Term "Lithosphere" has been used in science since the middle of the 19th century, but modern meaning he acquired less than half a century ago. The Geological Dictionary of the 1955 edition says: lithosphere- the same as the earth's crust. In the dictionary of the 1973 edition and in subsequent: lithosphere… v modern understanding includes the earth's crust ... and tough upper part top mantle Earth. The upper mantle is a geological term for a very large layer; the upper mantle has a thickness of up to 500, according to some classifications - over 900 km, and the lithosphere includes only the upper ones from several tens to two hundred kilometers.
The lithosphere is the outer shell of the "solid" Earth, located below the atmosphere and hydrosphere above the asthenosphere. The thickness of the lithosphere varies from 50 km (under the oceans) to 100 km (under the continents). It contains the earth's crust and the substrate that is part of the upper mantle. The spatial (horizontal) structure of the lithosphere is represented by its large blocks - the so-called. lithospheric plates, separated from each other by deep tectonic faults... Lithospheric plates move horizontally at an average speed of 5-10 cm per year.
Internal structure Of the earth includes three shells: the earth's crust, mantle and core. Such a structure of the Earth was established by remote sensing methods based on measuring the propagation velocity of seismic waves having two components - longitudinal and shear waves.
Earth's crust - a stony shell, composed of a solid with an excess of silica, alkali, water and an insufficient amount of magnesium and iron. It separates from the upper mantle the border of Mohorovicic(Moho layer), on which there is a jump in the velocities of longitudinal seismic waves up to about 8 km / s. This line, established in 1909 by the Yugoslav scientist A. Mohorovich, is believed to coincide with the outer peridotite shell of the upper mantle. The thickness of the earth's crust (1% of the total mass of the Earth) averages 35 km: under the young folded mountains on the continents, it increases to 80 km, and under the mid-ocean ridges it decreases to 6 - 7 km (counting from the surface of the ocean floor).
Mantle represents the largest shell of the Earth in terms of volume and weight, extending from the bottom of the earth's crust to Gutenberg boundaries, corresponding to a depth of approximately 2900 km and taken as the lower boundary of the mantle. The mantle is subdivided into bottom(50% of the Earth's mass) and upper(eighteen%). According to modern concepts, the composition of the mantle is rather uniform due to intense convective mixing by intramantle currents. There are almost no direct data on the material composition of the mantle. It is assumed that it is composed of a molten silicate mass saturated with gases. The velocities of propagation of longitudinal and transverse waves in the lower mantle increase, respectively, up to 13 and 7 km / s. The upper mantle from a depth of 50-80 km (under the oceans) and 200-300 km (under the continents) to 660-670 km is called asthenosphere. This is a layer of increased plasticity of a substance close to the melting point.
Core is a spheroid with an average radius of about 3500 km. There is also no direct information on the composition of the kernel. It is known that it is the most dense shell of the Earth. The core is also subdivided into two areas: external, to a depth of 5150 km, being in a liquid state, and internal - solid. In the outer core, the propagation speed longitudinal waves falls to 8 km / s, and shear waves do not propagate at all, which is taken as a proof of its liquid state... Deeper than 5150 km, the velocity of propagation of longitudinal waves increases and transverse waves pass again. The inner core accounts for 2% of the Earth's mass, and the outer - 29%.
The outer "hard" shell of the Earth, including the earth's crust and the upper part of the mantle, forms lithosphere... Its capacity is 50-200 km.
The lithosphere and the underlying moving layers of the asthenosphere, where intraterrestrial movements of a tectonic nature usually originate and are realized, and also often there are foci of earthquakes and molten magma, are called tectonosphere. The structure and thickness of the earth's crust are not the same: that part of it that can be called continental has three layers (sedimentary, granite and basalt) and an average thickness of about 35 km. Under the oceans, its structure is simpler (two layers: sedimentary and basaltic), the average thickness is about 8 km. Transitional types of the earth's crust are also distinguished (see topic 3).
The opinion that the earth's crust in the form in which it exists is a derivative of the mantle has become firmly established in science. Throughout geological history, there has been a directed irreversible process of enrichment of the Earth's surface with matter from the Earth's interior. Three main types are involved in the structure of the earth's crust. rocks: magmatic, sedimentary and metamorphic.
