Causes of tectonic activity of the lithosphere. Five cities of the world located on the faults of the earth's crust. Map of the lithospheric plates of the world

Last week, the public was stirred by the news that the Crimean peninsula is moving towards Russia, not only thanks to the political will of the population, but also according to the laws of nature. What are lithospheric plates and on which of them is Russia territorially located? What makes them move and where? Which territories still want to "join" Russia, and which ones threaten to "escape" to the USA?

"And we're going somewhere"

Yes, we are all going somewhere. While you are reading these lines, you are moving slowly: if you are in Eurasia, then east at a speed of about 2-3 centimeters per year, if in North America, then at the same speed west, and if somewhere at the bottom of the Pacific Ocean (how did you get there?), then it takes you to the northwest by 10 centimeters a year.

If you sit back in your chair and wait about 250 million years, you will find yourself on a new supercontinent that will unite all the earth's land - on the mainland Pangea Ultima, named so in memory of the ancient supercontinent Pangea, which existed just 250 million years ago.

Therefore, the news that "Crimea is moving" can hardly be called news. Firstly, because Crimea, together with Russia, Ukraine, Siberia and the European Union, is part of the Eurasian lithospheric plate, and all of them have been moving together in one direction for the last hundred million years. However, Crimea is also part of the so-called Mediterranean mobile belt, it is located on the Scythian plate, and most of the European part of Russia (including the city of St. Petersburg) - on the East European platform.

And this is where confusion often arises. The fact is that in addition to huge sections of the lithosphere, such as the Eurasian or North American plates, there are completely different smaller "tiles". If very conditionally, then the earth's crust is composed of continental lithospheric plates. They themselves consist of ancient and very stable platforms.and mountain building zones (ancient and modern). And already the platforms themselves are divided into slabs - smaller sections of the crust, consisting of two "layers" - the foundation and the cover, and shields - "single-layer" outcrops.

The cover of these non-lithospheric plates consists of sedimentary rocks (for example, limestone, composed of many shells of marine animals that lived in the prehistoric ocean above the surface of Crimea) or igneous rocks (thrown from volcanoes and solidified lava masses). A fslab foundations and shields most often consist of very old rocks, mainly of metamorphic origin. So called igneous and sedimentary rocks, plunged into the depths earth's crust, where, under the influence of high temperatures and enormous pressure, various changes occur with them.

In other words, most of Russia (with the exception of Chukotka and Transbaikalia) is located on the Eurasian lithospheric plate. However, its territory is "divided" between the West Siberian plate, the Aldan shield, the Siberian and East European platforms and the Scythian plate.

Probably, the director of the Institute of Applied Astronomy (IPA RAS), Doctor of Physical and Mathematical Sciences Alexander Ipatov, said about the movement of the last two plates. And later, in an interview with Indicator, he clarified: "We are engaged in observations that allow us to determine the direction of movement of the plates of the earth's crust. The plate on which the Simeiz station is located moves at a speed of 29 millimeters per year to the northeast, that is, to where Russia And the plate where Peter is located is moving, one might say, towards Iran, to the south-southwest."However, this is not such a discovery, because this movement has been around for several decades, and it itself began back in the Cenozoic era.

Wegener's theory was received with skepticism - mainly because he could not offer a satisfactory mechanism to explain the movement of the continents. He believed that the continents move, breaking through the earth's crust, like icebreakers through ice, due to the centrifugal force from the rotation of the Earth and tidal forces. His opponents said that the continents-"icebreakers" in the process of movement would change their appearance beyond recognition, and centrifugal and tidal forces too weak to serve as a "motor" for them. One critic calculated that if the tidal force were strong enough to move the continents so fast (Wegener estimated their speed at 250 centimeters per year), it would stop the rotation of the Earth in less than a year.

By the end of the 1930s, the theory of continental drift was rejected as unscientific, but by the middle of the 20th century it had to be returned to: mid-ocean ridges were discovered and it turned out that new crust was continuously forming in the zone of these ridges, due to which the continents were "moving apart" . Geophysicists have studied the magnetization of rocks along the mid-ocean ridges and found "bands" with multidirectional magnetization.

It turned out that the new oceanic crust "records" the state magnetic field Earth at the time of formation, and scientists have received an excellent "ruler" to measure the speed of this conveyor. So, in the 1960s, the theory of continental drift returned for the second time, for good. And this time, scientists were able to understand what moves the continents.

Ice floes in the boiling ocean

"Imagine an ocean where ice floes float, that is, there is water in it, there is ice, and, let's say, wooden rafts are also frozen into some ice floes. Ice is lithospheric plates, rafts are continents, and they float in the substance of the mantle," explains Corresponding Member of the Russian Academy of Sciences Valery Trubitsyn, chief researcher at the Institute of Physics of the Earth named after O.Yu. Schmidt.

Back in the 1960s, he put forward the theory of the structure of giant planets, and at the end of the 20th century he began to create a mathematically based theory of continental tectonics.

The intermediate layer between the lithosphere and the hot iron core in the center of the Earth - the mantle - consists of silicate rocks. The temperature in it varies from 500 degrees Celsius in the upper part to 4000 degrees Celsius at the border of the core. Therefore, from a depth of 100 kilometers, where the temperature is already more than 1300 degrees, the mantle substance behaves like a very thick resin and flows at a speed of 5-10 centimeters per year, says Trubitsyn.

As a result, in the mantle, as in a pot of boiling water, convective cells appear - areas where hot matter rises from one edge, and cooled down from the other.

"There are about eight of these large cells in the mantle and many more small ones," the scientist says. Mid-ocean ridges (for example, in the center of the Atlantic) are the place where the material of the mantle rises to the surface and where new crust is born. In addition, there are subduction zones, places where a plate begins to "creep" under the neighboring one and sinks down into the mantle. Subduction zones are, for example, the western coast of South America. This is where the most powerful earthquakes occur.

“In this way, the plates take part in the convective circulation of the mantle substance, which temporarily becomes solid while on the surface. Plunging into the mantle, the plate substance heats up and softens again,” explains the geophysicist.

In addition, separate jets of matter rise to the surface from the mantle - plumes, and these jets have every chance to destroy humanity. After all, it is mantle plumes that are the cause of the appearance of supervolcanoes (see). Such points are in no way connected with lithospheric plates and can remain in place even when the plates move. When the plume exits, a giant volcano arises. There are many such volcanoes, they are in Hawaii, in Iceland, a similar example is the Yellowstone caldera. Supervolcanoes can generate eruptions thousands of times more powerful than most ordinary volcanoes like Vesuvius or Etna.

"250 million years ago, such a volcano on the territory of modern Siberia killed almost all life, only the ancestors of dinosaurs survived," says Trubitsyn.

Agreed - dispersed

Lithospheric plates consist of relatively heavy and thin basaltic oceanic crust and lighter, but much thicker continents. A plate with a continent and oceanic crust "frozen" around it can move forward, while the heavy oceanic crust sinks under its neighbor. But when continents collide, they can no longer sink under each other.

For example, about 60 million years ago, the Indian plate broke away from what later became Africa and went north, and about 45 million years ago it met with the Eurasian plate, the Himalayas, the highest mountains on Earth, grew at the point of collision.

The movement of the plates will sooner or later bring all the continents into one, as leaves converge into one island in a whirlpool. In the history of the Earth, the continents have united and broken up approximately four to six times. The last supercontinent Pangea existed 250 million years ago, before it was the supercontinent Rodinia, 900 million years ago, before it - two more. "And already, it seems, the unification of the new continent will soon begin," the scientist clarifies.

He explains that the continents act as a thermal insulator, the mantle beneath them begins to heat up, updrafts occur, and therefore the supercontinents break apart again after a while.

America will "take away" Chukotka

Large lithospheric plates are drawn in textbooks, anyone can name them: Antarctic plate, Eurasian, North American, South American, Indian, Australian, Pacific. But at the boundaries between the plates there is a real chaos of many microplates.

For example, the boundary between the North American Plate and the Eurasian Plate does not run along the Bering Strait at all, but much to the west, along the Chersky Ridge. Chukotka thus turns out to be part of the North American Plate. At the same time, Kamchatka is partly located in the zone of the Okhotsk microplate, and partly in the zone of the Bering Sea microplate. And Primorye is located on the hypothetical Amur Plate, the western edge of which rests on Baikal.

