Is it fair to say that the spread of the continental crust. Types of the earth's crust
Types of the Earth's crust: oceanic, continental
The Earth's crust (the solid shell of the Earth above the mantle) consists of two types of crust and has two types of structure: continental and oceanic. The division of the Earth's lithosphere into the crust and upper mantle is rather conditional; the terms oceanic and continental lithosphere are often used.
Earth's continental crust
The continental crust of the Earth (mainland Earth's crust, the earth's crust of the continents) which consists of sedimentary, granite and basalt layers. The earth's crust of the continents has an average thickness of 35-45 km, the maximum thickness is up to 75 km (under mountain ranges).
The structure of the continental crust "American-style" is somewhat different. It contains layers of igneous, sedimentary and metamorphic rocks.
The continental crust has another name "sial" - because. granites and some other rocks contain silicon and aluminum - hence the origin of the term sial: silicon and aluminum, SiAl.
The average density of the crust of the continents is 2.6-2.7 g / cm³.
Gneiss is a (usually loose layered structure) metamorphic rock, composed of plagioclase, quartz, potassium feldspar, and the like.
Granite is "an acidic igneous intrusive rock. It consists of quartz, plagioclase, potassium feldspar and micas" (article "Granite", link - at the bottom of the page). Granites consist of feldspars, quartz. Granites have not been found on other bodies of the solar system.
Oceanic crust of the Earth
As far as is known, no granitic layer has been found in the Earth's crust at the bottom of the oceans; the sedimentary layer of the crust lies immediately on the basaltic layer. The oceanic type of crust is also called "sima", the rocks are dominated by silicon and magnesium - similar to sial, MgSi.
The thickness of the oceanic-type crust (thickness) is less than 10 kilometers, usually 3-7 kilometers. The average density of the sub-oceanic crust is about 3.3 g/cm³.
It is believed that the oceanic is formed in the mid-ocean ridges and absorbed in subduction zones (why, it is not very clear) - as a kind of transporter from the growth line in the mid-ocean ridge to the continent.
8. structure of minerals and mineral aggregates. Genetic types of minerals. Bowen's reaction series. Polymorphism and isomorphism. Paragenesis of minerals. Pseudomorphism of minerals
A mineral is a natural substance, consisting of one element or of a regular combination of elements, formed as a result of natural processes flowing in the depths of the earth's crust or on the surface. Each mineral has a specific structure and has its own physical and chemical characteristics.
Reaction series (Bowen)
- Empirically established by Bowen, the sequence of crystallization of minerals from magma in the form of two reaction series:
1. a discontinuous series of femic minerals: olivine -> orthorhombic pyroxene -> monoclinic pyroxene -> amphibole -> biotite;
2. a continuous series of salic minerals: basic plagioclase -> medium plagioclase -> acid plagioclase -> potassium feldspar. Joint crystallization of minerals of two rows proceeds with the formation of a eutectic, and in this case the sequence of separation depends on the composition of the melt. The reaction series of crystallization of minerals proposed by Bowen may be violated depending on the composition of the melt, on temperature, pressure, and others. conditions.
9. Physical properties of minerals. The chemical composition of minerals
Color. For most minerals, the color changes depending on various impurities.
Line color. This is the color of the mineral in powder. The fact is that not all minerals in a piece and in powder have the same color. In order to obtain a powder, it is enough to draw a mineral over the unglazed surface of a porcelain plate. The color of the line is given only by those minerals whose hardness is lower than the hardness of a porcelain plate.
Transparency. According to the degree of transparency, minerals are divided into groups: (transparent lamellar gypsum, muscovite, halite), through which objects are clearly visible; translucent through which only the contours of objects are visible; translucent, which transmit light, and the contours of objects are indistinguishable; opaque, through which light cannot pass.
Shine. Distinguish between metallic and non-metallic luster.
Cleavage. Cleavage is understood as the ability of a mineral to split in certain directions, forming even or mirror-smooth shiny cleavage planes. There are several types of cleavage: very perfect, perfect, medium or clear and imperfect.
kink- this is the type of surface formed when the mineral is broken. A fracture can be: 1) even - most often in minerals with perfect cleavage (calcite, halite); 2) uneven - characterized by an uneven surface without shiny, jointed areas (apatite); 3) splintery - characteristic of fibrous minerals (fibrous gypsum, hornblende); 4) granular - inherent in minerals of a granular structure (olivine); 5) conchoidal - very characteristic of silicon oxide minerals (quartz, chalcedony, opal); 6) hooked (malachite, native copper); 7) earthy (kaolin, phosphorite).
Hardness. Hardness refers to the resistance that a mineral provides to another mineral or body that crashes into it. This is the most important sign, as it is the most constant.
Density. In the field, minerals are divided into three groups by density: light (up to 2.5), medium (2.5 - 4.0) and heavy (more than 4). The lungs include gypsum, graphite, opal, halite; to medium - quartz, corundum, limonite, calcite, magnesite; to heavy - pyrite, chalcopyrite, magnesite, gold, silver. The most common is the group of minerals of medium specific gravity.
Taste.
0 optical properties. Birefringence has a variety of calcite - Icelandic spar, Labrador has a blue tint on the cleavage planes.
The basis for the classification of minerals is the chemical composition of minerals. On this basis, such classes of minerals are distinguished - Silicates - Oxides - Hydroxides (hydroxides) - Carbonates - Sulfates - Sulfides - Phosphates - Halides - Native elements - Organic compounds
10. The most important diagnostic signs of minerals
The most important characteristics of minerals are their crystal structure and chemical composition. All other properties of minerals follow from them or are interconnected with them. The main properties of minerals that are diagnostic features and allow them to be determined are as follows:
-Crystal Shape and the shape of the faces - are primarily due to the structure of the crystal lattice.
-Hardness. Determined by the Mohs scale
-Shine- the light effect caused by the reflection of part of the light flux incident on the mineral. Depends on the reflectivity of the mineral.
-Cleavage- the ability of a mineral to split along certain crystallographic directions.
-kink- the specificity of the surface of the mineral on a fresh non-cleavage chip.
-Color- a sign that definitely characterizes some minerals (green malachite, blue lapis lazuli, red cinnabar), and is very misleading in a number of other minerals, the color of which can vary over a wide range depending on the presence of impurities of chromophore elements or specific defects in crystal structure(fluorites, quartzes, tourmalines).