Igneous rocks are formed in the bowels of the Earth under conditions of high temperatures and pressures as a result of the crystallization of magma. They make up 95% of the mass of the substance that composes the earth's crust. Depending on the conditions in which the magma solidification process took place, intrusive (formed at depth) and effusive (poured onto the surface) rocks are formed. Intrusive includes: granite, gabbro, igneous - basalt, liparite, volcanic tuff, etc.
Sedimentary rocks are formed on the earth's surface in various ways: some of them are formed from the products of destruction of rocks that were formed earlier (clastic: sands, gelenoids), some due to the vital activity of organisms (organogenic: limestones, chalk, shell rock; siliceous rocks, coal and brown coal, some ores), clay (clays), chemical (rock salt, gypsum).
Metamorphic rocks are formed as a result of the transformation of rocks of other origin (igneous, sedimentary) under the influence of various factors: high temperature and pressure in the depths, contact with rocks of a different chemical composition, etc. (gneisses, crystalline schists, marble, etc.).
Most of the volume of the earth's crust is occupied by crystalline rocks of magmatic and metamorphic origin (about 90%). Directly in contact with water, air, takes an active part in geographic processes (thickness - 2.2 km: from 12 km in troughs, up to 400 - 500 m in the ocean bed). The most common are clays and shales, sands and sandstones, carbonate rocks. An important role in the geographic envelope is played by loesses and loesslike loams, which compose the surface of the earth's crust in the non-glacial regions of the northern hemisphere.
In the earth's crust - the upper part of the lithosphere - 90 chemical elements, but only 8 of them are widespread and account for 97.2%. oxygen - 49%, silicon - 26, aluminum - 7.5, iron - 4.2, calcium - 3.3, sodium - 2.4, potassium - 2.4, magnesium - 2.4%.
The earth's crust is divided into separate geologically different-aged, more or less active (dynamically and seismically) blocks, which are subject to constant movement, both vertical and horizontal. Large, relatively stable blocks of the earth's crust with low seismicity and poorly dissected relief are called platforms. They have a crystalline folded basement and a sedimentary cover of different ages. Depending on the age, the platforms are divided into ancient (Precambrian in age) and young (Paleozoic and Mesozoic). Ancient platforms are the cores of modern continents, the general uplift of which was accompanied by a more rapid rise or fall of their individual structures (shields and plates).
Ways of development of the lithosphere.
Until now, there is no unified understanding of the development paths of the lithosphere. There are several tectonic concepts, each of which, although based on indisputable facts, reflects one side of the tectonic history of the Earth, without covering its general course, and contradicts other facts, which, in turn, are successfully explained by another theory. This state of the tectonic problem is explained by the fact that geology and geophysics base their conclusions on the study of continents, which occupy only 29.2% of the Earth, and the study of the ocean floor, i.e. most of the planet has just begun.
1. "Fixists" (from Lat. Motionless, unchanging) argue that the continents have always remained in the places that they occupy now, and they try to explain the entire history of relief, paleoclimates and the organic world from these positions.
2. "Mobilists" (from Lat. - mobile) prove that the blocks of the lithosphere are moving. This theory was especially strengthened in last years in connection with the receipt of new factual materials when exploring the bottom of the oceans.
3. The concept of continental growth at the expense of the ocean floor. Supporters of this concept believe that the original continents were formed in the form of relatively small massifs (now constituting the platforms of the continents), and then grew due to the formation of mountains on the ocean floor, adjacent to the edges of the original "cores" of the land.
4. The increase in the size of the land occurs through the formation of mountains in geosynclines. The geosynclinal process, as one of the main ones in the development of the continental crust, is the basis for further explanation of the development of the land relief.
5. Rotational theory. Since the figure of the Earth does not coincide with the surface of a mathematical spheroid and is rearranged due to uneven rotation, zonal stripes and meridional sectors on a rotating planet are inevitably tectonically unequal, with varying degrees of activity react to tectonic stresses caused by intraterrestrial processes.
