Continental plates. How lithospheric plates move

. - Main lithospheric plates. - - - Lithospheric plates of Russia.

What is the lithosphere composed of?

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

• If oceanic and continental plates collide, the first one sinks under the second one. This creates deep-sea trenches, island arcs (Japanese islands) or mountain ranges (Andes).
• If two continental lithospheric plates collide, then at this point the edges of the plates are crushed 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 continent, this means that it was once the site of a collision between two lithospheric plates fused into one.

Thus, the earth's crust is in constant motion. In its irreversible development, the moving areas are geosynclines- are transformed through long-term transformations into relatively quiet 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,
• North American Plate– northeastern part of Russia,
• Amur lithospheric plate– south of Siberia,
• Sea of ​​Okhotsk plate– Sea of ​​Okhotsk and its coast.

Figure 2. Map of lithospheric plates in Russia.

In the structure of lithospheric plates, relatively flat ancient platforms and mobile folded belts are distinguished. In stable areas of the platforms there are plains, and in the area of ​​fold belts there are mountain ranges.

Figure 3. Tectonic structure of Russia.

Russia is located on two ancient platforms (East European and Siberian). Within the platforms there are slabs And shields. A plate is a section of the earth's crust, the folded base of which is covered with a layer of sedimentary rocks. Shields, as opposed to slabs, have very little sediment and only a thin layer of soil.

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

Figure 4. Platforms, slabs and shields on the territory of Russia.

The basis of theoretical geology at the beginning of the 20th century was the contraction hypothesis. The earth cools like a baked apple, and wrinkles appear on it in the form of mountain ranges. These ideas were developed by the theory of geosynclines, created on the basis of the study of folded structures. This theory was formulated by James Dana, who added the principle of isostasy to the contraction hypothesis. According to this concept, the Earth consists of granites (continents) and basalts (oceans). When the Earth contracts, tangential forces arise in the ocean basins, which press on the continents. The latter rise into mountain ranges and then collapse. The material that results from destruction is deposited in the depressions.

In addition, Wegener began to look for geophysical and geodetic evidence. However, at that time the level of these sciences was clearly not sufficient to record the modern movement of the continents. In 1930, Wegener died during an expedition in Greenland, but before his death he already knew that the scientific community did not accept his theory.

Initially continental drift theory was received favorably by the scientific community, but in 1922 it was subjected to severe criticism from several well-known specialists. The main argument against the theory was the question of the force that moves the plates. Wegener believed that the continents moved along the basalts of the ocean floor, but this required enormous force, and no one could name the source of this force. The Coriolis force, tidal phenomena and some others were proposed as a source of plate movement, but the simplest calculations showed that all of them were absolutely insufficient to move huge continental blocks.

Critics of Wegener's theory focused on the question of the force moving the continents, and ignored all the many facts that certainly confirmed the theory. Essentially, they found a single issue on which the new concept was powerless, and without constructive criticism they rejected the main evidence. After the death of Alfred Wegener, the theory of continental drift was rejected, becoming a fringe science, and the vast majority of research continued to be carried out within the framework of geosyncline theory. True, she also had to look for explanations of the history of the settlement of animals on the continents. For this purpose, land bridges were invented that connected the continents, but plunged into the depths of the sea. This was another birth of the legend of Atlantis. It is worth noting that some scientists did not recognize the verdict of world authorities and continued to search for evidence of continental movement. Tak du Toit ( Alexander du Toit) explained the formation of the Himalayan mountains by the collision of Hindustan and the Eurasian plate.

The sluggish struggle between the fixists, as supporters of the absence of significant horizontal movements were called, and the mobilists, who argued that the continents do move, flared up with renewed vigor in the 1960s, when, as a result of studying the ocean floor, clues were found to understanding the “machine” called Earth.

