The middle layer of the mainland crust. Oceanic Cora: Main properties, structure and global geological role. Tectonic plates and age of the crust

The earth's crust in a scientific understanding is the most upper and solid geological part of the shell of our planet.

Scientific studies allow us to study it thoroughly. This promotes multiple drilling of wells both on continents and on the ocean day. The structure of the Earth and the earth's crust in different parts of the planet is different and in composition, and according to the characteristics. The upper boundary of the earth's crust is visible relief, and the bottom - the separation zone of two environments, which is also known as the surface of Mochorovichich. Often it is called simply "border M". It received this name thanks to the Croatian seismologist Mochorovichich A. He watched the speed of seismic movements, depending on the level of depth. In 1909, he established the presence of a difference between the earth's crust and the grown mantle of the Earth. The m border runs at the level where the rate of seismic waves rises from 7.4 to 8.0 km / s.

Chemical composition of the Earth

Studying the shells of our planet, scientists did interesting and even stunning conclusions. The features of the structure of the earth's crust make it similar to the same sites on Mars and Venus. More than 90% of the components of it are represented by oxygen, silicon, iron, aluminum, calcium, potassium, magnesium, sodium. Combining among themselves in various combinations, they form homogeneous physical bodies - minerals. They can enter the composition of rocks in different concentrations. The structure of the earth's crust is extremely inhomogeneously. Thus, the rocks in generalized form are aggregates of a more or less permanent chemical composition. These are independent geological bodies. Under them is understood to be a clearly defined area of \u200b\u200bthe earth's crust, which has the same origin in its boundaries, age.

Mountain breeds in groups

1. Magmatic. The name speaks for itself. They arise from the cooled magma arising from the jar of ancient volcanoes. The structure of these breeds directly depends on the speed of frozen lava. Than it is more, the smaller the crystals of the substance. Granite, for example, was formed in the thickness of the earth's crust, and Basalt appeared as a result of the gradual outpouring of the magma on its surface. The variety of such breeds is pretty great. Considering the structure of the earth's crust, we see that it consists of magnifying minerals by 60%.

2. Sediment. These are breeds that have become the result of a gradual deposit on land and the bottom of the ocean of fragments of certain minerals. It can be like loose components (sand, pebbles), sempulated (sandstone), residues of microorganisms (stone coal, limestone), chemical reaction products (potash salt). They constitute up to 75% of the whole earthly crust on the mainland.
By physiological method of formation, sedimentary breeds are divided into:

Cholly. These are the remnants of various rocks. They were destroyed under the influence of natural factors (earthquake, typhoon, tsunami). These include sand, pebbles, gravel, crushed stone, clay.
Chemical. They are gradually formed from aqueous solutions of certain minerals (salts).
Organic or biogenic. Consist of remains of animals or plants. These are combustible shale, gas, oil, coal, limestone, phosphorites, chalk.

3. Metamorphic rocks. Other components can be transformed into them. This occurs under the influence of a changing temperature, large pressure, solutions or gases. For example, you can get marble from limestone, from granite - gneis, from sand - quartzite.

Minerals and rocks that humanity actively uses in their livelihoods are called minerals. What do they imagine?

These are natural mineral formations that affect the structure of the Earth and the earth's crust. They can be used in agriculture and industry both in natural form and being recycled.

Types of useful minerals. Their classification

Depending on the physical condition and aggregation, minerals can be divided into categories:

Solid (ore, marble, coal).
Liquid (mineral water, oil).
Gaseous (methane).

Characteristics of individual mineral types

In terms of composition and features of application distinguish:

Combustible (coal, oil, gas).
Ore. These include radioactive (radium, uranium) and noble metals (silver, gold, platinum). There are ores of black (iron, manganese, chromium) and non-ferrous metals (copper, tin, zinc, aluminum).
Nonetic minerals play a significant role in such a concept as the structure of the earth's crust. The geography of their extensive. These are non-metallic and non-combustible rocks. These are building materials (sand, gravel, clay) and chemicals (sulfur, phosphates, potash salts). A separate section is devoted to precious and diverse stones.

The distribution of minerals in our planet directly depends on external factors and geological patterns.

Thus, fuel minerals are primarily mined in oil and gas and coal basins. They have sedimentary origins and form on sedimentary covers of platforms. Oil and coal extremely rare together.

Ore minerals most often correspond to the foundation, protrusions and folded areas of platform plates. In such places they can create huge belt for the length.