Now the eastern edge of the Eurasian plate and the western edge of the North American plate are "spinning" like gears: America is turning counterclockwise, and Eurasia is turning clockwise. As a result, Chukotka may finally come off "along the seam", and in this case, a giant circular seam may appear on Earth, which will pass through the Atlantic, Indian, Pacific and Northern Arctic Ocean(where it is currently closed). And Chukotka itself will continue to move "in the orbit" of North America.

Speedometer for the lithosphere

Wegener's theory has been resurrected, not least because scientists have the ability to accurately measure the displacement of continents. Currently used for this satellite systems navigation, but there are other methods. All of them are needed to build a unified international system coordinates - International Terrestrial Reference Frame (ITRF).

One of these methods is very long baseline radio interferometry (VLBI). Its essence lies in simultaneous observations with the help of several radio telescopes in different points Earth. The difference in signal acquisition time makes it possible to determine offsets with high accuracy. Two other ways to measure speed are laser ranging observations using satellites and Doppler measurements. All these observations, including with the help of GPS, are carried out at hundreds of stations, all these data are brought together, and as a result, we get a picture of continental drift.

For example, Crimean Simeiz, where a laser sounding station is located, as well as a satellite station for determining coordinates, "moves" to the northeast (in azimuth about 65 degrees) at a speed of about 26.8 millimeters per year. Zvenigorod, near Moscow, is moving about a millimeter a year faster (27.8 millimeters a year) and keeps its course to the east - about 77 degrees. And, say, the Hawaiian volcano Mauna Loa is moving northwest twice as fast - 72.3 millimeters per year.

Lithospheric plates can also be deformed, and their parts can "live their own lives", especially at the boundaries. Although the scale of their independence is much more modest. For example, Crimea is still moving independently to the northeast at a speed of 0.9 millimeters per year (and at the same time growing by 1.8 millimeters), and Zvenigorod is moving somewhere to the southeast at the same speed (and down - by 0 .2 millimeters per year).

Trubitsyn says that this independence is partly explained by the "personal history" of different parts of the continents: the main parts of the continents, the platforms, may be fragments of ancient lithospheric plates that "fused" with their neighbors. For example, the Ural Range is one of the seams. Platforms are relatively rigid, but parts around them can deform and move at will.

How did the continents and islands appear? What determines the name of the largest plates of the Earth? Where did our planet come from?

How it all began?

Everyone at least once thought about the origin of our planet. For deeply religious people, everything is simple: God created the Earth in 7 days - period. They are unshakable in their confidence, even knowing the names of the largest lithospheric plates formed as a result of the evolution of the planet's surface. For them, the birth of our stronghold is a miracle, and no arguments of geophysicists, naturalists and astronomers can convince them.

Scientists, however, have a different opinion, based on hypotheses and assumptions. Ieeno they build guesses, put forward versions and come up with a name for everything. This also affected the largest plates of the Earth.

On this moment It is not known for certain how our firmament appeared, but there are many interesting opinions. It was scientists who unanimously decided that once there was a single giant continent, as a result of cataclysms and natural processes shattered into pieces. Also, scientists came up with not only the name of the largest plates of the Earth, but also designated the small ones.

Theory on the verge of fantasy

For example, Immanuel Kant and Pierre Laplace - scientists from Germany - believed that the Universe emerged from a gaseous nebula, and the Earth is a gradually cooling planet, the earth's crust of which is nothing more than a cooled surface.

Another scientist, Otto Yulievich Schmidt, believed that the Sun, when passing through a gas and dust cloud, captured part of it. His version is that our Earth has never been a completely molten substance and was originally a cold planet.

According to the theory of the English scientist Fred Hoyle, the Sun had its own twin star, which exploded like a supernova. Almost all of the fragments were thrown to great distances, and a small number of those remaining around the Sun turned into planets. One of these fragments became the cradle of mankind.

Version as an axiom

The most common story of the origin of the Earth is as follows:

About 7 billion years ago, the primary cold planet was formed, after which its bowels began to gradually warm up.
Then, during the so-called "lunar era", red-hot lava poured out in gigantic quantities to the surface. This led to the formation of the primary atmosphere and served as an impetus for the formation of the earth's crust - the lithosphere.
Thanks to the primary atmosphere, oceans appeared on the planet, as a result of which the Earth was covered with a dense shell, representing the outlines of oceanic depressions and continental protrusions. In those distant times, the area of water significantly prevailed over the area of \u200b\u200bland. By the way, the earth's crust and the upper part of the mantle is called the lithosphere, which forms the lithospheric plates that make up the overall "look" of the Earth. The names of the largest plates correspond to their geographical position.

giant split

How did continents and lithospheric plates form? About 250 million years ago, the Earth looked completely different than it does now. Then on our planet there was only one, just the same giant continent called Pangea. Its total area was impressive and equaled the area of all currently existing continents, including the islands. Pangea was washed on all sides by the ocean, which was called Panthalassa. This vast ocean occupied the entire remaining surface of the planet.

However, the existence of the supercontinent turned out to be short-lived. Processes were seething inside the Earth, as a result of which the substance of the mantle began to spread in different directions, gradually stretching the mainland. Because of this, Pangea first split into 2 parts, forming two continents - Laurasia and Gondwana. Then these continents gradually split into many parts, which gradually dispersed in different directions. In addition to new continents, lithospheric plates appeared. From the name of the largest plates, it becomes clear in which places giant faults formed.

The remnants of Gondwana are Australia and Antarctica known to us, as well as the South African and African lithospheric plates. It is proved that these plates are gradually diverging in our time - the speed of movement is 2 cm per year.

Fragments of Laurasia turned into two lithospheric plates - North American and Eurasian. At the same time, Eurasia consists not only of a fragment of Laurasia, but also of parts of Gondwana. The names of the largest plates that form Eurasia are Hindustan, Arabian and Eurasian.

Africa is directly involved in the formation of the Eurasian continent. Its lithospheric plate is slowly approaching the Eurasian one, forming mountains and uplands. It was because of this "union" that the Carpathians, the Pyrenees, the Ore Mountains, the Alps and the Sudetes appeared.

List of lithospheric plates

The names of the largest plates are as follows:

South American;
Australian;
Eurasian;
North American;
Antarctic;
Pacific;
South American;
Hindustan.

Medium sized slabs are:

Arabian;
Nazca;
Scotia;
Philippine;
Coconut;
Juan de Fuca.

Fb.ru

What are lithospheric plates. Map of lithospheric plates

If you like interesting facts about nature, then you probably would like to know what lithospheric plates are.

So, lithospheric plates are huge blocks into which the solid surface layer of the earth is divided. Given the fact that the rocks beneath them are melted, the plates move slowly, at a speed of 1 to 10 centimeters per year.

To date, there are 13 largest lithospheric plates that cover 90% of the earth's surface.

The largest lithospheric plates:

Australian Plate - 47,000,000 km²
Antarctic Plate - 60,900,000 km²
Arabian subcontinent - 5,000,000 km²
African Plate - 61,300,000 km²
Eurasian Plate - 67,800,000 km²
Hindustan Plate - 11,900,000 km²
Coconut Plate - 2,900,000 km²
Nazca Plate - 15,600,000 km²
Pacific Plate - 103,300,000 km²
North American Plate - 75,900,000 km²
Somali plate - 16,700,000 km²
South American Plate - 43,600,000 km²
Philippine Plate - 5,500,000 km²

Here it must be said that there is a continental and oceanic crust. Some plates are composed entirely of one type of crust (such as the Pacific Plate), and some are of mixed types, where the plate begins in the ocean and smoothly transitions to the continent. The thickness of these layers is 70-100 kilometers.

Lithospheric plates float on the surface of a partially molten layer of the earth - the mantle. When the plates move apart, liquid rock called magma fills the cracks between them. When magma solidifies, it forms new crystalline rocks. We will talk about magma in more detail in the article on volcanoes.

Map of lithospheric plates

The largest lithospheric plates (13 pcs.)

At the beginning of the 20th century, the American F.B. Taylor and the German Alfred Wegener simultaneously came to the conclusion that the location of the continents is slowly changing. By the way, this, to a large extent, is the cause of earthquakes. But scientists could not explain how this happens until the 60s of the twentieth century, when the doctrine of geological processes on the seabed was developed.

