Lithosphere. The internal structure of the Earth

The earth's crust and the upper (solid) part of the mantle form the lithosphere. It is a "ball" of solid matter with a radius of about 6400 km. The earth's crust is the outer shell of the lithosphere. Consists of sedimentary, granite and basalt layers. Distinguish between oceanic and continental crust. The first contains no granite layer. Maximum thickness crust about 70 km - under the mountain systems, 30-40 km - under the plains, the thinnest earth's crust - under the oceans, only 5-10 km.

The rest we call the inner lithosphere, which also includes the central part, called the core. We know almost nothing about the inner layers of the lithosphere, although they account for almost 99.5% of the entire mass of the Earth. They can only be studied using seismic surveys.

The lithosphere is divided into blocks - lithospheric plates are large rigid blocks of the earth's crust that move along a relatively plastic asthenosphere. The lithosphere under the oceans and continents varies considerably.

The lithosphere under the oceans has undergone many stages of partial melting as a result of the formation of the oceanic crust, it is highly depleted in low-melting trace elements and mainly consists of dunites and harzburgites.

The lithosphere under the continents is much colder, more powerful and, apparently, more diverse. It does not participate in the process of mantle convection, and has undergone fewer partial melting cycles. In general, it is richer in incompatible rare elements. In its composition, a significant role is played by lherzolites, wehrlites and other rocks rich in rare elements.

The lithosphere is split into about 10 large plates, the largest are the Eurasian, African, Indo-Australian, American, Pacific, Antarctic. Lithospheric plates move with land rising on them. At the heart of the theory of motion lithospheric plates- A. Wegener's hypothesis about continental drift.

Lithospheric plates are constantly changing their shape, they can split as a result of rifting and solder, forming a single plate as a result of collision. On the other hand, the division of the earth's crust into plates is not unambiguous, and as geological knowledge accumulates, new plates are identified, and some plate boundaries are recognized as non-existent. The movement of lithospheric plates is due to the movement of matter in the upper mantle. In rift zones, it breaks the earth's crust and pushes the plates apart. Most rifts are found at the bottom of the oceans, where the earth's crust is thinner. On land, the largest rifts are located in the African Great Lakes and Lake Baikal. The speed of movement of lithospheric plates is -1-6 cm per year.

When lithospheric plates collide at their boundaries, mountain systems are formed, if in the collision zone both plates bear the continental crust (Himalayas), and deep-sea trenches, if one of the plates carries oceanic crust (Peruvian Trench). This theory agrees with the assumption of the existence of ancient continents: the southern one - Gondwana and the northern one - Laurasia.

The boundaries of the lithospheric plates are mobile areas where mountain building occurs, areas of earthquakes and most active volcanoes (seismic belts) are concentrated. The most extensive seismic belts are Pacific and Mediterranean - Trans-Asian.

At a depth of 120-150 km under the continents and 60-400 km under the oceans, there is a layer of the mantle called the asthenosphere. All lithospheric plates seem to float in a semi-liquid asthenosphere, like ice floes in water.

lithosphere earth crust anthropogenic

Internal structure Earth. It is customary to divide the Earth's body into three main parts - the lithosphere (earth's crust), the mantle and the core.

Core, the average radius of which is about 3500 km, is assumed to consist of iron with an admixture of silicon. The outer part of the core is in a molten state, the inner, apparently, solid.

The core is changing mantle, which stretches for almost 3000 km. It is believed that it is solid, at the same time plastic and red-hot.

Lithosphere- the upper shell of the "solid" Earth, including the earth's crust and the upper part of the underlying upper mantle of the Earth.

Earth's crust- the upper shell of the "solid" Earth. The thickness of the earth's crust is from 5 km (under the oceans) to 75 km (under the continents). The earth's crust is heterogeneous. There are 3 layers in it - sedimentary, granite, basalt. The granite and basalt layers are so named because they contain rocks similar in physical properties to granite and basalt.

Distinguish continental and oceanic the earth's crust. The oceanic one differs from the continental one by the absence of a granite layer and by a much smaller thickness (from 5 to 10 km).

The position of the layers in the continental crust indicates a different time of its formation. The basalt layer is the oldest, younger than it is granite, and the youngest is the upper sedimentary layer, which is still developing at the present time. Each layer of the crust was formed over a long period of geological time.

Rocks- the main substance that composes the earth's crust. A hard or loose compound of minerals. By origin, rocks are divided into three groups:

1) magmatic - are formed as a result of the solidification of magma in the thickness of the earth's crust or on the surface. Allocate:

a) intrusive(formed in the thickness of the earth's crust, for example, granites);

b) effusive(formed during the outpouring of magma to the surface, for example, basalts).

2) sedimentary - are formed on the land surface or in water bodies as a result of the accumulation of products of destruction of pre-existing rocks of different origin. Sedimentary rocks cover about 75% of the surface of the continents. Among the sedimentary rocks are:

a) clastic- formed from various minerals and fragments of rocks during their transfer and redeposition (flowing waters, wind, glacier). For example: crushed stone, pebbles, sand, clay; the largest fragments are boulders and boulders;

b) chemical- are formed from substances soluble in water (potassium, sodium chloride, etc.);

v) organic(or biogenic) - consist of the remains of plants and animals or of minerals formed as a result of the vital activity of organisms (limestone-shell rock, chalk, fossil coals);

3) metamorphic - obtained by changing other types of rocks under the influence of heat and pressure in the depths of the earth's crust (quartzite, marble).