By the early 1960s, a relief map of the ocean floor was compiled, which showed that mid-ocean ridges are located in the center of the oceans, which rise 1.5-2 km above the abyssal plains covered with sediment. These data allowed R. Dietz and Harry Hess to put forward the spreading hypothesis in 1963. According to this hypothesis, convection occurs in the mantle at a speed of about 1 cm/year. The ascending branches of convection cells carry out mantle material under the mid-ocean ridges, which renews the ocean floor in the axial part of the ridge every 300-400 years. Continents do not float on the oceanic crust, but move along the mantle, being passively “soldered” into lithospheric plates. According to the concept of spreading, ocean basins have a variable and unstable structure, while continents are stable.

The same driving force (altitude difference) determines the degree of elastic horizontal compression of the crust by the force of viscous friction of the flow against the earth's crust. The magnitude of this compression is small in the region of the ascent of the mantle flow and increases as it approaches the place of descent of the flow (due to the transfer of compressive stress through the stationary hard crust in the direction from the place of ascent to the place of descent of the flow). Above the descending flow, the compression force in the crust is so great that from time to time the strength of the crust is exceeded (in the region of lowest strength and highest stress), and inelastic (plastic, brittle) deformation of the crust occurs - an earthquake. At the same time, entire mountain ranges, for example, the Himalayas, are squeezed out from the place where the crust is deformed (in several stages).

During plastic (brittle) deformation, the stress in it—the compressive force at the source of the earthquake and its surroundings—reduces very quickly (at the rate of crustal displacement during an earthquake). But immediately after the end of the inelastic deformation, the very slow increase in stress (elastic deformation), interrupted by the earthquake, continues due to the very slow movement of the viscous mantle flow, beginning the cycle of preparation for the next earthquake.

Thus, the movement of plates is a consequence of the transfer of heat from the central zones of the Earth by very viscous magma. In this case, part of the thermal energy is converted into mechanical work to overcome frictional forces, and part, having passed through the earth’s crust, is radiated into the surrounding space. So our planet is, in a sense, a heat engine.

There are several hypotheses regarding the cause of the high temperature of the Earth's interior. At the beginning of the 20th century, the hypothesis of the radioactive nature of this energy was popular. It seemed to be confirmed by estimates of the composition of the upper crust, which showed very significant concentrations of uranium, potassium and other radioactive elements, but it later turned out that the content of radioactive elements in the rocks of the earth's crust was completely insufficient to provide the observed deep heat flow. And the content of radioactive elements in the subcrustal material (close in composition to the basalts of the ocean floor) can be said to be negligible. However, this does not exclude a fairly high content of heavy radioactive elements that generate heat in the central zones of the planet.

Another model explains the heating by chemical differentiation of the Earth. The planet was originally a mixture of silicate and metallic substances. But simultaneously with the formation of the planet, its differentiation into separate shells began. The denser metal part rushed to the center of the planet, and silicates concentrated in the upper shells. At the same time, the potential energy of the system decreased and was converted into thermal energy.

Other researchers believe that the heating of the planet occurred as a result of accretion during meteorite impacts on the surface of the nascent celestial body. This explanation is doubtful - during accretion, heat was released almost on the surface, from where it easily escaped into space, and not into the central regions of the Earth.

Secondary forces

The force of viscous friction arising as a result of thermal convection plays a decisive role in the movements of plates, but in addition to it, other, smaller, but also important forces act on the plates. These are Archimedes' forces, ensuring the floating of a lighter crust on the surface of a heavier mantle. Tidal forces caused by the gravitational influence of the Moon and the Sun (the difference in their gravitational influence on points of the Earth at different distances from them). Now the tidal “hump” on Earth, caused by the attraction of the Moon, is on average about 36 cm. Previously, the Moon was closer and this was on a large scale, the deformation of the mantle leads to its heating. For example, the volcanism observed on Io (a moon of Jupiter) is caused precisely by these forces - the tide on Io is about 120 m. And also the forces arising due to changes in atmospheric pressure on various parts of the earth's surface - atmospheric pressure forces often change by 3%, which equivalent to a continuous layer of water 0.3 m thick (or granite at least 10 cm thick). Moreover, this change can occur in a zone hundreds of kilometers wide, while the change in tidal forces occurs more smoothly - over distances of thousands of kilometers.

