Geological structure and relief of North America. Geological structure, relief, minerals of North America
The main tectonic element of North America is the North American and Canadian platform crystal shield within the platform there are a number of large tectonic elements that control the location of oil and gas provinces and areas (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 zones of junction of the platform with fold belts, the Paleozoic Appalachian in the east and the Paleozoic-Mesozoic Rocky Mountains in the west are distinguished. In the southwest of the continent, the Gulf Coast Province (Gulf of Mexico) stands out, which is a passive continental margin of the North American continent developing from the Lower Mesozoic. On the Pacific Coast
Arctic Ocean
Rice. 54. Scheme of tectonic and petroleum geological 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-bearing territories of the North American platform, 6 - intermountain depressions of the Cordilleran fold belt.
Oil and gas bearing provinces and areas: 1 - Colville trough; 2 - Beaufort-Mackenzie basin; 3 - Alberta depression; 4 - Williston syneclise; 5 - intermountain depressions of the Rocky Mountains; 6 - Inner Western Province; 7 - Permian depression; 8 - Bend arch; 9 - Azark ledge; 10 - Illinois depression; 11 - Michigan depression; 12 - Cincinnati arch; 13 - Pre-Appalachian trough; 14 - Gulf of Mexico province; 15 - Atlantic province; 16 - California; 17 - Cook Bay.
The Californian province of alpine age stands out. There are two provinces on the Alaska Peninsula - the Paleozoic-Mesozoic - Arctic slope (Colville Depression) and the Cenozoic Cook Inlet on the Pacific coast of the peninsula.
The North American continent has the highest degree of exploration.
Here, deposits are known in sediments from the Cambrian to the Pliocene, confined to a wide variety of traps within large intraplatform depressions and uplifts, in the zones of junction of the platform with folded regions, various intermountain depressions and modern passive and active continental margins. An example of a large vault is the Cincinnati Vault, which is 1000 km long and up to 400 km wide. The deposits are confined to local brachyanticlines and sandstone pinchout zones. The main productive horizons are concentrated in the Ordovician and Silurian parts of the section. One of the richest intraplatform structures is the Permian Basin. 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 oil and gas province is typical example structures of the articulation zone of the ancient platform with folded area. Here the deposits are confined to local structures, pinch-out zones and reef structures; in the zone of junction 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 (Athabasca, Wabasca, etc. fields), 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 with the Permo-Triassic period. The stratigraphic range of oil and gas content is from Upper Jurassic to Quaternary deposits. The number of productive horizons exceeds 100. The deposits are confined to local structures, diapiric domes, and traps of stratigraphic and lithological types. A large number of deposits have been discovered in 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 are about 800 million tons). It is expected that this field will be developed for almost 100 years; by the beginning of the 90s, more than 600 million tons were produced at the field. oil (beginning of production 1933).
On the western coast of the continent there are numerous Cenozoic intermontane depressions, the productive horizons of which are confined to Miocene and Pliocene sediments. In the south of the Alaska Peninsula there is the oil and gas bearing region of Cook Inlet, genetically connected with the active continental margin that continues to develop. Oil and gas fields have been discovered here both on the mainland and in the waters of the bay.
The largest oil field in the northern hemisphere, Prudhoe Bay (province of the Arctic slope of Alaska), was discovered in the United States. The deposit is confined to an anticline cut off by an unconformity surface (Fig. SS). Three deposits have been identified at the field in the depth range of 2050-3200 m in Permian-Carboniferous, Triassic and Lower Cretaceous sediments. Recoverable oil reserves at the field are estimated at 1.3 billion m 3 .
Rme. 55 Schematic section of the Pru do Bay field (Gabrielyants, 1984). 1 - oil; 2 - gas; 3 - water; 4 - surface of stratigraphic unconformity.
More than half of the continent's territory is occupied by the ancient North American Platform, part of the North American lithospheric plate. The northeastern part of the platform is raised; here its ancient crystalline base emerges 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 folded system of the Cordillera. The youngest ranges of the Cordillera are the western ones. They formed in the Pacific fold belt at the convergence of the North American and Pacific Oceans. lithospheric plates.
The relief is closely related to the tectonic structure and geological history of the development of the continent. In the eastern part of the continent, on an ancient platform, there are lowland or elevated plains, differing in the shape of their relief.
