults were laid in the chalk. Thrusts were formed, volcanic activity became more active. Structural formation reached its greatest strength in the early Oligocene, when the Eastern Cordillera was formed. Volcanic activity began in the Andes and continues to this day. A new intensification of movements occurred in the Miocene. Then there were many faults and normal faults, accompanied by numerous intrusions. Intrusive rocks of this age are especially common in the foothills of the Andes. Later, a leveling surface was developed in the Andes. The last phase of mountain building occurred in the Pleistocene. As a result of the general arched uplift, the modern Andes were formed. The uplift was accompanied by grandiose faults and block movements, which created the modern topography of the mountains (King, 1967).

The structure of the South American Cordillera, as rightly stated by W. Oppenheim (Oppenheim, 1948), is final result development of the Late Mesozoic island arc composed of igneous rocks. The islands were separated from the mainland by a geosynclinal trough, and from the ocean by a deep depression. This structure emerged in the Cretaceous, during the first phase of orogeny in the Andes. Since then, the western structural boundary of the mainland has changed little. At the beginning of the Cenozoic, the islands, in the structure of which volcanic rocks took part, gradually united into one mountain shaft. The adjacent geosyncline was filled with terrigenous masses and limestones of marine origin. Accumulation continued until the Middle Oligocene. In the middle of the Cenozoic, the Eastern Cordillera took shape. The succession of mountain uplift is reflected in leveling surfaces and river terraces, indicating periodic rejuvenation of valley erosion.

Structural and geomorphological analysis shows that the mainland of South America has a heterogeneous structure. Its main components - the Guiana and Brazilian shields and the Amazonian trough that separates them - are the most ancient parts of the mainland. They are characterized by a sublatitudinal extent. The southern part of the mainland unites structures of different ages, the main elements of which are paleotectonic island systems, in the east - crystalline massifs of the southern part of the East Brazilian, Coastal and Uruguayan shields, in the west - the blocky country of the Pampas, the North and South Patagonian shields, etc. Between the eastern and the western systems, the La Plata depression in the south has the same importance in the structure of the mainland as the Amazonian depression in the north. With the formation in the Cenozoic of the complex folded system of the South American Cordillera at the site of island arcs, the final configuration and orography of South America was determined.

The main tectonic element of North America is the North Amer and Kan platform with the Canadian crystal shield within the platform, a number of large tectonic elements are distinguished that control the location of oil and gas provinces and regions (Fig. 54)

In the inner part of the platform, Paleozoic oil and gas bearing provinces are distinguished, within which oil and gas bearing areas associated with tectonic elements are isolated: with the arched uplifts of Cincinnati, Central Kansas, etc.; with intraplatform depressions Illinois, Michigan, Permian basin. In the junction zones of the platform with folded belts, the Paleozoic Appalachian in the east and the Paleozoic-Mesozoic of the Rocky Mountains in the west stand out. In the southwest of the continent, the Gulf Coast (Gulf of Mexico) province is distinguished, which is a passive continental margin of the North American continent that has been developing since the Lower Mesozoic. On the Pacific coast

arctic ocean

Rice. 54. Scheme of tectonic and petrogeological zoning of North America (according to Yu.N. Uspenskaya).

1 - outcrops of the Precambrian crystalline basement, 2 - area of ​​development of the Caledonian folding, 3 - area of ​​development of the Hercynian folding, 4 - areas of development of the Mesozoic-Cenozoic folding of the Cordillera, 5 - oil and gas areas of the North American platform, 6 - intermountain depressions of the Cordillera folded belt.

Oil and gas bearing provinces and regions: 1 - Colville trough; 2 - Beaufort-Mackenzie basin; 3 - Albert depression; 4 - syneclise Williston; 5 - intermontane depressions of the Rocky Mountains; 6 - Internal western province; 7 - Perm depression; 8 - bend arch; 9 - ledge Azark; 10 - Illinois depression; 11 - Michigan depression; 12 - the arch of Cincinnati; 13 - Pre-Appalachian trough; 14 - province Gulf of Mexico; 15 - Atlantic province; 16 - California; 17 - Cook's Bay.

the California province of Alpine age stands out. On the Alaska Peninsula, two provinces are distinguished - the Paleozoic-Mesozoic of the Arctic slope (Colville Basin) and the Cenozoic of Cook Inlet on the Pacific coast of the peninsula.