Lithospheric plate theory first expressed by E. Bykhanov (1877) and finally developed by the German geophysicist A. Wegener (1912). According to this hypothesis, before the Upper Paleozoic, the earth's crust was collected in the mainland Pangea.At first, this hypothesis (theory of mobilism) conquered everyone, it was accepted with enthusiasm, but after 2-3 decades it turned out that physical properties rocks do not allow such "swimming", and a fat cross was put on the theory of continental drift. Until the 1960s. the dominant system of views on the dynamics and development of the earth's crust was the so-called. fixism theory ( fixus- solid; unaltered; fixed (lat.), which asserted the constant (fixed) position of the continents on the surface of the Earth and the leading role of vertical movements in the development of the earth's crust.
Only by the 60s, when the global system of mid-oceanic ridges had already been discovered, a practically new theory was built, in which from A. Wegener's hypothesis there was only a change in the relative position of the continents, in particular, an explanation of the similarity of the outlines of the continents on both sides of the Atlantic.
The most important difference modern plate tectonics(new global tectonics) from A. Wegener's hypothesis is that A. Wegener's continents were moving along the substance that formed the ocean floor, in the modern theory, plates, which include both land areas and the ocean floor, participate in the movement; the boundaries between the plates can run along the ocean floor, and over land, and along the boundaries of continents and oceans.
The movement of lithospheric plates - spreading(English spreading - expansion, distribution). But the surface the globe cannot increase. The emergence of new sections of the earth's crust on the sides of the mid-oceanic ridges must somewhere be compensated for by its disappearance. If we believe that the lithospheric plates are sufficiently stable, it is natural to assume that the disappearance of the crust, like the formation of a new one, should occur at the boundaries of converging plates. In this case, there can be three different cases:
Two areas of the oceanic crust are converging;
An area of continental crust approaches an area of oceanic crust;
Two areas of the continental crust are converging.
The process that occurs when parts of the oceanic crust approach each other can be schematically described as follows: the edge of one plate rises somewhat, forming an island arc; the other goes under it, here the level of the upper surface of the lithosphere decreases, a deep-sea oceanic trench is formed. Such are the Aleutian Islands and the Aleutian Trench that surrounds them; Kurile Islands and the Kuril-Kamchatka trench; Japanese Islands and Japanese Trench; The Mariana Islands and the Mariana Trench are in Pacific... In the Atlantic - the Antilles and the Puerto Rico trench; South Sandwich Islands and South Sandwich Trench. The movement of plates relative to each other is accompanied by significant mechanical stresses, therefore, in all these places there is a high seismicity, intense volcanic activity... Earthquake foci are located mainly on the contact surface of two plates and can be at great depths. The edge of the slab, which has gone deep into the depths, plunges into the mantle, where it gradually turns into mantle matter. The sinking plate is heated, and magma is melted from it, which is poured into the volcanoes of the island arcs.
The process of immersing one plate under another is called subduction(literally - pushing). Typical example- Cordillera Central and South America and the coastal trench system - Central American, Peruvian and Chilean.
When two sections of the continental crust approach each other, the edge of each of them experiences folding (faults are characteristic, mountains are formed, seismic processes are intense). Volcanism is also observed, but less than in the first two cases, because the earth's crust in such places is very powerful. This is how the Alpine-Himalayan mountain belt was formed, stretching from North Africa and the western tip of Europe through all of Eurasia to Indochina; it includes the most high mountains on the Earth, along its entire length, there is a high seismicity, in the west of the belt there are active volcanoes.
According to the forecast, while maintaining the general direction of movement of the lithospheric plates, the Atlantic Ocean, East African rifts (they will be filled with the waters of the Moscow region) and the Red Sea, which will directly connect the Mediterranean Sea with the Indian Ocean, will expand significantly.
The rethinking of the ideas of A. Wegener led to the fact that, instead of continental drift, the entire lithosphere began to be regarded as a moving solidity of the Earth, and this theory, ultimately, was reduced to the so-called "tectonics of lithospheric plates" (today - "new global tectonics ").
The main provisions of the new global tectonics are as follows:
1. The lithosphere of the Earth, including the crust and the uppermost part of the mantle, is underlain by a more plastic, less viscous shell - the asthenosphere.
2. The lithosphere is divided into a limited number of large, several thousand kilometers across, and medium-sized (about 1000 km) relatively rigid and monolithic plates.