Map of the location of lithospheric plates

It was the fossils that played the main role here. On different continents, fossilized remains of animals were found that clearly could not swim across the ocean. This led to the assumption that once all the continents were connected and animals calmly passed between them.

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Lithospheric plates

Lithospheric plates are the largest blocks of the lithosphere. The earth's crust, together with part of the upper mantle, consists of several very large blocks, which are called lithospheric plates. Their thickness is different - from 60 to 100 km. Most plates include both continental and oceanic crust. There are 13 main plates, of which 7 are the largest: American, African, Antarctic, Indo-Australian, Eurasian, Pacific, Amur.

The plates lie on the plastic layer of the upper mantle (asthenosphere) and slowly move relative to each other at a speed of 1-6 cm per year. This fact was established by comparing photographs taken with artificial satellites Earth. They suggest that the configuration of continents and oceans in the future may be completely different from the current one, since it is known that the American lithospheric plate is moving towards the Pacific, and the Eurasian one is approaching the African, Indo-Australian, and also the Pacific. The American and African lithospheric plates are slowly moving apart.

The forces that cause the separation of lithospheric plates arise when the mantle substance moves. Powerful ascending flows of this substance push apart the plates, break the earth's crust, forming deep faults in it. Due to underwater outpourings of lavas, strata of igneous rocks are formed along the faults. Freezing, they seem to heal wounds - cracks. However, the stretch increases again, and breaks occur again. So, gradually growing, lithospheric plates diverge in different directions.

There are fault zones on land, but most of them are in the ocean ridges at the bottom of the oceans, where the earth's crust is thinner. The largest fault on land is located in eastern Africa. It stretched for 4000 km. The width of this fault is 80-120 km. Its outskirts are dotted with extinct and active volcanoes.

Collision is observed along other plate boundaries. It happens in different ways. If the plates, one of which has an oceanic crust and the other a continental one, approach each other, then the lithospheric plate, covered by the sea, sinks under the continental one. In this case, deep-sea trenches, island arcs (Japanese islands) or mountain ranges (Andes) arise. If two plates with a continental crust collide, then the edges of these plates are crushed into folds of rocks, volcanism and the formation of mountainous areas. This is how the Himalayas arose, for example, on the border of the Eurasian and Indo-Australian plates. The presence of mountainous regions in the inner parts of the lithospheric plate suggests that once there was a boundary between two plates, which were firmly soldered to each other and turned into a single, larger lithospheric plate. Thus, it is possible to make general conclusion: boundaries of lithospheric plates - mobile areas, which are confined to volcanoes, earthquake zones, mountainous areas, mid-ocean ridges, deep-water depressions and trenches. It is at the boundary of lithospheric plates that ore minerals are formed, the origin of which is associated with magmatism.

geographyofrussia.com

The theory of lithospheric plates on the world map: which is the largest

The theory of lithospheric plates is the most interesting direction in geography. As modern scientists suggest, the entire lithosphere is divided into blocks that drift in the upper layer. Their speed is 2-3 cm per year. They are called lithospheric plates.

Founder of the theory of lithospheric plates

Who founded the theory of lithospheric plates? A. Wegener was one of the first in 1920 to make the assumption that the plates move horizontally, but he was not supported. And only in the 60s, surveys of the ocean floor confirmed his assumption.

The resurrection of these ideas led to the creation of the modern theory of tectonics. Its most important provisions were determined by a team of American geophysicists D. Morgan, J. Oliver, L. Sykes and others in 1967-68.

Scientists cannot say for sure what causes such shifts and how the boundaries are formed. Back in 1910, Wegener believed that at the very beginning of the Paleozoic period, the Earth consisted of two continents.

Laurasia covered the region of present-day Europe, Asia (India was not included), North America. It was the northern mainland. Gondwana included South America, Africa, Australia.

About two hundred million years ago, these two continents merged into one - Pangea. And 180 million years ago, it is again divided into two. Subsequently, Laurasia and Gondwana were also divided. Due to this split, the oceans were formed. Moreover, Wegener found evidence that confirmed his hypothesis about a single continent.

Map of the lithospheric plates of the world

Over the billions of years that the plates have been moving, they have repeatedly merged and separated. The strength and vigor of the movement of the continents is greatly influenced by the internal temperature of the Earth. With its increase, the speed of movement of the plates increases.

How many plates and how are lithospheric plates located on the world map today? Their boundaries are very arbitrary. Now there are 8 major plates. They cover 90% of the entire territory of the planet:

Australian;
Antarctic;
African;
Eurasian;
Hindustan;
Pacific;
North American;
South American.

Scientists are constantly inspecting and analyzing the ocean floor, and exploring faults. Open new plates and correct the lines of old ones.

The largest lithospheric plate

What is the largest lithospheric plate? The most impressive is the Pacific plate, the crust of which has an oceanic type of addition. Its area is 10,300,000 km². The size of this plate, as well as the size of the Pacific Ocean, are gradually decreasing.

In the south, it borders on the Antarctic Plate. On the north side it creates the Aleutian Trench, and on the western side - Mariana Trench.

Not far from California, where the eastern border runs, the movement of the plate is carried out along the length of the North American. This is where the San Andreas Fault is formed.

What happens when plates move

The lithospheric plates of the earth in their movement can diverge, merge, slide with neighboring ones. In the first variant, stretching areas with cracks are formed between them along the bordering lines.

In the second variant, compression zones are formed, which are accompanied by thrusting (obduction) of plates on top of each other. In the third case, faults are observed along the length of which they slide. Where the plates meet, they collide. This gives rise to mountains.

Lithospheric plates as a result of the collision form:

Tectonic faults, which are called rift valleys. They form in tensile zones;
In the case when there is a collision of plates with a continental type of crust, then one speaks of convergent boundaries. This causes the formation of large mountain systems. The Alpine-Himalayan system was the result of a collision of three plates: Eurasian, Indo-Australian, African;
If plates collide different types crust (one is continental, the other is oceanic), mountains are forming on the coast, and deep depressions (troughs) are forming in the ocean. An example of such formation is the Andes and the Peruvian depression. It happens that together with the gutters island arcs (Japanese islands) are formed. This is how the Marianas and the trench were formed.

The lithospheric plate of Africa includes the African continent and has an oceanic type. This is where the biggest gap is located. Its length is 4000 km, and its width is 80-120. Its extremities are covered with numerous active and extinct volcanoes.

The lithospheric plates of the world, which have an oceanic type of crust structure, are often called oceanic. These include: Pacific, Coconut, Nazca. They occupy more than half of the world's oceans.

There are three of them in the Indian Ocean (Indo-Australian, African, Antarctic). The names of the plates correspond to the names of the continents that it washes. The lithospheric plates of the ocean are separated by underwater ridges.

Tectonics as a science

The tectonics of lithospheric plates studies their movement, as well as changes in the structure and composition of the Earth in a given area in a certain period of time. It assumes that it is not the continents that are drifting, but the lithospheric plates.

It is this movement that causes earthquakes and volcanic eruptions. It is confirmed by satellites, but the nature of such movement and its mechanisms are still unknown.

vsesravnenie.ru

Movement of lithospheric plates. Large lithospheric plates. Names of lithospheric plates

Earth's lithospheric plates are huge blocks. Their foundation is formed by highly folded granite metamorphosed igneous rocks. The names of the lithospheric plates will be given in the article below. From above they are covered with a three-four-kilometer "cover". It is formed from sedimentary rocks. The platform has a relief consisting of individual mountain ranges and vast plains. Next, the theory of the movement of lithospheric plates will be considered.

The emergence of the hypothesis

The theory of the movement of lithospheric plates appeared at the beginning of the twentieth century. Subsequently, she was destined to play a major role in the exploration of the planet. The scientist Taylor, and after him Wegener, put forward the hypothesis that over time there is a drift of lithospheric plates in a horizontal direction. However, in the thirties of the 20th century, a different opinion was established. According to him, the movement of lithospheric plates was carried out vertically. This phenomenon was based on the process of differentiation of the planet's mantle matter. It became known as fixism. Such a name was due to the fact that the permanently fixed position of sections of the crust relative to the mantle was recognized. But in 1960, after the discovery of a global system of mid-ocean ridges that encircle the entire planet and come out on land in some areas, there was a return to the hypothesis of the early 20th century. However, the theory has new form. Block tectonics has become the leading hypothesis in the sciences that study the structure of the planet.