North American Continent differs most a high degree intelligence.

Deposits are known here in deposits from the Cambrian to the Pliocene, confined to a wide variety of traps within large intra-platform depressions and uplifts, in zones of articulation of the platform with folded areas, various intermountain depressions and modern passive and active continental margins. As an example of a large vault, we can cite the Tsincinnati vault, which is 1000 km long and up to 400 km wide. The deposits are confined to local brachianticlines and zones of wedging out of sandstones. The main productive horizons are concentrated in the Ordovician and Silurian parts of the section. One of the richest intraplatform structures is the Permian depression. Its area is 365 thousand km 2. The deposits are confined to local structures and traps of stratigraphic and lithological types. The main productive horizons are concentrated in the Permian and Carboniferous parts of the section. In total, more than 5.5 thousand deposits have been discovered here. The Western Canadian Petroleum Province is a typical example structures of the junction zone of the ancient platform with the folded area. Here, the deposits are confined to local structures, pinchout zones, and reef structures; in the junction zone of the trough with the folded zone, deposits associated with thrust dislocations are widely developed; on the eastern side of the trough, the world's largest deposits of heavy oils and malts are known (fields Athabasca, Vabasca, etc.), with reserves of 120 billion tons. The oil and gas province of the Gulf of Mexico is an example of the oil and gas potential of a passive continental margin that continues its development. Its evolution begins from the Permo-Triassic period. The stratigraphic range of oil and gas potential is from Upper Jurassic to Quaternary deposits. The number of productive horizons exceeds 100. The deposits are associated with local structures, diapiric domes, stratigraphic and lithological types of traps. A large number of deposits discovered in the waters of the Gulf of Mexico (about 500). Among the largest fields in this province is the East Texas oil field, the second largest in the United States (initial recoverable reserves of about 800 million tons). It is assumed that this field will be developed for almost 100 years; by the beginning of the 1990s, more than 600 million tons were produced at the field. oil (beginning of production in 1933).

Numerous Cenozoic intermountain depressions are located on the western coast of the continent, the productive horizons in which are confined to Miocene and Pliocene sediments. In the south of the Alaska Peninsula, there is the oil and gas region of Cook Inlet, which is genetically related to the active continental margin that continues to develop. Oil and gas fields are discovered here both on the mainland and in the waters of the bay.

In the United States, the largest oil field in the northern hemisphere, Prudhoe Bay (province of the Arctic slope of Alaska), was discovered. The deposit is confined to an anticline cut by an unconformity (Fig. SS). Three deposits were found at the field in the depth interval of 2050-3200 m in the Permian-Carboniferous, Triassic and Lower Cretaceous deposits. The recoverable oil reserves at the field are estimated at 1.3 billion m 3 .

Rme. 55 Schematic section of the Prue do Bay field (Gabrieliants, 1984). 1 - oil; 2 - gas; 3 - water; 4 - surface of stratigraphic unconformity.

Geological structure North America

At the base North America and most Greenland lies the Precambrian North American Platform, which is sometimes called Canadian. The foundation of the platform in some places goes to surface, forming Canadian-Granland Shield. The shield formed by faults consists of metamorphosed volcanic rocks and granite gneisses of the Archean Early Proterozoic age. Grenville belt, which stretches in the southeastern part shield, formed by Early Precambrian rocks and metamorphosed Proterozoic carbonate-clastic formations.

As geophysical studies and drilling data show, the basement, covered with a sedimentary cover, is also composed of Early Precambrian metamorphosed sedimentary-volcanic rocks and granite-gneisses. In the building rocky mountains USA viewed Early Precambrian crystalline rocks. Sedimentary cover platform extends south, west and north of the Canadian Shield, and its greatest area observed in the area Midcontinent and Great Plains. The depth of the foundation changes, so a number of large hollows – syneclise, with a depth of $3$-$4$ km and vaults – anteclise. Part of the platform in the southwest dissects moving zone mountains washita.