3. Lithospheric plates move relative to each other in the horizontal direction; the nature of these movements can be threefold:
a) spreading (spreading) with filling of the resulting gaping with new oceanic type crust;
b) subduction (subduction) of the oceanic plate under the continental or oceanic plate with the emergence of a volcanic arc or a continental-marginal volcano-plutonic belt above the subduction zone;
c) sliding of one plate relative to another along the vertical plane of the so-called. transform faults, transverse to the axes of the median ridges.
4. The movement of lithospheric plates along the surface of the asthenosphere obeys Euler's theorem, which states that the movement of conjugate points on the sphere occurs along circles drawn with respect to an axis passing through the center of the Earth; the points of exit of the axis to the surface are called the poles of rotation, or opening.
5. On the scale of the planet as a whole, spreading is automatically compensated by subduction, that is, how much new oceanic crust is born during a given period of time, the same amount of older oceanic crust is absorbed in subduction zones, due to which the volume of the Earth remains unchanged.
6. The movement of lithospheric plates occurs under the influence of convective currents in the mantle, including the asthenosphere. Ascending currents are formed under the axes of the spreading of the median ridges; they become horizontal at the periphery of the ridges and descending in subduction zones at the margins of the oceans. Convection itself is caused by the accumulation of heat in the bowels of the Earth due to its release during the decay of naturally radioactive elements and isotopes.
New geological materials on the presence of vertical currents (streams) of molten matter, rising from the boundaries of the core and mantle to the earth's surface, formed the basis for the construction of a new, so-called. "Plume" tectonics, or the plume hypothesis. It is based on the concept of internal (endogenous) energy concentrated in the lower horizons of the mantle and in the outer liquid core of the planet, the reserves of which are practically inexhaustible. High-energy jets (plumes) penetrate the mantle and rush in the form of streams into the earth's crust, thereby determining all the features of tectonic-magmatic activity. Some adherents of the plume hypothesis are even inclined to believe that it is this energy exchange that underlies all physicochemical transformations and geological processes in the body of the planet.
V recent times many researchers are increasingly inclined to believe that the uneven distribution of the endogenous energy of the Earth, as well as the periodization of some exogenous processes, are controlled by external (cosmic) factors in relation to the planet. Of these, the most effective force that directly affects the geodynamic development and transformation of the Earth's matter is apparently the effect of the gravitational effect of the Sun, Moon and other planets, taking into account the inertial forces of the Earth's rotation around its axis and its orbital motion. Based on this postulate centrifugal planetary mill concept allows, firstly, to give a logical explanation of the mechanism of continental drift, and secondly, to determine the main directions of sublithospheric flows.
Lithosphere movements.
The interaction of the earth's crust with the upper mantle is the cause of deep tectonic movements, excited by the rotation of the planet, thermal convection or gravitational differentiation of the mantle material (slow sinking of heavier elements inward and lifting of lighter ones upward), the zone of their appearance to a depth of about 700 km was called tectonosphere.
There are several classifications of tectonic movements, each of which reflects one of the sides - direction (vertical, horizontal), place of manifestation (surface, deep), etc.
From a geographical point of view, the division of tectonic movements into oscillatory (epeirogenic) and fold-forming (orogenic) seems to be successful.
The essence epeirogenic movements boils down to the fact that huge sections of the lithosphere are undergoing slow rise or fall, are substantially vertical, deep, their manifestation is not accompanied abrupt change the initial bedding of rocks.
For the formation of modern landscapes, the oscillatory movements of the recent geological past - the Neogene and the Quaternary period - were of great importance. They got the name newest or neotectonic... The range of neotectonic movements is very significant. In the Tien Shan mountains, for example, their amplitude reaches 12-15 km and without neotectonic movements on the site of this high mountainous country there would be a peneplain - almost a plain that arose on the site of destroyed mountains. On the plains, the amplitude of neotectonic movements is much less, but here, too, many forms of relief - hills and lowlands, the position of watersheds and river valleys - are associated with neotectonics.
The newest tectonics is being manifested at the present time. The speed of modern tectonic movements is measured in millimeters, less often in the first centimeters (in the mountains). On the Russian Plain maximum speeds uplifts up to 10 mm per year are established for the Donbass and the northeast of the Dnieper Upland, maximum subsidence, up to 11.8 mm per year - in the Pechora lowland.