Minerals- natural mineral formations in the earth's crust of inorganic and organic, which at a given level of development of technology and economy can be used in the economy in a natural form or after appropriate processing. Minerals are classified according to many characteristics. For example, they emit solid (coal, metal ores), liquid (oil, mineral waters) and gaseous (combustible natural gases) minerals.

By composition and features of use usually distinguish:

a) combustible minerals - coal, oil, natural gas, oil shale, peat;

b) metal - ores of ferrous, non-ferrous, noble and other metals;

c) non-metallic minerals - limestone, rock salt, gypsum, mica, etc.

By the way of formation, minerals can be:

1) endogenous, the formation of which is associated with the eruption or outpouring of magma;

2) exogenous, arising from the accumulation of sedimentary rocks;

3) metamorphic, formed at high pressure or when hot lava comes into contact with sedimentary rocks.

Sometimes by origin there are two groups: ore and non-metallic(sedimentary) minerals. The features of the distribution of minerals on Earth are closely related to the origin.

Lithospheric plates- large rigid blocks of the Earth's lithosphere, limited by seismically and tectonically active fault zones.

The plates, as a rule, are separated by deep faults and move along the viscous layer of the mantle relative to each other at a speed of 2-3 cm per year. At the points of convergence of the continental plates, they collide, and mountain belts are formed. When the continental and oceanic plates interact, the plate with the oceanic crust moves 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 some parts of the mantle, there are powerful streams of heat and matter, rising from its depths to the surface of the planet.

The rift– a huge rift in the earth's crust, formed when it is stretched horizontally (that is, where the flows of heat and matter diverge).

An outpouring of magma occurs in the rifts, new faults, horsts, and grabens appear. Mid-ocean ridges are being formed.

Mid ocean ridges- powerful underwater mountain structures within the ocean floor, most often occupying the middle position. Near the mid-oceanic ridges, lithospheric plates move apart and a 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, as well as mid-ocean ridges, are characterized by seismic activity and volcanism.

Plate tectonics is a hypothesis that the lithosphere is broken up into large plates that move horizontally along the mantle. Near the mid-ocean ridges, lithospheric plates move apart and build up due to matter rising from the bowels of the Earth; in deep-sea trenches, one plate moves under the other and is absorbed by the mantle. In places where the plates collide, folded structures are formed.

Seismic belts of the Earth. The moving areas of the Earth are the boundaries of lithospheric plates (places of their rupture and divergence, collisions), i.e., these are rift zones on land, as well as mid-ocean ridges and deep-sea trenches in the ocean. Frequent volcanic eruptions and earthquakes are observed in these zones. This is explained by the emerging tension in the earth's crust and indicates that the process of the formation of the earth's crust in these zones is intensively going on at the present time.

Thus, the zones of modern volcanism and high seismic activity(ie, the spread of earthquakes) coincide with the faults of the earth's crust.

Areas where earthquakes occur are called seismic.

External and internal forces that change the surface of the Earth. Relief- a set of unevenness of the earth's surface. The formation of the relief is simultaneously influenced by external and internal forces that generate many geological processes.

The processes that change the surface of the Earth are divided into two groups:

1) internal processes - tectonic movements, earthquakes, volcanism. The source of energy for these processes is the internal energy of the Earth;

2) external processes - weathering (physical, chemical, biological), wind activity, surface flowing water activity, glacier activity. The energy source is solar heat.

Internal processes of relief formation (endogenous). Tectonic movements – mechanical movements of the earth's crust caused by forces acting in the earth's crust and the Earth's mantle. Lead to significant changes in the relief. Tectonic movements are diverse in form of manifestation, depth and reasons. Tectonic movements are divided into oscillatory (slow vibrations of the earth's crust), folded and discontinuous (the formation of cracks, grabens, horsts). In terms of time, the ancient (before the Cenozoic folding), the newest (starting from the Neogene period) and modern are distinguished. The newest and modern ones are sometimes combined into Neo-Quaternary movements.

Neogene Quaternary movements of the earth's crust. These include tectonic processes of the Neogene-Quaternary period (the last 30 million years), which covered all geostructures and determined the main appearance of the modern relief. In recent times, the movements of many previously formed large forms of relief continue - hills, mountain ranges rise, and some parts of the lowlands descend and are filled with precipitation.

Earthquakes. Earthquakes are called tremors of the earth's surface caused by natural causes. Depending on the causes of earthquakes, they are divided into 3 types:

1) tectonic earthquakes associated with the formation of faults in the earth's crust and the movement of blocks of the earth's crust along them. Tectonic earthquakes are the most common;

2) volcanic earthquakes associated with the movements of magma in the chamber and channel of the volcano and explosive emissions of volcanic gases.

Volcanic earthquakes are usually weak and cover small areas. In some cases, the strength of such earthquakes can be enormous - during the eruption of the Krakatoa volcano (Sunda Islands) in 1883, the explosion destroyed half of the volcano, and the shaking caused great destruction on the islands of Java, Sumatra, Kalimantan;

3) landslide earthquakes occurring during a collapse in underground voids due to the impact produced by the collapsed mass. This type of earthquake occurs infrequently and is of low intensity; spread over a very limited area.