Core

The earth's shell is known to be multi-layered. The kernel is located in the center, and its radius is approximately 3,500 km. Its temperature is much higher than that of the Sun and about 10,000 K. The accurate data on the chemical composition of the kernel is not obtained, but presumably it consists of nickel and iron.

The external kernel is in the molten state and has even greater power than the internal one. The latter is subjected to colossal pressure. The substances from which it consists are in constant hard state.

Mantle

The Earth's geosphere surrounds the kernel and is about 83 percent of the entire shell of our planet. The lower boundary of the mantle is at a great depth of almost 3000 km. This shell is customary to be divided into a less plastic and dense upper part (Magma is generated from it) and on the lower crystalline whose width is 2000 kilometers.

The composition and structure of the earth's crust

In order to talk about what elements are included in the lithosphere, you need to give some concepts.

The crust is the most outer sheath of the lithosphere. Its density is less than twice as compared with the average density of the planet.

From the mantle, the earth's bark is separated by the boundary of M, which was mentioned above. Since the processes occurring at both sites mutually influence each other, their symbiosis is called a lithosphere. This means the "stone shell". Its power fluctuates in the range of 50-200 kilometers.

Below the lithosphere is an asthenosphere, which has a less dense and viscous consistency. Its temperature is about 1200 degrees. A unique feature of the asthenosphere is the ability to break their borders and penetrate the lithosphere. It is a source of volcanism. Here are melted foci of magma, which is embedded in the earth's bark and is poured onto the surface. Studying these processes, scientists were able to make many amazing discoveries. This is how the structure of the earth's crust was studied. The lithosphere was formed many thousand years ago, but now active processes are happening in it.

Structural elements of the earth's crust

Compared to mantle and core, a lithosphere is a tough, thin and very fragile layer. It is composed of a combination of substances, which today detected more than 90 chemical elements. They are distributed in heterogeneously. 98 percent of the mass of the earth's crust falls on seven components. This is oxygen, iron, calcium, aluminum, potassium, sodium and magnesium. The age of the most ancient breeds and minerals is more than 4.5 billion years.

Studying the inner structure of the earth's crust, various minerals can be distinguished.
Mineral is a relatively homogeneous substance that can be both inside and on the surface of the lithosphere. This is quartz, plaster, talc, etc. Mountain breeds are composed of one or more minerals.

Processes forming a terrestrial bark

The structure of the oceanic crust

This part of the lithosphere mainly consists of basalt rocks. The structure of the oceanic earth crust is not as thoroughly studied as continental. The theory of tectonic plates explains that the ocean earth bark is relatively young, and its most recent sites can be dated late Yura.
Its thickness practically does not change over time, as it is determined by the amount of melts that are distinguished from the mantle in the mid-ocean ridge zone. It significantly affects the depth of sedimentary layers at the bottom of the ocean. In the most voluminous sections, it ranges from 5 to 10 kilometers. This type of earthly shell refers to the oceanic lithosphere.

Continental bark

The lithosphere interacts with the atmosphere, hydrosphere and biosphere. In the process of synthesis, they form the most complex and reactionary active shell of the Earth. It is in the tertonosphere that the processes that change the composition and structure of these shells occur.
Lithosphere on the earth's surface is not uniform. It has several layers.

Sedimentary. It is mainly formed by rocks. Clay and slates are dominated here, and carbonate, volcanogenic and sandy rocks are widespread. In sedimentary layers, you can find minerals such as gas, oil and stone coal. All of them have organic origin.
Granite layer. It consists of magmatic and metamorphic rocks that are closest in nature to granite. This layer is far from everywhere, it is most brightly expressed on continents. Here, its depth can be tens of kilometers.
The basalt layer form rocks close to the mineral to the same name. It is more dense than granite.

Depth and change in the temperature of the earth's crust

The surface layer is heated by solar heat. This is a heliometric shell. It experiences seasonal temperature fluctuations. The average layer power is about 30 m.

Below is a layer, even thinner and fragile. Its temperature is constant and is approximately equal to the average annual characteristic of this area of \u200b\u200bthe planet. Depending on the continental climate, the depth of this layer increases.
Even deeper in the earthly crust is another level. This is a geothermal layer. The structure of the earth's crust involves its presence, and its temperature is determined by the inner heat of the Earth and increases with depth.