-Dash color- the color of a mineral in a fine powder, usually determined by scratching the rough surface of a porcelain biscuit.
magnetism- depends on the content mainly of ferrous iron, is detected using a conventional magnet.
discoloration- a thin colored or multi-colored film that forms on the weathered surface of some minerals due to oxidation.
fragility- the strength of mineral grains (crystals), which is found during mechanical splitting. Fragility is sometimes linked or confused with hardness, which is incorrect. Other very hard minerals can easily split, i.e. be fragile (like a diamond)
These properties of minerals are easily determined in the field.
11. Rock-forming and ore-forming mineral
Rock-forming minerals are the constituent parts rocks, which differ from each other in chemical composition and physical properties.
Among the rock-forming minerals are:
-Characteristic, typomorphic minarals, having exclusively igneous, sedimentary or metamorphic origin.
- Minerals formed during various geological processes and found in rocks of any genesis.
The minerals contained in the composition of rocks are divided into rock-forming and secondary. The first, approximately 40 ... 50 minerals, are involved in the formation of rocks and determine their properties; minor ones are found in them only in the form of impurities. Among the rock-forming are primary and secondary.
The primary ones arose during the formation of rocks, the secondary ones - later as products of the modification of primary minerals.
Minerals have a number of characteristic properties that have a great influence on the technical properties of rocks, among which hardness, cleavage, fracture, luster, color, and density should be highlighted. These properties depend on the structure and strength of bonds in the crystal lattice.
An ore mineral is a mineral containing a metal. Only a few metals are found in elemental form in the native state. Mostly gold, platinum and silver. But the vast majority of metals are found in minerals in combination with other chemical elements. This is observed in sulfides: galena - an ore for lead, zinc, mercury, copper pyrite
- in oxides: hematite, magnetite, pyrolusite, cassiterite, rutile, chromite. They are an important raw material for obtaining metals.
- in carbonates: siderite (ferrous spar) FeCO 3 - ore for iron.
Many ores have complex nature, since they contain two or more minerals with different metals. Thus, copper ore often contains a certain amount of silver and gold and significant amounts of iron.
Minerals play a very important role in human economic activity. important role. Many minerals have great aesthetic appeal, not only when they are cut like gemstones, but also in their natural form. Collection material.
Many minerals are valuable as ore raw materials. This quality of minerals lies in their chemical composition, since it is the chemical composition that determines which elements can be extracted from a mineral by melting or otherwise destroying its structure. For example, chalcocite, galena and sphalerite (copper, lead and zinc sulfides), cassiterite (tin oxide) and many other minerals have such value.
12. genetic types of rocks, their texture, structure, material composition
According to the genetic classification, rocks are divided into three large groups: 1) igneous (magmatic), 2) sedimentary and 3) metamorphic.
1) Igneous rocks formed from molten magma that rose from the depths of the Earth and solidified when it cooled. deep rocks are massive, dense and consist of closely intergrown more or less large crystals; they have high density, high compressive strength and frost resistance, low water absorption and high thermal conductivity. Deep rocks have a granular crystalline structure, also called granite.
- Erupted rocks formed on the surface of the earth in the absence of pressure and with the rapid cooling of magma. in most cases, the erupted rocks consist of individual well-formed crystals interspersed in the main cryptocrystalline mass; such a structure is called porphyritic. In those cases when the outflowing rocks solidified in a thick layer, their structure was similar to deep rocks. If the layer was comparatively thin, then cooling occurred rapidly and their mass turned out to be glassy, and the upper layers of the erupted lava became porous due to the vigorous release of gases from the magma with a decrease in pressure. Clastic rocks were formed during the rapid cooling of crushed lava ejected during volcanic eruptions (pumice, volcanic ash.
2)Sedimentary rocks formed during the deposition of substances from any medium, mainly water. According to the nature of formation and composition, sedimentary rocks are divided into three groups: chemical, organogenic and mechanical.
-Chemical sediments are rocks formed during the precipitation of mineral substances from aqueous solutions with their subsequent compaction and cementation (gypsum, anhydrite, calcareous tuffs, etc.).
-Organogenic rocks were formed as a result of the deposition of the remains of some algae and animal organisms, followed by their compaction and cementation (most limestones, chalk, diatomites, etc.).
-Mechanical deposits formed as a result of sedimentation or accumulation of loose products during the physical and chemical decomposition of rocks. Some of them were further cemented with clay, ferruginous compounds, carbonates or other carbon cements, forming cemented sedimentary rocks - conglomerates, breccias.
3)Metamorphic (species igneous) rocks were formed as a result of more or less deep transformation of igneous or sedimentary rocks under the influence of high temperature and pressure, and sometimes chemical influences.
Under these conditions, recrystallization of minerals can occur without their melting; the resulting rocks are usually denser than the original sedimentary ones. In the process of metamorphism, the structure of rocks changed. In most cases, metamorphic rocks are characterized by a schistose structure.
13. igneous rocks, their classification by chemical and miner. composition, according to the conditions of education. The concept of intrusive, vein and effusive analogues. Structure and texture
The formation of igneous rocks is closely connected with the most complex problems of the origin of magmas and the structure of the Earth.
Depending on the conditions of education
Deep - these are rocks formed during the solidification of magma at different depths in the earth's crust.
- Erupted rocks were formed during volcanic activity, outpouring of magma from the depths and hardening on the surface.
At the heart of chemical classification lies the percentage of silica (SiO 2) in the rock. 1. ultra-acidic, 2. acidic, 3.medium, 4.basic 5.ultrabasic rocks.
Intrusive. The rocks are full-crystalline, with clearly visible crystals. They form batholiths, laccoliths, stocks, sills, and other intrusive bodies.
Effusive. Dense or almost dense porphyritic. Compose lava flows, but also subvolcanic intrusions.
Residential. Porphyritic or finely to microcrystalline. Compose veins, sills, marginal parts of intrusions, small intrusions
Structure- an essential feature that determines the physical and mechanical properties of the rock. The most durable are uniformly granular rocks, while rocks of the same mineral composition, but coarse-grained porphyritic structure, are destroyed faster both under mechanical action and under sharp temperature fluctuations (see Prakt Tetr)
Texture All intrusive rocks have a full-crystalline structure, massive or spotty texture, while effusive rocks have a predominantly glassy, porphyritic, cryptocrystalline structure, massive, slag, amygdaleous texture.
According to the genetic classification, rocks are divided into three large groups: igneous, sedimentary and metamorphic.
14. sedimentary rocks, their classification by origin and material composition. Structures and texture of sedimentary rocks
sedimentary rock It is formed under conditions of redeposition of weathering products and destruction of various rocks, chemical and mechanical precipitation from water, and plant life.