During the year, there are about 100,000 earthquakes on Earth, or about 300 per day. Earthquakes usually happen quickly, within a few seconds or even fractions of a second. The area in the bowels of the Earth, within which an earthquake occurs, is called the focus of the earthquake, its center - hypocenter, and the projection of the hypocenter onto the Earth's surface is the epicenter. Earthquake foci can be located at a depth of 20-30 km to 500-600 km. The strongest earthquakes had a source depth of 10-15 to 20-25 km. Earthquakes with a deep source are usually not very destructive at the surface.

The severity of earthquakes is measured on a 12-point scale. One point denotes the weakest earthquake, the strongest, 10-12 points, have catastrophic consequences. Earthquakes are recorded by special devices - seismographs. The science that studies the causes of earthquakes, their consequences, the connection between earthquakes and tectonic processes and the possibility of their prediction is called seismology .

One of the main tasks is to predict earthquakes, that is, to predict where, when and of what strength an earthquake will occur. This can be determined using a seismic zoning map.

Seismic zoning- division of the territory into regions according to their seismic activity, assessment and display on maps of the potential seismic hazard, which must be taken into account in earthquake-resistant construction.

In Russia, strong earthquakes are possible in the Baikal region, Kamchatka, the Kuril Islands, and southern Siberia.

The world distinguishes the Pacific seismic belt surrounding Pacific Ocean, and the Mediterranean, which runs from the Atlantic Ocean through Central Asia to the Pacific. The active seismic belt passing through East Africa, the Red Sea, the Tien Shan, the Baikal Basin, the Stanovoy Ridge is much younger.

Thus, most earthquakes are confined to the edges of the lithospheric plates, to the places of their interaction. There is a significant connection between earthquakes and volcanism.

Volcanism- a set of processes and phenomena associated with the outpouring of magma on the earth's surface.

Magma– molten material of rocks and minerals, a mixture of many components. Magma always contains volatile substances: water vapor, carbon dioxide, hydrogen sulfide, etc. The emergence and movement of magma is due to the internal energy of the Earth.

Volcanism can be:

1) internal(intrusive) - the movement of magma inside the earth's crust leads to the formation of laccoliths - underdeveloped forms of volcanoes, in which magma did not reach the earth's surface, but invaded through cracks and channels in the sedimentary rocks, lifting them. Sometimes the upper sedimentary cover over the laccoliths is washed away, and a laccolith core of solidified magma is exposed on the surface. Laccoliths are known in the vicinity of Pyatigorsk (Mount Mashuk), in the Crimea (Mount Ayudag);

2) external(effusive) - the movement of magma with its release to the surface. Magma that poured out onto the surface, which has lost a significant part of the gases, is called lava .

Volcanoes – geological formations, which are usually cone-shaped or dome-shaped, composed of eruption products. In the central part of them there is a channel through which these products are released. Less commonly, modern volcanoes look like cracks, along which volcanic products erupt from time to time.

Modern volcanoes are common where intense movements of the earth's crust occur:

1. Pacific volcanic ring.

2. Mediterranean-Indonesian belt.

3. Atlantic belt.

In addition, volcanic activity is also developed in rift zones and mid-ocean ridges.

External processes of relief formation (exogenous). Weathering- the process of destruction of rocks at the place of their occurrence under the influence of temperature fluctuations, chemical interaction with water, as well as the action of animals and plants.

Depending on what exactly caused the process of destruction, a distinction is made between physical, chemical and organic weathering.

Wind activity. Aeolian processes(as the geological activity of the wind is called) are most developed where there is no or poorly developed vegetation cover. The wind carrying loose sediments is capable of creating various forms of relief: blowing hollows, sand ridges, hills, including sickle-shaped dunes.

Surface flowing water activity. Surface water create forms of erosion (erosion) and accumulation of deposits (accumulative). The formation of these landforms occurs simultaneously: if there is erosion in one place, there must be deposition in the other. There are two forms of destructive activity of flowing waters: plane washout and erosion. Geological activity flat flush lies in the fact that rain and melt waters flowing down the slope pick up small weathering products and carry them down. Thus, the slopes are flattened, and the waste products are more and more deposited below. Under erosion, or linear erosion, understand the destructive activity of water streams flowing in a certain channel. Linear erosion leads to the dissection of slopes by ravines and river valleys.

Ravine- a linearly elongated pothole with steep, non-sodded slopes. It grows upward due to the erosion of the ledge at its top by temporary streams of storm and melt water. Erosion products form a ravine fan at the bottom. The development of ravines has a harmful effect on various structures and agricultural land, therefore, to combat them, they fill in gullies, sow grasses, plant trees, etc.

River valley- a linearly elongated depression, at the bottom of which there is a constant water stream... All valleys have slopes and bottom. The fast mountain rivers have narrow valleys, and the whole bottom is occupied by the river. Plain rivers flow slowly in wide valleys.