In the north and center, landforms created by ancient continental glaciation are widespread. The ancient glacier covered more than half of the continent and reached the 38th parallel. The glacier turned the hard rocks of the Canadian Shield into gentle hills and ridges, rounded rocks like ram's foreheads. He expanded and deepened river valleys, turning them into long narrow bays - fjords. The glacier left moraine deposits with numerous boulders on the lower Central Plains. In loose sedimentary rocks, he plowed out the basins of modern lakes.
The Great Plains stretch along the eastern slopes of the Cordillera 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 are called badlands (“bad lands”) because they are completely unsuitable for agricultural use. In the south, the Central Plains turn into coastal flat swampy lowlands - the Mexican and Atlantic.
Along the southeastern edge of the continent stretch the Appalachian Mountains (the highest point is Mount Mitchell, 2037 m), formed in an ancient fold belt. They are heavily destroyed by modern erosion processes, have gentle slopes and flat tops. There are many karst caves in the Appalachian foothills. 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 continent is occupied by the powerful Cordillera mountain system. In its northern part is the highest point of the continent - McKinley (6194 m). The Cordillera consists of three mountain belts stretching from north to south. The eastern belt is formed by the high Rocky Mountains, the Central belt is formed by the chains of extinct volcanoes of the Cascade Mountains and the Sierra Nevada Mountains, the Western belt is formed by 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, the Yellowstone volcanic plateau, the Great Basin plateau and the Colorado plateau, cut by deep canyons, stand out. Canyon - deep river valley with steep slopes and a relatively narrow bottom occupied by the river bed.
The Yellowstone Plateau is covered with hardened lava with many mud volcanoes, hot pools, springs (more than 3000) and geysers. In the crater of the largest volcano on the continent there is one of the largest high-altitude lakes on the continent - Lake Yellowstone.
The Colorado Plateau is famous for its Grand Canyon - the valleys of the Colorado River and its tributaries. Its depth reaches 1800 m, length - 446 km. Having cut through the plateau, the rivers opened up and exposed ancient geological layers of different ages. That's why the Grand Canyon is called an open-air geological museum.
From the west, the central belt is outlined by a strip of deep narrow valleys, including the California Valley and the lowest point on the continent's surface - the lifeless Death Valley (–86 m).
In the south of the mainland, all the mountain belts of the Cordillera converge, forming the lava Mexican Highlands. In the south of the highlands there are many active volcanoes, the highest of which is the Orizaba volcano (5610 m). The Coast Ranges, California Valley, and Mexican Highlands are part of the Pacific Ring of Fire.
Minerals of North America
North America is rich in various minerals. Of the combustible mineral resources, 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, and on the shelf marginal seas Arctic Ocean, Alaska, southern Central and Great Plains. The eastern Central Plains and the foothills of the Appalachians are rich in coal. There are brown coal deposits on the Great Plains, in the intermountain basins of the Cordillera, and in Alaska.
Largest reserves iron ores concentrated in crystalline rocks of the Canadian Shield in the area of Lake Superior and the Labrador Peninsula, in the Northern Appalachians. Non-ferrous metal ores are widespread: copper (Rocky Mountains, Mexican Highlands, Canadian Shield), lead-zinc (Mississippi Valley, Cordillera), bauxite (Jamaica), nickel (Laurentine Upland, Cuba). Powerful reserves of uranium ores are concentrated on the Colorado Plateau, gold - in the river basin. Yukon and southwestern United States.
Among non-metallic minerals, there are significant reserves of phosphorites (Florida Peninsula), asbestos (Appalachia) and potassium salts (southern Great Plains, Great Lakes region).
The continent is part of the North American lithospheric plate. Its core is the ancient North American Plate. In the north, east and south it is bordered by the ancient systems of the Canadian Arctic Archipelago, Greenland and the Appalachians, and in the west by the young folded belt of the Cordillera. Western Cordillera chains and Central America are characterized by high seismicity and are part of the Pacific “Ring of Fire”. The continent is rich in minerals.