Origin classification:
1) clastic rocks - products of predominantly physical weathering of parent rocks and minerals with subsequent transfer of material and its deposition in other areas;
2) colloid-sedimentary rocks - the result of predominantly chemical decomposition with the transition of a substance into a colloidal state (colloidal solutions);
3) chemogenic rocks - sediments that fall out of aqueous, mostly true, solutions - the waters of the seas, oceans, lakes and other basins chemically, i.e. as a result of chemical reactions or supersaturation of solutions caused by various reasons;
4) biochemical rocks, including rocks formed in the course of chemical reactions with the participation of microorganisms, and rocks that can have a dual origin: chemical and biogenic;
5) organogenic rocks formed with the participation of living organisms;
Classification by composition, structure (notebook practical).
Texture: -layered - the rock consists of heterogeneous in composition, color, density of layers with more or less well-defined boundaries between them
-
porous - rock with an abundance of large holes, caverns, unfilled with secondary minerals
15. metamorphic rocks: mineral composition, structure, texture. Facies of metamorphism
metamorphic rocks- the result of the transformation of rocks of different genesis, leading to a change in the primary structure, texture and mineral composition in accordance with the new physical and chemical environment. The main factors of metamorphism are endogenous heat, all-round pressure, chemical action of gases and fluids. The gradual increase in the intensity of the factors of metamorphism makes it possible to observe all the transitions from primary sedimentary or igneous rocks to the metamorphic rocks formed from them.
STRUCTURE: Metamorphic rocks have a full crystalline structure. The sizes of crystalline grains, as a rule, increase with increasing temperatures of metamorphism.
TEXTURE: - slate texture, due to the mutually parallel arrangement of mineral grains of prismatic or lamellar forms;
- gneissic, or gneissic texture, characterized by alternating strips of different mineral composition;
- in the case of alternating bands consisting of grains of light and colored minerals, the texture is called banded. Externally, these textures resemble the layering of sedimentary rocks, but their origin is not associated with the process of accumulation of sediments, but with recrystallization and reorientation of mineral grains under conditions of oriented pressure. All metamorphic rocks have a dense texture. Since metamorphic rocks similar in composition, structures and textures can be formed due to the change in both igneous and sedimentary rocks,. Facia metamorphism - a set of metamorphic rocks of various compositions that meet certain conditions of formation in relation to the main factors of metamorphism (temperature, lithostatic pressure and partial pressures of volatile components in fluids) involved in metamorphic reactions between minerals .
Types of facies by the name of the main rocks:
1.
greenschist and glaucophane shale (low temperature, medium and high pressures); 2.
epidote-amphibolite and amphibolite (medium temperature, medium and high pressures); 3.
granulite and eclogite (high temperature and pressure); 4.
sanidinite and pyroxene hornfelsic (very high temperature and very low pressure).
17. Exogenous processes. Weathering. Exogenous (external)
processes are called earth's surface or at shallow depths in the earth's crust. These processes are carried out, for example, by flowing waters, glaciers, wind, etc. These processes include two the most important types works: destruction of rocks and their accumulation (accumulation). The nature of the work performed is determined, on the one hand, by the speed of movement and the mass of the geological agent, and on the other hand, by the nature of the rock formations. So, the higher the speed of movement and the mass of the geological agent, the more active the destruction of rocks and the transportation of debris. With a decrease in velocity, the accumulation process begins, and at the beginning the largest particles settle on the surface, and then smaller ones. The main energy sources of exogenous processes are solar radiation and gravity. Since solar radiation over the earth's surface is distributed zonally and unevenly, its arrival varies according to the seasons of the year, then the activity of external processes is subject to the same laws. The work of external forces leads to such a change in the earth's surface, which is aimed at changing the forms created by internal processes. Ultimately, such a change leads to the redistribution of rocks and the leveling of the relief. That is, the protrusions of land created by internal forces are destroyed and lowered, and the fragments of rocks carried away from them accumulate in the oceans and reduce their depth.
weathering called the totality of processes of physical and chemical destruction of rocks and minerals. An important role is played by living organisms. There are two main types of weathering: physical and chemical. . physical weathering leads to successive crushing of rocks into smaller fragments. It can be divided into two groups of processes: thermal and mechanical weathering. Thermal weathering occurs as a result of sharp diurnal temperature changes, leading to the expansion of rocks when heated and contraction when cooled. Thus, the intensity of destruction of rocks is affected by: the magnitude of the daily temperature difference; mineral composition of rocks; coloring of rocks; the size of the mineral grains that make up the rocks. The most intense temperature weathering occurs on exposed high-mountain peaks and slopes, as well as in the desert zone, where, in conditions of low humidity and lack of vegetation, the daily temperature difference on the surface of rocks can exceed 60 ° C. In this case, the process desquamation(peeling) of rock ledges, expressed in the layer-by-layer separation of scales and rock plates parallel to the surface of the ledge.
mechanical weathering It is carried out by freezing water, as well as living organisms and newly formed mineral crystals. The maximum value of water freezing in the pores and cracks of rocks, which at the same time increases in volume by 9 - 10% and wedges the rock into separate fragments. Such weathering is called frosty. It is most active at frequent (daily) temperature transitions through 0°C, observed in high and temperate latitudes and above the snow line in the mountains. Plant roots, burrowing animals, and mineral crystals growing in the pores and cracks of rocks also have a wedging effect on rocks. chemical weathering leads to a change in the mineral composition of rocks or their complete dissolution. The most important factors here are water, as well as the oxygen, carbonic and organic acids contained in it. The greatest activity of chemical weathering processes is observed in humid and hot climates.
As a result of weathering, a special genetic type of deposits is formed on the earth's surface - eluvium- a layer of loose undisplaced weathering products. The composition and thickness of the eluvium are determined by the composition of primary rocks and the time factor, as well as the nature of weathering processes, which, first of all, depends on the climate. Consequently, seasonal rhythm and latitudinal zonality are observed in the development of weathering processes. weathering bark called the totality of eluvial formations of the upper part of the earth's crust.
Plan
1. Earth's crust (continental, oceanic, transitional).
2. The main components of the earth's crust - chemical elements, minerals, rocks, geological bodies.
3. Fundamentals of the classification of igneous rocks.
Earth's crust (continental, oceanic, transitional)
Based on the data of deep seismic soundings, a number of layers are distinguished in the thickness of the earth's crust, characterized by different rates of passage of elastic vibrations. Of these layers, three are considered basic. The uppermost of them is known as a sedimentary shell, the middle one is granite-metamorphic, and the lower one is basalt (Fig.).