The consequences of epeirogenic movements are:
1. Redistribution of the ratio between the areas of land and sea (regression, transgression). The slow transgression of the sea to steep coasts is accompanied by the development of abrasion(abrasion - cutting off the coast by the sea) of the surface and the abrasive scarp limiting it from the land side.
2. Due to the fact that vibrations of the earth's crust occur at different points or with different sign, or with different intensity - the very appearance of the earth's surface changes. Most often, ups and downs, covering vast areas, create large waves on it: during uplifts - domes of huge sizes, during downs - bowls and huge depressions
Folding movements- movements of the earth's crust, as a result of which folds are formed, i.e. undulating bending of layers of varying complexity. They differ from oscillatory (epeirogenic) in a number of essential features: they are episodic in time, in contrast to oscillatory, which never stop; they are not ubiquitous and each time they are confined to a relatively restricted areas the earth's crust; Covering very long periods of time, folding movements nevertheless proceed faster than oscillatory ones, and are accompanied by high magmatic activity. In the processes of folding, the movement of the earth's crust matter always goes in two directions: horizontally and vertically, i.e. tangentially and radially. The result of the tangential movement is the formation of folds, thrusts, etc.
Oscillatory and folding movements are two extreme forms of a single process of movement of the earth's crust. Oscillatory movements are primary, universal, at times, with certain conditions and in certain territories they develop into orogenic movements: folding occurs in the ascending areas.
The most characteristic external expression of complex processes of movement of the earth's crust is the formation of mountains, mountain ranges and mountainous countries .. These two cases are most characteristic and correspond to two main types of mountainous countries: type of folded mountains(Alps, Caucasus, Cordillera, Andes) and type of blocky mountains(Tien Shan, Altai).
The earth consists of many chemical elements - oxygen, nitrogen, silicon, iron, etc. When combined with each other, chemical elements form minerals. In total, there are about 2650 minerals in nature, which form 3780 mineral varieties (Table 4). For their determination and study, physical properties are of great importance, which include the appearance of crystals, luster, color of a mineral, color of a mineral's trait, transparency, hardness, cleavage, fracture and specific gravity.
Table 4
Crystal-chemical clarkes (average content) of distribution of minerals in nature
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Mineral classification group |
Percent minerals given group |
The main compositions minerals |
WITH approximate accounting chemical varieties minerals |
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1. Native |
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2. Sulfides |
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3. Chromates (chrome spinels) |
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4. Tungstates and molybdates |
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6. Silicates |
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7. Phosphates |
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8. Nitrates |
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9. Sulfates |
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10. Halides |
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11. Yodates |
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12. Borates |
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13. Carbonates |
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14. Organic compounds |
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Crystals with isometric shapes, elongated in one or two directions, are distinguished by their appearance.
The luster of minerals is subdivided into glass, diamond, semi-metallic, metallic, greasy, waxy, and matte. The mineral
fishing with a parallel-fibrous structure, there is a silky tide (asbestos, selenite, tiger's eye), transparent minerals with a layered crystal structure - a mother-of-pearl tint (muscovite, gypsum, talc, etc.).
The color of minerals is one of the most important signs by which minerals are diagnosed. The term "line color" refers to the color of a fine mineral powder, if drawn over the matte surface of a porcelain plate.
Transparency is the property of a substance to transmit light through itself. It distinguishes between transparent, translucent and opaque minerals.
To assess the hardness, the Mohs scale was adopted, represented by ten minerals, of which each subsequent one scratches all the previous ones with its sharp end: talc - gypsum - calcite - fluorite - apatite - orthoclase - quartz - topaz - corundum - diamond.
Cleavage is the ability of crystals to split or split along certain crystallographic planes parallel to actual or possible faces. Here, a five-step cleavage scale is adopted: very perfect, perfect, average, imperfect, very imperfect, turning into a conch-like fracture, like in thick glass.
The specific gravity of minerals varies from small values (2.1-2.5 t / m 3 for halite) to very high (23 t / m 3 for osmous iridium).