In the meridian Great Plains continued into the Mesozoic subsidence and accumulation coastal-marine and continental precipitation. Finally, marine sediments were displaced by continental ones at the beginning cenozoic era , followed by a complete platform drainage.

Paleozoic cover platforms in addition to the Midcontinent and the Great Plains extends to Arctic her slope. Here it forms the southern part of the Canadian Arctic archipelago. Shallow but big syneclise Hudson Bay is filled with formations similar in composition and age. Its central part is thin continental precipitation jura and chalk.

Caledonides Northeast Greenland are the most ancient link folded framing of the North American platform. In the form of tectonic covers, they are pushed over the edge of the platform, and are composed of a thick layer of sedimentary terrigenous-carbonate rocks of the Lower Paleozoic. Along the fault, the so-called logan line, the fold system of Newfoundland and the Northern Appalachians border the Canadian Shield.

Line Logan represents thrust geosynclinal Paleozoic strata to platform Paleozoic and Precambrian. Narrow grabens with continental sediments and basaltic lavas are also present in Northern and Southern Appalachian. This is evidence that before entering the platform stage of development, the Appalachian system was fragmented.

Zone Hercynian folding within the coastal lowlands - from the Gulf of Mexico - blocked by powerful Cenozoic deposits. System Canadian Arctic Archipelago and north Greenland related to Hercynian folding, are composed of terrigenous-carbonate deposits of the Cambrian-Devonian.

Folded Cordillera belt, located along the Pacific coast, almost along its entire length borders on North American platform, with the exception of Alaska. Here this belt is limited by the ridge system Brooks. Along the Pacific coast is the main seismically active zone of North America.

Remark 1

The zone is characterized by destructive earthquakes- Alaskan ($1964), Mexican ($1985), San Francisco ($1906). In the future, this area is still seismic, especially in those places where it intersects with the latitudinal transform faults of the Pacific Ocean.

Relief of North America

The relief of North America is characterized by a fairly large variety and contrast.

To replace almost flat plains in the central part of the mainland come extensive rolling expanses, neighboring in the east with low Appalachians.

To the west, the Central Plains adjoin Cordillera. The peaks of these mountain structures are sharp and reach a height of more than $6000 m. The relief of the mainland and its features are connected with history. geological development territory. Ancient The North American Platform and its crystalline basement formed over the course of Archean and Proterozoic eras. Canadian Crystal shield in relief corresponds Laurentian elevation.

On the stove, located south of the Canadian Shield, are Central and Great Plains. The Great Plains stretch from north to south for $3500$ km and are located in the western part of the platform. Their height reaches $1500$ m, which can be explained by powerful uplifts of the earth's crust in the region of the Cordillera folding.

south of Laurentian hills are located Central Plains. In the south of the mainland are Mexican and Atlantic lowlands formed on the foundation of a young platform covered with a layer of sedimentary deposits. Appalachians are old, ruined mountains, with smoothed and low ridges. Folding in them occurred in the Caledonian and Hercynian periods.

In the west of the mainland, grandiose folding began as early as mesozoic era as a result of the collision of lithospheric plates and continues to the present. Arising here Cordillera stretched in the meridional direction for $9000$ km, with a width of $1600$ km.

The mountains do not end in the south of the mainland, but continue into South America . The peak of the Cordillera is the mountain McKinley, whose height is $6193$ m. Numerous faults of the Pacific ocean floor continue in the Cordillera ranges. The mountains are characterized by the largest volcanoes planets - Popocatepetl and Orizaba.

Remark 2

Not only internal but also external processes took part in the formation of the relief. Northern regions mainland up to $40$ parallels covered glacier, which in its size exceeded the area of ​​Australia by $2$ times. The movement of the glacier leveled the surface, polished even the rocks. The glacier created thousands of hills long distance and many small landforms.

Beyond the glacier in landform formation Active participation accepted surface water, groundwater and wind. For example, the work of the river Colorado created Grand Canyon, the depth of which is $1600$ m, and the length is $400$ km. The largest on the planet Mamontov a cave was formed underground water, and activities wind led to the emergence of dunes, dunes and other landforms.