The temperature increase occurs due to the decay of radioactive substances, which are part of rocks. First of all it is radium and uranium.

Geometric gradient - the magnitude of the increase in temperature depending on the degree of increasing the depth of the layers. This parameter depends on different factors. The structure and types of earthly crust affect it, as well as the composition of rocks, the level and conditions of their occurrence.

The heat of the earth's crust is an important energy source. His study is very relevant today.

Earth's crust – External solid land sheath, top of a lithosphere. From the mantle of the earth, the earth's bark is separated by the surface of Mochorovichich.

It is customary to allocate mainland and oceanic bark, which differ in their composition, power, structure and age. Mainland barklocated under the mainland and their underwater outskirts (shelves). The Ground Core of the mainland thickness of 35-45 km is located under the plains of up to 70 km in the field of young mountains. The most ancient areas of the mainland cortex have a geological age greater than 3 billion years. It consists of such shells: the crust of weathered, sedimentary, metamorphic, granite, basalt.

Ocean globe much younger, its age does not exceed 150-170 million years. It has a smaller power – 5-10 km. Within the oceanic earth crust, there is no boundary layer. The following layers are distinguished in the structure of the earth's crust of the oceanic type: non-relaxed sedimentary rocks (up to 1 km), volcanic oceanic, which consists of compacted precipitation (1-2 km), basalt (4-8 km).

The stone shell of the Earth does not constitute a single whole. It consists of separate blocks – Lithospheric plates.In total, there are 7 large and slightly smaller plates on the globe. The majority include Eurasian, North American, South American, African, Indo-Australian (Indian), Antarctic and Pacific plates. Within all major plates, with the exception of the latter, the continents are located. The boundaries of lithospheric plates pass, as a rule, along the mid-ocean ridges and deep-sea gutters.

Lithospheric platesconstantly change: two plates can be saved into a single collision; As a result of the rifting, the slabs can occur on several parts. Lithospheric plates can be immersed in the land mantle, reaching the earthly kernel. Therefore, the separation of the earth's crust on the stove is not definitely: with the accumulation of new knowledge, some borders of the slabs are recognized as non-existent, new plates are distinguished.

Within lithospheric plates there are areas with different types of earth's crust.So, the eastern part of the Indo-Australian (Indian) plate is mainland, and the Western is located at the base of the Indian Ocean. At the African Plate, the continental terrestrial crust is surrounded by oceanic. The mobility of the atmospheric plate is determined by the ratio within its limits of the mainland and oceanic crust.

When colliding lithospheric slabs occurs folding of layers of rocks. Folded belts – Movable, strongly dissected areas of the earth's surface. In their development, two stages are allocated. At the initial stage, the Earth Bark experiences predominantly lowering, sedimentary rocks and their metamorphization occur. At the final stage, lowering is replaced by a raising, rock rocks are crushed into the folds. During the last billion years on Earth there were several epochs of intensive properties: Baikal skills, Caledonian, Gersinskoye, Mesozoic and Cenozoic. In accordance with this, different collaboration areas are distinguished.

Subsequently, rocks from which the folded area loses mobility and begin to collapse. The surface accumulates sedimentary rocks. Sustainable parts of the earth's crust are formed – platforms. They usually consist of a folded foundation (residues of ancient mountains), blocked on top of the layers of horizontally occurring sedimentary rocks forming a cover. In accordance with the age of the foundation, ancient and young platforms are distinguished. Plots of rocks, where the foundation is immersed on the depth and blocked by sedimentary rocks, called plates. The location of the foundation on the surface is called shields. They are more characteristic of ancient platforms. At the base of all the mainland, ancient platforms are located, the edges of which are folded areas of different ages.

Distribution of platform and folded areas can be seen on the tectonic geographic map, or on the map of the structure of the earth's crust.

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I can not say that the school was the place of incredible discoveries for me, but there were really memorable moments in the lessons. For example, once in the lesson of literature, I leafed by a textbook on geography (do not ask), and somewhere in the middle I found the chapter about the differences in the oceanic and mainland bark. I really surprised me this information. So I remember.

Oceanic crust: properties, layers, thickness

It is common, as obviously, under the oceans. Although under some seas is not even oceanic, but the continental bark. This applies to those seas that are located above the continental shelf. Some underwater plateau - microcontinents in the ocean are also composed of mainland, and not oceanic cortex.

But most of our planet is still covered by the ocean bark. The average thickness of its layer: 6-8 km. Although there are places with a thickness and 5 km, and 15 km.