Geological structure North America
At the base North America and most of Greenland lies Precambrian North American Platform, which is sometimes called Canadian. The foundation of the platform in some places faces surface, forming Canadian-Granland Shield. The shield formed by faults consists of metamorphosed volcanic rocks and granite gneisses of Archean and 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 foundation, covered with a sedimentary cover, is also composed of Early Precambrian metamorphosed sedimentary-volcanic rocks and granite-gneisses. In the building Rocky Mountains USA is being viewed early Precambrian crystalline rocks. Sedimentary cover platforms extend to the south, west and north of the Canadian Shield, and its greatest area observed in the region Midcontinent and Great Plains. The depth of the foundation changes, so a number of large depressions – syneclise, with a depth of $3$-$4$ km and vaults – anteclise. Part of the platform in the southwest cuts mobile zone mountains Ouachita.
In the meridional strip Great Plains continued in the Mesozoic subsidence and accumulation coastal-marine and continental sediments. Finally, marine sediments were replaced by continental sediments at the beginning Cenozoic era, and after this came complete platform drainage.
Paleozoic cover platforms in addition to the Midcontinent and the Great Plains also extends to Arctic its slope. Here he lays down southern part Canadian Arctic Archipelago. Shallow but large syneclise Hudson Bay is filled with formations that are similar in composition and age. Its central part is made up thin continental sediments Jurassic and Cretaceous.
Caledonides Northeast Greenland are the most ancient link folded frame of the North American platform. In the form of tectonic nappes, they are thrust onto 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 the island of Newfoundland and the Northern Appalachians border the Canadian Shield.
Line Logan represents thrust geosynclinal Paleozoic strata into the platform Paleozoic and Precambrian. Narrow grabens with continental sediments and basaltic lavas there are also Northern and Southern Appalachia. 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, composed of Cambrian-Devonian terrigenous-carbonate deposits.
folded Cordillera belt, located along the Pacific coast, borders almost the entire length with North American platform, with the exception of Alaska. Here this belt is limited by the ridge system Brooks. The main seismically active North American zone.
Note 1
The zone is characterized by destructive earthquakes– Alaskan ($1964), Mexican ($1985), San Francisco ($1906). In the future this zone still remains earthquake-prone, especially in those places where it intersects with 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.
Almost replaced flat plains in the central part of the continent there are vast hilly expanses, neighboring in the east with low Appalachia.
To the west, the Central Plains are adjacent to Cordilleras. The peaks of these mountain structures are sharp and reach a height of more than $6000$ m. The relief of the continent and its features are associated with the history of the geological development of the territory. Ancient The North American Plate and its crystalline basement formed throughout Archean and Proterozoic eras. Canadian crystal shield in relief corresponds Laurentian elevation.
On stove, located south of the Canadian Shield, are Central and Great Plains. The Great Plains stretch from north to south for $3,500 km and are located in the western part of the platform. Their height reaches $1500$ m, which can be explained by powerful uplifts earth's crust in the area of the Cordilleran folding.
south of Laurentian the hills are located Central Plains. In the south of the mainland are Sub-Mexican and Atlantic lowlands formed on the foundation of a young platform covered with sedimentary deposits. Appalachia are old, eroded mountains, with flattened and low ridges. Folding in them occurred during the Caledonian and Hercynian periods.
In the west of the continent, grandiose folding began in Mesozoic era as a result of the collision of lithospheric plates and continues to this day. Originated 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 continent, but continue in South America . The summit of the Cordillera is Mt. McKinley, whose height is $6193$ m. Numerous faults in the bottom of the Pacific Ocean continue in the Cordillera ridges. The mountains are characterized by the largest volcanoes planets - Popocatepetl and Orizaba.
Note 2
Not only internal, but also external processes took part in the formation of the relief. The northern regions of the mainland up to $40$ parallels were covered glacier, which in size exceeded the area of Australia by $2$ times. The movement of the glacier leveled the surface and even polished the rocks. The glacier created thousands of hills of great extent and many small landforms.
In addition to the glacier, they took an active part in the formation of the relief superficial, The 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 the cave was formed underground water, and activity wind led to the emergence of dunes, dunes and other forms of relief.
Mainland minerals
Subsoil of North America rich in minerals and are related to its geological structure. The largest in the world ore deposits occur in the area Canadian crystal shield , where igneous and metamorphic rocks are found 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 sediments oil and gas. Hydrocarbon production is carried out both on land and from Mexican bay. The intermontane depressions of the Appalachians also have significant reserves stone coal
IN Cordillera concentrated large deposits minerals of both igneous and sedimentary origin. There is non-ferrous metal ores, gold, mercury. In the east and in the trough of the earth's crust between Cordilleras and the North American Plate lie oil, gas, coal. Significant reserves and diverse mineral resources are an important natural raw material base for the economic development of countries located on this continent.
