Plate tectonics
Definition 1
A tectonic plate is a moving part of the lithosphere that moves on the asthenosphere as a relatively rigid block.
Note 1
Plate tectonics is the science that studies the structure and dynamics of the earth's surface. It has been established that the upper dynamic zone of the Earth is fragmented into plates moving along the asthenosphere. Plate tectonics describes the direction in which lithospheric plates move and how they interact.
The entire lithosphere is divided into larger and smaller plates. Tectonic, volcanic and seismic activity manifests itself at the edges of plates, which leads to the formation of large mountain basins. Tectonic movements capable of changing the topography of the planet. At the point of their connection, mountains and hills are formed, at the points of divergence, depressions and cracks in the ground are formed.
Currently, the movement of tectonic plates continues.
Movement of tectonic plates
Lithospheric plates move relative to each other at an average speed of 2.5 cm per year. As plates move, they interact with each other, especially along their boundaries, causing significant deformations in the earth's crust.
As a result of interaction tectonic plates massive mountain ranges and associated fault systems (for example, the Himalayas, Pyrenees, Alps, Urals, Atlas, Appalachians, Apennines, Andes, San Andreas fault system, etc.).
Friction between the plates causes most earthquakes on the planet, volcanic activity and the formation of ocean pits.
Tectonic plates contain two types of lithosphere: continental crust and oceanic crust.
A tectonic plate can be of three types:
- continental plate,
- oceanic plate,
- mixed slab.
Theories of tectonic plate movement
In the study of the movement of tectonic plates, special merit belongs to A. Wegener, who suggested that Africa and East End South America were previously a single continent. However, after a fault that occurred many millions of years ago, parts of the earth’s crust began to shift.
According to Wegener's hypothesis, tectonic platforms, having different masses and having a rigid structure, were placed on a plastic asthenosphere. They were in an unstable state and moved all the time, as a result of which they collided, overlapped each other, and zones of moving apart plates and joints were formed. In places of collisions, areas with increased tectonic activity were formed, mountains were formed, volcanoes erupted and earthquakes occurred. The displacement occurred at a rate of up to 18 cm per year. Magma penetrated into the faults from the deep layers of the lithosphere.
Some researchers believe that the magma coming to the surface gradually cooled and formed new structure bottom. The unused earth's crust, under the influence of plate drift, sank into the depths and again turned into magma.
Wegener's research touched upon the processes of volcanism, the study of stretching of the surface of the ocean floor, as well as viscous-liquid internal structure land. The works of A. Wegener became the foundation for the development of the theory of tectonics lithospheric plates.
Schmelling's research proved the existence of convective movement within the mantle leading to the movement of lithospheric plates. The scientist believed that the main reason for the movement of tectonic plates is thermal convection in the planet’s mantle, during which the lower layers of the earth’s crust heat up and rise, and the upper layers cool and gradually sink.
The main position in the theory of plate tectonics is occupied by the concept of geodynamic setting, characteristic structure with a certain ratio of tectonic plates. In the same geodynamic setting, the same type of magmatic, tectonic, geochemical and seismic processes are observed.
The theory of plate tectonics does not fully explain the relationship between plate movements and processes occurring deep within the planet. A theory is needed that could describe internal structure the earth itself, the processes occurring in its depths.
Positions of modern plate tectonics:
- the upper part of the earth's crust includes the lithosphere, which has a fragile structure, and the asthenosphere, which has a plastic structure;
- the main reason for plate movement is convection in the asthenosphere;
- the modern lithosphere consists of eight large tectonic plates, about ten medium plates and many small ones;
- small tectonic plates are located between large ones;
- igneous, tectonic and seismic activity is concentrated at plate boundaries;
- The movement of tectonic plates obeys Euler's rotation theorem.
Types of tectonic plate movements
Highlight Various types movements of tectonic plates:
- divergent movement - two plates diverge, and an underwater mountain range or chasm in the ground forms between them;
- convergent movement - two plates converge and a thinner plate moves under a larger plate, resulting in the formation of mountain ranges;
- sliding movement - plates move in opposite directions.
Depending on the type of movement, divergent, convergent and sliding tectonic plates are distinguished.
Convergence leads to subduction (one plate sits on top of another) or collision (two plates crush and form mountain ranges).
Divergence leads to spreading (the separation of plates and the formation of ocean ridges) and rifting (the formation of a break in the continental crust).
The transform type of movement of tectonic plates involves their movement along a fault.
Figure 1. Types of tectonic plate movements. Author24 - online exchange of student work
The lithosphere is the rocky shell of the Earth. From the Greek “lithos” - stone and “sphere” - ball
Lithosphere - external hard shell 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. Bottom line lithosphere is fuzzy 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's consider in general view geological structure Earth. The third planet beyond the distance from the Sun, Earth, has a radius of 6370 km, average density- 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 were 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 has three layers: sedimentary rocks cover granite, and granite lie on basalt. 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 central regions oceans (5-7 km). The predominant part earth's surface- These are the plains of 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 it is now used obsolete term sial, derived from the name of the basic elements rocks Si (lat. Silicium - silicon) and Al (lat. 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 Hindustan and Arabian Peninsula) and contains the largest part continental crust;
- Indo-Australian- it includes Australian continent and the Indian subcontinent. Due to constant clashes with Eurasian plates oh 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 northeastern Siberia, northwestern 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 due to the unification of moving continents.
When a collision of oceanic and continental plates occurs, the edge of the oceanic crust plunges under the continental crust, while on the other side 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 along the edges of tectonic plates the most large forms Earth's topography - mountain ranges with active volcanoes and deep-sea trenches.
