Together with part of the upper mantle, it 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, Indo-, 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 as a result of a comparison of images taken from artificial earth satellites. They suggest that the configuration 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 are formed along the faults. Freezing, they seem to heal wounds - cracks. However, the stretch increases again, and breaks occur again. So, gradually increasing lithospheric plates diverge in different directions.

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

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, arcs () or mountain ranges () arise. If two plates with a continental crust collide, then the edges of these plates are crushed into folds of rocks, and mountainous regions are formed. So they arose, for example, on the border of the Eurasian and Indo-Australian plates. The presence of mountainous areas in the inner parts of the lithospheric plate suggests that once there was a boundary between two plates, firmly soldered to each other and turned into a single, larger lithospheric plate. Thus, we can draw a general conclusion: the boundaries of lithospheric plates are mobile areas to which volcanoes are confined, zones, mountainous areas, mid-ocean ridges, deep-water depressions and trenches. It is at the boundary of lithospheric plates that are formed, the origin of which is associated with magmatism.

Discovery of continental drift.

World map showing the location of the major lithospheric plates. Each plate is surrounded by ocean ridges,
from the axes of which there is tension (thick lines), collision and subduction zones (jagged lines) and / or
transform faults (thin lines). Names are given only for some of the largest plates.
The arrows indicate the directions of the relative motions of the plates.

At the beginning of the 20th century, a German meteorologist Alfred Wegener began to collect and study information about the flora and fauna of the continents separated by the Atlantic Ocean. He also carefully examined everything that was then known about their geology and paleontology, about the fossil remains of organisms found on them. After analyzing the data, Veneger came to the conclusion that the various continents, including South America and Africa, formed a single whole in the distant past. He discovered, for example, that some of the geological structures of South America, which are cut off abruptly by the coastline of the Atlantic Ocean, seem to be continued in Africa. He cut out these continents from the map, moved these cuttings towards each other and saw that the geological features of these continents coincided, as if continuing each other.

He also discovered that there are geological signs of an ancient glaciation that engulfed Australia, India and South Africa at about the same time, and noticed that it was possible to combine these continents in such a way that their regions of glaciation would form a single area. Based on his research, Wegener published in Germany the book "The Origin of Continents and Oceans" (1915), in which he put forward his theory of "continental drift". But the author of this book was not able to convincingly defend his theory, he selected some facts in support of it quite arbitrarily. Largely for these reasons, his hypothesis was not accepted by most scientists at the time. For example, eminent physicists of the time stated that the continents could not drift like ships in the sea because the outer parts of the lithosphere were very rigid. They also pointed out that the centrifugal forces resulting from the rotation of the Earth around its axis are too weak to move the continents, as Wegener suggested.

But Wegener was still on the right track. The revival of Wegener's ideas in the form of the theory of plate tectonics occurred in the 1950s and 1960s. During these years, studies of the ocean floor, begun during the Second World War, were carried out. The US Navy, while developing submarines, was very interested in learning as much as possible about the ocean floor. Perhaps this is the rare case when military interests benefited science. At that time, and even until the 1960s, the ocean floor was almost unexplored territory. Geologists said then that we know more about the surface of the moon facing us than about the seabed. The US Navy was generous and well paid. Oceanographic research quickly acquired a large scope. Although a significant part of the research results were classified, nevertheless, the discoveries made pushed Earth science to a new, higher level of understanding of the processes occurring on Earth.

One of the main results of the intensive study of the ocean floor has been new knowledge about its topography. The knowledge of the sea floor that had been gained up to this point, gathered from a long history of sea voyages, was woefully inadequate. Most first depth measurements were produced by the simplest methods - measuring cables. The lot was thrown overboard and the length of the etched cable was measured. But even these measurements were limited to shallow, coastal areas.

At the beginning of the 20th century, echo sounders appeared on ships, which were continuously improved. The measurements carried out in the 1950s - 1960s with the help of echo sounders provided a lot of information about the topography of the ocean floor. The principle of operation of the echo sounder is to measure the time required for the passage of a sound pulse from the ship to the seabed and back. Knowing the speed of sound in sea water, it is easy to calculate the depth of the sea at any location. The echo sounder can work continuously, around the clock, no matter what the ship is doing.

At present, the topography of the ocean floor has become easier to map: equipment installed on Earth's satellites accurately measures the “height” of the sea surface. There is no need to send ships to sea. Interestingly, the differences in sea level from place to place accurately reflect the topography of the seafloor. This is explained by the fact that slight variations in gravity, the bottom, affect the level of the sea surface in a particular place. For example, over a place where there is a large volcano of enormous mass, the sea level rises compared to neighboring areas. On the contrary, over a deep ditch, a basin, the sea level is lower than over raised areas of the seabed. It was impossible to “examine” such details of the seabed topography during its study from the board of ships.