Divergent boundaries or plate boundaries

These are boundaries between plates moving in opposite directions. In the Earth's topography, these boundaries are expressed as rifts, where tensile deformations predominate, the thickness of the crust is reduced, the heat flow is maximum, and active volcanism occurs. If such a boundary forms on a continent, then a continental rift is formed, which can later turn into an oceanic basin with an oceanic rift in the center. In oceanic rifts, new oceanic crust is formed as a result of spreading.

Ocean rifts

Scheme of the structure of the mid-ocean ridge

Continental rifts

The breakup of the continent into parts begins with the formation of a rift. The crust thins and moves apart, and magmatism begins. An extended linear depression with a depth of about hundreds of meters is formed, which is limited by a series of faults. After this, two scenarios are possible: either the expansion of the rift stops and it is filled with sedimentary rocks, turning into an aulacogen, or the continents continue to move apart and between them, already in typical oceanic rifts, oceanic crust begins to form.

Convergent boundaries

Convergent boundaries are boundaries where plates collide. Three options are possible:

1. Continental plate with oceanic plate. Oceanic crust is denser than continental crust and sinks beneath the continent at a subduction zone.
2. Oceanic plate with oceanic plate. In this case, one of the plates creeps under the other and a subduction zone is also formed, above which an island arc is formed.
3. Continental plate with continental one. A collision occurs and a powerful folded area appears. A classic example is the Himalayas.

In rare cases, oceanic crust is pushed onto continental crust - obduction. Thanks to this process, ophiolites of Cyprus, New Caledonia, Oman and others arose.

Subduction zones absorb oceanic crust, thereby compensating for its appearance at mid-ocean ridges. Extremely complex processes and interactions between the crust and mantle take place in them. Thus, the oceanic crust can pull blocks of continental crust into the mantle, which, due to their low density, are exhumed back into the crust. This is how metamorphic complexes of ultra-high pressures arise, one of the most popular objects of modern geological research.

Most modern subduction zones are located along the periphery of the Pacific Ocean, forming the Pacific Ring of Fire. The processes occurring in the plate convergence zone are rightfully considered to be among the most complex in geology. It mixes blocks of different origins, forming a new continental crust.

Active continental margins

Active continental margin

An active continental margin occurs where oceanic crust subducts beneath a continent. The standard of this geodynamic situation is considered to be the western coast of South America; it is often called Andean type of continental margin. The active continental margin is characterized by numerous volcanoes and generally powerful magmatism. Melts have three components: the oceanic crust, the mantle above it, and the lower continental crust.

Beneath the active continental margin, there is active mechanical interaction between the oceanic and continental plates. Depending on the speed, age and thickness of the oceanic crust, several equilibrium scenarios are possible. If the plate moves slowly and has a relatively low thickness, then the continent scrapes off the sedimentary cover from it. Sedimentary rocks are crushed into intense folds, metamorphosed and become part of the continental crust. The resulting structure is called accretionary wedge. If the speed of the subducting plate is high and the sedimentary cover is thin, then the oceanic crust erases the bottom of the continent and draws it into the mantle.

Island arcs

Island arc

Island arcs are chains of volcanic islands above a subduction zone, occurring where an oceanic plate subducts beneath another oceanic plate. Typical modern island arcs include the Aleutian, Kuril, Mariana Islands, and many other archipelagos. The Japanese Islands are also often called an island arc, but their foundation is very ancient and in fact they were formed by several island arc complexes at different times, so the Japanese Islands are a microcontinent.

Island arcs are formed when two oceanic plates collide. In this case, one of the plates ends up at the bottom and is absorbed into the mantle. Island arc volcanoes form on the upper plate. The curved side of the island arc is directed towards the absorbed plate. On this side there is a deep-sea trench and a forearc trough.

Behind the island arc there is a back-arc basin (typical examples: Sea of ​​Okhotsk, South China Sea, etc.) in which spreading can also occur.