Key points

It was determined that there are large lithospheric plates. Their number is limited. There are also smaller lithospheric plates of the Earth. The boundaries between them are drawn according to the concentration in the sources of earthquakes.

The names of the lithospheric plates correspond to the continental and oceanic regions located above them. There are only seven blocks with a huge area. The largest lithospheric plates are the South and North American, Euro-Asian, African, Antarctic, Pacific and Indo-Australian.

Blocks floating in the asthenosphere are characterized by solidity and rigidity. The above areas are the main lithospheric plates. In accordance with initial views It was believed that the continents make their way through the ocean floor. At the same time, the movement of lithospheric plates was carried out under the influence of an invisible force. As a result of the research, it was revealed that the blocks float passively over the material of the mantle. It is worth noting that their direction is vertical at first. The mantle material rises under the crest of the ridge. Then there is a spread in both directions. Accordingly, there is a divergence of lithospheric plates. This model represents the ocean floor as a giant conveyor belt. It comes to the surface in the rift regions of the mid-ocean ridges. Then hides in deep-sea trenches.

The divergence of lithospheric plates provokes the expansion of oceanic beds. However, the volume of the planet, despite this, remains constant. The point is that birth new cortex is compensated by its absorption in areas of subduction (underthrust) in deep-water trenches.

Why does lithospheric plates move?

The reason is the thermal convection of the planet's mantle material. The lithosphere is stretched and uplifted, which occurs over ascending branches from convective currents. This provokes the movement of lithospheric plates to the sides. As the platform moves away from the mid-ocean rifts, the platform becomes compacted. It becomes heavier, its surface sinks down. This explains the increase in ocean depth. As a result, the platform plunges into deep-sea trenches. When the ascending flows from the heated mantle die down, it cools and sinks with the formation of basins, which are filled with sediments.

Plate collision zones are areas where the crust and platform experience compression. In this regard, the power of the first increases. As a result, the upward movement of lithospheric plates begins. It leads to the formation of mountains.

Research

The study today is carried out using geodetic methods. They allow us to conclude that the processes are continuous and ubiquitous. Collision zones of lithospheric plates are also revealed. The lifting speed can be up to tens of millimeters.

Horizontally large lithospheric plates float somewhat faster. In this case, the speed can be up to ten centimeters during the year. So, for example, St. Petersburg has already risen by a meter over the entire period of its existence. Scandinavian Peninsula - 250 m in 25,000 years. The mantle material moves relatively slowly. However, earthquakes, volcanic eruptions and other phenomena occur as a result. This allows us to draw a conclusion about the high power of moving the material.

Using the tectonic position of the plates, researchers explain many geological phenomena. At the same time, during the study, it turned out that the complexity of the processes occurring with the platform is much greater than it seemed at the very beginning of the appearance of the hypothesis.

Plate tectonics could not explain changes in the intensity of deformations and movement, the presence of a global stable network of deep faults, and some other phenomena. The question of the historical beginning of the action also remains open. Direct signs indicating plate-tectonic processes have been known since the late Proterozoic. However, a number of researchers recognize their manifestation from the Archean or early Proterozoic.

Expanding Research Opportunities

The advent of seismic tomography led to the transition of this science to a qualitatively new level. In the mid-eighties of the last century, deep geodynamics became the most promising and young direction of all the existing geosciences. However, the solution of new problems was carried out using not only seismic tomography. Other sciences also came to the rescue. These include, in particular, experimental mineralogy.

Thanks to the availability of new equipment, it became possible to study the behavior of substances at temperatures and pressures corresponding to the maximum at the depths of the mantle. The methods of isotope geochemistry were also used in the studies. This science studies, in particular, the isotopic balance of rare elements, as well as noble gases in various earthly shells. In this case, the indicators are compared with meteorite data. Methods of geomagnetism are used, with the help of which scientists are trying to uncover the causes and mechanism of reversals in a magnetic field.

Modern painting

The platform tectonics hypothesis continues to satisfactorily explain the evolution of the oceanic and continental crust over at least the last three billion years. At the same time, there are satellite measurements, according to which the fact that the main lithospheric plates of the Earth do not stand still is confirmed. As a result, a certain picture emerges.

There are three most active layers in the cross section of the planet. The thickness of each of them is several hundred kilometers. It is assumed that the main role in global geodynamics is assigned to them. In 1972, Morgan substantiated the hypothesis put forward in 1963 by Wilson about ascending mantle jets. This theory explained the phenomenon of intraplate magnetism. The resulting plume tectonics has become increasingly popular over time.

Geodynamics

With its help, the interaction of rather complex processes that occur in the mantle and the crust is considered. In accordance with the concept set forth by Artyushkov in his work "Geodynamics", the main source of energy is the gravitational differentiation of matter. This process is noted in the lower mantle.

After heavy components (iron, etc.) are separated from the rock, a lighter mass remains. solids. She descends into the core. The location of the lighter layer under the heavy one is unstable. In this regard, the accumulating material is collected periodically into fairly large blocks that float into the upper layers. The size of such formations is about a hundred kilometers. This material was the basis for the formation of the Earth's upper mantle.

The lower layer is probably an undifferentiated primary substance. During the evolution of the planet, due to the lower mantle, the upper mantle grows and the core increases. It is more likely that blocks of light material are uplifted in the lower mantle along the channels. In them, the temperature of the mass is quite high. At the same time, the viscosity is significantly reduced. The increase in temperature is facilitated by the release of a large volume potential energy in the process of lifting a substance into the region of gravity for a distance of about 2000 km. In the course of movement along such a channel, a strong heating of light masses occurs. In this regard, the substance enters the mantle, having a sufficiently high temperature and significantly less weight in comparison with the surrounding elements.

Due to the reduced density, light material floats into the upper layers to a depth of 100-200 kilometers or less. With decreasing pressure, the melting point of the components of the substance decreases. After the primary differentiation at the "core-mantle" level, the secondary one occurs. At shallow depths, light matter is partially subjected to melting. During differentiation, more dense substances. They sink into the lower layers of the upper mantle. The released lighter components rise accordingly.

The complex of motions of substances in the mantle, associated with the redistribution of masses with different densities as a result of differentiation, is called chemical convection. The rise of light masses occurs at intervals of about 200 million years. At the same time, intrusion into the upper mantle is not observed everywhere. In the lower layer, the channels are located at a sufficiently large distance from each other (up to several thousand kilometers).

Boulder lifting

As mentioned above, in those zones where large masses of light heated material are introduced into the asthenosphere, its partial melting and differentiation occur. In the latter case, the separation of components and their subsequent ascent are noted. They quickly pass through the asthenosphere. When they reach the lithosphere, their speed decreases. In some areas, matter forms accumulations of anomalous mantle. They lie, as a rule, in the upper layers of the planet.

anomalous mantle

Its composition approximately corresponds to normal mantle matter. The difference between the anomalous accumulation is a higher temperature (up to 1300-1500 degrees) and a reduced speed of elastic longitudinal waves.

The influx of matter under the lithosphere provokes isostatic uplift. Due to the elevated temperature, the anomalous cluster has a lower density than the normal mantle. In addition, there is a small viscosity of the composition.

In the process of entering the lithosphere, the anomalous mantle is rather quickly distributed along the sole. At the same time, it displaces the denser and less heated matter of the asthenosphere. In the course of movement, the anomalous accumulation fills those areas where the sole of the platform is in an elevated state (traps), and it flows around deeply submerged areas. As a result, in the first case, an isostatic uplift is noted. Above submerged areas, the crust remains stable.

Traps

The process of cooling the upper mantle layer and the crust to a depth of about a hundred kilometers is slow. In general, it takes several hundred million years. In this regard, inhomogeneities in the thickness of the lithosphere, explained by horizontal temperature differences, have a rather large inertia. In the event that the trap is located not far from the upward flow of the anomalous accumulation from the depth, a large amount of the substance is captured very heated. As a result, a rather large mountain element is formed. In accordance with this scheme, high uplifts occur in the area of epiplatform orogeny in folded belts.