The valley slopes are often stepped. In mountain rivers, this is usually associated with the alternation of layers of different hardness. In plain rivers on the slopes, as a rule, there are steps (river terraces), indicating the incision of the river. Each terrace was the bottom of a valley into which a river crashed. This is evidenced by river sediments covering the terraces or completely composing them. River sediments are called alluvial deposits, or alluvium. Rivers carry a large amount of various material, depositing it in the delta. The incision of the river and the formation of terraces can be caused by the uplift of the area along which the river flows, the lowering of the level of the reservoir into which it flows, and the change in the water level in the river. Thus, the rivers provide big influence on the formation of the relief.

Glacier activity. Glaciers form where the snow that falls during the winter does not completely melt in the summer.

There are two types of glaciers:

- mountain

- continental (or integumentary).

Mountain glaciers are found on high mountains with sharp, jagged peaks. Glaciers here lie in various depressions of the slopes or move along the valleys, like an icy river.

Mainland glaciers are developed in the polar regions (Antarctica, New earth, Greenland, etc.). All the unevenness of the relief are buried here under the ice. The ice sheets of the ice sheets move from the center to the edges.

Moving, a glacier of any type produces a great destructive work, intensified by the fact that fragments of rocks freeze into the ice from the bottom.

The accumulation of debris (boulders, pebbles, sand, clay) carried and deposited by glaciers is called stained... Streams of melt glacial waters carry out and deposit a significant amount of washed clastic material. Deposits of such streams are called water-glacial.

With the general melting of a stationary glacier, all the material contained in it is projected onto the underlying surface, and extensive moraine plains, mostly hilly. If the edge of the glacier lingers in one place for a long time, finite moraine shafts and ridges... If the glacier retreats slowly, it remains finite moraine plain... Sandy plains called outwash, are formed by streams of glacier melt water carrying fine-grained material.

There is a number of factual data indicating that periods of glaciation have been observed repeatedly in the history of the Earth. The main centers of glaciation in Eurasia were the Scandinavian Mountains, Novaya Zemlya, and the Northern Urals. For example, glaciers descended to the East European Plain from the Scandinavian Mountains and from the Polar Urals, to West Siberian Plain- from the Polar Urals, the Putorana and Byrranga mountains. To the North Siberian lowland and to the northern part of the Central Siberian plateau - from the Byrranga and Putorana mountains. Glaciation had a great impact on the formation of the relief of loose sediments and the change in flora and fauna, as well as the displacement natural areas and high-altitude belts.

The relief of subsequent glaciations was superimposed on the relief created by previous glaciations, which led to a complication of the relief.

Mountain glaciers moving along the erosional plains transform them. At the same time, the valleys become wider, the slopes - steeper, acquire a trough-like shape. Such valleys are called trogami. On the slopes of the mountains, glaciers create depressions that look like chairs - glacial circuses.

In the mountains, they distinguish snow line - the height above which the snow does not melt completely even in summer. The height of the snow line depends on the latitude of the place, the amount of precipitation, the nature and position of the mountain slopes.

Forms of the earth's surface... Plains are vast areas of land with a flat or hilly surface, which have different heights relative to the level of the World Ocean.

Plains, depending on the nature of the relief, can be flat(West Siberian, US Coastal Plains, etc.) and hilly(East European, Kazakh Upland).

Depending on the height at which the plains are located, they are divided into:

1) lowlands - having an absolute height of no more than 200 m;

2) hills - located at an altitude of no higher than 500 m;

3) plateaus - above 500 m.

The mountains – certain territories of the land surface, rising above the level of the World Ocean above 500 m and having a dissected relief with steep slopes and clearly distinguished peaks.

Highlands- vast mountain areas, including individual ridges, intermontane depressions, small plateaus. The difference in heights in the highlands does not reach a great value.

Erosional mountains are formed as a result of tectonic uplifts and their subsequent deep dissection. Outlier mountains are a particular case of erosional mountains. The modern relief of erosional mountains is created mainly by the activity of flowing waters.

Depending on the height, the mountains are divided into low (up to 1000 m), medium (from 1000 to 2000 m) and high - above 2000 m.

Tectonic structures – a set of structural forms of the earth's crust. Elementary structural forms - layers, folds, cracks, etc. The largest are platforms, plates, geosynclines, etc. The formation of tectonic structures occurs as a result of tectonic movements.

Platform- the most stable area of ​​the lithosphere, which has a two-tiered structure - a folded crystalline base at the bottom and a sedimentary cover at the top. The largest structural units of the platform: shields- places where the crystalline basement of the platform reaches the surface (for example, the Baltic Shield, Anabar Shield).

Stove called a platform in which the foundation is deeply hidden under a sedimentary cover (West Siberian plate). The platforms are divided into ancient - with a Precambrian basement (for example, East European, Siberian) and young - with a basement of the Paleozoic and Mesozoic age (for example, Scythian, West Siberian, Turanian). Ancient platforms make up the cores of the continents. Young platforms are located along the periphery of ancient platforms or between them.

In the relief, the platforms are usually expressed by plains. Although mountain-building phenomena are also possible (activation of the platform). The reason may be mountain building near the platform, or the continuing pressure of lithospheric plates.

Edge deflection- a linearly elongated deflection arising between the platform and the folded mountain structure. Foredeeps are filled with products of destruction of mountains and adjacent platforms. They usually concentrate deposits of ore and sedimentary minerals. So, in the Ural foredeep, chromium and copper ores, sodium chloride and potassium salts, and oil are concentrated.