It consists of three main layers:

sedimentary;
basalt;
gabbro-Serpentinite.

Material earth bark: properties, layers, thickness

It is also called continental. It takes less square than the oceanic, but at times exceeds it in thickness. On the smooth areas, the thickness ranges from 25 to 45 km, and in the mountains can reach 70 km!

It has from two to three layers (bottom up):

nizhny ("basalt", it is also granulite-baasing);
top (granite);
"Case" from sedimentary rocks (not always).

Those areas of the bark where the "case" breed is missing, called shields.

The puff structure resembles oceanic, but it can be seen that the basis of them is completely different. The granite layer, the comprehensive part of the continental cortex, the oceanic is absent as such.

It should be noted that the names of the layers are sufficiently conditional. This is due to the difficulties of studying the composition of the earth's crust. The drilling capabilities are limited, so the deep layers were initially studied and studied not so much according to the "live" samples, as in the speed of passing seismic waves. Passage speed, like granite? Let's call granite, it means. How much "granite" is the composition, it is difficult to judge.

The characteristic feature of the evolution of the Earth is the differentiation of the substance, the expression of which serves as the shell structure of our planet. Lithosphere, hydrosphere, atmosphere, the biosphere form the main shells of the Earth, characterized by the chemical composition, power and condition of the substance.

The inner structure of the Earth

Chemical composition of the Earth (Fig. 1) is similar to the composition of other planets of the earth group, such as Venus or Mars.

In general, elements such as iron, oxygen, silicon, magnesium, nickel prevail. The content of light elements is small. The average density of the substance of the Earth is 5.5 g / cm 3.

The internal structure of the land of reliable data is very little. Consider Fig. 2. He depicts the internal structure of the Earth. The earth consists of the earth's crust, mantle and core.

Fig. 1. Chemical composition of the Earth

Fig. 2. The internal structure of the Earth

Core

Core (Fig. 3) is located in the center of the Earth, its radius is about 3.5 thousand km. The kernel temperature reaches 10,000 K, i.e. it is higher than the temperature of the outer layers of the Sun, and its density is 13 g / cm 3 (compare: water is 1 g / cm 3). The core presumably consists of iron and nickel alloys.

The external core of the Earth has a greater power than the internal (radius of 2,200 km) and is in a liquid (molten) state. The inner core is susceptible to colossal pressure. The substances that lay it are in a solid state.

Mantle

Mantle - The geosphere of the Earth, which surrounds the kernel and is 83% of our planet (see Fig. 3). The lower an annilateral is located at a depth of 2900 km. Mantle is divided into a less dense and plastic top (800-900 km), which is formed magma (translated from Greek means "thick ointment"; this is the molten substance of the earth's subsoil - a mixture of chemical compounds and elements, including gases, in a special semi-liquid state); And the crystal lower, tire about 2000 km.

Fig. 3. The structure of the Earth: the core, mantle and earth

Earth's crust

Earth's crust - The outer shell of the lithosphere (see Fig. 3). Its density is about two times less than the average density of the Earth, 3 g / cm 3.

From the mantle of the earth boron separates Border Mochorovichich (It is often referred to as the moss boundary), characterized by a sharp increase in the rates of seismic waves. It was installed in 1909. Croatian scientists Andrey Mohovichichich (1857- 1936).

Since the processes occurring in the upper part of the mantle affect the movement of the substance in the earth's crust, they are combined under the general name. Lithosphere(Stone shell). Lithosphere power ranges from 50 to 200 km.

Below the lithosphere is located Asthenosphere - Less solid and less viscous, but more plastic shell with a temperature of 1200 ° C. It can cross the border of Mokho, embedded in the earth's bark. Asthenosphere is a source of volcanism. It contains the foci of molten magma, which is embedded in the earth's bark or poured onto the earth's surface.

The composition and structure of the earth's crust

Compared to the mantle and the core, the earth's crust is a very thin, rigid and fragile layer. It is composed of a lighter substance, which currently discovered about 90 natural chemical elements. These elements are not equally represented in the earth's crust. On seven elements - oxygen, aluminum, iron, calcium, sodium, potassium and magnesium - accounting for 98% of the mass of the earth's crust (see Fig. 5).

A peculiar combinations of chemical elements form various rocks and minerals. The age of the most ancient of them has at least 4.5 billion years.