Description of processes

In the trap, the anomalous layer undergoes compression by 1–2 kilometers during cooling. The bark located on top is immersed. Precipitation begins to accumulate in the formed trough. Their heaviness contributes to even greater subsidence of the lithosphere. As a result, the depth of the basin can be from 5 to 8 km. At the same time, during the compaction of the mantle in the lower part of the basalt layer, a phase transformation of the rock into eclogite and garnet granulite can be observed in the crust. Due to the heat flow leaving the anomalous substance, the overlying mantle is heated and its viscosity decreases. In this regard, a gradual displacement of the normal cluster is observed.

Horizontal offsets

During the formation of uplifts in the process of the anomalous mantle reaching the crust on the continents and oceans, there is an increase in the potential energy stored in the upper layers of the planet. To dump excess substances, they tend to disperse to the sides. As a result, additional stresses are formed. They are associated with different types of movement of plates and crust.

The expansion of the ocean floor and the floating of the continents are the result of the simultaneous expansion of the ridges and the sinking of the platform into the mantle. Under the first are large masses of highly heated anomalous matter. In the axial part of these ridges, the latter is directly under the crust. The lithosphere here has a much smaller thickness. At the same time, the anomalous mantle spreads in the area of high pressure - in both directions from under the ridge. At the same time, it quite easily breaks the ocean's crust. The crevice is filled with basaltic magma. It, in turn, is melted out of the anomalous mantle. In the process of solidification of magma, a new oceanic crust is formed. This is how the bottom grows.

Process Features

Beneath the mid-ridges, the anomalous mantle has reduced viscosity due to elevated temperatures. The substance is able to spread quite quickly. As a result, the growth of the bottom occurs at an increased rate. The oceanic asthenosphere also has a relatively low viscosity.

The main lithospheric plates of the Earth float from the ridges to the places of immersion. If these areas are in the same ocean, then the process occurs at a relatively high speed. This situation is typical today for the Pacific Ocean. If the expansion of the bottom and the subsidence occurs in different areas, then the continent located between them drifts in the direction where the deepening occurs. Under the continents, the viscosity of the asthenosphere is higher than under the oceans. Due to the resulting friction, there is a significant resistance to movement. As a result, the rate at which the bottom expands is reduced if there is no compensation for the mantle subsidence in the same area. Thus, the expansion in the Pacific is faster than in the Atlantic.

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Wonderful-planet - Lithospheric plates.

You can find details in the section: Lithosphere

Lithospheric plates are large blocks of the earth's crust and parts of the upper mantle, of which the lithosphere is composed.

What is the composition of the lithosphere. - The main lithospheric plates. - Map of the Earth's lithosphere. - The movement of the lithosphere. - Lithospheric plates of Russia.

What is the composition of the lithosphere.

The lithosphere is made up of large blocks called lithospheric plates. Lithospheric blocks are 1-10,000 km across and their thickness varies from 60 to 100 km. Most of the lithospheric blocks include both the continental crust and the oceanic one. Although there are cases when the lithospheric plate consists exclusively of oceanic crust (Pacific Plate).

Lithospheric plates consist of igneous, metamorphosed and granitic rocks strongly crumpled into folds at the base, and a 3-4 km layer of sedimentary rocks on top.

At the heart of each continent is one or more ancient platforms, along the border of which a chain of mountain ranges runs. Inside the platform, the relief is usually represented by flat plains with separate mountain ranges.

The boundaries of lithospheric plates are characterized by high tectonic, seismic and volcanic activity. There are three types of plate boundaries: divergent, convergent, and transform. The outlines of the lithospheric plates are constantly changing. The big ones split, the small ones stick together. Some plates can sink into the Earth's mantle.

Usually at one point the globe converges only three lithospheric plates. The configuration, when four or more plates converge at one point, is unstable, and quickly collapses with time.

The main lithospheric plates of the Earth.

Most of the earth's surface, about 90%, is covered by 14 major lithospheric plates. This:

australian plate
Antarctic Plate
Arabian subcontinent
African plate
Eurasian plate
Hindustan plate
Cooker Coconut
Nazca plate
Pacific Plate
Scotia plate
North American Plate
Somali plate
South American Plate
Philippine plate

Fig 1. Map of the Earth's lithospheric plates.

Movement of the Earth's lithosphere.

Lithospheric plates are constantly moving relative to each other at a speed of up to several tens of centimeters per year. This fact was recorded by photographs taken from artificial satellites of the Earth. It is now known that the American lithospheric plate is moving towards the Pacific, and the Eurasian is approaching the African, Indo-Australian, and also the Pacific. The American and African lithospheric plates are slowly moving apart.

Lithospheric plates - the main components of the lithosphere - lie on the plastic layer of the upper mantle - the asthenosphere. It is she who plays the main role in the movement of the earth's crust. The substance of the asthenosphere as a result of thermal convection (heat transfer in the form of jets and flows) slowly “flows”, dragging blocks of the lithosphere with it and causing them to move horizontally. If the substance of the asthenosphere rises or falls, this leads to the vertical movement of the earth's crust. The speed of the vertical movement of the lithosphere is much less than the horizontal one - only up to 1-2 tens of millimeters per year.

With the vertical movement of the lithosphere above the ascending branches of the convective currents of the asthenosphere, lithospheric plates are ruptured and faults are formed. Lava rushes into the faults and, cooling down, fills the empty cavities with strata of igneous rocks. But then the growing stretching of the moving lithospheric plates again leads to a break. So, gradually growing in places of faults, lithospheric plates diverge in different directions. This strip of horizontal divergence of plates is called rift zone. With distance from the rift zone, the lithosphere cools, becomes heavier, thickens and, as a result, sinks deeper into the mantle, forming areas of relief depression.

Fault zones are observed both on land and in the ocean. The largest continental fault, more than 4000 km long and 80-120 km wide, is located in Africa. There are a large number of active and dormant volcanoes on the slopes of the fault.

At this time, on the boundary opposite from the fault, a collision of lithospheric plates occurs. This collision can proceed in different ways depending on the types of colliding plates.

If the oceanic and continental plates collide, the first sinks under the second. In this case, deep-sea trenches, island arcs (Japanese islands) or mountain ranges (Andes) arise.
If two continental lithospheric plates collide, then at this point the edges of the plates are crumpled into folds, which leads to the formation of volcanoes and mountain ranges. Thus, the Himalayas arose on the border of the Eurasian and Indo-Australian plates. In general, if there are mountains in the center of the mainland, this means that once it was a place of collision of two lithospheric plates welded into one.

Thus, the earth's crust is in constant motion. In its irreversible development, mobile areas - geosynclines - turn through long-term transformations into relatively calm areas - platforms.

Lithospheric plates of Russia.

Russia is located on four lithospheric plates.

Eurasian plate - most of the western and northern parts of the country,
The North American Plate is the northeastern part of Russia,
Amur lithospheric plate - south of Siberia,
Sea of Okhotsk plate - the Sea of Okhotsk and its coast.

Fig 2. Map of the lithospheric plates of Russia.

In the structure of lithospheric plates, relatively even ancient platforms and mobile folded belts stand out. Plains are located on stable areas of the platforms, and mountain ranges are located in the region of folded belts.

Fig 3. Tectonic structure of Russia.

Russia is located on two ancient platforms (East European and Siberian). Slabs and shields stand out within the platforms. A plate is a section of the earth's crust, the folded base of which is covered with a layer of sedimentary rocks. Shields, in contrast to plates, have very little sedimentary deposits and only a thin layer of soil.

In Russia, the Baltic Shield is distinguished on the East European Platform and the Aldan and Anabar Shields on the Siberian Platform.

Figure 4. Platforms, slabs and shields in Russia.

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Lithospheric Plate

The lithospheric plate is a large stable area of the earth's crust, part of the lithosphere. According to the theory of plate tectonics, lithospheric plates are limited by zones of seismic, volcanic and tectonic activity - plate boundaries. There are three types of plate boundaries: divergent, convergent, and transform.

From geometric considerations, it is clear that only three plates can converge at one point. A configuration in which four or more plates converge at one point is unstable, and quickly collapses over time.

There are two fundamental different types the earth's crust - continental crust and oceanic crust. Some lithospheric plates are composed exclusively of oceanic crust (an example is the largest Pacific plate), others consist of a block of continental crust soldered into the oceanic crust.