The results of the study of the seabed in the 60s of the XX century posed many questions to science. Until that time, scientists believed that the bottom of the deep seas is a calm, flat relief areas of the earth's surface, covered with a thick layer of silt and other sediments washed away from the continents for an infinitely long time.

However, the research materials received showed that the seabed has a completely different relief: instead of a flat surface, huge mountain ranges, deep ditches (rifts), steep cliffs and largest volcanoes were found on the bottom of the oceans. In particular, the Atlantic Ocean is cut exactly in the middle by the Mid-Atlantic Ridge, which repeats all the protrusions and depressions of the coastline on each side of the ocean. The ridge rises an average of 2.5 km above the deepest parts of the ocean; almost along its entire length, a rift runs along the axial line of the ridge, i.e. gorge or valley with steep slopes. In the North Atlantic Ocean, the Mid-Atlantic Ridge rises above the ocean surface, forming the island of Iceland.

This ridge is only part of a ridge system that stretches across all the oceans. The ridges surround Antarctica, go out in two branches to the Indian Ocean and to the Arabian Sea, bend along the shores of the eastern Pacific Ocean, approach lower California, and appear off the coast of the northwestern United States.

Why was this system of underwater ridges not buried under a layer of sediments carried from the continents? What is the relationship between these ridges and the drift of the continents and tectonic plates?

The answers to these questions are obtained from the results of a study ... of the magnetic properties of the rocks that make up the ocean floor. Geophysicists, wanting to know as much as possible about the seafloor, have taken magnetic field measurements along numerous research vessel routes along with other activities. It was found that in contrast to the structure of the magnetic field of the continents, which is usually very complex, the pattern of magnetic anomalies at the bottom of the oceans has a certain regularity. The reason for this phenomenon was not clear at first. And in the 60s of the XX century, American scientists conducted an airborne magnetic survey of the Atlantic Ocean south of Iceland. The results were startling: the patterns of the magnetic field above the seafloor change symmetrically about the centerline of the ridge. At the same time, the graph of the change in the magnetic field along the route crossing the ridge was basically the same on different routes. When the measurement points and the measured values ​​of the magnetic field strength were mapped and contour lines (lines of equal values ​​of the magnetic field characteristics) were drawn, they formed a striped zebra-like pattern. A similar pattern, but with less pronounced symmetry, was previously obtained in the study of the magnetic field in the northeast Pacific Ocean. And here the nature of the field differed sharply from the structure of the field over the continents. With the accumulation of scientific data, it became clear that the symmetry of the magnetic field pattern is observed everywhere along the system of oceanic ridges. The reason for this phenomenon lies in the following physical processes.

The rocks erupted from the bowels of the Earth are cooled from the initial molten state, and the iron-containing materials formed in them are magnetized by the earth's magnetic field. All elementary magnets of these minerals are oriented in the same way under the influence of the surrounding magnetic field of the Earth. This magnetization is a continuous process in time. So the plot of the magnetic field along the route crossing the ridge is a kind of fossil record of the changes in the magnetic field during rock formation. This record is kept for a long time. As expected, geophysical surveys along tracks perpendicular to the location of the Mid-Atlantic Ridge have shown that rocks just above the axis of the ridge are strongly magnetized in the direction of the Earth's current magnetic field. The symmetrical zebra pattern of the magnetic field indicates that the seafloor is magnetized differently in different areas parallel to the direction of the ridge. We are talking not only about the different intensity (intensity) of the magnetic field of different sections of the seabed, but also about the different direction of their magnetization. This has already become a major scientific discovery: it turned out that the Earth's magnetic field has repeatedly changed its polarity during geological time. Evidence of the periodic change of the Earth's magnetic poles was also obtained in the study of the magnetization of rocks on the continents. It was found that in areas of accumulation of large basalt masses, one part of the basalt flows has a magnetization direction corresponding to the direction of the modern magnetic field of the Earth, while other flows are magnetized in the opposite direction.

It has become clear to researchers that seafloor magnetic stripes, magnetic polarity fluctuations, and continental drift are all interconnected. The zebra-shaped pattern of the distribution of the magnetization of the rocks of the seabed reflects the sequence of the change in the polarity of the earth's magnetic field. Most geologists are now convinced that the seafloor is moving away from oceanic faults - this is a reality.

The new oceanic crust is formed by lava continuously coming from the depths in the axial parts of the oceanic ridges. The magnetic pattern of the seabed rocks is symmetrical on both sides of the ridge axis because the newly arrived portion of the lava is magnetized during its solidification into solid rock and expands evenly on both sides of the median fault. Since the dates of the change in the polarity of the Earth's magnetic field have become known as a result of the analysis of rocks on land, the magnetic stripes of the ocean floor can be considered as a kind of time scale.

