Plan:
Introduction 2
1. General information about the structure of the Earth and the composition of the earth's crust 3
2. Types of rocks that make up the earth's crust 4
2.1. Sedimentary rocks 4
2.2. Igneous rocks 5
2.3. Metamorphic rocks 6
3. The structure of the earth's crust 6
4. Geological processes occurring in the earth's crust 9
4.1. Exogenous processes 10
4.2. Endogenous processes 10
Conclusion 12
References 13
Introduction
All knowledge about the structure and history of the development of the earth's crust constitutes a subject called geology. The earth's crust is the upper (stone) shell of the Earth, also called the lithosphere (in Greek, "cast" - stone).
Geology as a science is subdivided into a number of independent departments that study certain questions of the structure, development, and history of the earth's crust. These include: general geology, structural geology, geological mapping, tectonics, mineralogy, crystallography, geomorphology, paleontology, petrography, lithology, and mineral geology, including oil and gas geology.
The basic provisions of general and structural geology are the foundation for understanding the issues of oil and gas geology. In turn, the main theoretical provisions on the origin of oil and gas, the migration of hydrocarbons and the formation of their accumulations underlie the search for oil and gas. In the geology of oil and gas, the patterns of distribution of various types of hydrocarbon accumulations in the earth's crust are also considered, which serve as the basis for predicting the oil and gas content of the studied areas and regions and are used in exploration for oil and gas.
In this paper, issues related to the earth's crust will be considered: its composition, structure, processes taking place in it.
1. General information about the structure of the Earth and the composition of the earth's crust
In general, the planet Earth has the shape of a geoid, or an ellipsoid flattened at the poles and equator, and consists of three shells.
In the center is core(radius 3400 km), around which is located mantle in the depth interval from 50 to 2900 km. The inner part of the core is assumed to be solid, iron-nickel composition. The mantle is in a molten state, in the upper part of which there are magma chambers.
At a depth of 120 - 250 km under the continents and 60 - 400 km under the oceans lies a layer of the mantle called asthenosphere. Here the substance is in a state close to melting, its viscosity is greatly reduced. All lithospheric plates seem to float in the semi-liquid asthenosphere, like ice floes in water.
Above the mantle is Earth's crust, the power of which changes dramatically on the continents and in the oceans. The sole of the crust (the surface of Mohorovichich) under the continents is located at an average depth of 40 km, and under the oceans - at a depth of 11 - 12 km. Therefore, the average thickness of the crust under the oceans (excluding the water column) is about 7 km.
The earth's crust is made up mountain porosdy, i.e., mineral communities (polymineral aggregates) that have arisen in the earth's crust as a result of geological processes. Minerals- natural chemical compounds or native elements that have certain chemical and physical properties and have arisen in the earth as a result of chemical-physical processes. Minerals are divided into several classes, each of which combines tens and hundreds of minerals. For example, sulfur compounds of metals form a class of sulfides (200 minerals), salts of sulfuric acid form 260 minerals of the sulfate class. There are classes of minerals: carbonates, phosphates, silicates, the latter of which are the most widespread in the earth's crust and form more than 800 minerals.
2. Types of rocks that make up the earth's crust
So, rocks are natural aggregates of minerals of more or less constant mineralogical and chemical composition, forming independent geological bodies that make up the earth's crust. The shape, size and relative position of mineral grains determine the structure and texture of rocks.
According to the conditions of education (genesis) distinguish: sedimentary,igneous and metamorphic rocks.
2.1. Sedimentary rocks
Genesis sedimentary rocks- either the result of the destruction and redeposition of pre-existing rocks, or precipitation from aqueous solutions (various salts), or - the result of the vital activity of organisms and plants. A characteristic feature of sedimentary rocks is their layering, which reflects the changing conditions of the deposition of geological sediments. They make up about 10% of the mass of the earth's crust and cover 75% of the earth's surface. With sedimentary rocks, St. 3/4 minerals (coal, oil, gas, salts, ores of iron, manganese, aluminum, placers of gold, platinum, diamonds, phosphorites, building materials). Depending on the source material, sedimentary rocks are divided into clastic (terrygenetic), chemogenic, organogenic (biogenic) and mixed.
clastic rocks are formed due to the accumulation of fragments of collapsed rocks, i.e. these are rocks consisting of fragments of older rocks and minerals. According to the size of the fragments, coarse clastic (blocks, crushed stones, gravel, pebbles), sandy (sandstones), silty (siltstones, siltstones) and clayey rocks are distinguished. The most widespread in the earth's crust are clastic rocks such as sands, sandstones, siltstones, and clays.