Continental collision

Collision of continents

The collision of continental plates leads to the collapse of the crust and the formation of mountain ranges. An example of a collision is the Alpine-Himalayan mountain belt, formed as a result of the closure of the Tethys Ocean and the collision with the Eurasian plate of Hindustan and Africa. As a result, the thickness of the crust increases significantly; under the Himalayas it reaches 70 km. This is an unstable structure; it is intensively destroyed by surface and tectonic erosion. In the crust with a sharply increased thickness, granites are smelted from metamorphosed sedimentary and igneous rocks. This is how the largest batholiths were formed, for example, Angara-Vitimsky and Zerendinsky.

Transform boundaries

Where plates move in parallel courses, but at different speeds, transform faults arise - enormous shear faults, widespread in the oceans and rare on continents.

Transform faults

In the oceans, transform faults run perpendicular to mid-ocean ridges (MORs) and break them into segments averaging 400 km wide. Between the ridge segments there is an active part of the transform fault. Earthquakes and mountain building constantly occur in this area; numerous feathering structures are formed around the fault - thrusts, folds and grabens. As a result, mantle rocks are often exposed in the fault zone.

On both sides of the MOR segments there are inactive parts of transform faults. There are no active movements in them, but they are clearly expressed in the topography of the ocean floor by linear uplifts with a central depression.

Transform faults form a regular network and, obviously, do not arise by chance, but due to objective physical reasons. A combination of numerical modeling data, thermophysical experiments and geophysical observations made it possible to find out that mantle convection has a three-dimensional structure. In addition to the main flow from the MOR, longitudinal currents arise in the convective cell due to the cooling of the upper part of the flow. This cooled substance rushes down along the main direction of the mantle flow. Transform faults are located in the zones of this secondary descending flow. This model agrees well with the data on heat flow: a decrease in heat flow is observed above transform faults.

Continental shifts

Strike-slip plate boundaries on continents are relatively rare. Perhaps the only currently active example of a boundary of this type is the San Andreas Fault, separating the North American Plate from the Pacific Plate. The 800-mile San Andreas Fault is one of the most seismically active areas on the planet: plates move relative to each other by 0.6 cm per year, earthquakes with a magnitude of more than 6 units occur on average once every 22 years. The city of San Francisco and much of the San Francisco Bay area are built in close proximity to this fault.

Within-plate processes

The first formulations of plate tectonics argued that volcanism and seismic phenomena are concentrated along plate boundaries, but it soon became clear that specific tectonic and magmatic processes also occur within plates, which were also interpreted within the framework of this theory. Among intraplate processes, a special place was occupied by the phenomena of long-term basaltic magmatism in some areas, the so-called hot spots.

Hot Spots

There are numerous volcanic islands at the bottom of the oceans. Some of them are located in chains with successively changing ages. A classic example of such an underwater ridge is the Hawaiian Underwater Ridge. It rises above the surface of the ocean in the form of the Hawaiian Islands, from which a chain of seamounts with continuously increasing age extends to the northwest, some of which, for example, Midway Atoll, come to the surface. At a distance of about 3000 km from Hawaii, the chain turns slightly north and is called the Imperial Ridge. It is interrupted in a deep-sea trench in front of the Aleutian island arc.

To explain this amazing structure, it was suggested that beneath the Hawaiian Islands there is a hot spot - a place where a hot mantle flow rises to the surface, which melts the oceanic crust moving above it. There are many such points now installed on Earth. The mantle flow that causes them has been called a plume. In some cases, an exceptionally deep origin of the plume material is assumed, right down to the core-mantle boundary.

Traps and oceanic plateaus

In addition to long-term hot spots, enormous outpourings of melts sometimes occur inside plates, which form traps on continents and oceanic plateaus in oceans. The peculiarity of this type of magmatism is that it occurs in a short geological time - on the order of several million years, but covers huge areas (tens of thousands of km²); at the same time, a colossal volume of basalts is poured out, comparable to their amount crystallizing in the mid-ocean ridges.