Rice. . Diagram of the structure of the crust and upper mantle, including the solid lithosphere
and plastic asthenosphere
Sedimentary layer It is composed mainly of the softest, loose and denser (due to cementation of loose) rocks. Sedimentary rocks are usually arranged in layers. The thickness of the sedimentary layer on the Earth's surface is very variable and varies from a few meters to 10-15 km. There are areas where the sedimentary layer is completely absent.
Granite-metamorphic layer It is composed mainly of igneous and metamorphic rocks rich in aluminum and silicon. Places where there is no sedimentary layer and the granite layer comes to the surface are called crystal shields(Kola, Anabar, Aldan, etc.). The thickness of the granite layer is 20-40 km, in some places this layer is absent (at the bottom of the Pacific Ocean). According to the study of the speed of seismic waves, the density of rocks at the lower boundary from 6.5 km/sec to 7.0 km/sec changes dramatically. This boundary of the granite layer, which separates the granite layer from the basalt layer, is called Conrad borders.
Basalt layer stands out at the base of the earth's crust, is present everywhere, its thickness varies from 5 to 30 km. The density of matter in the basalt layer is 3.32 g/cm 3 , it differs in composition from granites and is characterized by a much lower silica content. At the lower boundary of the layer, there is an abrupt change in the velocity of the passage of longitudinal waves, which indicates a sharp change in the properties of the rocks. This boundary is taken as the lower boundary of the earth's crust and is called the Mohorovichic boundary, as discussed above.
In various parts the globe The earth's crust is heterogeneous both in composition and thickness. Types of the earth's crust - mainland or continental, oceanic and transitional. The oceanic crust occupies about 60%, and the continental crust about 40% of the earth's surface, which differs from the distribution of the areas of the oceans and land (71% and 29%, respectively). This is due to the fact that the boundary between the types of crust under consideration runs along the continental foot. Shallow seas, such as, for example, the Baltic and Arctic seas of Russia, belong to the World Ocean only from a geographical point of view. In the area of the oceans, they distinguish ocean type, characterized by a thin sedimentary layer, under which there is a basalt layer. Moreover, the oceanic crust is much younger than the continental one - the age of the first is no more than 180 - 200 million years. The earth's crust under the continent contains all 3 layers, has a large thickness (40-50 km) and is called mainland. The transitional crust corresponds to the underwater margin of the continents. In contrast to the continental, the granite layer is sharply reduced here and disappears into the ocean, and then the thickness of the basalt layer also decreases.
Sedimentary, granite-metamorphic and basalt layers together form a shell, which received the name sial - from the words silicium and aluminum. It is usually believed that in the sialic shell it is expedient to identify the concept of the earth's crust. It has also been established that throughout the geological history, the earth's crust absorbs oxygen, and to date, it consists of 91% of it by volume.
The main components of the earth's crust are chemical elements, minerals, rocks, geological bodies
The substance of the Earth consists of chemical elements. Within the stone shell, chemical elements form minerals, minerals form rocks, and rocks, in turn, form geological bodies. Our knowledge of the chemistry of the Earth, or otherwise geochemistry, catastrophically decreases with depth. Deeper than 15 km, our knowledge is gradually replaced by hypotheses.
American chemist F.W. Clark together with G.S. Washington, having begun analysis of various rocks (5159 samples) at the beginning of the last century, published data on the average contents of about ten of the most common elements in the earth's crust. Frank Clark proceeded from the position that the solid earth's crust to a depth of 16 km consists of 95% of igneous rocks and 5% of sedimentary rocks formed due to igneous rocks. Therefore, for the calculation, F. Clark used 6000 analyzes of various rocks, taking their arithmetic mean. Subsequently, these data were supplemented by average data on the contents of other elements. It turned out that the most common elements of the earth's crust are (wt.%): O - 47.2; Si - 27.6; Al - 8.8; Fe - 5.1; Ca - 3.6; Na, 2.64; Mg - 2.1; K - 1.4; H - 0.15, which is 99.79% in total. These elements (except hydrogen), as well as carbon, phosphorus, chlorine, fluorine, and some others, are called rock-forming or petrogenic.
Subsequently, these figures were repeatedly specified by various authors (Table).
Comparison of various estimates of the composition of the earth's crust of the continents,
bark type | Upper continental crust | continental crust | |||
Author of Oksida | Clark, 1924 | Goldschmidt, 1938 | Vinogradov, 1962 | Ronov et al., 1990 | Ronov et al., 1990 |
SiO2 | 60,3 | 60,5 | 63,4 | 65,3 | 55,9 |
TiO2 | 1,0 | 0,7 | 0,7 | 0,55 | 0,85 |
Al2O3 | 15,6 | 15,7 | 15,3 | 15,3 | 16,5 |
Fe2O3 | 3,2 | 3,1 | 2,5 | 1,8 | 1,0 |
FeO | 3,8 | 3,8 | 3,7 | 3,7 | 7,4 |
MNO | 0,1 | 0,1 | 0,1 | 0,1 | 0,15 |
MgO | 3,5 | 3,5 | 3,1 | 2,9 | 5,0 |
CaO | 5,2 | 5,2 | 4,6 | 4,2 | 8,8 |
Na2O | 3,8 | 3,9 | 3,4 | 3,1 | 2,8 |
K2O | 3,2 | 3,2 | 3,0 | 2,9 | 1,4 |
P2O5 | 0,3 | 0,3 | 0,2 | 0,15 | 0,2 |
Sum | 100,0 | 100,0 | 100,0 | 100,0 | 100,0 |
Medium mass fractions chemical elements in the earth's crust were named at the suggestion of academician A. E. Fersman clarks. The latest data on the chemical composition of the Earth's spheres are summarized in the following scheme (Fig.).
All matter of the earth's crust and mantle consists of minerals, diverse in form, structure, composition, abundance and properties. Currently, more than 4000 minerals have been isolated. It is impossible to give an exact figure because every year the number of mineral species is replenished with 50-70 names of mineral species. For example, in the territory former USSR about 550 minerals were discovered (320 species are stored in the A.E. Fersman Museum), more than 90% of them in the 20th century.