Folded areas, unlike platforms, are mobile areas of the earth's crust that have experienced mountain building. Folded areas in the relief are expressed by mountains of different ages. Folded regions and mountains are usually formed in places of collision of lithospheric plates.

Modern platforms and folded regions have not always existed. The face of the Earth throughout her geological history was constantly changing. There are several hypotheses for the origin of continents and oceans. According to one of them, in the beginning, only oceanic type crust existed on Earth. Then, as a result of the action of the internal forces of the Earth, the first folded regions arose. After going through the stages of folded, folded-block and block mountains, with constant simultaneous exposure external forces relief formation, the first platforms were gradually formed. The formation of the continents took place gradually through a sequential increase in their area due to the joining of folded areas to ancient platforms.

In the history of the Earth there were several epochs of intensification of folding processes - epochs of mountain building. The foundations of ancient platforms, for example, were formed during the Precambrian folding. Then there were the epochs of the Baikal, Caledonian, Hercynian, Mesozoic, Cenozoic folding, in each of which mountains were formed. So, for example, the mountains of the Baikal region were formed in the era of the Baikal and Early Caledonian folds, the Urals in the Hercynian, the Verkhoyansk ridge in the Mesozoic, and the Kamchatka mountains in the Cenozoic. The era of Cenozoic folding continues to this day, as evidenced by earthquakes and volcanic eruptions.

Changing the outlines of the continents. The outlines of the continents have changed over time. The location, size and configuration of continents and oceans in the distant past were different and will change in the distant future. In Paleozoic Australia, South America, Africa and Antarctica made up a single continent - Gondwana. In the Northern Hemisphere, a single continent supposedly existed - Laurasia, and before that, there may have been one continent - Pangea.

The outlines of the ancient continents also changed as a result of mountain-building processes. The ancient platforms turned out to be, as it were, "welded" newly formed mountains, or during the formation of mountains at the edge of the platforms, the land area increased, the outlines of the coast changed.

The lithosphere is the fragile, outer, solid layer of the Earth. Tectonic plates are segments of the lithosphere. Its top is easy to see - it is on the surface of the Earth, but the base of the lithosphere is located in the transition layer between the earth's crust and, which is an area of ​​active research.

Bending of the lithosphere

The lithosphere is not completely rigid, but slightly elastic. It bends when an additional load acts on it or, on the contrary, bends if the load is weakened. Glaciers are one type of load. For example, in Antarctica, a thick ice cap has severely lowered the lithosphere to sea level. While in Canada and Scandinavia, where the glaciers melted about 10,000 years ago, the lithosphere is not strongly affected.

Some other types of load on the lithosphere are:

• Volcanic eruption;
• Deposition of sediments;
• Sea level rise;
• Formation of large lakes and reservoirs.

Examples of mitigating impact on the lithosphere:

• Mountain erosion;
• Formation of canyons and valleys;
• Drying out of large bodies of water;
• Decrease in sea level.

The bend of the lithosphere, for the reasons given above, is usually relatively small (usually much less than a kilometer, but measurable). We can model the lithosphere using simple engineering physics and get an idea of ​​its thickness. We are also able to study the behavior of seismic waves and place the base of the lithosphere at depths where these waves begin to slow down, indicating the presence of softer rock.

These models suggest lithosphere thickness ranges from less than 20 km near mid-ocean ridges to about 50 km in older oceanic regions. The lithosphere is thicker under the continents - from 100 to 350 km.

The same studies show that under the lithosphere there is a hotter and softer layer of rock called the asthenosphere. The rock of the asthenosphere is viscous, not tough and slowly deforms under stress, like a putty. Therefore, the lithosphere can move through the asthenosphere under the influence of plate tectonics. This also means that earthquakes form cracks that only extend through the lithosphere, not beyond.

The structure of the lithosphere

The lithosphere includes the crust (continental mountains and ocean floor) and the uppermost part of the mantle below the earth's crust. These two layers differ in mineralogy, but are very similar mechanically. For the most part, they act like one slab.

The lithosphere appears to end where the temperature reaches a certain level that makes the middle mantle rock (peridotite) too soft. But there are many complications and assumptions, and we can only say that these temperatures range from 600º to 1200ºC. Much depends on pressure and temperature, as well as changes in the composition of rocks due to tectonic mixing. Probably, it is impossible to accurately determine the clear lower boundary of the lithosphere. Researchers often indicate the thermal, mechanical, or chemical properties of the lithosphere in their work.

The oceanic lithosphere is very thin at the expanding centers where it forms, but becomes thicker over time. As it cools, hotter rock from the asthenosphere cools down on the underside of the lithosphere. Over the course of about 10 million years, the oceanic lithosphere becomes denser than the asthenosphere below it. Therefore, most oceanic plates are always ready for subduction.

Bending and destruction of the lithosphere

The forces that bend and break the lithosphere come primarily from plate tectonics. When plates collide, the lithosphere on one plate sinks into the hot mantle. In this subduction process, the plate is bent downward 90 degrees. As it bends and sinks, the subductive lithosphere cracks violently, causing earthquakes in the descending mountain plate. In some cases (for example, in northern California), the subductive part can completely collapse, sinking deep into the Earth, as the plates above it change their orientation. Even at great depths, the subductive lithosphere can be fragile for millions of years if relatively cool.