Chemogenic rocks are chemical compounds that are formed as a result of precipitation from aqueous solutions. These include: limestones, dolomites, rock salts, gypsum, anhydrite, iron and manganese ores, phosphorites, etc.
Organogenic rocks accumulate as a result of the death and burial of animals and plants, i.e. organogenic rocks (from organ and Greek genes - giving birth, born) (biogenic rocks) - sedimentary rocks consisting of the remains of animal and plant organisms or their metabolic products (shell limestone, chalk, fossil coals, oil shale, etc.).
breeds mixed genesis, as a rule, are formed due to a different combination of all the factors considered above. Among these rocks, sandy and clayey limestones, marls (highly calcareous clays), and others stand out.
2.2. Igneous rocks
Genesis igneous rocks- the result of solidification of magma at depth or on the surface. Magma, being molten and saturated with gaseous components, pours out from the upper part of the mantle.
The composition of magma mainly includes the following elements: oxygen, silicon, aluminum, iron, calcium, magnesium, sodium, potassium, hydrogen. Magma contains small amounts of carbon, titanium, phosphorus, chlorine, and other elements.
Magma, penetrating into the earth's crust, can solidify at different depths or pour out onto the surface. In the first case, there are intrusive rocks, in the second - effusive. In the process of cooling hot magma in the layers of the earth's crust, minerals of various structures (crystalline, amorphous, etc.) are formed. These minerals form rocks. For example, at great depths, when magma solidifies, granites are formed, at relatively shallow depths, quartz porphyries, etc.
effusive rocks Formed when magma solidifies rapidly on the Earth's surface or on the seafloor. An example is tuffs, volcanic glass.
intrusive rocks- igneous rocks formed as a result of solidification of magma in the thickness of the earth's crust.
Igneous rocks according to the content of SiO 2 (quartz and other compounds) are divided into: acidic (SiO 2 more than 65%), medium - 65-52%, basic (52-40%) and ultrabasic (less than 40% SiO 2). According to the content of quartz in the rocks, the color of the rocks changes. Acidic acids are usually light in color, basic and ultrabasic are dark to black. Acid rocks include: granites, quartz porphyries; to medium: syenites, diorites, nepheline syenites; to the main ones: gabbro, diabases, basalts; to ultramafic ones: pyroxenes, peridotites and dunites.
2.3. metamorphic rocks
metamorphic rocks are formed as a result of the action of high temperatures and pressures on rocks of a different primary genesis (sedimentary or magmatic), i.e., due to chemical transformations under the influence of metamorphism. Metamorphic rocks include: gneisses, schists, marble. For example, marble is formed due to the metamorphism of the primary sedimentary rock - limestone.
3. The structure of the earth's crust
The earth's crust is conditionally divided into three layers: sedimentary, granite and basalt. The structure of the earth's crust is shown in fig. 1.
1 - water, 2 - sedimentary layer, 3 - granite layer, 4 - basalt layer, 5 - deep faults, igneous rocks, 6 - mantle, M - Mohorovicich (Moho) surface, K - Konrad surface, OD - island arc, SH - mid-ocean ridge
Rice. 1. Scheme of the structure of the earth's crust (according to M.V. Muratov)
Each of the layers is heterogeneous in composition, however, the name of the layer corresponds to the predominant type of rocks, characterized by the corresponding seismic wave propagation velocities.
The top layer is presented sedimentary rocks, where the velocity of propagation of longitudinal seismic waves is less than 4.5 km/s. For the middle granite layer, wave velocities of the order of 5.5-6.5 km / s are characteristic, which experimentally corresponds to granites.
The sedimentary layer is thin in the oceans, but has a significant thickness on the continents (in the Caspian region, for example, according to geophysical data, 20-22 km is assumed).
granite layer absent in oceans where the sediment layer directly overlies basaltic. The basaltic layer is the lower layer of the earth's crust, located between the Konrad surface and the Mohorovichic surface. It is characterized by the propagation velocity of longitudinal waves from 6.5 to 7.0 km/s.