Lithospheric plates are constantly changing their outlines, they can split as a result of rifting and solder, forming a single plate as a result of collision. Lithospheric plates can also sink into the planet's mantle, reaching deep into the core. On the other hand, the division of the earth's crust into plates is ambiguous, and as geological knowledge accumulates, new plates are distinguished, and some plate boundaries are recognized as non-existent. Therefore, the outlines of the plates change with time in this sense as well. This is especially true for small plates, for which geologists have proposed many kinematic reconstructions, often mutually exclusive.

Map of lithospheric plates Tectonics plates (preserved surfaces)

More than 90% of the Earth's surface is covered by the 14 largest lithospheric plates:

Medium slabs:

Microplates

Disappeared plates:

Disappeared oceans:

Supercontinents:

Notes

Calculation of the thickness of the slab foundation

According to modern theories of lithospheric plates the entire lithosphere is divided into separate blocks by narrow and active zones - deep faults - moving in the plastic layer of the upper mantle relative to each other at a speed of 2-3 cm per year. These blocks are called lithospheric plates.

A feature of lithospheric plates is their rigidity and ability, in the absence of external influences, to maintain their shape and structure unchanged for a long time.

Lithospheric plates are mobile. Their movement along the surface of the asthenosphere occurs under the influence of convective currents in the mantle. Separate lithospheric plates can diverge, approach or slide relative to each other. In the first case, tension zones arise between the plates with cracks along the boundaries of the plates, in the second case, compression zones accompanied by thrusting of one plate onto another (thrust - obduction; underthrust - subduction), in the third case - shear zones - faults along which sliding of neighboring plates occurs. .

At the convergence of continental plates, they collide, forming mountain belts. This is how the Himalaya mountain system arose, for example, on the border of the Eurasian and Indo-Australian plates (Fig. 1).

Rice. 1. Collision of continental lithospheric plates

When the continental and oceanic plates interact, the plate with the oceanic crust moves under the plate with the continental crust (Fig. 2).

Rice. 2. Collision of continental and oceanic lithospheric plates

As a result of the collision of continental and oceanic lithospheric plates, deep-sea trenches and island arcs are formed.

The divergence of lithospheric plates and the formation of an oceanic type of earth's crust as a result of this is shown in Fig. 3.

The axial zones of mid-ocean ridges are characterized by rifts(from English. rift- crevice, crack, fault) - a large linear tectonic structure of the earth's crust with a length of hundreds, thousands, a width of tens, and sometimes hundreds of kilometers, formed mainly during horizontal stretching of the crust (Fig. 4). Very large rifts are called rift belts, zones or systems.

Since the lithospheric plate is a single plate, each of its faults is a source seismic activity and volcanism. These sources are concentrated within relatively narrow zones, along which mutual displacements and frictions of adjacent plates occur. These zones are called seismic belts. Reefs, mid-ocean ridges and deep-sea trenches are mobile areas of the Earth and are located at the boundaries of lithospheric plates. This indicates that the process of formation of the earth's crust in these zones is currently very intensive.

Rice. 3. Divergence of lithospheric plates in the zone among the nano-oceanic ridge

Rice. 4. Scheme of rift formation

Most of the faults of the lithospheric plates are at the bottom of the oceans, where the earth's crust is thinner, but they are also found on land. The largest fault on land is located in eastern Africa. It stretched for 4000 km. The width of this fault is 80-120 km.

At present, seven largest plates can be distinguished (Fig. 5). Of these, the largest in area is the Pacific, which consists entirely of oceanic lithosphere. As a rule, the Nazca plate is also referred to as large, which is several times smaller in size than each of the seven largest ones. At the same time, scientists suggest that in fact the Nazca plate is much larger than we see it on the map (see Fig. 5), since a significant part of it went under the neighboring plates. This plate also consists only of oceanic lithosphere.

Rice. 5. Earth's lithospheric plates

An example of a plate that includes both continental and oceanic lithosphere is, for example, the Indo-Australian lithospheric plate. The Arabian Plate consists almost entirely of the continental lithosphere.

The theory of lithospheric plates is important. First of all, it can explain why mountains are located in some places on the Earth, and plains in others. With the help of the theory of lithospheric plates, it is possible to explain and predict catastrophic phenomena occurring at the boundaries of plates.

Rice. 6. The outlines of the continents really seem compatible

Continental drift theory

The theory of lithospheric plates originates from the theory of continental drift. Back in the 19th century many geographers noted that when looking at a map, one can notice that the coasts of Africa and South America seem compatible when approaching (Fig. 6).

The emergence of the hypothesis of the movement of the continents is associated with the name of the German scientist Alfred Wegener(1880-1930) (Fig. 7), who most fully developed this idea.

Wegener wrote: “In 1910, the idea of moving the continents first occurred to me ... when I was struck by the similarity of the outlines of the coasts on both sides Atlantic Ocean". He suggested that in the early Paleozoic there were two large continents on Earth - Laurasia and Gondwana.

Laurasia was the northern mainland, which included the territories of modern Europe, Asia without India and North America. The southern mainland - Gondwana united the modern territories of South America, Africa, Antarctica, Australia and Hindustan.

Between Gondwana and Laurasia was the first sea - Tethys, like a huge bay. The rest of the Earth's space was occupied by the Panthalassa ocean.

About 200 million years ago, Gondwana and Laurasia were united into a single continent - Pangea (Pan - universal, Ge - earth) (Fig. 8).

Rice. 8. The existence of a single mainland Pangea (white - land, dots - shallow sea)

Approximately 180 million years ago, the mainland of Pangea again began to be divided into constituent parts, which mixed up on the surface of our planet. The division took place as follows: first, Laurasia and Gondwana reappeared, then Laurasia divided, and then Gondwana also split. Due to the split and divergence of parts of Pangea, oceans were formed. The young oceans can be considered the Atlantic and Indian; old - Quiet. The Arctic Ocean became isolated with the increase in land mass in the Northern Hemisphere.

Rice. 9. Location and directions of continental drift in the Cretaceous period 180 million years ago

A. Wegener found a lot of evidence for the existence of a single continent of the Earth. The existence in Africa and in South America remains of ancient animals - leafosaurs. These were reptiles, similar to small hippos, that lived only in freshwater reservoirs. This means that they could not swim huge distances in salty sea water. He found similar evidence in the plant world.

Interest in the hypothesis of the movement of the continents in the 30s of the XX century. decreased slightly, but in the 60s it revived again, when, as a result of studies of the relief and geology of the ocean floor, data were obtained indicating the processes of expansion (spreading) of the oceanic crust and the “diving” of some parts of the crust under others (subduction).

The surface shell of the Earth consists of parts - lithospheric or tectonic plates. They are integral large blocks that are in continuous motion. This leads to the emergence of various phenomena on the surface of the globe, as a result of which the relief inevitably changes.

Plate tectonics

Tectonic plates are the constituent parts of the lithosphere responsible for the geological activity of our planet. Millions of years ago, they were a single entity, making up the largest supercontinent called Pangea. However, as a result of high activity in the bowels of the Earth, this continent split into continents, which moved away from each other to the maximum distance.

According to scientists, in a few hundred years this process will go in the opposite direction, and the tectonic plates will again begin to combine with each other.

Rice. 1. Tectonic plates of the Earth.

Earth is the only planet in solar system, whose surface shell is broken into separate parts. The thickness of tectonic reaches several tens of kilometers.

According to tectonics, a science that studies lithospheric plates, huge areas of the earth's crust are surrounded on all sides by zones of increased activity. At the junctions of neighboring plates and occur natural phenomena, which most often cause large-scale catastrophic consequences: volcanic eruptions, strong earthquakes.

Movement of the Earth's tectonic plates

The main reason why the entire lithosphere of the globe is in continuous motion is thermal convection. Critically high temperatures reign in the central part of the planet. When heated, the upper layers of matter in the bowels of the Earth rise, while the upper layers, already cooled, sink towards the center. The continuous circulation of matter sets in motion parts of the earth's crust.

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The speed of movement of lithospheric plates is approximately 2-2.5 cm per year. Since their movement occurs on the surface of the planet, strong deformations occur in the earth's crust at the boundary of their interaction. As a rule, this leads to the formation of mountain ranges and faults. For example, on the territory of Russia, the mountain systems of the Caucasus, Urals, Altai and others were formed in this way.

Rice. 2. Greater Caucasus.