The mineral composition of the earth's crust is as follows (vol.%): feldspars - 43.1; pyroxenes - 16.5; olivine - 6.4; amphiboles - 5.1; mica - 3.1; clay minerals - 3.0; orthosilicates - 1.3; chlorites, serpentines - 0.4; quartz - 11.5; cristobalite - 0.02; tridymite - 0.01; carbonates - 2.5; ore minerals - 1.5; phosphates - 1.4; sulfates - 0.05; iron hydroxides - 0.18; others - 0.06; organic matter- 0.04; chlorides - 0.04.
These figures are, of course, very relative. In general, the mineral composition of the earth's crust is the most varied and rich in comparison with the composition of deeper geospheres and meteorites, the substance of the Moon and the outer shells of other planets. terrestrial group. So, 85 minerals were found on the moon, and 175 in meteorites.
Natural mineral aggregates that make up independent geological bodies in the earth's crust are called rocks. The concept of "geological body" is a multi-scale concept, it includes volumes from a mineral crystal to continents. Each rock forms a three-dimensional body in the earth's crust (layer, lens, array, cover ...), characterized by a certain material composition and a specific internal structure.
The term "rock" was introduced into Russian geological literature at the end of the 18th century by Vasily Mikhailovich Severgin. The study of the earth's crust has shown that it is composed of various rocks, which by origin can be divided into 3 groups: igneous or igneous, sedimentary and metamorphic.
Before proceeding to the description of each of the groups of rocks separately, it is necessary to dwell on their historical relationships.
It is generally accepted that the original globe was a molten body. From this primary melt or magma, the solid earth's crust was formed by cooling, at the beginning it was composed entirely of igneous rocks, which should be considered as the historically most ancient group of rocks.
Only in a later phase of the development of the Earth could rocks of a different origin arise. This became possible after the emergence of all its outer shells: the atmosphere, hydrosphere, biosphere. Primary igneous rocks under their influence and solar energy were destroyed, the destroyed material was moved by water and wind, sorted and cemented again. This is how sedimentary rocks arose, which are secondary to igneous rocks, due to which they were formed.
Both igneous and sedimentary rocks served as the material for the formation of metamorphic rocks. As a result of various geological processes there was a subsidence of large sections of the earth's crust, within these areas there was an accumulation of sedimentary rocks. In the course of these subsidences, the lower parts of the sequence fall to ever greater depths into the area of high temperatures and pressures, into the area of penetration of various vapors and gases from the magma and the circulation of hot water solutions, introducing new chemical elements into the rocks. The result of this is metamorphism.
The distribution of these breeds is not the same. It is estimated that the lithosphere is 95% composed of igneous and metamorphic rocks and only 5% is sedimentary rocks. On the surface, the distribution is somewhat different. Sedimentary rocks cover 75% of the earth's surface and only 25% are igneous and metamorphic rocks.
The continental crust, both in composition and structure, differs sharply from the oceanic one. Its thickness varies from 20-25 km under island arcs and areas with a transitional type of crust to 80 km under the young folded belts of the Earth, for example, under the Andes or the Alpine-Himalayan belt. On average, the thickness of the continental crust under the ancient platforms is approximately 40 km, and its mass, including the subcontinental crust, reaches 2.2510 × 25 g. The relief of the continental crust is very complex. However, it distinguishes vast sediment-filled plains, usually located above the Proterozoic platforms, protrusions of the most ancient (Archaean) shields, and younger mountain systems. The relief of the continental crust is also characterized by maximum height differences, reaching 16-17 km from the foot of the continental slopes in deep-water trenches to the highest mountain peaks.
The structure of the continental crust is very heterogeneous, however, as in the oceanic crust, in its thickness, especially in ancient platforms, three layers are sometimes distinguished: the upper sedimentary and two lower layers composed of crystalline rocks. Under the young mobile belts, the structure of the crust is more complex, although its general dissection approaches two-layer.
The sedimentary layer on the continents has been studied quite fully both with the help of geophysical exploration methods and direct drilling. The structure of the surface of the consolidated crust in places where it was exposed on ancient shields was studied both by direct geological and geophysical methods, and on continental platforms covered by sediments, mainly by geophysical research methods. Thus, it was found that the velocities of seismic waves in the layers of the earth's crust increase from top to bottom from 2-3 to 4.5-5.5 km / s in the lower sedimentary strata; up to 6-6.5 km/s in the upper layer of crystalline rocks and up to 6.6-7.0 km/s in the lower layer of the crust. Almost everywhere, the continental crust, like the oceanic one, is underlain by high-velocity rocks of the Mokhorovichich boundary with seismic wave velocities from 8.0 to 8.2 km/s, but these are already properties of the subcrustal lithosphere composed of mantle rocks.
The thickness of the upper sedimentary layer of the continental crust varies over a wide range - from zero on ancient shields to 10-12 and even 15 km on the passive margins of the continents and in the marginal troughs of the platforms. The average thickness of sediments on stable Proterozoic platforms is usually close to 2-3 km. The sediments on such platforms are dominated by clayey sediments and carbonates from shallow marine basins. In foredeeps and on the passive margins of Atlantic-type continents, sedimentary sections usually begin with coarse clastic facies, which are replaced upstream by sandy-argillaceous deposits and carbonates of coastal facies. Both at the base and in the uppermost parts of the sections of the sedimentary strata of the marginal troughs, chemogenic sediments are sometimes found - evaporites, which mark the conditions of sedimentation in narrow semi-enclosed marine basins with an arid climate. Typically, such basins appear only at the initial or final stage of the development of marine basins and oceans, if, of course, these oceans and basins at the time of their formation or closure were located in arid climate zones. Examples of the deposition of such formations at the early stages of the formation of oceanic basins are evaporites at the base of sedimentary sections of the African shelf zones in the Atlantic Ocean and salt-bearing deposits of the Red Sea. Examples of the deposition of salt-bearing formations confined to closing basins are the evaporites of the Reno-Hercynian zone in Germany and the Permian salt-gypsum-bearing sequences in the Cis-Ural marginal foredeep in the east of the Russian Platform.
The upper part of the section of the consolidated continental crust is usually represented by ancient, mainly Precambrian rocks of granite-gneiss composition or alternation of granitoids with belts of greenstone rocks of basic composition. Sometimes this part of the section of the hard crust is called the "granite" layer, thereby emphasizing the predominance of rocks of the granitoid series in it and the subordination of basaltoids. The rocks of the "granite" layer are usually transformed by processes of regional metamorphism up to and including the amphibolite facies. The upper part of this layer is always a denudation surface, along which the erosion of tectonic structures and igneous formations of the ancient folded (mountainous) belts of the Earth once occurred. Therefore, the overlying sediments on the bedrocks of the continental crust always occur with a structural unconformity and usually with a large time shift in age.