Relief of North America mainly flat, because most of it lies within platforms. The western and eastern parts of the continent were formed at different geological times - western Part in the Mesozoic and Cenozoic, A eastern part - in Paleozoic.
Note 3
The ancient and ruined Appalachians are located in the east of the continent, and the high and young Cordilleras are located in the west. Associated with the peculiarities of the geological structure richness and variety mineral resources of the mainland. And such minerals as coal, oil, natural gas, iron, nickel, molybdenum ores and uranium have global significance.
Page 1
The North American platform is surrounded on all sides by mountain-fold structures of various ages: in the north - the Caledonian-Early Hercynian folded system, in the east and south - the Paleozoic folded system of the Appalachians, Ouachita and Marathon. The western limitation of the platform is the mountainous folded-block Mesozoic-Cenozoic Cordillera belt. The Cordillera is characterized by the presence of zones of more ancient folding or remnants of ancient platforms in the form of median massifs. The eastern part of the Cordillera is the modern epi-platform orogens of the Rocky Mountains in the USA and Richardson-Franklin in Canada.
The North American platform are subaqueous and formations, the accumulation of which occurred predominantly in an anaerobic environment, against the background of a relatively stable subsidence of the sedimentation basin during the period of geological time under consideration.
The North American platform are subaquatic formations, the accumulation of which occurred predominantly in an anaerobic environment, against the background of a relatively stable subsidence of the sedimentation basin during the period of geological time under consideration.
Russian or North American platform, rich in oil, then all these manifestations of magmatism belong to long ago, past eras, rooted in ancient times to logical history, but we can talk about young foundation splits, for example, about the Zhiguli fault or about fault dislocations in the Saratov Volga region, they are not accompanied even by traces of magmatism. At the same time, we must remember once again that the thickest stratum of Archean crystalline rocks itself is formed almost entirely by metamorphic sedimentary rocks.
In the zone of junction of the North American platform with the mountain-fold structures framing it, there are large forward troughs - Western Canadian, Pre-Washite, Pre-Appalachian, Anticosti, Melville-Victoria, Pirie-Ellesmere. The Crazy Bull Mountains, Powder River, Denver, and Raton foredeeps connect the epiplatform orogeny region of the Rocky Mountains with the southern part of the North American Platform.
A number of oil-bearing provinces are distinguished within the North American Platform plate. In the Midcontinent Province, the richest oil deposits are associated with Permian sediments. Most of the deposits are located in the states of Kansas and Oklahoma. Some old fields have not yet lost their industrial significance, for example the Eyts field, in which 65 million tons of oil have already been produced out of 100 million tons.
The region is located between the North American Plate to the north, the Pacific deep trench system to the west, and the Atlantic thalassocraton to the east. The Precambrian Brazilian Plate occupies most of the South American continent. It consists of the Guiana, West and East Brazilian shields and a number of massifs. The Pampas Massif is an epiplatform orogen of the Brazilian Platform. In the southern part of the continent there is the Patagonian platform with Precambrian and Caledonian folded complexes at the base. The northeastern part of the region is occupied by the southern end of the Atlantic Platform, hidden by the waters of the Gulf of Mexico and the Atlantic Ocean.
The largest geotectonic element in the region is the ancient North American Platform. It covers most of the continent, almost all of Greenland and the waters of Hudson Bay, the Baffin Sea and numerous straits of the southern part of the Arctic archipelago of Canada. The extensive Baffin-Labrador depression is filled with Mesozoic-Cenozoic sedimentary cover up to 9 km thick. The southern and western parts of the platform, covered with sedimentary cover of varying thicknesses and stratigraphic ranges, are divided into the Midcontinent and Great Plains plates. The major West Texas (Permian) syneclise, made primarily of Permian sediments, the Alberta and Dodge City depressions, the Anadarko trough, the Williston and Michigan-Illinois syneclises are distinguished here.
At the same time, deposits of the same tertiary system, developed within western regions The North American platform in the Rocky Mountains, as well as in the central part of the Alberta / Coy basin (Canada), represented in continental facies, are regionally unproductive and only in places (in some mountain basins of the Rocky Mountains) contain relatively small oil deposits.