There are several types of lithospheric plate movement:

divergent - two platforms diverge, forming an underwater mountain range or a hole in the ground.
Convergent - two plates approach each other, while the thinner one sinks under the more massive one. At the same time, mountain ranges are formed.
sliding - two plates move in opposite directions.

Africa is literally splitting into two parts. Large cracks in the ground have been recorded, stretching across much of Kenya. According to scientists, in about 10 million years the African continent as a whole will cease to exist.

December 10th, 2015

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According to modern theories of lithospheric plates the entire lithosphere is divided by narrow and active zones - deep faults - into separate blocks moving in the plastic layer of the upper mantle relative to each other at a speed of 2-3 cm per year. These blocks are called lithospheric plates.

Alfred Wegener first suggested horizontal movement of crustal blocks in the 1920s as part of the “continental drift” hypothesis, but this hypothesis did not receive support at that time.

Only in the 1960s, studies of the ocean floor provided indisputable evidence of the horizontal movement of plates and the processes of expansion of the oceans due to the formation (spreading) of the oceanic crust. The revival of ideas about the predominant role of horizontal movements occurred within the framework of the "mobilistic" direction, the development of which led to the development of the modern theory of plate tectonics. The main provisions of plate tectonics were formulated in 1967-68 by a group of American geophysicists - W. J. Morgan, C. Le Pichon, J. Oliver, J. Isaacs, L. Sykes in the development of earlier (1961-62) ideas of American scientists G. Hess and R. Digts on the expansion (spreading) of the ocean floor.

It is argued that scientists are not entirely sure what causes these very shifts and how the boundaries of tectonic plates were designated. There are countless various theories, but none of them fully explains all aspects of tectonic activity.

Let's at least find out how they imagine it now.

Wegener wrote: "In 1910, the idea of moving the continents first occurred to me ... when I was struck by the similarity of the outlines of the coasts on both sides of the Atlantic Ocean." He suggested that in the early Paleozoic there were two large continents on Earth - Laurasia and Gondwana.

Between Gondwana and Laurasia was the first sea - Tethys, like a huge bay. The rest of the Earth's space was occupied by the Panthalassa ocean.

About 200 million years ago, Gondwana and Laurasia were united into a single continent - Pangea (Pan - universal, Ge - earth)

A. Wegener found a lot of evidence for the existence of a single continent of the Earth. The existence in Africa and South America of the remains of ancient animals - leafosaurs seemed especially convincing to him. These were reptiles, similar to small hippos, that lived only in freshwater reservoirs. This means that they could not swim huge distances in salty sea water. He found similar evidence in the plant world.

The structure of the continental rift

The upper stone part of the planet is divided into two shells, which differ significantly in rheological properties: a rigid and brittle lithosphere and an underlying plastic and mobile asthenosphere.
The base of the lithosphere is an isotherm approximately equal to 1300°C, which corresponds to the melting temperature (solidus) of mantle material at lithostatic pressure existing at depths of a few hundreds of kilometers. The rocks lying in the Earth above this isotherm are quite cold and behave like a rigid material, while the underlying rocks of the same composition are quite heated and deform relatively easily.

The lithosphere is divided into plates, constantly moving along the surface of the plastic asthenosphere. The lithosphere is divided into 8 large plates, dozens of medium plates and many small ones. Between the large and medium slabs there are belts composed of a mosaic of small crustal slabs.

Plate boundaries are areas of seismic, tectonic, and magmatic activity; the inner areas of the plates are weakly seismic and are characterized by a weak manifestation of endogenous processes.
More than 90% of the Earth's surface falls on 8 large lithospheric plates:

Some lithospheric plates are composed exclusively of oceanic crust (for example, the Pacific Plate), others include fragments of both oceanic and continental crust.

Diagram of rift formation

There are three types of relative plate movements: divergence (divergence), convergence (convergence) and shear movements.

Divergent boundaries are boundaries along which plates move apart. The geodynamic setting in which the process of horizontal stretching of the earth's crust occurs, accompanied by the appearance of extended linearly elongated fissured or ravine-shaped depressions, is called rifting. These boundaries are confined to continental rifts and mid-ocean ridges in ocean basins. The term "rift" (from the English rift - gap, crack, gap) is applied to large linear structures deep origin, formed during the stretching of the earth's crust. In terms of structure, they are graben-like structures. Rifts can be laid both on the continental and oceanic crust, forming a single global system oriented relative to the geoid axis. In this case, the evolution of continental rifts can lead to a break in the continuity of the continental crust and the transformation of this rift into an oceanic rift (if the expansion of the rift stops before the stage of break of the continental crust, it is filled with sediments, turning into an aulacogen).

The process of plate expansion in the zones of oceanic rifts (mid-ocean ridges) is accompanied by the formation of a new oceanic crust due to magmatic basaltic melts coming from the asthenosphere. Such a process of formation of a new oceanic crust due to the influx of mantle matter is called spreading (from the English spread - to spread, unfold).

The structure of the mid-ocean ridge. 1 - asthenosphere, 2 - ultrabasic rocks, 3 - basic rocks (gabbroids), 4 - complex of parallel dikes, 5 - basalts of the ocean floor, 6 - segments of the oceanic crust that formed in different time(I-V as it gets older), 7 - near-surface magma chamber (with ultramafic magma in the lower part and basic in the upper part), 8 - sediments of the ocean floor (1-3 as they accumulate)

In the course of spreading, each stretching pulse is accompanied by the inflow of a new portion of mantle melts, which, while solidifying, build up the edges of the plates diverging from the MOR axis. It is in these zones that the formation of young oceanic crust occurs.

Collision of continental and oceanic lithospheric plates

Subduction is the process of subduction of an oceanic plate under a continental or other oceanic one. The subduction zones are confined to the axial parts of deep-sea trenches conjugated with island arcs (which are elements of active margins). Subduction boundaries account for about 80% of the length of all convergent boundaries.

When continental and oceanic plates collide, a natural phenomenon is the subduction of the oceanic (heavier) plate under the edge of the continental one; when two oceanic ones collide, the older one (that is, the cooler and denser) of them sinks.

The subduction zones have a characteristic structure: their typical elements are a deep-water trough - a volcanic island arc - a back-arc basin. A deep-water trench is formed in the zone of bending and underthrust of the subducting plate. As this plate sinks, it begins to lose water (which is found in abundance in sediments and minerals), the latter, as is known, significantly reduces the melting point of rocks, which leads to the formation of melting centers that feed island arc volcanoes. In the rear of the volcanic arc, some extension usually occurs, which determines the formation of a back-arc basin. In the zone of the back-arc basin, the extension can be so significant that it leads to the rupture of the plate crust and the opening of the basin with oceanic crust (the so-called back-arc spreading process).

The volume of oceanic crust absorbed in subduction zones is equal to the volume of crust formed in spreading zones. This provision emphasizes the opinion about the constancy of the volume of the Earth. But such an opinion is not the only and definitively proven. It is possible that the volume of the plans changes pulsatingly, or there is a decrease in its decrease due to cooling.

The subduction of the subducting plate into the mantle is traced by earthquake foci that occur at the contact of the plates and inside the subducting plate (which is colder and therefore more fragile than the surrounding mantle rocks). This seismic focal zone is called the Benioff-Zavaritsky zone. In subduction zones, the process of formation of a new continental crust begins. A much rarer process of interaction between the continental and oceanic plates is the process of obduction - thrusting of a part of the oceanic lithosphere onto the edge of the continental plate. It should be emphasized that in the course of this process, the oceanic plate is stratified, and only its upper part is advancing - the crust and several kilometers of the upper mantle.

Collision of continental lithospheric plates

When continental plates collide, the crust of which is lighter than the substance of the mantle and, as a result, is not able to sink into it, a collision process occurs. In the course of collision, the edges of colliding continental plates are crushed, crushed, and systems of large thrusts are formed, which leads to the growth of mountain structures with a complex fold-thrust structure. A classic example of such a process is the collision of the Hindustan plate with the Eurasian one, accompanied by the growth of the grandiose mountain systems of the Himalayas and Tibet. The collision process replaces the subduction process, completing the closure of the ocean basin. At the same time, at the beginning of the collision process, when the edges of the continents have already approached, the collision is combined with the subduction process (the remains of the oceanic crust continue to sink under the edge of the continent). Collision processes are characterized by large-scale regional metamorphism and intrusive granitoid magmatism. These processes lead to the creation of a new continental crust (with its typical granite-gneiss layer).