In the deeper parts of the crust (approximately at depths of about 15-20 km), a scattered and unstable boundary is often traced, along which the propagation velocity of longitudinal waves increases by about 0.5 km/s. This is the so-called Konrad boundary, outlining from above the lower layer of the continental crust, sometimes conditionally called "basalt", although we still have very little definite data on its composition. Most likely, the lower parts of the continental crust are composed of rocks of intermediate and basic composition, metamorphosed to amphibolite or even to granulite facies (at temperatures above 600 °C and pressure above 3–4 kbar). It is possible that at the base of those blocks of continental crust that were once formed due to collisions of island arcs, there may be fragments of ancient oceanic crust, including not only basic, but also serpentinized ultrabasic rocks.
The heterogeneity of the continental crust is especially clearly visible even with a simple glance at geological map continents. Usually, separate and closely intertwined blocks of the crust, heterogeneous in composition and structure, are geological structures of different ages - the remains of ancient folded belts of the Earth, successively adjoining each other during the growth of continental masses. Sometimes such structures, on the contrary, are traces of former splits of ancient continents (for example, aulacogenes). Such blocks are usually in contact with each other along suture zones, often called, not very successfully, deep faults.
Studies of the deep structure of the continental crust conducted in the last decade by the seismic method of reflected waves with signal accumulation (COCORT project) have shown that the suture zones separating folded belts of different ages are, as a rule, giant thrust faults. The thrust surfaces, which are steep in the upper parts of the crust, rapidly flatten with depth. Horizontally, such thrust structures are often traced for many tens and up to hundreds of kilometers, while in depth they sometimes approach the very base of the continental crust, marking ancient and now dead zones of lithospheric plate underthrust or associated secondary thrusts.
There are two main types of earth's crust: oceanic and continental. There is also a transitional type of the earth's crust.
Oceanic crust. The thickness of the oceanic crust in the modern geological epoch ranges from 5 to 10 km. It consists of the following three layers:
1) the upper thin layer of marine sediments (thickness is not more than 1 km);
2) middle basalt layer (thickness from 1.0 to 2.5 km);
3) the lower gabbro layer (about 5 km thick).
Continental (continental) crust. The continental crust has more complex structure and greater thickness than the oceanic crust. Its average thickness is 35-45 km, and in mountainous countries it increases to 70 km. It also consists of three layers, but differs significantly from the ocean:
1) the lower layer composed of basalts (about 20 km thick);
2) the middle layer occupies the main thickness of the continental crust and is conditionally called granite. It is composed mainly of granites and gneisses. This layer does not extend under the oceans;
3) the upper layer is sedimentary. Its average thickness is about 3 km. In some areas, the thickness of precipitation reaches 10 km (for example, in the Caspian lowland). In some regions of the Earth, the sedimentary layer is absent altogether and a granite layer comes to the surface. Such areas are called shields (eg Ukrainian Shield, Baltic Shield).
On the continents, as a result of weathering of rocks, a geological formation is formed, called weathering crusts.
The granite layer is separated from the basalt Conrad surface , at which the speed of seismic waves increases from 6.4 to 7.6 km/sec.
The boundary between the earth's crust and mantle (both on the continents and on the oceans) runs along Mohorovichic surface (Moho line). The speed of seismic waves on it jumps up to 8 km/h.
In addition to the two main types - oceanic and continental - there are also areas of a mixed (transitional) type.
On continental shoals or shelves, the crust is about 25 km thick and is generally similar to the continental crust. However, a layer of basalt may fall out in it. In East Asia, in the area of island arcs (the Kuril Islands, the Aleutian Islands, the Japanese Islands, and others), the earth's crust is of a transitional type. Finally, the earth's crust of the mid-ocean ridges is very complex and still little studied. There is no Moho boundary here, and the material of the mantle rises along faults into the crust and even to its surface.
The concept of "earth's crust" should be distinguished from the concept of "lithosphere". The concept of "lithosphere" is broader than "the earth's crust". Into the lithosphere modern science includes not only the earth's crust, but also the uppermost mantle to the asthenosphere, that is, to a depth of about 100 km.
The concept of isostasy . The study of the distribution of gravity has shown that all parts of the earth's crust - continents, mountainous countries, plains - are balanced on the upper mantle. This balanced position is called isostasy (from Latin isoc - even, stasis - position). Isostatic equilibrium is achieved due to the fact that the thickness of the earth's crust is inversely proportional to its density. Heavy oceanic crust is thinner than lighter continental crust.
Isostasy is, in essence, not even an equilibrium, but a striving for equilibrium, continuously disturbed and restored again. So, for example, the Baltic Shield after melting continental ice Pleistocene glaciation rises by about 1 meter per century. The area of Finland is constantly increasing due to the seabed. The territory of the Netherlands, on the contrary, is decreasing. The zero balance line is currently running somewhat south of 60 0 N.L. Modern St. Petersburg is about 1.5 m higher than St. Petersburg during the time of Peter the Great. As data from modern scientific research, even the severity big cities is sufficient for isostatic fluctuations of the territory under them. Consequently, the earth's crust in the areas of large cities is very mobile. In general, the relief of the earth's crust is a mirror reflection of the Moho surface, the soles of the earth's crust: elevated areas correspond to depressions in the mantle, lower areas correspond to more high level its upper limit. So, under the Pamirs, the depth of the Moho surface is 65 km, and in the Caspian lowland - about 30 km.
Thermal properties of the earth's crust . Daily fluctuations in soil temperature extend to a depth of 1.0–1.5 m, and annual fluctuations in temperate latitudes in countries with a continental climate to a depth of 20–30 m. a layer of constant soil temperature. It is called isothermal layer . Below the isothermal layer deep into the Earth, the temperature rises, and this is already caused by the internal heat of the earth's interior. Internal heat does not participate in the formation of climates, but it serves as the energy basis for all tectonic processes.
The number of degrees by which the temperature increases for every 100 m of depth is called geothermal gradient . The distance in meters, when lowered by which the temperature rises by 1 0 C, is called geothermal stage . The value of the geothermal step depends on the relief, the thermal conductivity of rocks, the proximity of volcanic foci, the circulation of groundwater, etc. On average, the geothermal step is 33 m. In volcanic areas, the geothermal step can be only about 5 m, and in geologically calm areas (for example, on platforms) it can reach 100 m.