On the continents and oceans, the earth's crust differs in composition and thickness. The continental crust under mountain structures reaches 70 km, on the plains - 25-35 km. In this case, the upper layer (sedimentary) is usually 10-15 km, with the exception of the Caspian and others. Below is a granite layer up to 40 km thick, and at the base of the crust - a basalt layer also up to 40 km.
The boundary between the crust and mantle is called Mohorovicic surface. In it, the speed of propagation of seismic waves increases abruptly. In general terms, the shape of the Mohorovichic surface is a mirror reflection of the topography of the outer surface of the lithosphere: it is higher under the oceans, lower under the continental plains.
Konrad surface(after the Austrian geophysicist W. Konrad, 1876-1962) - the interface between the "granite" and "basalt" layers of the continental crust. The velocity of longitudinal seismic waves when passing through the Konrad surface increases abruptly from about 6 to 6.5 km/sec. In a number of places, the Konrad surface is absent and the seismic wave velocities increase gradually with depth. Sometimes, on the contrary, there are several surfaces of an abrupt increase in velocities.
The oceanic crust is thinner than the continental crust and has a two-layer structure (sedimentary and basalt layers). The sedimentary layer is usually loose, several hundred meters thick, basalt - from 4 to 10 km.
In the transitional regions, where there are marginal seas and island arcs, the so-called transitionbark type. In such areas, the continental crust passes into the oceanic one and is characterized by average layer thicknesses. At the same time, under the marginal sea, as a rule, there is no granite layer, and it can be traced under the island arc.
island arc- an underwater mountain range, the peaks of which rise above the water in the form of an arched archipelago. Island arcs are part of the transition zone from the mainland to the ocean; characterized by seismic activity and vertical movements of the earth's crust.
mid-ocean ridges- the largest relief forms of the ocean floor, forming a single system of mountain structures with a length of over 60 thousand km, with relative heights of 2-3 thousand meters and a width of 250-450 km (in some areas up to 1000 km). They are uplifts of the earth's crust, with strongly dissected ridges and slopes; in the Pacific and Arctic oceans, mid-ocean ridges are located in the marginal parts of the oceans, in the Atlantic - in the middle.
4. Geological processes occurring in the earth's crust
Various geological processes have taken place and are taking place on the earth's surface and inside the earth's crust throughout geological history that affect the formation of mineral deposits.
Sedimentary strata and minerals such as coal, oil, gas, oil shale, phosphorites and others are the result of the activity of living organisms, water, wind, sunlight and everything else associated with them.
In order to form oil, for example, it is first of all necessary to accumulate a huge amount of fossil remains in sedimentary strata, sinking to a considerable depth, where, under the influence of high temperatures and pressures, this biomass is converted into oil or natural gas.
All geological processes are divided into exogenous (surface) and endogenous (internal).
4.1. Exogenous processes
Exogenous processes- this is the destruction of rocks on the surface of the Earth, the transfer of their fragments and the accumulation in the seas, lakes, rivers. Elevated areas of the terrain (mountains, hills) are subject to destruction to a greater extent, and the accumulation of fragments of destroyed rocks, on the contrary, occurs in low areas (depressions, reservoirs).
Exogenous processes occur under the influence of atmospheric phenomena (the effect of precipitation, wind, melting glaciers, the vital activity of animals and plants, the movement of rivers and other water flows, etc.).
Surface processes associated with the destruction of rocks are also called weathering or denudation. Under the influence of weathering, a kind of leveling of the relief occurs, as a result of which exogenous processes are weakened, and in a number of places (on the plains) they practically die out.
4.2. Endogenous processes
Also important in oil formation are endogenous processes, which include various movements of sections of the earth's crust (horizontal and vertical tectonic movements), earthquakes, volcanic eruptions and outpourings of magma (liquid fiery lava) on the surface of the Earth, on the bottom of the seas and oceans, as well as deep faults in the earth's crust, tectonic disturbances, folding, etc. I.e. endogenous processes include processes occurring inside the Earth.
The earth's crust during the course of geological history has been subjected to both vertical oscillatory movements and horizontal movements of lithospheric plates. These global changes in the Earth's stony shell undoubtedly influenced the formation of oil and gas deposits.
Due to vertical movements, large depressions and troughs were formed, where thick layers of sediments accumulated.
The latter, in turn, could produce hydrocarbons (oil and gas). In other areas, on the contrary, large uplifts arose, which are also of interest in terms of oil and gas, since they could accumulate hydrocarbons.