The continental lithosphere can split, with the lower part collapsing and sinking. This process is called delamination. Top part the continental lithosphere is always less dense than the mantle part, which, in turn, is denser than the asthenosphere below. Gravity or drag from the asthenosphere can pull out layers of the earth's crust and mantle. Deamination allows the hot mantle to rise and melt beneath parts of the continents, causing widespread uplift and volcanism. Places such as the California Sierra Nevada, eastern Turkey, and parts of China are being explored with the stratification process in mind.

And any negative lithospheric changes can aggravate the global crisis. From this article you will learn about what the lithosphere and lithospheric plates are.

Definition of the concept

The lithosphere is the outer hard shell of the earth, which consists of the earth's crust, part of the upper mantle, sedimentary and igneous rocks. It is rather difficult to determine its lower boundary, but it is generally accepted that the lithosphere ends with a sharp decrease in the viscosity of rocks. The lithosphere occupies the entire surface of the planet. The thickness of its layer is not the same everywhere, it depends on the terrain: on the continents - 20-200 km, and under the oceans - 10-100 km.

The lithosphere of the Earth is mostly composed of igneous igneous rocks (about 95%). These rocks are dominated by granitoids (on the continents) and basalts (under the oceans).

Some people think that the terms "hydrosphere" / "lithosphere" mean the same thing. But this is far from the case. The hydrosphere is a kind of water shell of the earth, and the lithosphere is solid.

Geological structure of the globe

The lithosphere as a concept also includes the geological structure of our planet, therefore, in order to understand what the lithosphere is, it should be considered in detail. The upper part of the geological layer is called the earth's crust, and its thickness varies from 25 to 60 kilometers on the continents, and from 5 to 15 kilometers in the oceans. The lower layer is called the mantle, it is separated from the earth's crust by the Mohorovichich section (where the density of matter changes sharply).

The globe consists of the earth's crust, mantle and core. The earth's crust is solid, but its density changes sharply at the border with the mantle, that is, on the Mohorovichich line. Therefore, the density of the earth's crust is an unstable value, but the average density of a given layer of the lithosphere can be calculated, it is equal to 5.5223 grams / cm 3.

The globe is a dipole, that is, a magnet. Earth's magnetic poles are located in the southern and northern hemispheres.

Layers of the Earth's lithosphere

The lithosphere on the continents consists of three layers. And the answer to the question of what the lithosphere is would not be complete without considering them.

The top layer is built from a wide variety of sedimentary rocks. The middle one is conventionally called granite, but it consists not only of granites. For example, under the oceans there is no granite layer of the lithosphere at all. The approximate density of the middle layer is 2.5-2.7 grams / cm 3.

The bottom layer is also conventionally called basalt. It consists of heavier rocks, its density is correspondingly higher - 3.1-3.3 grams / cm 3. The lower basalt layer is located under the oceans and continents.

The earth's crust is also classified. Distinguish between continental, oceanic and intermediate (transitional) types of the earth's crust.

The structure of lithospheric plates

The lithosphere itself is not homogeneous; it consists of peculiar blocks called lithospheric plates. They include both oceanic and continental crust. Although there is a case that can be considered an exception. The Pacific lithospheric plate consists only of the oceanic crust. Lithospheric blocks consist of folded metamophysical and igneous rocks.

Each continent is based on an ancient platform, the boundaries of which are determined by mountain ranges. Plains and only individual mountain ranges are located directly on the platform area.

Seismic and volcanic activity is often observed at the boundaries of lithospheric plates. There are three types of lithospheric boundaries: transform, convergent and divergent. The outlines and boundaries of lithospheric plates change quite often. Small lithospheric plates are interconnected, while large ones, on the contrary, split.

List of lithospheric plates

It is customary to distinguish 13 main lithospheric plates:

• Philippine plate.
• Australian.
• Eurasian.
• Somali.
• South American.
• Hindustan.
• African.
• Antarctic plate.
• Nazca slab.
• Pacific;
• North American.
• Scotia stove.
• Arabian plate.
• Coconut plate.

So, we have given a definition of the concept of "lithosphere", examined the geological structure of the Earth and lithospheric plates. With the help of this information, we can now confidently answer the question of what the lithosphere is.

Lithosphemra (from the Greek.Lyapt - stone and utsbyasb - sphere, sphere) is the solid shell of the Earth. It consists of the earth's crust and the upper part of the mantle, up to the asthenosphere, where the velocities of seismic waves decrease, indicating a change in the plasticity of rocks. In the structure of the lithosphere, mobile regions (folded belts) and relatively stable platforms are distinguished.

The scheme of the internal structure of the earth

Scheme of the continental and oceanic crust

The main landforms on land are mountains and plains.

Relief form classifications:

Taking into account the properties of the relief, several classifications have been developed:

1) Morphological classification, taking into account the size of landforms

Planetary forms are continents, mobile belts, ocean floor and mid-ocean ridges;

Megaforms are parts of planetary forms, i.e. plains and mountains;

Macroforms are parts of megaforms: mountain ranges, large valleys and depressions;

Mesoforms are medium-sized forms: beams, ravines;

Microforms are irregularities that complicate the surface of mesoforms: sinkholes, gullies;

Nanoforms are very small irregularities that complicate meso- and microforms: bumps, ripples on the slopes of dunes, etc.