During its eruption along the ridge and subsequent solidification, the basalt is magnetized
under the influence of the Earth's magnetic field and then diverges away from the fault.

The rate of new seabed formation can be fairly easily calculated by measuring the distance from the ridge axis, where the age of the seabed is zero, to the bands corresponding to known periods of magnetic field reversal.

The rate of formation of the sea floor varies from place to place, its value, calculated from the location of the magnetic stripes, is on average several centimeters per year. Continents located on opposite sides of the Atlantic Ocean are moving away from each other at this speed. For this reason, the oceans are not covered with a thick layer of sediments; they (the oceans) are very young on a geological scale. At a speed of a few centimeters per year (which is very slow, of course), the Atlantic Ocean could have formed in two hundred million years, which is not so much by geological standards. The bottom of any of the oceans that exist on Earth is not much older. Compared with the rocks of the continents, the age of the ocean floor is much younger.

Thus, it is proved that the continents on both sides of the Atlantic Ocean diverge to the sides with a speed that depends on the rate of formation of new sections of the seabed on the axis of the Mid-Atlantic Ridge. Both the continents and the oceanic crust move together as one whole, since they are parts of the same lithospheric plate.

Vladimir Kalanov,
"Knowledge is power"

What do we know about the lithosphere?

Tectonic plates are large stable areas of the Earth's crust that are the constituent parts of the lithosphere. If we turn to tectonics, the science that studies lithospheric platforms, we learn that large areas of the earth's crust are limited on all sides by specific zones: volcanic, tectonic and seismic activities. It is at the junctions of neighboring plates that phenomena occur, which, as a rule, have catastrophic consequences. These include both volcanic eruptions and strong earthquakes on the scale of seismic activity. In the process of studying the planet, platform tectonics played a very important role. Its significance can be compared to the discovery of DNA or the heliocentric concept in astronomy.

If we recall the geometry, then we can imagine that one point can be the point of contact of the boundaries of three or more plates. The study of the tectonic structure of the earth's crust shows that the most dangerous and rapidly collapsing are the junctions of four or more platforms. This formation is the most unstable.

The lithosphere is divided into two types of plates, different in their characteristics: continental and oceanic. It is worth highlighting the Pacific platform, composed of oceanic crust. Most of the others consist of the so-called block, when the continental plate is soldered into the oceanic one.

The location of the platforms shows that about 90% of the surface of our planet consists of 13 large, stable areas of the earth's crust. The remaining 10% fall on small formations.

Scientists have compiled a map of the largest tectonic plates:

• Australian;
• Arabian subcontinent;
• Antarctic;
• African;
• Hindustan;
• Eurasian;
• Nazca plate;
• Cooker Coconut;
• Pacific;
• North and South American platforms;
• Scotia plate;
• Philippine plate.

From theory, we know that the solid shell of the earth (lithosphere) consists not only of the plates that form the relief of the surface of the planet, but also of the deep part - the mantle. Continental platforms have a thickness of 35 km (in the flat areas) to 70 km (in the zone of mountain ranges). Scientists have proven that the plate in the Himalayas has the greatest thickness. Here the thickness of the platform reaches 90 km. The thinnest lithosphere is found in the ocean zone. Its thickness does not exceed 10 km, and in some areas this figure is 5 km. Based on the information about the depth at which the epicenter of the earthquake is located and what is the speed of propagation of seismic waves, calculations are made of the thickness of the sections of the earth's crust.

The process of formation of lithospheric plates

The lithosphere consists mainly of crystalline substances formed as a result of cooling of magma upon reaching the surface. The description of the structure of the platforms speaks of their heterogeneity. The process of formation of the earth's crust took place over a long period, and continues to this day. Through microcracks in the rock, molten liquid magma came to the surface, creating new bizarre forms. Its properties changed depending on the change in temperature, and new substances were formed. For this reason, minerals that are at different depths differ in their characteristics.

The surface of the earth's crust depends on the influence of the hydrosphere and atmosphere. There is constant weathering. Under the influence of this process, the forms change, and the minerals are crushed, changing their characteristics with the same chemical composition. As a result of weathering, the surface became looser, cracks and microdepressions appeared. In these places deposits appeared, which we know as soil.

Map of tectonic plates

At first glance it seems that the lithosphere is stable. Its upper part is such, but the lower part, which is distinguished by viscosity and fluidity, is mobile. The lithosphere is divided into a certain number of parts, the so-called tectonic plates. Scientists cannot say how many parts the earth's crust consists of, since in addition to large platforms, there are also smaller formations. The names of the largest plates were given above. The process of formation of the earth's crust is ongoing. We do not notice this, since these actions occur very slowly, but by comparing the results of observations for different periods, we can see how many centimeters a year the boundaries of formations are shifting. For this reason, the tectonic map of the world is constantly updated.

