Lithospheric plates. Plate tectonics Mark the boundaries of lithospheric plates on the world map

Discovery of continental drift.

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

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 obtained, Weneger came to the conclusion that various continents, including South America and Africa, formed a single whole in the distant past. He discovered, for example, that some geological structures of South America, which abruptly end with the coastline of the Atlantic Ocean, have a continuation 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 were geological signs of an ancient glaciation that affected Australia, India and South Africa at about the same time, and noted that it was possible to combine these continents in such a way that their glaciated areas would form a single area. Based on his research, Wegener published the book “The Origin of Continents and Oceans” in Germany (1915), in which he put forward his theory of “continental drift.” But the author of this book could not defend his theory convincingly enough; he selected some facts to support it quite arbitrarily. Largely for these reasons, his hypothesis was not accepted by most scientists at the time. For example, eminent physicists of that time stated that continents cannot drift like ships at sea, since the outer parts of the lithosphere are very rigid. They also pointed out that the centrifugal forces resulting from the Earth's rotation on its axis were too weak to move the continents, as Wegener assumed.

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, which began during the Second World War, were carried out. The American Navy, while developing submarines, was very interested in learning as much as possible about the ocean floor. Perhaps this is a 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 paid well. Oceanographic research quickly became widespread. Although a significant part of the research results was classified, 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 intensive research of the ocean floor has been new knowledge about its topography. Previous knowledge of the seabed, accumulated over a long history of sea voyages, was extremely insufficient. The most first depth measurements were made using the simplest methods - measuring cables. The lot was thrown overboard and the length of the etched cable was measured. But these measurements were limited to shallow, coastal areas.

At the beginning of the 20th century, echo sounders appeared on ships, which were continuously improved. Measurements carried out in the 1950s and 1960s using echo sounders provided a lot of information about the topography of the ocean floor. The principle of operation of an echo sounder is to measure the time required for a sound pulse to travel 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 operate continuously, around the clock, no matter what the ship is doing.

Nowadays, the topography of the ocean floor has become easier to map: equipment installed on Earth 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 and the bottom affect the sea surface level 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, above a deep ditch or basin, the sea level is lower than above raised areas of the seabed. It was impossible to “consider” such details of the seabed relief when studying it from board ships.

The results of research of the seabed in the 60s of the 20th century raised many questions for science. Until this time, scientists believed that the bottom of the deep seas were calm, flat areas of the earth's surface, covered with a thick layer of silt and other sediments washed away from the continents over an infinitely long time.

However, the received research materials showed that the seabed has a completely different topography: instead of a flat surface, enormous mountain ranges, deep ditches (rifts), steep cliffs and large volcanoes were discovered on the ocean floor. In particular, the Atlantic Ocean is cut exactly down the middle by the Mid-Atlantic Ridge, which follows 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, along the axial line of the ridge, there is a rift, i.e. a gorge or valley with steep sides. In the North Atlantic Ocean, the Mid-Atlantic Ridge rises above the ocean's surface to form the island of Iceland.

This ridge is only part of a system of ridges that stretches across all oceans. The ridges surround Antarctica, extend in two branches into 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 sediment carried from the continents? What is the connection between these ridges and the drift of 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 seabed, along with other work, were engaged in measuring the magnetic field along numerous routes of research ships. It was discovered that, unlike the structure of the magnetic field of continents, which is usually very complex, the pattern of magnetic anomalies on the ocean floor differs in a certain pattern. The reason for this phenomenon was not clear at first. And in the 60s of the 20th century, American scientists conducted an aerial magnetic survey of the Atlantic Ocean south of Iceland. The results were striking: magnetic field patterns above the seafloor varied symmetrically around the centerline of the ridge. At the same time, the graph of changes in the magnetic field along the route crossing the ridge was basically the same on different routes. When the measurement points and measured magnetic field strengths were plotted on a map and isolines (lines of equal values ​​of magnetic field characteristics) were drawn, they formed a striped zebra-like pattern. A similar pattern, but with less pronounced symmetry, was previously obtained when studying the magnetic field in the northeastern part of the Pacific Ocean. And here the nature of the field differed sharply from the structure of the field above the continents. As scientific data accumulated, it became clear that symmetry in the magnetic field pattern was observed throughout the ocean ridge system. The reason for this phenomenon lies in the following physical processes.