For example, quartz (8102) has a prismatic crystal shape, a glassy luster, no cleavage, a concave fracture, a hardness of 7 points, a specific gravity of 2.65 g / cm 3, does not have a line due to its high hardness; halite (no. C1) has a cubic crystal shape, hardness 2 points, specific gravity 2.1 g / cm 3, glass luster, white color, line color is also white, perfect cleavage, salty taste, etc.
Most minerals have crystal structure... The crystal shape for a given mineral is always constant. For example, quartz crystals have the shape of a prism, halite - the shape of a cube, etc. The sizes of minerals range from microscopic to gigantic. So, on the island of Madagascar, a beryl crystal was found with a length of 8 m and a cross section of 3 m.Its weight is almost 400 tons.
Volumetric separation of minerals of the Earth. Minerals by origin are subdivided into magmatic, sedimentary, metamorphic, metasomatic, contact pneumatolytic and pneumatolytic, hydrothermal, exogenous weathering, and organogenic origin. The distribution of rock-forming minerals in the earth's crust corresponds to the ratio of the main groups of rocks (Table 5). In the earth's crust, about 40-50 minerals are most common, which are called rock-forming.
Exists different classifications minerals: by origin, crystal shape, etc. But greatest value for use
The development of minerals for industrial purposes has their chemical classification. Most of minerals are made up of two or more chemical elements. Some minerals are formed by one chemical element. You can find out about the content of chemical elements in a mineral by its chemical formula.
Table 5
Distribution of rock-forming minerals in the earth's crust
Term "Lithosphere" has been used in science since the middle of the 19th century, but it acquired its modern significance less than half a century ago. The Geological Dictionary of the 1955 edition says: lithosphere- the same as the earth's crust. In the dictionary of the 1973 edition and in subsequent: lithosphere... in the modern sense includes the earth's crust ... and tough the top of the upper mantle Earth. The upper mantle is a geological term for a very large layer; the upper mantle has a thickness of up to 500, according to some classifications - over 900 km, and the lithosphere includes only the upper ones from several tens to two hundred kilometers.
The lithosphere is the outer shell of the "solid" Earth, located below the atmosphere and hydrosphere above the asthenosphere. The thickness of the lithosphere varies from 50 km (under the oceans) to 100 km (under the continents). It contains the earth's crust and the substrate that is part of the upper mantle. The boundary between the earth's crust and the substrate is the Mohorovichich surface, when crossing which from top to bottom the velocity of longitudinal seismic waves increases abruptly. The spatial (horizontal) structure of the lithosphere is represented by its large blocks - the so-called. lithospheric plates separated from each other by deep tectonic faults. Lithospheric plates move horizontally at an average speed of 5-10 cm per year.
The structure and thickness of the earth's crust are not the same: that part of it that can be called continental has three layers (sedimentary, granite and basalt) and an average thickness of about 35 km. Under the oceans, its structure is simpler (two layers: sedimentary and basaltic), the average thickness is about 8 km. Transitional types of the earth's crust are also distinguished (see topic 3).
The opinion that the earth's crust in the form in which it exists is a derivative of the mantle has become firmly established in science. Throughout geological history, there has been a directed irreversible process of enrichment of the Earth's surface with matter from the Earth's interior. Three main types of rocks are involved in the structure of the earth's crust: magmatic, sedimentary and metamorphic.
Igneous rocks are formed in the bowels of the Earth under conditions of high temperatures and pressures as a result of the crystallization of magma. They make up 95% of the mass of the substance that composes the earth's crust. Depending on the conditions in which the magma solidification process took place, intrusive (formed at depth) and effusive (poured onto the surface) rocks are formed. Intrusive includes: granite, gabbro, igneous - basalt, liparite, volcanic tuff, etc.
Sedimentary rocks are formed on the earth's surface in various ways: some of them are formed from the products of destruction of rocks that were formed earlier (clastic: sands, gelenoids), some due to the vital activity of organisms (organogenic: limestones, chalk, shell rock; siliceous rocks, coal and brown coal, some ores), clay (clays), chemical (rock salt, gypsum).
Metamorphic rocks are formed as a result of the transformation of rocks of a different origin (igneous, sedimentary) under the influence of various factors: high temperature and pressure in the bowels, contact with rocks of a different chemical composition, etc. (gneisses, crystalline schists, marble, etc.).