The Siberian traps on the East Siberian Platform, the Deccan Plateau traps on the Hindustan continent and many others are known. Hot mantle flows are also considered to be the cause of the formation of traps, but unlike hot spots, they act for a short time, and the difference between them is not entirely clear.

Hot spots and traps gave rise to the creation of the so-called plume geotectonics, which states that not only regular convection, but also plumes play a significant role in geodynamic processes. Plume tectonics does not contradict plate tectonics, but complements it.

Plate tectonics as a system of sciences

Now tectonics can no longer be considered as a purely geological concept. It plays a key role in all geosciences; several methodological approaches with different basic concepts and principles have emerged in it.

From point of view kinematic approach, the movements of the plates can be described by the geometric laws of movement of figures on a sphere. The Earth is seen as a mosaic of plates of different sizes moving relative to each other and the planet itself. Paleomagnetic data allows us to reconstruct the position of the magnetic pole relative to each plate at different points in time. Generalization of data for different plates led to the reconstruction of the entire sequence of relative movements of the plates. Combining this data with information obtained from fixed hot spots made it possible to determine the absolute movements of the plates and the history of the movement of the Earth's magnetic poles.

Thermophysical approach considers the Earth as a heat engine, in which thermal energy is partially converted into mechanical energy. Within this approach, the movement of matter in the inner layers of the Earth is modeled as a flow of a viscous fluid, described by the Navier-Stokes equations. Mantle convection is accompanied by phase transitions and chemical reactions, which play a decisive role in the structure of mantle flows. Based on geophysical sounding data, the results of thermophysical experiments and analytical and numerical calculations, scientists are trying to detail the structure of mantle convection, find flow velocities and other important characteristics of deep processes. These data are especially important for understanding the structure of the deepest parts of the Earth - the lower mantle and core, which are inaccessible for direct study, but undoubtedly have a huge impact on the processes occurring on the surface of the planet.

Geochemical approach. For geochemistry, plate tectonics is important as a mechanism for the continuous exchange of matter and energy between the different layers of the Earth. Each geodynamic setting is characterized by specific rock associations. In turn, these characteristic features can be used to determine the geodynamic environment in which the rock was formed.

Historical approach. In terms of the history of planet Earth, plate tectonics is the history of continents joining and breaking apart, the birth and decline of volcanic chains, and the appearance and closure of oceans and seas. Now for large blocks of the crust the history of movements has been established in great detail and over a significant period of time, but for small plates the methodological difficulties are much greater. The most complex geodynamic processes occur in plate collision zones, where mountain ranges are formed, composed of many small heterogeneous blocks - terranes. When studying the Rocky Mountains, a special direction of geological research arose - terrane analysis, which incorporated a set of methods for identifying terranes and reconstructing their history.

Plate tectonics on other planets

There is currently no evidence of modern plate tectonics on other planets in the Solar System. Studies of the magnetic field of Mars conducted by the Mars Global Surveyor space station indicate the possibility of plate tectonics on Mars in the past.

In past [ When?] the flow of heat from the interior of the planet was greater, so the crust was thinner, the pressure under the much thinner crust was also much lower. And at significantly lower pressure and slightly higher temperature, the viscosity of mantle convection currents directly below the crust was much lower than it is today. Therefore, in the crust floating on the surface of a mantle flow that was less viscous than today, only relatively small elastic deformations occurred. And the mechanical stresses generated in the crust by convection currents that were less viscous than today were insufficient to exceed the tensile strength of crustal rocks. Therefore, perhaps there was not such tectonic activity as at a later time.

Past plate movements

For more information on this topic, see: History of plate movement.

Reconstructing past plate movements is one of the main subjects of geological research. With varying degrees of detail, the position of the continents and the blocks from which they were formed has been reconstructed up to the Archean.