Minerals of the mainland

Subsoil of North America rich in minerals and related to its geological structure. The biggest in the world ore deposits occur in the area Canadian Crystal Shield where igneous and metamorphic rocks are shallow. The largest deposits are concentrated here iron, nickel, copper, uranium, molybdenum.

Coal located in a thick layer of sedimentary rocks Central Plains , and coastal lowlands and shelf seas have large deposits oil and gas. Hydrocarbon production is carried out both onshore and from the day Mexican bay. The intermountain depressions of the Appalachians also have significant reserves stone coal.

AT Cordillera large mineral deposits of both igneous and sedimentary origin are concentrated. There is non-ferrous metal ores, gold, mercury. In the east and in the trough of the earth's crust between Cordillera and North American Platform lie down oil, gas, coal. Significant reserves and diverse minerals are an important natural resource. raw material base for the development of the economy of the countries located on this mainland.

Relief of North America predominantly flat, because most of it lies within platforms. The western and eastern parts of the mainland were formed at different geological times - western part in Mesozoic and Cenozoic, a eastern part - in Paleozoic.

Remark 3

The ancient and ruined Appalachians are located in the east of the mainland, and the high and young Cordilleras are located in the west. associated with the peculiarities of the geological structure. wealth and diversity minerals of the mainland. And such minerals as coal, oil, natural gas, iron, nickel, molybdenum ores and uranium have global importance.

More than half of the mainland is occupied by the ancient North American Platform, part of the North American lithospheric plate. The northeastern part of the platform is uplifted; here its ancient crystalline base comes to the surface, forming the Canadian Shield. In the western and southern parts of the platform, the crystalline basement is hidden under a layer of sedimentary rocks.

The North American Platform is bordered by folded belts: in the north, east and south - by the ancient systems of the Canadian Arctic Archipelago, Greenland and the Appalachians, in the west - by the younger Cordillera folded system. The youngest ranges of the Cordillera are western. They were formed in the Pacific fold belt during the convergence of the North American and Pacific lithospheric plates.

The landscape is closely related to tectonic structure and geological history mainland development. In the eastern part of the continent, on an ancient platform, there are low-lying or elevated plains, which differ in the forms of their relief.

In the north and in the center, landforms created by ancient continental glaciation are widespread. ancient glacier covered more than half of the mainland and reached the 38th parallel. The glacier turned the hard rocks of the Canadian Shield into gentle hills and ridges, rounded rocks and sheep's foreheads. He expanded and deepened the river valleys, turning them into long narrow bays - fjords. Morainic deposits with numerous boulders were left by the glacier in the lower Central Plains. In loose sedimentary rocks, he plowed the basins of modern lakes.

Along eastern slopes The Great Plains stretch from north to south. These are high plateaus (500-1500 m), descending in “steps” to the Central Plains. The surface of the plains is indented by numerous deep ravines. These territories were called badlands (“bad lands”), because they are completely unsuitable for use in the economy. In the south, the Central Plains pass into the coastal flat marshy lowlands - the Mexican and Atlantic.

Along the southeastern margin of the mainland stretch the Appalachian Mountains (the highest point is Mount Mitchell, 2037 m), formed in the ancient belt of folding. They are strongly destroyed by modern erosion processes, have gentle slopes and flat tops. There are many karst caves in the foothills of the Appalachians. Here is the famous Mammoth Cave - one of the largest on Earth (the length of the explored part is 587 km).

The western part of the mainland is occupied by a powerful mountain system Cordillera. In its northern part is the highest point of the continent - Mt. McKinley (6194 m). The Cordilleras consist of three mountain belts stretched from north to south. The eastern belt is formed by the high Rocky Mountains, the Central - by the chains extinct volcanoes The Cascade Mountains and the Sierra Nevada Mountains, Western - the Coast Ranges system, part of the modern Pacific fold belt. In the northern part of the Cordillera, all three belts are pressed against each other, in the center they are separated by valleys and plateaus.