Fig. 4. The structure of the earth's crust

Fig. 5. The composition of the earth's crust

Mineral - It is relatively homogeneous in its composition and properties of the natural body, sampled both in depths and on the surface of the lithosphere. Examples of minerals are diamond, quartz, gypsum, talc, etc. (the characteristic of the physical properties of various minerals can be found in Appendix 2.) The composition of the earth minerals is shown in Fig. 6.

Fig. 6. General mineral composition of the Earth

Rocks Consist of minerals. They can be designed both from one and from several minerals.

Sedimentary rocks - Clay, limestone, chalk, sandstone, etc. - formed by precipitation of substances in the aquatic environment and on land. They are laying. Geologists refer to their pages of the Earth's history, as it can be found about natural conditions that existed on our planet in ancient times.

Among sedimentary rocks, organogenic and non-naigneous (chip and chemogenic) are distinguished.

Organogenic Mountain breeds are formed as a result of the accumulation of remains of animals and plants.

Chip rocks It is formed as a result of weathered, psswing with water, ice, or wind products of destruction of previously arising rock rocks (Table 1).

Table 1. Chip rocks depending on the size of the debris

Breed name	Babr size con (particles)
	More than 50 cm


	5 mm - 1 cm
	1 mm - 5 mm
Sand and sandstone	0.005 mm - 1 mm
	Less than 0.005 mm

Chemogenic Mountain breeds are formed as a result of sedimentation of the seas and lakes dissolved in them substances.

In the thickness of the earth's crust from magma are formed Magmatic rocks (Fig. 7), for example, granite and basalt.

Sedimentary and magmatic rocks at high depths under the influence of pressure and high temperatures are subjected to significant changes, turning into Metamorphic rocks. So, for example, limestone turns into marble, quartz sandstone - in quartzite.

In the structure of the earth's crust, three layers are distinguished: sedimentary, "granite", "basalt".

Sedimentary layer (See fig. 8) is formed mainly by sedimentary rocks. Clay and clay slates are dominated here, sandy, carbonate and volcanogenic rocks are widely represented. In the sedimentary layer there are deposits of such mineral, Like stone coal, gas, oil. All of them organic origin. For example, stone coal is a product of conversion of plants ancient times. The power of the sedimentary layer varies widely - from the complete absence in some areas of sushi to 20-25 km in deep depressions.

Fig. 7. Classification of rocks by origin

"Granite" layer It consists of metamorphic and magmatic rocks close to their properties to granite. The most common gneisses, granites, crystal slates, etc. There is no granite layer not everywhere, but on continents, where it is well expressed, its maximum power can reach several tens of kilometers.

"Basalt" layer Educated rocks close to basalts. These are metamorphized magmatic rocks, more denser compared to the rocks of the "granite" layer.

The power and vertical structure of the earth's crust are different. Several types of earth's crust are isolated (Fig. 8). According to the easiest classification, the oceanic and mainland terrestrial bark differ.

Continental and ocean bark are different in thickness. So, the maximum thickness of the earth's crust is observed under the mining systems. It is about 70 km. Under the plains, the power of the earth's crust is 30-40 km, and under the oceans it is the most thin - only 5-10 km.

Fig. 8. Types of the earth's crust: 1 - water; 2- sedimentary layer; 3 - Moving sedimentary breeds and basalts; 4 - basalts and crystalline ultrasound breeds; 5 - granite-metamorphic layer; 6 - granulite-basite layer; 7 - Normal mantle; 8 - Splitted Mantle

The difference in the continental and ocean terrestrial crust in the composition of the rocks is manifested in the fact that the granite layer is absent in the oceanic cortex. And the basalt layer of the oceanic crust is very peculiar. In the composition of the breed, it is different from the similar layer of continental cortex.

The boundary of the sushi and ocean (zero mark) does not fix the transition of the continental earth crust into the oceanic. The substitution of the continental bark of the oceanic occurs in the ocean at about a depth of 2450 m.

Fig. 9. The structure of the mainland and oceanic crust

The transitional types of the earth's crust are isolated - subochanic and subcontinental.

Suboxian bark Located along the continental slopes and fit, it can occur in the outskirts and Mediterranean seas. It is a continental cohere with a capacity of up to 15-20 km.

Subcontinental bark Located, for example, on volcanic island arcs.