TOPIC 5. continents and oceans
Continents and parts of the world
Two qualitatively different types of the earth's crust - continental and oceanic - correspond to two main levels of planetary relief - the surface of the continents and the bed of the oceans.
Structural-tectonic principle of allocation of continents. The fundamental qualitative difference between the continental and oceanic crust, as well as some significant differences in the structure of the upper mantle under the continents and oceans, make it necessary to distinguish continents not according to their visible surroundings by oceans, but according to the structural-tectonic principle.
The structural-tectonic principle states that, firstly, the mainland includes a continental shelf (shelf) and a continental slope; secondly, at the heart of each continent there is a core or an ancient platform; thirdly, each continental block is isostatically balanced in the upper mantle.
From the point of view of the structural-tectonic principle, the mainland is an isostatically balanced array of the continental crust, which has a structural core in the form of an ancient platform, to which younger folded structures adjoin.
In total, there are six continents on Earth: Eurasia, Africa, North America, South America, Antarctica and Australia. Each continent contains one platform, and there are six of them at the heart of Eurasia: East European, Siberian, Chinese, Tarim (Western China, the Takla-Makan desert), Arabian and Hindustan. The Arabian and Hindustan platforms are parts of ancient Gondwana that joined Eurasia. Thus, Eurasia is a heterogeneous anomalous continent.
The boundaries between the continents are quite obvious. The border between North America and South America runs along the Panama Canal. The border between Eurasia and Africa is drawn along the Suez Canal. The Bering Strait separates Eurasia from North America.
Two rows of continents . AT modern geography the following two rows of continents are distinguished:
1. Equatorial series of continents (Africa, Australia and South America).
2. Northern row of continents (Eurasia and North America).
Outside these rows remains Antarctica - the southernmost and coldest continent.
The current location of the continents reflects the long history of the development of the continental lithosphere.
The southern continents (Africa, South America, Australia and Antarctica) are parts ("fragments") of the Gondwana megacontinent that was united in the Paleozoic. The northern continents at that time were united into another megacontinent - Laurasia. Between Laurasia and Gondwana in the Paleozoic and Mesozoic was a system of vast marine basins, called the Tethys Ocean. The Tethys Ocean stretched from North Africa, through southern Europe, the Caucasus, Asia Minor, the Himalayas to Indochina and Indonesia. In the Neogene (about 20 million years ago), an Alpine folded belt arose on the site of this geosyncline.
According to its large size, the supercontinent Gondwana. According to the law of isostasy, it had a thick (up to 50 km) earth's crust, which was deeply immersed in the mantle. Beneath them, in the asthenosphere, convection currents were especially intense, the softened substance of the mantle moved actively. This led first to the formation of a swelling in the middle of the continent, and then to its splitting into separate blocks, which, under the influence of the same convection currents, began to move horizontally. As proved mathematically (L. Euler), the movement of the contour on the surface of the sphere is always accompanied by its rotation. Consequently, parts of Gondwana not only moved, but also unfolded in geographic space.
The first split of Gondwana occurred at the border of the Triassic and Jurassic (about 190-195 million years ago); Afro-America seceded. Then, on the border of the Jurassic and Cretaceous (about 135-140 million years ago), South America separated from Africa. On the border of the Mesozoic and Cenozoic (about 65-70 million years ago), the Hindustan block collided with Asia and Antarctica moved away from Australia. In the present geological era, the lithosphere, according to neomobilists, is divided into six slab-blocks, which continue to move.
The collapse of Gondwana successfully explains the shape of the continents, their geological similarity, as well as the history of vegetation and wildlife. southern continents.
The history of the split of Laurasia has not been studied as carefully as Gondwana.
The concept of the parts of the world . In addition to the geologically determined division of land into continents, there is also a division of the earth's surface into separate parts of the world that has developed in the process of the cultural and historical development of mankind. In total there are six parts of the world: Europe, Asia, Africa, America, Australia with Oceania, Antarctica. On one mainland of Eurasia there are two parts of the world (Europe and Asia), and two continents of the Western Hemisphere (North America and South America) form one part of the world - America.
The border between Europe and Asia is very conditional and is drawn along the watershed line of the Ural Range, the Ural River, the northern part of the Caspian Sea and the Kuma-Manych depression. Along the Urals and the Caucasus, there are lines of deep faults that separate Europe from Asia.
Area of continents and oceans. The land area is calculated within the current coastline. The surface area of the globe is approximately 510.2 million km2. About 361.06 million km 2 is occupied by the World Ocean, which is approximately 70.8% of the total surface of the Earth. Approximately 149.02 million km 2 falls on land, which is about 29.2% of the surface of our planet.
Area of modern continents characterized by the following values:
Eurasia - 53.45 km 2, including Asia - 43.45 million km 2, Europe - 10.0 million km 2;
Africa - 30.30 million km 2;
North America - 24.25 million km 2;
South America - 18.28 million km 2;
Antarctica - 13.97 million km 2;
Australia - 7.70 million km 2;
Australia with Oceania - 8.89 km 2.
Modern oceans have an area:
Pacific Ocean- 179.68 million km 2;
Atlantic Ocean - 93.36 million km 2;
Indian Ocean- 74.92 million km 2;
The Arctic Ocean - 13.10 million km 2.
Between the northern and southern continents, in accordance with their different origin and development, there is a significant difference in the area and nature of the surface. The main geographical differences between the northern and southern continents are as follows:
1. Incomparable in size with other continents of Eurasia, which concentrates more than 30% of the planet's land.
2. The northern continents have a significant shelf area. The shelf in the Arctic Ocean is especially significant and Atlantic Oceans, as well as in the Yellow, China and Bering Seas of the Pacific Ocean. The southern continents, with the exception of the underwater continuation of Australia in the Arafura Sea, are almost devoid of a shelf.
3.Most of southern continents falls on ancient platforms. AT North America and Eurasia ancient platforms occupy a smaller part total area, and most of it falls on the territories formed by the Paleozoic and Mesozoic mountain building. In Africa, 96% of its territory falls on platform sites and only 4% on mountains of Paleozoic and Mesozoic age. In Asia, only 27% are ancient platforms and 77% are mountains of various ages.
4. The coastline of the southern continents, formed mostly by split cracks, is relatively straight; there are few peninsulas and mainland islands. The northern continents are characterized by an exceptionally winding coastline, an abundance of islands, peninsulas, often reaching far into the ocean. Of the total area, islands and peninsulas account for about 39% in Europe, 25% in North America, 24% in Asia, 2.1% in Africa, South America- 1.1% and Australia (excluding Oceania) - 1.1%.