With horizontal displacements of lithospheric plates, some continents merged and others split, which also affected the processes of formation and accumulation of oil and gas. At the same time, in some parts of the earth's crust, favorable conditions arose for the accumulation of significant concentrations of hydrocarbons.
Endogenous processes also include metamorphism, i.e., recrystallization of rocks under the influence of high temperatures and pressures. Metamorphism is divided into three types.
Regional metamorphism- this is a change in the composition of rocks that sink to great depths and are exposed to high temperature and pressure.
Another kind - dynamometamorphism occurs when tectonic lateral pressure acts on rocks, which are crushed, split into tiles and acquire a slate appearance.
In the process of magma intrusion into rocks, there is also contact metamorphism, resulting in partial remelting and recrystallization of the latter near the zone of contact between magmatic melts and host rocks.
Conclusion
Oil and gas forecasting, prospecting and exploration of oil and gas are based on knowledge of the geology of oil and gas, which, in turn, relies on a solid foundation - general and structural geology.
The questions of general geology include the study of the geological age of the layers of the earth's crust, the composition of the rocks that make up the crust, the geological history of the earth, and the geological processes occurring in the depths and on the surface of the planet.
Structural geology studies the structure, movement and development of the earth's crust, the forms of occurrence of rocks, the causes of their occurrence and development.
The conditions for the occurrence of rocks must be known in order to properly approach the identification of mineral deposits, including the discovery of deposits and deposits of oil and gas. It is known that most accumulations of oil and gas are located in anticlines, which are hydrocarbon traps. Therefore, the search for structural oil and gas traps is carried out on the basis of studying the structural features of the earth's crust in the study areas.
List of used literature:
internal structure Lands (4)
Abstract >> GeologyMantle. She, like earthly bark, has a complex structure.Even in the 19th century, it became ... external and internal forces of the Earth. Structure terrestrial bark heterogeneous (Fig. 19). Upper... the waves are small. Rice. 19. Structure terrestrial bark Below, under the continents, there is a granite ...
Mstislavskaya L.P., Pavlinich M.F., Filippov V.P., Fundamentals of Oil and Gas Production, Oil and Gas Publishing House, Moscow, 2003
Mikhailov A.E., "Structural geology and geological mapping", Moscow, "Nedra", 1984
BUILDING Ground ...
The pear shape is characterized by narrow shoulders, small chest and wide hips. If this is your body type, check out what you should wear and what you should avoid. We will advise you on how to focus on the best. But also skillfully hide any figure flaws.
The figure of a pear for many of us is far from uncommon. However, it is enough to know a few simple tricks, thanks to which we will emphasize the correct proportions of the figure. Before you go shopping, read these stylist tips.
Pear figure - characteristic
The pear shape is one of the most popular body types according to men. They have it, in particular, Jennifer Lopez, Shakira, Katie Holmes, Rihanna. Here are the features characteristic of the pear figure:
- small breasts,
- slim waist,
- wide and massive hips,
- slender calves.
Pear figure - what to wear?
One of the most common mistakes with such a figure is wearing wide tunics or sweaters. If you are still making this mistake, then it's time to change your wardrobe.
The pear figure, like the hourglass figure, is characterized by a narrow waist. As a result, she is considered the best female trump card. That is why people of this type of shape should wear appropriate clothing.
Also, you must wear skirts (preferably high-waisted), knee-length or longer dresses, high heels.
However, it is worth paying attention to the details. Blouses are fastened with buttons, ruffles at the neckline, round, square and boat necklines, embroidered appliqués. Beads and beads are materials that can be worn without problems.
Pear shape - what should be avoided?
If you have a pear shape, you should refuse:
- blouses and jackets that reach the hip line,
- short skirts,
- tight shorts,
- skinny jeans,
- ankle length coat.
In this video lesson, everyone will be able to study the topic "The structure of the Earth." Users will learn about how the earth's crust is studied, what properties it has, what layers our planet consists of. The teacher will talk about the structure of the Earth, how it was studied at different times.
2. Mantle.
As we move deeper into the Earth, temperature and pressure increase. In the center of the Earth is the core, its radius is about 3500 km, and the temperature is more than 4500 degrees. The core is surrounded by a mantle, its thickness is about 2900 km. Above the mantle is the earth's crust, its thickness varies from 5 km (under the oceans) to 70 km (under the mountain systems). The earth's crust is the hardest shell. The substance of the mantle is in a special plastic state; this substance can slowly flow under pressure.