Rocks erupted from the Earth's interior cool from their original 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. This means that a graph of the magnetic field along a route crossing a ridge is a kind of fossil record of changes in the magnetic field during the formation of rocks. This record is stored for a long time. As would be expected, geophysical surveys along routes directed perpendicular to the location of the Mid-Atlantic Ridge have shown that rocks located exactly above the ridge axis are highly magnetized in the direction of the Earth's modern magnetic field. The symmetrical zebra-shaped magnetic field pattern 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 strength (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 over the course of geological time. Evidence of the periodic change of the Earth's magnetic poles was also obtained by studying the magnetization of rocks on the continents. It was found that in areas where large basalt masses accumulate, one part of the basalt flows has a direction of magnetization corresponding to the direction of the modern magnetic field of the Earth, while other flows are magnetized in the opposite direction.

It became clear to researchers that seafloor magnetic stripes, magnetic polarity fluctuations and continental drift are all interconnected phenomena. The zebra-shaped pattern of magnetization distribution of seafloor rocks reflects the sequence of changes in the polarity of the earth's magnetic field. Most geologists are now convinced that seafloor movement away from ocean faults is a reality.

New oceanic crust is formed by lava that continuously flows from deep within the axial parts of oceanic ridges. The magnetic pattern of the seafloor rocks is symmetrical on both sides of the ridge axis because the newly arrived portion of lava is magnetized when it solidifies into solid rock and expands evenly on both sides of the median fault. Since the dates of changes 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 becomes magnetized
under the influence of the Earth's magnetic field and then diverges away from the fault.

The rate of emergence of a new section of the seabed can be quite simply calculated by measuring the distance from the ridge axis, where the age of the seabed is zero, to the stripes corresponding to known periods of reversal of the magnetic field polarity.

The rate of formation of the seabed varies from place to place; its value, calculated from the location of the magnetic stripes, averages 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 sediment; they (the oceans) are very young on a geological scale. At a speed of a few centimeters per year (this is very slow, of course), the Atlantic Ocean could have formed in two hundred million years, which by geological standards is not that long. The bottom of any of the oceans existing on Earth is not much older. Compared to the rocks of the continents, the age of the ocean floor is much younger.

Thus, it has been proven that the continents on both sides of the Atlantic Ocean are moving apart at a rate 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 because... they are parts of the same lithospheric plate.

Vladimir Kalanov,
"Knowledge is power"

Then surely you would like to know what are lithospheric plates.

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

Today there are 13 largest lithospheric plates, which cover 90% of the earth's surface.

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 solely 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.

Map of lithospheric plates

At the beginning of the 20th century, American F.B. Taylor and the German Alfred Wegener simultaneously came to the conclusion that the location of the continents was slowly changing. By the way, this is, to a large extent, what it is. But scientists were unable to explain how this happens until the 60s of the twentieth century, when the doctrine of geological processes on the seabed was developed.

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

Subscribe to. We have many interesting facts and fascinating stories from people's lives.

Together with part of the upper mantle, it consists of several very large blocks called lithospheric plates. Their thickness varies - 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 a 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 images taken from artificial Earth satellites. They suggest that the configuration in the future may be completely different from the present one, since it is known that the American lithospheric plate is moving towards the Pacific, and the Eurasian plate is moving closer to the African, Indo-Australian, and also the Pacific. The American and African lithospheric plates are slowly moving apart.

The forces that cause the divergence of lithospheric plates arise when the material of the mantle moves. Powerful upward flows of this substance push the plates apart, tearing apart the earth's crust, forming deep faults in it. Due to underwater outpourings of lavas, strata are formed along faults. By freezing, they seem to heal wounds - cracks. However, the stretching increases again, and ruptures occur again. So, gradually increasing, lithospheric plates diverge in different directions.

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

Along other plate boundaries, plate collisions are observed. It happens in different ways. If plates, one of which has oceanic crust and the other continental, come closer together, then the lithospheric plate, covered by the sea, sinks under the continental one. In this case, arcs () or mountain ranges () appear. If two plates that have continental crust collide, the edges of these plates are crushed into folds of rock, and mountainous regions are formed. This is how they arose, for example, on the border of the Eurasian and Indo-Australian plates. The presence of mountainous areas in the internal parts of the lithospheric plate suggests that once there was a boundary of two plates that were firmly fused with 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, zones, mountain areas, mid-ocean ridges, deep-sea depressions and trenches are confined. It is at the border of lithospheric plates that they are formed, the origin of which is associated with magmatism.

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, plates are giant blocks of the lithosphere.
According to this theory, the entire lithosphere is divided into parts - lithospheric plates, which are separated by deep tectonic faults and move through 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 varies in different sources).

Convergence of oceanic and continental lithospheric plates

Lithospheric plates

Lithospheric plates - these are large blocks of the earth’s crust and parts of the upper mantle that make up the lithosphere.

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.