Tectonic Plate Cocos

The Cocos platform is a typical representative of the oceanic parts of the earth's crust. It is located in the Pacific region. In the west, its boundary runs along the ridge of the East Pacific Rise, and in the east its boundary can be defined by a conventional line along the coast of North America from California to the Isthmus of Panama. This plate is subducting under the neighboring Caribbean plate. This zone is characterized by high seismic activity.

Mexico suffers the most from earthquakes in this region. Among all the countries of America, it is on its territory that the most extinct and active volcanoes are located. The country has suffered a large number of earthquakes with a magnitude greater than 8 points. The region is quite densely populated, therefore, in addition to destruction, seismic activity also leads to a large number of victims. Unlike Cocos, located in another part of the planet, the Australian and West Siberian platforms are stable.

Movement of tectonic plates

For a long time, scientists have been trying to find out why one region of the planet has mountainous terrain, while another is flat, and why earthquakes and volcanic eruptions occur. Various hypotheses were built mainly on the knowledge that was available. Only after the 50s of the twentieth century was it possible to study the earth's crust in more detail. Mountains formed at the sites of plate faults, the chemical composition of these plates were studied, and maps of regions with tectonic activity were also created.

In the study of tectonics, a special place was occupied by the hypothesis of the displacement of lithospheric plates. Back in the early twentieth century, the German geophysicist A. Wegener put forward a bold theory about why they move. He carefully studied the outlines of the western coast of Africa and the eastern coast of South America. The starting point in his research was precisely the similarity of the outlines of these continents. He suggested that, perhaps, these continents used to be a single whole, and then a break occurred and the shift of parts of the Earth's crust began.

His research touched upon the processes of volcanism, stretching of the surface of the ocean floor, and the viscous-liquid structure of the globe. It was the works of A. Wegener that formed the basis of the research conducted in the 60s of the last century. They became the foundation for the emergence of the theory of "lithospheric plate tectonics".

This hypothesis described the model of the Earth as follows: tectonic platforms with a rigid structure and different masses were placed on the plastic substance of the asthenosphere. They were in a very unstable state and were constantly moving. For a simpler understanding, we can draw an analogy with icebergs that are constantly drifting in ocean waters. Similarly, tectonic structures, being on a plastic substance, are constantly moving. During displacements, the plates constantly collided, came one on top of the other, joints and zones of separation of the plates arose. This process was due to the difference in mass. Areas of increased tectonic activity were formed at the collision sites, mountains arose, earthquakes and volcanic eruptions occurred.

The displacement rate was no more than 18 cm per year. Faults formed, into which magma entered from the deep layers of the lithosphere. For this reason, the rocks that make up the oceanic platforms are of different ages. But scientists have put forward an even more incredible theory. According to some representatives of the scientific world, magma came to the surface and gradually cooled, creating a new bottom structure, while the "excess" of the earth's crust, under the influence of plate drift, sank into the earth's interior and again turned into liquid magma. Be that as it may, the movements of the continents occur in our time, and for this reason new maps are being created to further study the process of drifting tectonic structures.

Lithospheric plates - These 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.

At this time, on the boundary opposite from the fault, collision of lithospheric plates. 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- are transformed 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,
• North American Plate- 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). Within the platforms stand out plates 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, in contrast to slabs, 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.

Plate tectonics- modern geological theory about the movement and interaction of lithospheric plates.
The word "tectonics" comes from the Greek "tecton" - "builder" or "a carpenter", In tectonics, giant blocks of the lithosphere are called plates.
According to this theory, the entire lithosphere is divided into parts - lithospheric plates, which are separated by deep tectonic faults and move along the viscous layer of the asthenosphere relative to each other at a speed of 2-16 cm per year.
There are 7 large lithospheric plates and about 10 smaller plates (the number of plates in different sources is different).

When lithospheric plates collide, the earth's crust is destroyed, and when they diverge, a new one is formed. At the edges of the plates, where the tension inside the Earth is the strongest, various processes occur: strong earthquakes, volcanic eruptions and the formation of mountains. It is at the edges of the lithospheric plates that the largest landforms are formed - mountain ranges and deep-sea trenches.

Why do lithospheric plates move?
The direction and movement of lithospheric plates is influenced by internal processes occurring in the upper mantle - the movement of matter in the mantle.
When lithospheric plates diverge in one place, then in another place their opposite edges collide with other lithospheric plates.

Convergence (convergence) of oceanic and continental lithospheric plates

A thinner oceanic lithospheric plate "dives" under a powerful continental lithospheric plate, creating a deep depression or trench on the surface.
The area where this happens is called subductive. Plunging into the mantle, the plate begins to melt. The crust of the upper plate is compressed and mountains grow on it. Some of them are volcanoes formed by magma.

Lithospheric plates