Rice. 1. The internal structure of the Earth ()
Earth's crust- the upper part of the lithosphere, the outer solid shell of the Earth.
The earth's crust is made up of rocks and minerals.
Rice. 2. The structure of the Earth and the earth's crust ()
There are two types of earth's crust:
1. Continental (it consists of sedimentary, granite and basalt layers).
2. Oceanic (it consists of sedimentary and basalt layers).
Rice. 3. The structure of the earth's crust ()
The mantle accounts for 67% of the total mass of the Earth and 87% of its volume. Separate the upper and lower mantle. The material of the mantle can move under pressure. Internal heat from the mantle is transferred to the earth's crust.
The core is the deepest part of the Earth. There is an outer liquid core and an inner solid core.
Most of the earth's crust is covered by the waters of the oceans and seas. The continental crust is much larger than the oceanic and has three layers. The upper part of the earth's crust is heated by the sun's rays. At a depth of more than 20 meters, the temperature practically does not change, and then increases.
The most accessible for human study is the upper part of the earth's crust. Sometimes deep wells are made to study the internal structure of the earth's crust. The deepest well is over 12 km deep. Help to study the earth's crust and mines. In addition, the internal structure of the Earth is studied using special instruments, methods, images from space and sciences: geophysics, geology, seismology.
Homework
Paragraph 16.
1. What parts does the Earth consist of?
Bibliography
Main
1. Initial course of geography: Proc. for 6 cells. general education institutions / T.P. Gerasimova, N.P. Neklyukov. - 10th ed., stereotype. - M.: Bustard, 2010. - 176 p.
2. Geography. Grade 6: atlas. - 3rd ed., stereotype. - M.: Bustard, DIK, 2011. - 32 p.
3. Geography. Grade 6: atlas. - 4th ed., stereotype. - M.: Bustard, DIK, 2013. - 32 p.
4. Geography. 6 cells: cont. cards. - M.: DIK, Bustard, 2012. - 16 p.
Encyclopedias, dictionaries, reference books and statistical collections
1. Geography. Modern illustrated encyclopedia / A.P. Gorkin. - M.: Rosmen-Press, 2006. - 624 p.
Literature for preparing for the GIA and the Unified State Examination
1. Geography: an initial course. Tests. Proc. allowance for students 6 cells. - M.: Humanit. ed. center VLADOS, 2011. - 144 p.
2. Tests. Geography. Grades 6-10: Teaching aid / A.A. Letyagin. - M .: LLC "Agency" KRPA "Olimp": "Astrel", "AST", 2001. - 284 p.
Materials on the Internet
1. Federal Institute of Pedagogical Measurements ().
2. Russian Geographical Society ().
4. 900 presentations for children and 20,000 presentations for schoolchildren ().
The earth's crust is the hard surface layer of our planet. It was formed billions of years ago and is constantly changing its appearance under the influence of external and internal forces. Part of it is hidden under water, the other part forms land. The earth's crust is made up of various chemicals. Let's find out which ones.
planet surface
Hundreds of millions of years after the formation of the Earth, its outer layer of boiling molten rocks began to cool and formed the earth's crust. The surface changed from year to year. Cracks, mountains, volcanoes appeared on it. The wind smoothed them out so that after a while they reappeared, but in other places.
Due to the external and internal solid layer of the planet is heterogeneous. From the point of view of structure, the following elements of the earth's crust can be distinguished:
- geosynclines or folded areas;
- platforms;
- marginal faults and deflections.
Platforms are vast, sedentary areas. Their upper layer (up to a depth of 3-4 km) is covered with sedimentary rocks that occur in horizontal layers. The lower level (foundation) is strongly crumpled. It is composed of metamorphic rocks and may contain igneous inclusions.
Geosynclines are tectonically active areas where mountain building processes take place. They arise at the junction of the ocean floor and the continental platform, or in the trough of the ocean floor between the continents.
If mountains form close to the platform boundary, marginal faults and troughs may occur. They reach up to 17 kilometers in depth and stretch along the mountain formation. Over time, sedimentary rocks accumulate here and deposits of minerals (oil, rock and potassium salts, etc.) are formed.
