Tectonics of lithospheric plates. Plate movement

The lithosphere is the rocky shell of the Earth. From the Greek “lithos” - stone and “sphere” - ball

The lithosphere is the outer solid shell of the Earth, which includes the entire Earth's crust with part of the Earth's upper mantle and consists of sedimentary, igneous and metamorphic rocks. The lower boundary of the lithosphere is unclear and is determined by a sharp decrease in the viscosity of rocks, a change in the speed of propagation of seismic waves and an increase in the electrical conductivity of rocks. The thickness of the lithosphere on continents and under oceans varies and averages 25 - 200 and 5 - 100 km, respectively.

Let us consider in general terms the geological structure of the Earth. The third planet beyond the distance from the Sun, Earth, has a radius of 6370 km, an average density of 5.5 g/cm3 and consists of three shells - bark, mantle and and. The mantle and core are divided into internal and external parts.

The Earth's crust is the thin upper shell of the Earth, which is 40-80 km thick on the continents, 5-10 km under the oceans and makes up only about 1% of the Earth's mass. Eight elements - oxygen, silicon, hydrogen, aluminum, iron, magnesium, calcium, sodium - form 99.5% of the earth's crust.

According to scientific research, scientists have been able to establish that the lithosphere consists of:

• Oxygen – 49%;
• Silicon – 26%;
• Aluminum – 7%;
• Iron – 5%;
• Calcium – 4%
• The lithosphere contains many minerals, the most common being spar and quartz.

On continents, the crust is three-layered: sedimentary rocks cover granite rocks, and granite rocks overlie basaltic rocks. Under the oceans the crust is “oceanic”, of a two-layer type; sedimentary rocks simply lie on basalts, there is no granite layer. There is also a transitional type of the earth's crust (island-arc zones on the margins of the oceans and some areas on continents, for example the Black Sea).

The earth's crust is thickest in mountainous regions(under the Himalayas - over 75 km), the average - in the areas of the platforms (under the West Siberian Lowland - 35-40, within the borders of the Russian Platform - 30-35), and the smallest - in the central regions of the oceans (5-7 km). The predominant part of the earth's surface is the plains of the continents and the ocean floor.

The continents are surrounded by a shelf - a shallow strip with a depth of up to 200 g and an average width of about 80 km, which, after a sharp steep bend of the bottom, turns into a continental slope (the slope varies from 15-17 to 20-30°). The slopes gradually level out and turn into abyssal plains (depths 3.7-6.0 km). The oceanic trenches have the greatest depths (9-11 km), the vast majority of which are located on the northern and western edges of the Pacific Ocean.

The main part of the lithosphere consists of igneous igneous rocks (95%), among which granites and granitoids predominate on the continents, and basalts in the oceans.

Blocks of the lithosphere - lithospheric plates - move along a relatively plastic asthenosphere. The section of geology on plate tectonics is devoted to the study and description of these movements.

To designate the outer shell of the lithosphere, the now obsolete term sial was used, derived from the name of the main rock elements Si (Latin: Silicium - silicon) and Al (Latin: Aluminum - aluminum).

Lithospheric plates

It is worth noting that the largest tectonic plates are very clearly visible on the map and they are:

• Pacific- the largest plate on the planet, along the boundaries of which constant collisions of tectonic plates occur and faults form - this is the reason for its constant decrease;
• Eurasian– covers almost the entire territory of Eurasia (except for Hindustan and the Arabian Peninsula) and contains the largest part of the continental crust;
• Indo-Australian– it includes the Australian continent and the Indian subcontinent. Due to constant collisions with the Eurasian plate, it is in the process of breaking;
• South American– consists of the South American continent and part of the Atlantic Ocean;
• North American– consists of the North American continent, part of northeastern Siberia, the northwestern part of the Atlantic and half of the Arctic oceans;
• African– consists of the African continent and the oceanic crust of the Atlantic and Indian oceans. Interestingly, the plates adjacent to it move in the opposite direction from it, so the largest fault on our planet is located here;
• Antarctic plate– consists of the continent of Antarctica and the nearby oceanic crust. Due to the fact that the plate is surrounded by mid-ocean ridges, the remaining continents are constantly moving away from it.

Movement of tectonic plates in the lithosphere

Lithospheric plates, connecting and separating, constantly change their outlines. This allows scientists to put forward the theory that about 200 million years ago the lithosphere had only Pangea - a single continent, which subsequently split into parts, which began to gradually move away from each other at a very low speed (on average about seven centimeters per year ).