From an analysis of the movements of the continents, an empirical observation was made that the continents gather into a huge continent every 400-600 million years, containing almost the entire continental crust - a supercontinent. Modern continents formed 200-150 million years ago, as a result of the breakup of the supercontinent Pangea. Now the continents are at a stage of almost maximum separation. The Atlantic Ocean is expanding and the Pacific Ocean is closing. Hindustan is moving north and crushing the Eurasian plate, but, apparently, the resource of this movement is almost exhausted, and in the near geological time a new subduction zone will arise in the Indian Ocean, in which the oceanic crust of the Indian Ocean will be absorbed under the Indian continent.

The influence of plate movements on climate

The location of large continental masses in the subpolar regions contributes to a general decrease in the temperature of the planet, since ice sheets can form on the continents. The more widespread glaciation is, the greater the planet's albedo and the lower the average annual temperature.

In addition, the relative position of the continents determines oceanic and atmospheric circulation.

However, a simple and logical scheme: continents in the polar regions - glaciation, continents in the equatorial regions - increase in temperature, turns out to be incorrect when compared with geological data about the Earth's past. The Quaternary glaciation actually occurred when Antarctica moved into the region of the South Pole, and in the northern hemisphere, Eurasia and North America moved closer to the North Pole. On the other hand, the strongest Proterozoic glaciation, during which the Earth was almost completely covered with ice, occurred when most of the continental masses were in the equatorial region.

In addition, significant changes in the position of the continents occur over a period of about tens of millions of years, while the total duration of ice ages is about several million years, and during one ice age cyclical changes of glaciations and interglacial periods occur. All of these climate changes occur quickly compared to the speed of continental movement, and therefore plate movement cannot be the cause.

From the above it follows that plate movements do not play a decisive role in climate change, but can be an important additional factor “pushing” them.

The meaning of plate tectonics

Plate tectonics has played a role in the earth sciences comparable to the heliocentric concept in astronomy, or the discovery of DNA in genetics. Before the adoption of the theory of plate tectonics, earth sciences were descriptive in nature. They achieved a high level of perfection in describing natural objects, but rarely could explain the causes of processes. Opposite concepts could dominate in different branches of geology. Plate tectonics connected the various earth sciences and gave them predictive power.

see also

Notes

Literature

• Wegener A. Origin of continents and oceans / trans. with him. P. G. Kaminsky, ed. P. N. Kropotkin. - L.: Nauka, 1984. - 285 p.
• Dobretsov N. L., Kirdyashkin A. G. Deep geodynamics. - Novosibirsk, 1994. - 299 p.
• Zonenshain, Kuzmin M. I. Plate tectonics of the USSR. In 2 volumes.
• Kuzmin M. I., Korolkov A. T., Dril S. I., Kovalenko S. N. Historical geology with basics of plate tectonics and metallogeny. - Irkutsk: Irkut. univ., 2000. - 288 p.
• Cox A., Hart R. Plate tectonics. - M.: Mir, 1989. - 427 p.
• N.V. Koronovsky, V.E. Khain, Yasamanov N.A. Historical geology: Textbook. M.: Academy Publishing House, 2006.
• Lobkovsky L. I., Nikishin A. M., Khain V. E. Modern problems of geotectonics and geodynamics. - M.: Scientific world, 2004. - 612 p. - ISBN 5-89176-279-X.
• Khain, Viktor Efimovich. The main problems of modern geology. M.: Scientific World, 2003.

Links

In Russian

• Khain, Viktor Efimovich Modern geology: problems and prospects
• V. P. Trubitsyn, V. V. Rykov. Mantle convection and global tectonics of the earth Joint Institute of Physics of the Earth RAS, Moscow
• Causes of tectonic faults, continental drift and the physical heat balance of the planet (USAP)
• Khain, Viktor Efimovich Plate tectonics, their structures, movements and deformations

In English

EVOLUTION OF THE EARTH

EARTH IN THE SOLAR SYSTEM

The Earth belongs to the terrestrial planets, which means that, unlike gas giants such as Jupiter, it has a solid surface. It is the largest of the four terrestrial planets in the Solar System, both in size and mass. Additionally, Earth has the highest density, strongest surface gravity, and strongest magnetic field among the four planets.