Most of the volume of the earth's crust is occupied by crystalline rocks of magmatic and metamorphic origin (about 90%). However, for the geographic envelope, the role of a thin and discontinuous sedimentary layer is more significant, which on most of the earth's surface is in direct contact with water, air, takes an active part in geographic processes (thickness - 2.2 km: from 12 km in troughs, to 400 - 500 m in the ocean bed). The most common are clays and shales, sands and sandstones, carbonate rocks. An important role in the geographic envelope is played by loesses and loesslike loams, which compose the surface of the earth's crust in the non-glacial regions of the northern hemisphere.
In the earth's crust - the upper part of the lithosphere - 90 chemical elements have been found, but only 8 of them are widespread and make up 97.2%. According to A.E. Fersman, they are distributed as follows: oxygen - 49%, silicon - 26, aluminum - 7.5, iron - 4.2, calcium - 3.3, sodium - 2.4, potassium - 2.4, magnesium - 2, 4%.
The earth's crust is divided into separate geologically different ages, more or less active (dynamically and seismically) blocks, which are subject to constant movements, both vertical and horizontal. Large (several thousand kilometers across), relatively stable blocks of the earth's crust with low seismicity and poorly dissected relief are called platforms ( plat- flat, form- form (fr.). They have a crystalline folded basement and a sedimentary cover of different ages. Depending on the age, the platforms are divided into ancient (Precambrian in age) and young (Paleozoic and Mesozoic). Ancient platforms are the cores of modern continents, the general uplift of which was accompanied by a more rapid rise or fall of their individual structures (shields and plates).
The substrate of the upper mantle, located on the asthenosphere, is a kind of rigid platform on which the earth's crust was formed during the geological development of the Earth. The substance of the asthenosphere, apparently, has a low viscosity and undergoes slow movements (currents), which, presumably, are the cause of the vertical and horizontal movements of the lithospheric blocks. They are in a position of isostasy, which implies their mutual balancing: the raising of some areas causes the lowering of others.
The lithosphere is the outer solid shell of the Earth, which includes the earth's crust and the upper part of the mantle. The lithosphere includes sedimentary, igneous and metamorphic rocks.
The lower boundary of the lithosphere is indistinct and is determined by a decrease in the viscosity of the medium, the speed of seismic waves and an increase in thermal conductivity. The lithosphere covers the earth's crust and the upper part of the mantle several tens of kilometers thick to the asthenosphere, in which the plasticity of rocks changes. The main methods for determining the boundary between the upper boundary of the lithosphere and the asthenosphere are magnetotelluric and seismological.
The thickness of the lithosphere under the oceans ranges from 5 to 100 km ( maximum value at the periphery of the oceans, the minimum - under the Mid-Oceanic ridges), under the continents - 25-200 km (maximum - under ancient platforms, minimum - under relatively young mountain ranges, volcanic arcs). The structure of the lithosphere under the oceans and continents has significant differences. Under the continents, in the structure of the earth's crust of the lithosphere, sedimentary, granite and basalt layers are distinguished, the thickness of which generally reaches 80 km. Below the oceans, the earth's crust has repeatedly undergone partial melting processes during the formation of the oceanic crust. Therefore, it is depleted in low-melting rare compounds, devoid of a granite layer, and its thickness is much less than that of the continental part of the earth's crust. The thickness of the asthenosphere (a layer of softened, pasty rocks) is about 100-150 km.
Formation of the atmosphere, hydrosphere and crust
The formation took place during the release of substances from the upper layer of the mantle of the young Earth. At present, the process of formation of the earth's crust continues on the ocean floor in the middle ridges, which is accompanied by the release of gases and small volumes of water. Oxygen is present in high concentrations in the modern earth's crust, followed by silicon and aluminum in percentage terms. Basically, the lithosphere is formed by such compounds as silicon dioxide, silicates, aluminosilicates. Crystalline substances of magmatic origin took part in the formation of most of the lithosphere. They were formed during the cooling of magma released to the surface of the Earth, which is in a molten state in the bowels of the planet.