Based on seismic sensing - The speed of passing seismic waves - we receive data on the deep structure of the earth's crust. So, the Kola ultra-deep well, first allowed to see the species of rocks from the depth of more than 12 km, brought a lot of unexpected. It was assumed that the "basalt" layer should begin at a depth of 7 km. In fact, it was not discovered, and Gneus prevailed among rocks.

Change in the temperature of the earth's crust with depth. The near-surface layer of the earth's crust has a temperature determined by solar heat. it Heliometric layer (from Grech. Helio - Sun), experiencing seasonal temperature fluctuations. Its average power is about 30 m.

Below is an even thinner layer, a characteristic feature of which is a constant temperature corresponding to the average annual temperature of observation location. The depth of this layer increases under continental climate.

Even deeper in the earth's crust, the geothermal layer is allocated, the temperature of which is determined by the inner heat of the Earth and with depth increases.

An increase in temperature occurs mainly due to the decay of radioactive elements included in rocks, primarily radium and uranium.

The magnitude of the increase in the temperature of rocks with depth is called geothermal gradient. It fluctuates in fairly wide limits - from 0.1 to 0.01 ° C / M - and depends on the composition of rocks, the conditions for their occurrence and a number of other factors. Under the oceans, the temperature with a depth increases faster than on continents. On average, each 100 M depths is warmer at 3 ° C.

The value inverse the geothermal gradient is called geothermal step. It is measured in m / ° C.

The heat of the earth's crust is an important energy source.

Part of the earth's crust extending the depths available for geological study forms bowels of the earth. Earth's subsoil require special protection and reasonable use.

- limited to the surface of the sushi or the bottom of the World Ocean. It also has a geophysical border, which is the section Mocho. The boundary is characterized by the fact that the speeds of seismic waves are sharply increasing. Installed it at $ 1909 $ Croatian scientist A. Mochorovichich ($1857$-$1936$).

Ground Craer Factory sedimentary, magmatic and metamorphic rock rocks, and in composition it is highlighted in it Three layers. Mountain breeds of sedimentary origin, the destroyed material of which was transferred to the lower layers and formed sedimentary layer The earth's crust covers the entire surface of the planet. In some places it is very thin and maybe interrupted. In other places, it reaches the power of several kilometers. The sediments are clay, limestone, chalk, sandstone, etc. They are formed by deposition of substances in water and on land, they are usually layered. By sedimentary rocks, you can learn about the natural conditions that existed on the planet, so geologists call them pages of land history. Sedimentary breeds are divided into organogenicwhich are formed by accumulating the remains of animals and plants and nonorganogenicwhich in turn are divided into Chip and chemogenic.

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Chlutical breeds are a product of weathered, and chemogenic - The result of precipitation of substances dissolved in the water seas and lakes.

Magmatic breeds are found Granitis layer of earthly bark. These breeds were formed as a result of frozen melted magma. On continents, the power of this layer $ 15 $ is $ 20 $ km, it is completely absent or very much reduced under the oceans.

Magmatic substance, but poor silica fighters basaltic A layer having a large proportion. This layer is well developed at the base of the earth's crust of all regions of the planet.

The vertical structure and power of the earth's crust are different, so there are several types of its types. On a simple classification exists oceanic and mainland Earth's crust.

Mainland earth bark

The mainland or continental bark is different from the oceanic cortex Thick and device. The continental bark is located under the mainland, but its land does not coincide with the coastline. From the point of view of geology, this mainland is the entire area of \u200b\u200bsolid mainland bark. Then it turns out that geological continents are more geographical mainland. Coastal zones of continents, called shelf - It is temporarily filled with the sea parts of the mainland. Such seas like white, East Siberian, Azov - are located on the mainland shelf.

Three layers are allocated in the continental earth crust:

Top layer - sedimentary;
The middle layer is granite;
Nizhny layer - basalt.

Under the young mountains, such a type of bark has a thickness of $ 75 $ km, under the plains - up to $ 45 $ km, and under island arcs - up to $ 25 $ km. The upper sedimentary layer of the mainland cortex is formed by clay sediments and carbonates of shallow marine pools and thorough-grained facies in the boundary deflection, as well as on the passive outskirts of the continents of the Atlantic type.

Invgested in the cracks of the earth's crust of Magma formed granite layer As part of which there is silica, aluminum and other minerals. The thickness of the granite layer can reach up to $ 25 $ km. This layer is very ancient and has a solid age - $ 3 $ billion. Between the granite and basalt layer, at a depth of $ 20 $ km, the border is traced. Conrad.. It is characterized by the fact that the speed of propagation of longitudinal seismic waves increases here, by $ 0.5 $ km / s.