At the same time, sediments of the same tertiary system, developed within the western regions of the North American platform and the Rocky Mountains, as well as in the central part of the Alberta Basin (Canada), presented in continental facies, are regionally unproductive and only in places (in some intermountain basins of the Rocky Mountains ) contain relatively small oil deposits.
Map oil and gas basins United States of America, compiled by V. G. Levinson (Fig. 6), covers most of the North American platform and adjacent folded structures. The map is built on a schematized tectonic basis.
The map of oil and gas basins of the United States of America, compiled by V. G. Levinson (Fig. 6), covers most of the North American platform and adjacent folded structures. The map is built on a schematized tectonic basis.
The fourth pattern - the dependence of oil content on subaqueous sediments and recovery conditions - is substantiated by A. A. Bakirov on the example of the continental Upper Permian and Triassic, which contain very little oil on the North American platform, and on the example of Tertiary sediments developed in marine facies in the Gulf of Mexico basin both in California, where they are oil-rich, and in the continental facies of the Rocky Mountains, where they are oil-free.
: North American and Caribbean. The larger of these is the North American Plate, which contains almost the entire continent, as well as the islands of the Arctic Ocean, including Greenland. It should be noted that the western boundary of the plate passes through the territory of Eurasia along the Verkhoyansk Range in such a way that the northern tip Far East Russia is geologically also part of North America. The Caribbean plate includes the south of the continent, as well as the islands of the Caribbean Sea. Tectonic activity is most pronounced here, as there is an active collision of the plate with the North and South American plates.
North America can be divided into three parts: the western mountainous, ancient platform and the eastern, related to the ancient folding. The western one was formed mainly in the Mesozoic and includes the Cordillera; some of its sections continue to form today. The platform includes Greenland, the Canadian Shield, Labrador, and the Center of North America. Ancient folding dates back to the Hercynian age and is represented by the Appalachians, the Atlantic and Mexican lowlands.
The most tectonically active areas of America are located on its western Pacific coast, from the Aleutian Islands to the Isthmus of Panama. Most of the volcanoes are located here, many of them remain active, such as: Momotombo, Tajumulco, Orizaba, Popocatepetl, Colima, Shasta, Rainier, Sanford and Velyaminova volcano in Alaska. There are also a number of tectonic faults in the area, in the area of which there is a constant threat of earthquakes. The most famous of them is the San Andreas Fault. The danger of this fault lies in the fact that next to it there are big cities United States - primarily San Francisco and Los Angeles. Destructive earthquakes have already occurred here in the past, however, over the past decades, the cities have grown significantly, so that new similar cataclysms today will lead to colossal destruction. Another dangerous volcano is the dormant volcano in the territory of the first US national park - Yellowstone. Today the volcano manifests itself only in the form of more than three thousand geysers in the park, which is a beautiful and unique natural monument. One of the most famous geysers is the Old Faithful Geyser, which has erupted on average every 90 minutes for many years (Pictured). However, according to geologists, in the event of awakening Yellowstone Volcano, there will be an explosion greater in power than the eruption of Krakatoa, and the consequences of this eruption will affect the climate of the entire planet. Fortunately, such cataclysms occur on Earth no more often than once every few tens of thousands of years. As noted above, the islands of the Caribbean Sea are also characterized by very high seismic activity. The last terrible earthquake occurred there in January 2010 in the region of the island of Haiti, from the consequences of which this poorest country The Western Hemisphere has not yet fully recovered.
The rivers had a huge impact on the topography of the continent, cutting huge valleys and canyons into the mountain slopes, the most outstanding of which is the Colorado River Canyon or Grand Canyon. As a result, the geological outcrops formed here represent the history of the last 1.5 billion years.
In addition to rivers, the relief of North America was affected by the activity of glaciers. The continent is the most northern continent Earth, and during glaciations, a significant part of it was under an glacial shell, up to several kilometers thick (now such an glacial layer remains only in Greenland and on the islands of the Canadian Arctic archipelago). As the glacier formed, it changed the surface of the earth beneath it, forming hills and basins. The basins were later filled with water and today, when the glacier has retreated, they have turned into countless large and small lakes.
Great Bear Lake The largest glacial lake in North America, formed during the Pleistocene, with countless smaller glacial lakes around it. (With a more detailed magnification, you can see how the lakes stretch into grooves carved by the glacier in the rocks)