Lithosphere problems
The intensive development of industry has led to the fact that man and the lithosphere in Lately began to get along extremely poorly with each other: the pollution of the lithosphere is acquiring catastrophic proportions. This happened due to an increase industrial waste together with household waste and used in agriculture fertilizers and pesticides, which negatively affects chemical composition 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, lithosphere pollution has become actual 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 have a negative impact on the main culprit of the problem - the person.
The nature of plate movement also determines what happens at their boundaries. Some plates move apart, others collide, and some rub against each other.
Colliding plates
Where plates move, several types of boundary plates are created, depending on the type of plates colliding. For example, at the boundary between the oceanic and continental plates, formed by the oceanic crust, “dives” under the continental crust, creating a deep depression, or trench, on the surface. The zone where this occurs is called subductive. As the plate sinks deeper into the mantle, it begins to melt. The crust of the upper plate is compressed, and mountains grow on it. Some of them are formed by magma that breaks up through the lithosphere.
Zones where plates move away from each other occur in some areas of the ocean floor. They are characterized by mountain ranges of volcanic rocks. Such volcanoes do not have steep slopes or a conical shape. Usually these are long chains of mountains with gentle slopes. The two chains are separated by a deep crack marking the boundary between the plates. A crack opens when magma (molten rock) rising from the asthenosphere is released to the surface. Once at the surface, the magma cools and hardens along the edges of the plates, forming new areas of the ocean floor. At the same time, the magma pushes the plates further and further away from each other. This process, known as expansion seabed, has no end, because the crack opens again and again. The place where this occurs is called the median ridge.
Deep depressions also form at the boundaries of two colliding plates. oceanic lithosphere. One of these plates goes under the other and melts, sinking into the mantle. Magma rushes upward through the lithosphere, and a chain of volcanoes forms near the boundary on the plate on top.
Continental plates
In those places where two plates of the continental lithosphere collide head-on, high mountain ranges are formed. At the boundary, the continental crust of both plates compresses, cracks and gathers into giant folds. With further movement of the plates, the mountain ranges become higher and higher, as all this tone is increasingly pushed upward.
Ocean trenches
Depressions formed at plate boundaries are the most deep holes earth's surface. It is considered the deepest Mariana Trench V Pacific Ocean(11,022 meters below sea level). The world's highest Mount Everest (8848 meters above sea level) could drown in it. For research oceanic trenches These are the types of deep-sea vehicles that are used.
Friction plates
Not all plates are moving away from each other or colliding head-on. Some of them rub sideways, moving either in opposite directions, or in the same direction, but with at different speeds. At the boundaries of such plates, both on land and on seabed, a new lithosphere is not formed, and the existing one is not destroyed. When the plates of the continental lithosphere move towards each other, the entire boundary zone is pushed upward, forming high mountain ranges. When the plates move side by side at different speeds, they appear to move in opposite directions.
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 photographs taken with artificial satellites Earth. 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 ocean ridges on, where the earth's crust is thinner. Most major fault on land it 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 internal parts lithospheric plate indicates that once there was a boundary between two plates that were firmly welded together and turned into a single, larger lithospheric plate. Thus, it is possible to make general conclusion: boundaries of lithospheric plates - moving areas to which volcanoes, zones, mountain areas, mid-ocean ridges are confined, deep-sea trenches and gutters. It is at the border of lithospheric plates that they are formed, the origin of which is associated with magmatism.
Lithospheric plates have high rigidity and are capable of maintaining their structure and shape without changes for a long time in the absence of external influences.
Plate movement
Lithospheric plates are located in constant movement. This is a movement that occurs in upper layers, is due to the presence of convective currents present in the mantle. Individual lithospheric plates approach, diverge, and slide relative to each other. When the plates come together, compression zones arise and subsequent thrusting (obduction) of one of the plates onto the neighboring one, or pushing (subduction) of adjacent formations. When divergence occurs, tension zones appear with characteristic cracks appearing along the boundaries. When sliding, faults are formed, in the plane of which nearby plates are observed.
Movement results
In areas of convergence of huge continental plates, when they collide, mountain ranges. In a similar way, at one time arose mountain system The Himalayas formed at the boundary of the Indo-Australian and Eurasian plates. The result of the collision of oceanic lithospheric plates with continental formations is island arcs and deep-sea trenches.
In the axial zones of mid-ocean ridges, rifts (from the English Rift - fault, crack, crevice) of a characteristic structure arise. Similar linear formations tectonic structure of the earth's crust, with a length of hundreds and thousands of kilometers, with a width of tens or hundreds of kilometers, arise as a result of horizontal stretching of the earth's crust. Rifts are very large sizes usually called rift systems, belts or zones.
Due to the fact that each lithospheric plate is a single plate, increased seismic activity and volcanism are observed in its faults. These sources are located within fairly narrow zones, in the plane of which friction and mutual movements of neighboring plates occur. These zones are called seismic belts. Deep-sea trenches, mid-ocean ridges and reefs are mobile areas of the earth's crust, they are located at the boundaries of individual lithospheric plates. This once again confirms that the process of formation of the earth's crust in these places continues quite intensively at the present time.
The importance of the theory of lithospheric plates cannot be denied. Since it is she who is able to explain the presence of mountains in some regions of the Earth, and in others. The theory of lithospheric plates makes it possible to explain and predict the occurrence catastrophic events, capable of arising in the area of their borders.