Bark composition
The mass of the bark is 2.8 1019 tons. This is only 0.473% of the mass of the entire planet. The content of substances in it is not as diverse as in the mantle. It is formed by basalts, granites and sedimentary rocks.
99.8% of the earth's crust consists of eighteen elements. The rest account for only 0.2%. The most common are oxygen and silicon, which make up the bulk of the mass. In addition to them, the bark is rich in aluminum, iron, potassium, calcium, sodium, carbon, hydrogen, phosphorus, chlorine, nitrogen, fluorine, etc. The content of these substances can be seen in the table:
Element name
Oxygen
Aluminum
Manganese
Astatine is considered the rarest element - an extremely unstable and poisonous substance. Tellurium, indium, and thallium are also rare. Often they are scattered and do not contain large clusters in one place.
continental crust
The mainland or continental crust is what we commonly refer to as dry land. It is quite old and covers about 40% of the entire planet. Many of its sections reach an age of 2 to 4.4 billion years.
The continental crust consists of three layers. From above it is covered with a discontinuous sedimentary cover. The rocks in it lie in layers or layers, as they are formed due to the pressing and compaction of salt deposits or microbial residues.
The lower and older layer is represented by granites and gneisses. They are not always hidden under sedimentary rocks. In some places they come to the surface in the form of crystalline shields.
The lowest layer consists of metamorphic rocks like basalts and granulites. The basalt layer can reach 20-35 kilometers.
oceanic crust
The part of the earth's crust hidden under the waters of the oceans is called oceanic. It is thinner and younger than continental. By age, the crust does not even reach two hundred million years, and its thickness is approximately 7 kilometers.
The continental crust is composed of sedimentary rocks from deep-sea remnants. Below is a basalt layer 5-6 kilometers thick. Below it begins the mantle, represented here mainly by peridotites and dunites.
Every hundred million years the crust is renewed. It is absorbed in subduction zones and re-formed at mid-ocean ridges with the help of outward minerals.
EARTH'S CRUST, the upper solid shell of the Earth, bounded from below by the Mohorovichich boundary. The term "earth's crust" appeared in the 18th century in the works of M.V. Lomonosov and in the 19th century in the works of C. Lyell; with the development of the contraction hypothesis in the 19th century, it received a certain value in accordance with the idea of cooling the Earth until a crust was formed (J. Dana). The ideas about the composition, structure and physical properties of the Earth's crust are based on geophysical data on the propagation velocities of seismic waves (mainly longitudinal, Vp), which at the Mohorovichich boundary, when moving to the rocks of the Earth's mantle, increase abruptly from 7.5-7.8 km/s to 8.1-8.2 km/s. The nature of the lower boundary of the earth's crust, apparently, is due to a change in the chemical composition of rocks (basic rocks - ultrabasic) or phase transitions (in the gabbro - eclogite system).
The earth's crust is characterized by horizontal heterogeneity (anisotropy), which is expressed in the difference in composition, structure, thickness, and other characteristics of the crust within its individual structural elements: continents and oceans, platforms and folded belts, depressions and uplifts, etc. There are two main types of the earth's crust - continental and oceanic.