This is interesting! There is an assumption that, thanks to the movement of the lithosphere, in 250 million years a new continent will form on our planet due to the unification of moving continents.

When the oceanic and continental plates collide, the edge of the oceanic crust subducts under the continental crust, while on the other side of the oceanic plate its boundary diverges from the adjacent plate. The boundary along which the movement of lithospheres occurs is called the subduction zone, where the upper and subducting edges of the plate are distinguished. It is interesting that the plate, plunging into the mantle, begins to melt when the upper part of the earth’s crust is compressed, as a result of which mountains are formed, and if magma also erupts, then volcanoes.

In places where tectonic plates come into contact with each other, zones of maximum volcanic and seismic activity are located: during the movement and collision of the lithosphere, the earth's crust is destroyed, and when they diverge, faults and depressions are formed (the lithosphere and the Earth's topography are connected to each other). This is the reason that the Earth's largest landforms—mountain ranges with active volcanoes and deep-sea trenches—are located along the edges of tectonic plates.

Lithosphere problems

The intensive development of industry has led to the fact that man and the lithosphere have recently begun to get along extremely poorly with each other: the pollution of the lithosphere is acquiring catastrophic proportions. This happened due to the increase in industrial waste in combination with household waste and fertilizers and pesticides used in agriculture, which negatively affects the chemical composition of the soil and living organisms. Scientists have calculated that about one ton of garbage is generated per person per year, including 50 kg of hard-to-degrade waste.

Today, pollution of the lithosphere has become an urgent problem, since nature is not able to cope with it on its own: the self-cleaning of the earth’s crust occurs very slowly, and therefore harmful substances gradually accumulate and, over time, negatively affect the main culprit of the problem - humans.

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.

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.

The Earth's crust is divided by faults into lithospheric plates, which are huge solid blocks that reach the upper layers of the mantle. They are large, stable parts of the earth's crust and are in continuous motion, sliding along the surface of the Earth. Lithospheric plates consist of either continental or oceanic crust, and some combine a continental massif with an oceanic one. There are 7 largest lithospheric plates, which occupy 90% of the surface of our planet: Antarctic, Eurasian, African, Pacific, Indo-Australian, South American, North American. In addition to them, there are dozens of medium-sized slabs and many small ones. Between the medium and large slabs there are belts in the form of mosaics of small slabs of bark.

Theory of plate tectonics

The theory of lithospheric plates studies their movement and the processes associated with this movement. This theory states that the cause of global tectonic changes is the horizontal movement of lithosphere blocks - plates. Plate tectonics examines the interaction and movement of blocks of the earth's crust.

Wagner's theory

The idea that lithospheric plates move horizontally was first suggested in the 1920s by Alfred Wagner. He put forward a hypothesis about “continental drift”, but it was not recognized as reliable at that time. Later, in the 1960s, studies of the ocean floor were carried out, as a result of which Wagner’s guesses about the horizontal movement of plates were confirmed, and the presence of processes of ocean expansion, caused by the formation of oceanic crust (spreading), was revealed. The main provisions of the theory were formulated in 1967-68 by American geophysicists J. Isaacs, C. Le Pichon, L. Sykes, J. Oliver, W. J. Morgan. According to this theory, plate boundaries are located in zones of tectonic, seismic and volcanic activity. Boundaries are divergent, transformative and convergent.

Movement of lithospheric plates

Lithospheric plates begin to move due to the movement of matter located in the upper mantle. In rift zones, this substance breaks through the crust, pushing plates apart. Most rifts are located on the ocean floor, since the earth's crust there is much thinner. The largest rifts that exist on land are located near Lake Baikal and the African Great Lakes. The movement of lithospheric plates occurs at a speed of 1-6 cm per year. When they collide with each other, mountain systems arise at their boundaries in the presence of continental crust, and in the case when one of the plates has a crust of oceanic origin, deep-sea trenches are formed.

The basic principles of plate tectonics come down to several points.

1. In the upper rocky part of the Earth, there are two shells that differ significantly in geological characteristics. These shells are the hard and brittle lithosphere and the mobile asthenosphere underneath. The base of the lithosphere is a hot isotherm with a temperature of 1300°C.
2. The lithosphere consists of plates of the earth's crust continuously moving along the surface of the asthenosphere.

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.

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’ll talk more about magma in the article on volcanoes.

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.

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