Among them are the volcanic Yellowstone Plateau, the Great Basin Plateau and the Colorado Plateau, indented by deep canyons. Canyon - deep river valley with steep slopes and a relatively narrow bottom occupied by the riverbed.

The Yellowstone plateau is covered with solidified lava with many mud volcanoes, hot reservoirs, springs (over 3000) and geysers. In the crater of the largest volcano on the continent is one of the largest alpine lakes on the mainland - Lake Yellowstone.

The Colorado Plateau is famous for its Grand Canyon - the valleys of the Colorado rivers and its tributaries. Its depth reaches 1800 m, its length is 446 km. Having cut through the plateau, the rivers opened up and exposed ancient geological layers of different ages. Therefore, the Grand Canyon is called an open-air geological museum.

From the west, the central belt is contoured by a strip of deep narrow valleys, including the California Valley and the most low point surface of the mainland - lifeless Death Valley (-86 m).

In the south of the mainland, all the mountain belts of the Cordillera converge, forming the lava Mexican Highlands. There are many active volcanoes in the south of the highlands, the highest of which is the Orizaba volcano (5610 m). The Coast Ranges, the California Valley and the Mexican Highlands are part of the Pacific Ring of Fire.

Minerals of North America

North America is rich in various minerals. Of the combustible minerals, the most significant reserves are oil, gas, and coal. Oil and gas fields are located on the Pacific coast of the United States, the Mexican lowland, on the shelf marginal seas the Arctic Ocean, Alaska, the south of the Central and Great Plains. hard coal the east of the Central Plains and the foothills of the Appalachians are rich. Place of Birth brown coal there are on the Great Plains, in the intermountain basins of the Cordilleras, in Alaska.

The largest reserves of iron ores are concentrated in the crystalline rocks of the Canadian Shield in the area of ​​Lake Superior and the Labrador Peninsula, in the Northern Appalachians. Ores of non-ferrous metals are widespread: copper (Rocky Mountains, Mexican Highlands, Canadian Shield), lead-zinc (Mississippi Valley, Cordillera), bauxite (Jamaica), nickel (Laurentian Upland, Cuba). Powerful reserves of uranium ores are concentrated on the Colorado Plateau, gold - in the river basin. Yukon and the southwestern United States.

Among non-metallic minerals, there are significant reserves of phosphorites (Florida Peninsula), asbestos (Appalachians) and potash salts (south of the Great Plains, Great Lakes region).

The mainland is part of the North American lithospheric plate. Its core is the ancient North American Platform. In the north, east and south, it is bordered by the ancient systems of the Canadian Arctic Archipelago, Greenland and the Appalachians, in the west by the young folded Cordillera belt. The western chains of the Cordilleras and Central America are characterized by high seismicity and are part of the Pacific Ring of Fire. The mainland is rich in minerals.

NORTH AMERICAN (CANADIAN) platform - Precambrian platform, covering most Sev. America and about. Greenland. The basement protrudes to the surface within the Canadian Shield in the central and northeastern parts of the platform. The sedimentary cover of the plates is composed of rocks of the Ordovician-Carboniferous and Permian ages (Midcontinent plate), Paleozoic, Mesozoic and Cenozoic (Great Plains plate).

• - In the history of polar research, several moments can be distinguished, such as: the search for the northeast and northwest passages and then the study of the polar countries, carried out already with a direct scientific goal ...

  Encyclopedic Dictionary of Brockhaus and Euphron

• - North American platform, ancient platform in the central part of the mainland of the same name. See North America, section Geological structure and minerals...
• - lowering of the bottom of the Atlantic Ocean between the underwater North Atlantic Ridge, the continental slope of North America and the underwater elevation of the arc of the West Indies ...

  Great Soviet Encyclopedia

• - lowering of the bottom in the northwestern part of the Atlantic Ocean, off the coast of the North. America...
• - NORTH AMERICAN platform - Precambrian platform, covering most of the North. America and about. Greenland...

  Large encyclopedic Dictionary

• - SOUTH AMERICAN platform - Precambrian platform, occupying the central and eastern parts of the South. America. The foundation protrudes to the surface within the Guiana and Brazilian shields...

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