The continental crust, distributed within the continents and microcontinents in the oceans, has an average thickness of 35-40 km, which decreases to 25-30 km at the continental margins (on the shelf) and in the areas of rifting and increases to 45-75 km in the areas of mountain building. In the continental crust, sedimentary (V p up to 4.5 km/s), "granite" (V p 5.1-6.4 km/s) and "basalt" (V p 6.1-7.5 km/s) layers are distinguished. The sedimentary layer is absent on shields and smaller uplifts of the basement of ancient platforms, as well as in the axial zones of folded structures. In the depressions of young and ancient platforms, the frontal and intermountain troughs of folded structures, the thickness of the sedimentary layer reaches 10 km (rarely 20-25 km). It is composed mainly of continental and shallow-sea sedimentary rocks less than 1.7 billion years old, as well as plateau basalts (traps), sills of basic igneous rocks, and tuffs. The names of the "granite" and "basalt" layers are conditional and historically associated with the identification of the Konrad boundary (V p 6.2 km/s), which separates the layers in which the velocities of longitudinal seismic waves correspond to the velocities in granite and basalt. Subsequent studies (including ultra-deep drilling) questioned the existence of a clear seismic boundary, so both of these layers are combined into a consolidated crust. The "granite" layer protrudes to the surface within the shields and arrays of platforms and in the axial zones of folded structures; it was also penetrated by ultra-deep drilling (including the Kola super-deep well to a depth of more than 12 km). Its thickness on platforms is 15-20 km, in folded structures 25-30 km. Within the shields of ancient platforms, this layer includes gneisses, various crystalline schists, amphibolites, marbles, quartzites and granitoids, therefore it is often called granite-gneiss (V p 6-6.4 km/s). In the basement of young platforms and within young folded structures, the upper layer of the consolidated crust is composed of less metamorphosed rocks and contains less granites, which is why it is also called granite metamorphic (Vp 5.1-6 km/s). Direct study of the "basalt" layer of the continental crust is impossible. The values of seismic wave velocities, according to which it is distinguished, can be satisfied both by igneous rocks of the basic composition (mafic rocks) and rocks that have experienced a high degree of metamorphism (granulites), therefore the lower layer of the consolidated crust is sometimes called granulite-mafic. The attribution to the earth's crust or upper mantle of rocks with longitudinal seismic wave velocities of more than 7 km/s is debatable. The age of the most ancient rocks of the consolidated crust reaches 4 billion years.
The main differences between the oceanic crust and the continental one are the absence of a "granite" layer, a significantly lower thickness (5-7 km on average), a younger age (Jurassic, Cretaceous, Cenozoic; less than 170 million years), greater lateral uniformity. The oceanic crust, whose structure has been studied by deep-sea drilling, dredging, and observation from underwater vehicles in fault walls, consists of three layers. The first layer, or sedimentary, consists of pelagic siliceous, carbonate and clayey sediments (Vp 1.6-5.4 km/s). In the direction of the continental foothills, its thickness increases to 10-15 km. The sedimentary layer may be absent in the axial zones of the mid-ocean ridges. In deep-water basins of back-arc basins, some of which are underlain by oceanic crust, the thickness of the sedimentary layer, which usually includes turbidites, can reach 15–20 km. The second layer (V p 4.5-5.5 km/s) in the upper part is composed of basalts (often with pillow-shaped separation - pillow basalts) with rare interlayers of pelagic sediments; in the lower part of the layer, a complex of parallel dolerite dikes is developed (total thickness 1.2-2 km). The third layer (V p 6-7.5 km/s) in the upper part consists of massive gabbro, in the lower part - of a layered complex in which gabbro alternate with ultramafic rocks (total thickness 2-5 km). Within the limits of the internal uplifts of the oceans, the earth's crust is thickened up to 25-30 km due to an increase in the thickness of the second and third layers. Ophiolites are an ancient analogue of the oceanic crust on the continents.
The oceanic crust is formed at the divergent boundaries of lithospheric plates (stretch along the axial parts of the mid-ocean ridges), on which basalt magma rises to the surface and solidifies. Continental crust is formed during the refining of oceanic crust at active continental margins.
In addition to the two main types of the earth's crust, transitional types are distinguished. The suboceanic crust is a continental crust thinned as a result of rifting up to 15-20 km, penetrated by dikes and sills of basic igneous rocks; It is developed along the continental slopes and foothills, and also underlies the deep-water basins of some back-arc basins. Subcontinental crust (underconsolidated, less than 25 km thick) is observed in volcanic island arcs, where oceanic crust turns into continental.
The earth's crust experiences horizontal and vertical tectonic movements. Earthquake centers are located in it, magma chambers are formed, rocks locally or over large areas undergo metamorphism. The tectonic movements of the earth's crust and the endogenous processes occurring in it are due to the existence of a partially molten asthenosphere in the bowels of the earth. Under the influence of tectonic movements and deformations, magmatic activity, metamorphism, exogenous processes (displacement of glaciers, landslides, karst, river erosion, etc.), the rocks of the earth's crust are involved in folded and discontinuous tectonic dislocations. The impact on the rocks of the earth's crust of the atmo-, hydro- and biosphere leads to their weathering.
For the evolution of the earth's crust throughout geological history, see the article Earth.
Lit .: Khain V. E., Lomize M. G. Geotectonics with the basics of geodynamics. 2nd ed. M., 2005; Khain V. E., Koronovsky N. V. Planet Earth from the core to the ionosphere. M., 2007.