Shape of the Earth

Comparison of the sizes of the terrestrial planets (from left to right): Mercury, Venus, Earth, Mars.

Earth movement

The Earth moves around the Sun in an elliptical orbit at a distance of about 150 million km with an average speed of 29.765 km/sec. The speed of the Earth's orbit is not constant: in July it begins to accelerate (after passing aphelion), and in January it begins to slow down again (after passing perihelion). The Sun and the entire Solar System revolve around the center of the Milky Way galaxy in an almost circular orbit at a speed of about 220 km/s. Carried away by the movement of the Sun, the Earth describes a helical line in space.

Currently, the Earth's perihelion occurs around January 3, and aphelion occurs around July 4.

For the Earth, the radius of the Hill sphere (sphere of influence of Earth's gravity) is approximately 1.5 million km. This is the maximum distance at which the influence of Earth's gravity is greater than the influence of the gravity of other planets and the Sun.

Earth structure Internal structure

General structure of planet Earth

The Earth, like other terrestrial planets, has a layered internal structure. It consists of hard silicate shells (crust, extremely viscous mantle) and a metallic core. The outer part of the core is liquid (much less viscous than the mantle), and the inner part is solid.

The planet's internal heat is most likely provided by the radioactive decay of the isotopes potassium-40, uranium-238 and thorium-232. All three elements have half-lives of more than a billion years. At the center of the planet, the temperature may rise to 7,000 K, and the pressure may reach 360 GPa (3.6 thousand atm.).

The Earth's crust is the upper part of the solid Earth.

The earth's crust is divided into lithospheric plates of different sizes, moving relative to each other.

The mantle is the silicate shell of the Earth, composed mainly of rocks consisting of silicates of magnesium, iron, calcium, etc.

The mantle extends from depths of 5–70 km below the boundary with the earth's crust, to the boundary with the core at a depth of 2900 km.

The core consists of an iron-nickel alloy mixed with other elements.

Plate tectonic theory Tectonic platforms

According to plate tectonic theory, the outer part of the Earth consists of the lithosphere, which includes the Earth's crust and the solidified upper part of the mantle. Beneath the lithosphere is the asthenosphere, which makes up the inner part of the mantle. The asthenosphere behaves like a superheated and extremely viscous liquid.

The lithosphere is divided into tectonic plates and seems to float on the asthenosphere. The plates are rigid segments that move relative to each other. These periods of migration span many millions of years. Earthquakes, volcanic activity, mountain building, and the formation of ocean basins can occur on faults between tectonic plates.

Among tectonic plates, ocean plates move the fastest. Thus, the Pacific plate moves at a speed of 52 – 69 mm per year. The lowest rate is on the Eurasian plate – 21 mm per year.

Supercontinent

A supercontinent is a continent in plate tectonics that contains almost all of the Earth's continental crust.

A study of the history of continental movements has shown that with a periodicity of about 600 million years, all continental blocks gather into a single block, which then splits.

American scientists predict the formation of the next supercontinent in 50 million years based on satellite observations of the movement of continents. Africa will merge with Europe, Australia will continue to move north and unite with Asia, and the Atlantic Ocean, after some expansion, will disappear altogether.

Volcanoes

Volcanoes are geological formations on the surface of the earth’s crust or the crust of another planet, where magma comes to the surface, forming lava, volcanic gases, and stones.

The word "Vulcan" comes from the name of the ancient Roman God of fire, Vulcan.

The science that studies volcanoes is volcanology.

1. Volcanic activity

Volcanoes are divided depending on the degree of volcanic activity into active, dormant and extinct.

There is no consensus among volcanologists on how to define an active volcano. The period of volcanic activity can last from several months to several million years. Many volcanoes exhibited volcanic activity tens of thousands of years ago, but are not considered active today.

Often there are lakes of liquid lava in the craters of volcanoes. If the magma is viscous, then it can clog the vent, like a “plug”. This leads to strong explosive eruptions, when a flow of gases literally knocks the “plug” out of the vent.