The main cause of plate movement is mantle convection, caused by mantle heat and gravity currents.

The source of energy for these currents is the temperature difference between the central regions of the Earth and the temperature of its near-surface parts. At the same time, the main part of the endogenous heat is released at the boundary of the core and mantle during the process of deep differentiation, which determines the decay of the primary chondritic substance, during which the metal part rushes to the center, increasing the core of the planet, and the silicate part is concentrated in the mantle, where it further undergoes differentiation.

The rocks heated in the central zones of the Earth expand, their density decreases, and they float, giving way to descending colder and therefore heavier masses, which have already given up part of the heat in near-surface zones. This process of heat transfer goes on continuously, resulting in the formation of ordered closed convective cells. At the same time, in the upper part of the cell, the flow of matter occurs in an almost horizontal plane, and it is this part of the flow that determines the horizontal movement of the matter of the asthenosphere and the plates located on it. In general, the ascending branches of convective cells are located under the zones of divergent boundaries (MOR and continental rifts), while the descending branches are located under the zones of convergent boundaries. Thus, the main reason for the movement of lithospheric plates is "drag" by convective currents. In addition, a number of other factors act on the plates. In particular, the surface of the asthenosphere turns out to be somewhat elevated above the zones of ascending branches and more lowered in the zones of subsidence, which determines the gravitational "sliding" of the lithospheric plate located on an inclined plastic surface. Additionally, there are processes of pulling the heavy cold oceanic lithosphere in the subduction zones into the hot, and, as a result, less dense, asthenosphere, as well as hydraulic wedging by basalts in the MOR zones.

The main driving forces plate tectonics – mantle “drag” forces FDO under the oceans and FDC under the continents, the magnitude of which depends primarily on the speed of the asthenospheric current, and the latter is determined by the viscosity and thickness of the asthenospheric layer. Since the thickness of the asthenosphere under the continents is much less and the viscosity is much higher than under the oceans, the magnitude of the FDC force is almost an order of magnitude inferior to that of the FDO. Under the continents, especially their ancient parts (continental shields), the asthenosphere almost wedges out, so the continents seem to be “sitting aground”. Since most of the lithospheric plates modern earth include both oceanic and continental parts, it should be expected that the presence of a continent in the composition of the plate in the general case should “slow down” the movement of the entire plate. This is how it actually happens (the fastest moving are the almost purely oceanic plates Pacific, Cocos and Nasca; the slowest are the Eurasian, North American, South American, Antarctic and African, a significant part of the area of which is occupied by continents). Finally, at convergent plate boundaries, where the heavy and cold edges of lithospheric plates (slabs) sink into the mantle, their negative buoyancy creates the FNB force (negative buoyance). The action of the latter leads to the fact that the subducting part of the plate sinks in the asthenosphere and pulls the entire plate along with it, thereby increasing the speed of its movement. Obviously, the FNB force acts episodically and only in certain geodynamic settings, for example, in the cases of the collapse of slabs through the 670 km section described above.

Thus, the mechanisms that set the lithospheric plates in motion can be conventionally assigned to the following two groups: 1) associated with the forces of the mantle “dragging” (mantle drag mechanism) applied to any points of the bottom of the plates, in the figure - the forces of FDO and FDC; 2) associated with the forces applied to the edges of the plates (edge-force mechanism), in the figure - the forces FRP and FNB. The role of this or that driving mechanism, as well as these or those forces, is evaluated individually for each lithospheric plate.

The totality of these processes reflects the general geodynamic process, covering areas from the surface to deep zones of the Earth. At present, two-cell closed-cell mantle convection is developing in the Earth's mantle (according to the through-mantle convection model) or separate convection in the upper and lower mantle with the accumulation of slabs under subduction zones (according to the two-tier model). The probable poles of the rise of the mantle matter are located in northeast Africa (approximately under the junction zone of the African, Somali and Arabian plates) and in the area of Easter Island (under the middle ridge of the Pacific Ocean - the East Pacific Rise). The mantle subsidence equator runs approximately along a continuous chain of convergent plate boundaries along the periphery of the Pacific and eastern Indian Oceans. convection) or (according to alternative model) convection will become through the mantle due to the collapse of slabs through the 670 km section. This may lead to the collision of the continents and the formation of a new supercontinent, the fifth in the history of the Earth.

Plate movements obey the laws of spherical geometry and can be described on the basis of Euler's theorem. Euler's rotation theorem states that any rotation of three-dimensional space has an axis. Thus, rotation can be described by three parameters: the coordinates of the rotation axis (for example, its latitude and longitude) and the angle of rotation. Based on this position, the position of the continents in past geological epochs can be reconstructed. An analysis of the movements of the continents led to the conclusion that every 400-600 million years they unite into a single supercontinent, which is further disintegrated. As a result of the split of such a supercontinent Pangea, which occurred 200-150 million years ago, modern continents were formed.

Plate tectonics is the first general geological concept that could be tested. Such a check has been made. In the 70s. deep-sea drilling program was organized. As part of this program, several hundred wells were drilled by the Glomar Challenger drillship, which showed good agreement of ages estimated from magnetic anomalies with ages determined from basalts or from sedimentary horizons. The distribution scheme of uneven-aged sections of the oceanic crust is shown in Fig.:

The age of the oceanic crust according to magnetic anomalies (Kenneth, 1987): 1 - areas of lack of data and dry land; 2–8 - age: 2 - Holocene, Pleistocene, Pliocene (0–5 Ma); 3 - Miocene (5–23 Ma); 4 - Oligocene (23–38 Ma); 5 - Eocene (38–53 Ma); 6 - Paleocene (53–65 Ma) 7 - Cretaceous (65–135 Ma) 8 - Jurassic (135–190 Ma)

At the end of the 80s. completed another experiment to test the movement of lithospheric plates. It was based on baseline measurements relative to distant quasars. Points were selected on two plates, at which, using modern radio telescopes, the distance to quasars and their declination angle were determined, and, accordingly, the distances between points on two plates were calculated, i.e., the baseline was determined. The accuracy of the determination was a few centimeters. Several years later, the measurements were repeated. Very good convergence of results calculated from magnetic anomalies with data determined from baselines was obtained.

Scheme illustrating the results of measurements of the mutual displacement of lithospheric plates, obtained by the method of interferometry with an extra long baseline - ISDB (Carter, Robertson, 1987). The movement of the plates changes the length of the baseline between radio telescopes located on different plates. The map of the Northern Hemisphere shows the baselines from which the ISDB measured enough data to make a reliable estimate of the rate of change in their length (in centimeters per year). The numbers in parentheses indicate the amount of plate displacement calculated from the theoretical model. In almost all cases, the calculated and measured values are very close.

Thus, lithospheric plate tectonics has been tested over the years by a number of independent methods. It is recognized by the world scientific community as the paradigm of geology at the present time.

Knowing the position of the poles and the speed of the current movement of lithospheric plates, the speed of expansion and absorption of the ocean floor, it is possible to outline the path of movement of the continents in the future and imagine their position for a certain period of time.

Such a forecast was made by American geologists R. Dietz and J. Holden. In 50 million years, according to their assumptions, the Atlantic and Indian oceans will expand at the expense of the Pacific, Africa will shift to the north, and due to this, the Mediterranean Sea will gradually be liquidated. The Strait of Gibraltar will disappear, and the “turned” Spain will close the Bay of Biscay. Africa will be split by the great African faults and the eastern part of it will shift to the northeast. The Red Sea will expand so much that it will separate the Sinai Peninsula from Africa, Arabia will move to the northeast and close the Persian Gulf. India will increasingly move towards Asia, which means that the Himalayan mountains will grow. California will separate from North America along the San Andreas Fault, and a new ocean basin will begin to form in this place. Significant changes will occur in the southern hemisphere. Australia will cross the equator and come into contact with Eurasia. This forecast requires significant refinement. Much here is still debatable and unclear.

sources

http://www.pegmatite.ru/My_Collection/mineralogy/6tr.htm

http://www.grandars.ru/shkola/geografiya/dvizhenie-litosfernyh-plit.html

http://kafgeo.igpu.ru/web-text-books/geology/platehistory.htm

http://stepnoy-sledopyt.narod.ru/geologia/dvizh/dvizh.htm

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