The continents at one time were formed from massifs of the earth's crust, which, to one degree or another, protrudes above the water level in the form of land. These blocks of the earth's crust have been splitting, moving, and crushing parts of them for more than one million years to appear in the form that we know now.
Today we will consider the largest and smallest thickness of the earth's crust and the features of its structure.
A little about our planet
At the beginning of the formation of our planet, multiple volcanoes were active here, there were constant collisions with comets. Only after the bombardment stopped, the hot surface of the planet froze.
That is, scientists are sure that initially our planet was a barren desert without water and vegetation. Where so much water came from is still a mystery. But not so long ago, large reserves of water were discovered underground, perhaps it was they who became the basis of our oceans.
Alas, all hypotheses about the origin of our planet and its composition are more assumptions than facts. According to the statements of A. Wegener, initially the Earth was covered with a thin layer of granite, which in Paleozoic era transformed into the mainland Pangea. In the Mesozoic era, Pangea began to split into parts, the formed continents gradually sailed away from each other. The Pacific Ocean, Wegener argues, is the remnant of the primary ocean, while the Atlantic and Indian are regarded as secondary.
Earth's crust
The composition of the earth's crust is almost the same as that of our planets. solar system- Venus, Mars, etc. After all, the same substances served as the basis for all the planets of the solar system. And more recently, scientists believe that the collision of the Earth with another planet, called Thea, caused the merger of two celestial bodies, and the moon was formed from the broken fragment. This explains why the mineral composition of the moon is similar to that of our planet. Below we will consider the structure of the earth's crust - a map of its layers on land and in the ocean.
The crust makes up only 1% of the Earth's mass. It mainly consists of silicon, iron, aluminum, oxygen, hydrogen, magnesium, calcium and sodium, and 78 other elements. It is assumed that, in comparison with the mantle and core, the Earth's crust is a thin and fragile shell, consisting mainly of light substances. Heavy substances, according to geologists, descend to the center of the planet, and the heaviest are concentrated in the core.
The structure of the earth's crust and a map of its layers are shown in the figure below.
continental crust
The Earth's crust has 3 layers, each of which covers the previous one with uneven layers. Most of its surface is continental and oceanic plains. The continents are also surrounded by a shelf, which, after a steep bend, passes into the continental slope (the area of the underwater margin of the continent).
The earth's continental crust is divided into layers:
1. Sedimentary.
2. Granite.
3. Basalt.
The sedimentary layer is covered with sedimentary, metamorphic and igneous rocks. The thickness of the continental crust is the smallest percentage.
Types of continental crust
Sedimentary rocks are accumulations that include clay, carbonate, volcanogenic rocks, and other solids. This is a kind of sediment that was formed as a result of certain natural conditions that previously existed on earth. It allows researchers to draw conclusions about the history of our planet.
The granite layer consists of igneous and metamorphic rocks similar to granite in their properties. That is, not only granite makes up the second layer of the earth's crust, but these substances are very similar in composition to it and have approximately the same strength. The speed of its longitudinal waves reaches 5.5-6.5 km/s. It consists of granites, schists, gneisses, etc.
The basalt layer is composed of substances similar in composition to basalts. It is denser in comparison with the granite layer. A viscous mantle of solids flows under the basalt layer. Conventionally, the mantle is separated from the crust by the so-called Mohorovichich boundary, which, in fact, separates the layers of different chemical composition. It is characterized by a sharp increase in the speed of seismic waves.
That is, a relatively thin layer of the earth's crust is a fragile barrier that separates us from the red-hot mantle. The thickness of the mantle itself is on average 3,000 km. Together with the mantle, tectonic plates also move, which, as part of the lithosphere, are a section of the earth's crust.
Below we consider the thickness of the continental crust. It is up to 35 km.
The thickness of the continental crust
The thickness of the earth's crust varies from 30 to 70 km. And if under the plains its layer is only 30-40 km, then under mountain systems reaches 70 km. Under the Himalayas, the thickness of the layer reaches 75 km.
The thickness of the continental crust is from 5 to 80 km and directly depends on its age. Thus, cold ancient platforms (East European, Siberian, West Siberian) have a fairly high thickness - 40-45 km.
Moreover, each of the layers has its own thickness and thickness, which can vary in different areas of the mainland.
The thickness of the continental crust is:
1. Sedimentary layer - 10-15 km.
2. Granite layer - 5-15 km.
3. Basalt layer - 10-35 km.
Temperature of the Earth's crust
The temperature rises as you go deeper into it. It is believed that the temperature of the core is up to 5,000 C, but these figures remain conditional, since its type and composition are still not clear to scientists. As you go deeper into the earth's crust, its temperature rises every 100 m, but its figures vary depending on the composition of the elements and depth. The oceanic crust has a higher temperature.
oceanic crust
Initially, according to scientists, the Earth was covered precisely with an oceanic layer of crust, which is somewhat different in thickness and composition from the continental layer. probably arose from the upper differentiated layer of the mantle, that is, it is very close to it in composition. The thickness of the earth's crust of the oceanic type is 5 times less than the thickness of the continental type. At the same time, its composition in deep and shallow areas of the seas and oceans differs insignificantly from each other.
Layers of the continental crust
The thickness of the oceanic crust is:
1. A layer of ocean water, the thickness of which is 4 km.
2. A layer of loose sediments. The thickness is 0.7 km.
3. A layer composed of basalts with carbonate and siliceous rocks. The average power is 1.7 km. It does not stand out sharply and is characterized by compaction of the sedimentary layer. This version of its structure is called suboceanic.
4. Basalt layer, not different from the continental crust. The thickness of the oceanic crust in this layer is 4.2 km.
The basaltic layer of the oceanic crust in subduction zones (a zone in which one layer of the crust absorbs another) turns into eclogites. Their density is so high that they sink deep into the crust to a depth of more than 600 km, and then sink into the lower mantle.
Considering that the smallest thickness of the earth's crust is observed under the oceans and is only 5-10 km, scientists have long been nurturing the idea to start drilling the crust at the depth of the oceans, which would make it possible to study in more detail internal structure Earth. However, the layer of the oceanic crust is very strong, and research at the depth of the ocean makes this task even more difficult.
Conclusion
The earth's crust is perhaps the only layer that has been studied in detail by mankind. But what is under it still worries geologists. One can only hope that one day the unexplored depths of our Earth will be explored.