There are two types of lithosphere. The oceanic lithosphere has oceanic crust about 6 km thick. It is mostly covered by the sea. The continental lithosphere is covered by continental crust with a thickness of 35 to 70 km. Most of this crust protrudes above, forming land.

Plates

Rocks and minerals

Moving plates

The plates of the earth's crust are constantly moving in different directions, although very slowly. The average speed of their movement is 5 cm per year. Your nails grow at about the same rate. Since all the plates fit tightly together, the movement of any one of them affects the surrounding plates, causing them to gradually move. Plates can move in different ways, which can be seen at their boundaries, but the reasons that cause plate movement are still unknown to scientists. Apparently, this process may have neither beginning nor end. Nevertheless, some theories claim that one type of plate movement can be, so to speak, “primary”, and from it all other plates begin to move.

One type of plate movement is the “diving” of one plate under another. Some scholars believe that it is this type of movement that causes all other plate movements. At some boundaries, molten rock pushing up to the surface between two plates solidifies at their edges, pushing the plates apart. This process can also cause all the other plates to move. It is also believed that, in addition to the primary shock, the movement of plates is stimulated by giant heat flows circulating in the mantle (see article ““).

Drifting continents

Scientists believe that since the formation of the primary earth's crust, the movement of plates has changed the position, shape and size of continents and oceans. This process was called tectonics slabs. Various proofs of this theory are given. For example, the outlines of continents such as South America and Africa look as if they once formed a single whole. Undoubted similarities were also discovered in the structure and age of the rocks that make up the ancient mountain ranges on both continents.

1. According to scientists, the land masses that now form South America and Africa were connected to each other more than 200 million years ago.

2. Apparently, the floor of the Atlantic Ocean gradually expanded as new rock formed at plate boundaries.

3. Currently, South America and Africa are moving away from each other at a rate of about 3.5 cm per year due to plate movement.

Lithospheric plates– large rigid blocks of the Earth’s lithosphere, bounded by seismically and tectonically active fault zones.

The plates, as a rule, are separated by deep faults and move through the viscous layer of the mantle relative to each other at a speed of 2-3 cm per year. Where continental plates converge, they collide and form mountain belts . When the continental and oceanic plates interact, the plate with the oceanic crust is pushed under the plate with the continental crust, resulting in the formation of deep-sea trenches and island arcs.

The movement of lithospheric plates is associated with the movement of matter in the mantle. In certain parts of the mantle there are powerful flows of heat and matter rising from its depths to the surface of the planet.

More than 90% of the Earth's surface is covered 13 -th largest lithospheric plates.

Rift– a huge fracture in the earth's crust, formed during its horizontal stretching (i.e., where the flows of heat and matter diverge). In rifts, magma outflows, new faults, horsts, and grabens arise. Mid-ocean ridges form.

First continental drift hypothesis (i.e. horizontal movement of the earth's crust) put forward at the beginning of the twentieth century A. Wegener. Created on its basis lithospheric theory t. According to this theory, the lithosphere is not a monolith, but consists of large and small plates “floating” on the asthenosphere. The boundary areas between lithospheric plates are called seismic belts - these are the most “restless” areas of the planet.

The earth's crust is divided into stable (platforms) and mobile areas (folded areas - geosynclines).

- powerful underwater mountain structures within the ocean floor, most often occupying a middle position. Near mid-ocean ridges, lithospheric plates move apart and young basaltic oceanic crust appears. The process is accompanied by intense volcanism and high seismicity.

Continental rift zones are, for example, the East African Rift System, the Baikal Rift System. Rifts, like mid-ocean ridges, are characterized by seismic activity and volcanism.

Plate tectonics- a hypothesis suggesting that the lithosphere is divided into large plates that move horizontally through the mantle. Near mid-ocean ridges, lithospheric plates move apart and grow due to material rising from the bowels of the Earth; in deep-sea trenches, one plate moves under another and is absorbed by the mantle. Fold structures are formed where plates collide.