Formation Basalt The layer occurred as a result of the exhaustion on the surface of the sushi of basalt lava in the zones of intraple magmatism. Basalts contain more iron, magnesium and calcium, so they are heavier granite. Within this layer, the speed of propagation of longitudinal seismic waves from $ 6.5 $ - $ 7.3 $ km / sec. Where the border becomes blurred, the speed of longitudinal seismic waves grows gradually.

Note 2.

The total mass of the earth's crust of the entire planet is only $ 0.473 $%.

One of the first tasks associated with the determination of the composition top continental bark, took to solve a young science geochemistry. Since the bark consists of a variety of variety of breeds, this task was very complex. Even in the same geological body, the composition of rocks can vary greatly, and different types of breeds can be distributed in different areas. Based on this, the task was to determine the general one average That part of the earth's crust, which on the continents goes to the surface. This first assessment of the composition of the upper terrestrial crust did Clark. He worked as an employee of the US geological service and was engaged in chemical analysis of rocks. In the course of many years of analytical work, he managed to summarize the results and calculate the average composition of the rocks that was close to granite. Work Clark He was tough criticism and had opponents.

The second attempt to determine the average composition of the earth's crust did V. Goldshmidt. He suggested that moving along the continental crust glacier, It may scrape and mix the rocks overlooking the surface, which during the glacial erosion will be made. They will reflect the composition of the average continental bark. After analyzing the composition of the ribbon clay, which during the last glaciation was put in Baltic Sea, he got the result close to the result Clark. Different methods gave the same estimates. Geochemical methods were confirmed. These questions were engaged, and evaluations were widely recognized Vinogradova, Yaroshevsky, Ronova and others.

Ocean globe

Oceanic bark Located where the depth of the sea is more than $ 4 $ km, which means that it takes not the entire space of the oceans. The rest is covered with a bark intermediate type. The oceanic type bark is not as the continental bark, although it is also divided into layers. It is almost completely absent granite layerAnd the sediment is very thin and has a power of less than $ 1 $ km. Second layer still Unknowntherefore it is called simply second layer. Nizhny, third layer - basaltic. Basalt layers of continental and oceanic crust are similar to the speeds of seismic waves. The basalt layer in the oceanic crust prevails. As the theory of tectonics plates says, the ocean bark is constantly formed in the mid-oceanic ridges, then it moves away from them in the regions subduction absorbed into the mantle. This suggests that the ocean bark is relatively young. The greatest number of subducts zones are characteristic of Pacific Oceanwhere powerful fruitry is connected with them.

Definition 1.

Subduction - This is lowering rocks from the edge of one tectonic plate into a semi-plane asthenosphere

In the case when the top plate is the continental plate, and the bottom - oceanic - formed oceanic chub.
Its thickness in different geographic zones varies from $ 5 $ - $ 7 $ km. Over time, the thickness of the oceanic bark almost does not change. This is due to the amount of melt distinguished from the mantle in the mid-ocean ridges and the thickness of the sedimentary layer at the bottom of the oceans and the seas.

Sedimentary layer Oceanic bark small and rarely exceeds a thickness of $ 0.5 $ km. It consists of sand, deposits of the remains of animals and precipitated minerals. The carbonate rocks of the lower part at high depth are not detected, and at a depth of more than $ 4.5 $ km carbonate rocks are replaced by red deep-water clays and siliceal sludge.

Basalt lava of the crowded composition formed at the top basalt layer, and below lies dike complex.

Definition 2.

Dike - These are channels for which basalt lava is poured onto the surface

Basalt layer in zones subduction turns into eccoliteswhich are immersed in depth, because they have a greater density of surrounding mantle breeds. Their mass is about $ 7 $% of the mass of the entire mantle of the Earth. Within the basalt layer, the speed of longitudinal seismic waves is $ 6.5 $ - $ 7 $ km / sec.

The average age of the oceanic bark is $ 100 $ million, while its oldest sections have an age of $ 156 million and are located in the depression Pedajafet in the Pacific Ocean.The ocean bark is concentrated not only within the fodge of the ocean, it can be in closed pools, for example, the Northern Wpadin of the Caspian Sea. Oceanicthe earth Cora has a total area of \u200b\u200b$ 306 million km.