2) Classification by genetic characteristics

There are two classes:

• 1. Forms formed as a result of the activity of internal, endogenous forces;
• 2. Forms formed due to exogenous, external forces.

The first class includes two subclasses: a) forms associated with the movement of the earth's crust; b) forms associated with volcanic activity. The second class includes: a) fluvial forms; b) aeolian forms; c) glacial; d) karst, etc.

3) Morphogenetic classification:

It was first proposed at the beginning of the 20th century by Engelny. He identified three categories of relief:

• 1. Geotecture;
• 2. Morphostructures;
• 3. Morphosculptures.

At the same time, the following stand out:

Geotecture - the most large forms relief on Earth: planetary, and mega-forms. They are created by cosmic and planetary forces.

Morphostructures are large forms of the earth's surface, which are created under the influence of endogenous and exogenous processes, but with the leading and active role of tectonic movements.

Morphosculptures are medium and small forms of relief (meso-, micro and nanoforms), created with the participation of endo- and exogenous forces, but with the leading and active role of exogenous forces.

4. Classification of relief by age

The development of the relief of any territory, as shown by the American geomorphologist W. Davis, occurs in stages. The age of a relief can be understood to mean certain stages of its development. For example, the formation of a river valley after the retreat of a glacier: at first, the river cuts into the underlying rocks, there are many irregularities in the longitudinal profile, and there is no floodplain. This is the youthful stage of the river valley. Then a normal profile is formed, the river floodplain is formed. This is the maturity stage of the valley. Due to lateral erosion, the floodplain expands, the course of the river slows down, and the channel becomes meandering. The stage of old age begins in the development of the river valley.

W. Davis took into account the complex of morphological and dynamic characteristics and identified three stages: youth, maturity and old age of the relief.

Geosynclines are mobile belts of the lithosphere, in which, during the tectonic cycle, the forces of extension and subsidence are consistently manifested at first, then compression and uplift of the earth's crust, as well as accumulation and dislocation, metamorphism and granitization of sedimentary rocks and the transformation of geosynclinal regions into platform and oceanic regions into continental.

Geosynclines have the following features:

• 1) Colossal dimensions (many thousands of kilometers in length and up to a thousand kilometers in width);
• 2) Shape (rectilinear, arcuate and circular);
• 3) Increased permeability of the lithosphere for endogenous heat flows, as well as magmatic melts and other fluids. The main mass of intrusive and effusive bodies is confined to geosynclinal areas;
• 4) Morphotectonic severity. At the first stage of development, geosynclines are represented by sea troughs, and at the final stage - by continental high-mountain folded systems;
• 5) Specific formations;
• 6) Sharp changes in the thickness of sedimentary rocks in the strike of geosynclines. The total thickness of precipitation in some places can reach 20-25 km;
• 7) Processes of dislocation, metamorphism and granitization of sedimentary rocks.

In the structural division of geosynclines, the element of the first magnitude is the geosynclinal belt - a mobile zone of the lithosphere of planetary dimensions, experiencing tectogenesis of a constructive direction. Large geosynclinal belts mainly divide and flank the ancient platforms and are believed to have begun to form in the Late Proterozoic. crust continental platform

Platforms - sedentary large isometric blocks of the earth's crust or a basement of igneous and metamorphic rocks, sedimentary cover, characterized by a relatively low permeability of the earth's crust, low seismicity and volcanism.

Platforms are divided into continental (cratons) and oceanic. Their main difference is:

• 1) the heterogeneous composition of the second layer of the crust;
• 2) a large difference in the layer-by-layer and total thickness of the lithosphere;
• 3) in the unequal internal structure of these platforms;

The sedimentary cover of the platforms is characterized by horizontal or almost horizontal bedding of layers, comparative constancy of their composition, consistency of thickness, and a set of certain platform formations.

Continental platforms are, as it were, the cores of the continents and occupy large parts of the area of ​​the continents. The continental platforms are composed of typical continental crust, 35-40 km thick. Within the platforms, the thickness of the lithosphere reaches 150-200 km, and in some cases 400 km. A significant part of the platforms is covered with a non-metamorphosed sedimentary cover, 3 - 5 km thick, and in the folds and depressions the thickness can reach 10 - 12 km, and in some cases 25 km. The sedimentary cover can include covers of plateau basalts, and sometimes more acidic volcanics. Where the platforms are not covered by a cover, a basement comes to the surface, composed of metamorphic rocks of varying degrees of metamorphism, as well as intrusive-magmatic rocks, mainly granites.

The platforms have a flat relief (low or plateau). Some parts of the platforms may be covered by the shallow epicontinental sea (White and Azov seas). The platforms are characterized by low modern vertical movements, very weak seismicity, no volcanic activity, and a lower heat flow (compared to the average terrestrial).

Continental platforms are classified as ancient and young.

The ancients are the most typical platforms with a Precambrian, mainly Early Precambrian basement and constitute the most ancient central parts of the continents. The ancient platforms include the North American, East European, Siberian, Sino-Korean. These platforms make up the northern row of platforms. Next are South American, African, Hindustan, Australian, Antarctic, which occupy the southern row. A separate group includes the South China Platform, which Japanese geologists call the Yangtze. The basement of these platforms is dominated by Archean formations. They are followed by the Early Proterozoic, Middle Proterozoic and Upper Proterozoic.

Ancient platforms have a polygonal outline and are separated from adjacent strike-slip structures by forward troughs. These deflections are superimposed on the lowered edges of the platforms, or are directly tectonically overlapped by their thrust peripheral zones. On the periphery of the East European Platform, both types of such relations are observed.

Thus, the main features of the ancient continental platforms are:

• 1) a two-story structure (the basement is composed of Precambrian rocks and sedimentary cover);
• 2) a wide distribution of sedimentary cover of consistent thickness and the same composition;
• 3) intermittent folding;
• 4) the absence of a direct inherited connection between the structures of the cover and the folding of the basement.

Young continental platforms occupy a much smaller area of ​​continents (about 5%) and are located mainly along the periphery of continents or between ancient platforms.

The young platforms include the Central European and Western European, East Australian, Patagonian platforms. They are located on the outskirts of continents. The West Siberian Platform refers to the platforms located between the ancient platforms.

The basement of young platforms is mainly composed of volcanic sedimentary rocks of Phanerozoic age, which are weakly metamorphosed. Granites and other intrusive formations play a subordinate role in the composition of the basement, and therefore the basement of young platforms is called not crystalline, but folded. Therefore, the basement of young platforms differs from the basement of the sedimentary cover only in its high degree of dislocation. In this regard, depending on the age of the final folding of the basement of young platforms, all plateaires or their parts are subdivided into Epicaledonian, Epigercyn, and Epikimmerian.

The sedimentary cover of young platforms is composed of Jurassic or Cretaceous-Quaternary deposits. So, on the Epigercynian platforms, the cover begins with the upper feathers, and on the Epicaledonian platforms, with the upper Devon. Due to the fact that young platforms in to a greater extent covered with a sedimentary cover than the ancients, in the literature they are often called slabs.

Thus, young platforms are characterized by the following features:

• 1) three-story structure: basement, intermediate complex and sedimentary cover;
• 2) young platforms are located at the periphery of geosynclinal belts and at the junction of ancient platforms;
• 3) partial inheritance of the structural plan and the type of base folding in the sedimentary cover;
• 4) the presence of both discontinuous and linear types of folding.

Tectonic structures underlying the territory	Relief shape	Minerals	Conclusion about the connection
Kola Peninsula	The relief of the Kola Peninsula is represented by depressions, terraces, mountains, plateaus. The mountain ranges of the peninsula rise more than 800 meters above sea level. The plains of the Kola Peninsula are occupied by swamps and numerous lakes.	In terms of the variety of mineral species, the Kola Peninsula has no analogues in the world. About 1000 minerals have been discovered on its territory - almost 1/3 of all known on Earth. About 150 minerals are not found anywhere else. Deposits of apatite-nepheline ores (Khibiny), iron, nickel, platinum metals, rare earth metals, lithium, titanium, beryllium, construction and jewelry and ornamental stones (amazonite, amethyst, chrysolite, garnet, jasper, iolite, etc.), ceramic pegmatites , micas (muscovite, phlogopite and vermiculite - the world's largest reserves)
Ural mountains	Ural is an area where various forms of relief border. The Ural mountains are not high. Only a few peaks reach an altitude of 1500 m. The highest peak in the Urals is Mount Narodnaya (1895 m). The mountains consist of several chains parallel to each other. Chains along and across are separated by depressions along which rivers flow. Moreover, they are badly damaged. There are many relatively flat surfaces here. But although the Ural Mountains are not high, they are still mountains. Largest cities The Urals are located either on flat territories or at altitudes up to 400 m above sea level.	The Ural is a treasury of various minerals. Of the 55 types of the most important minerals that were developed in the USSR, 48 are represented in the Urals. For the eastern regions of the Urals, the most typical deposits of copper pyrite ores (Gayskoye, Sibayskoye, Degtyarskoye deposits, Kirovgrad and Krasnouralskaya group of deposits), skarn-magnetite (Goroblagodatskoye, Magnitogorskoye deposits), titanium-magnetite (Kachkanarskoye, Pervouralskoye), nickel oxide ores (group of Orsko-Khalilovsky deposits) and chromite ores (Kempirsai massif deposits), confined mainly to the greenstone belt of the Urals, coal deposits (Chelyabinsk coal basin), placers and deposits of gold (Kochkarskoe, Berezovskoe) and platinum (Isovskoe). The largest deposits of bauxite (Severo-Uralsky bauxite region) and asbestos (Bazhenovskoe) are located here. On the western slope of the Urals and in the Urals there are deposits of coal (Pechora coal basin, Kizelovsky coal basin), oil and gas (Volga-Ural oil and gas region, Orenburg gas condensate field), potassium salts (Verkhnekamsky basin). The Urals are especially famous for their "gems" - precious, semi-precious and ornamental stones (emerald, amethyst, aquamarine, jasper, rhodonite, malachite, etc.). The depths of the mountains contain more than two hundred different minerals. The bowls of the St. Petersburg Hermitage, as well as the interior decoration and the altar of the Church of the Savior on Spilled Blood were made of Ural malachite and jasper.