In cold regions, the thickness of the lithosphere is greatest, and in warm regions, the least. The thickness of the lithosphere can increase with a general decrease in the heat flux density. The upper layer of the lithosphere is elastic, and the lower layer is plastic by the nature of the reaction to constantly acting loads. In tectonically active areas of the lithosphere, horizons of reduced viscosity are distinguished, where seismic waves travel at a lower speed. According to scientists, according to these horizons, some layers in relation to others "slip". This phenomenon is called the stratification of the lithosphere. In the structure of the lithosphere, there are mobile areas (folded belts) and relatively stable areas (platforms). Blocks of the lithosphere (lithospheric plates) move along the relatively plastic asthenosphere, reaching sizes from 1 to 10 thousand kilometers in diameter. Currently, the lithosphere is divided into seven main and a number of small plates. The boundaries separating the plates from each other are the zones of maximum volcanic and seismic activity.
The lithosphere is the outer, especially strong shell of the planet Earth, mainly of solid matter. For the first time the concept of "lithosphere" was defined by the scientist J. Burrell. Until the 60s of the last century, the term "earth's crust" was synonymous with the lithosphere; it was believed that this was one and the same concept. But, later, scientists proved that the lithosphere also includes the upper layer of the mantle, which has a thickness of several tens of kilometers. It is characterized by a decrease in soil viscosity and an increase in the electrical conductivity of minerals. This circumstance made it possible to consider that the lithosphere is a rather complex shell of the Earth in its composition and structure.
In the structure of the lithosphere, both relatively mobile platforms and stable regions can be distinguished. The interaction of living and mineral matter is carried out on the surface, i.e. in the soil. After the decomposition of organisms occurs, the remains pass into the state of humus (black soil). The composition of the soil consists mainly of minerals, living things, gases, water and substances of organic nature. From the minerals that make up the lithosphere, rocks are formed, such as:
- Magmatic;
- Sedimentary;
- Metamorphic rocks.
About 96% of the structure of the lithosphere is made up of rocks. In turn, the following minerals can be distinguished in the composition of rocks: granite, diarite and diffusives make up 20.8% of the total composition, while gabbro basalts make up 50.34%. Crystalline shale accounts for 16.9%, the rest is sedimentary rocks such as shales and sands.
V chemical composition lithosphere, the following elements can be distinguished:
- Oxygen, its mass fraction in the composition of the solid shell of the Earth was 49.13%;
- the share of Aluminum and Silicon was 26% each;
- iron was 4.2%;
- the proportion of Calcium in the lithosphere is only 3.25%;
- sodium, magnesium, potassium accounted for about 2.4%;
- such elements as Carbon, Titanium, Chlorine and Hydrogen constituted an insignificant share in the structure, their indicators ranged from 1 to 0.2%.
The earth's crust is composed mostly of various minerals that were formed through igneous rocks. different forms... Today, the concept of "earth's crust" includes a solidified layer of the earth's surface located above the seismic boundary. As a rule, the border is on different levels, where there are sharp fluctuations in the readings of seismic waves. These waves occur during various types of earthquakes. Scientists distinguish two types of the earth's crust: continental and oceanic.
Continental crust occupies about 45% of the earth's surface, while it has a higher thickness than oceanic. Under the thickness of the mountains, its length is 60-70 km. The crust consists of basalt, granite and sedimentary layers.
Oceanic crust thinner than continental. It consists of a basalt and sedimentary layer; the mantle begins below the basalt layer. As a rule, the topography of the ocean floor has a complex structure. In addition to the usual landforms, ocean ridges are distinguished. It is in these places that the formation of basalt layers from the mantle takes place. In places of the fault, passing along the central part of the ridge, lava flows are formed, which serves the formation of basalt. Basically, the ridges rise above the ocean floor for several thousand kilometers, due to this, the reef zones are considered the most not calm in terms of seismic indicators.
In the solid shell of the Earth are constantly observed chemical processes, during which, the destruction of rocks occurs. These processes occur under the influence of sharp fluctuations in temperature, water, oxygen and precipitation. From this, we can conclude that the chemical change in the earth's crust is inextricably linked with other equally important shells of the Earth. As a rule, chemical reactions in the lithosphere occur under the influence of components of other shells. Most of the processes take place with the participation of water, minerals, which can act as components of oxidation or reduction in chemical reactions.
Chemical reactions in soil
The soil is the upper layer of the lithosphere, plays crucial role in the interaction of all the shells of the Earth. It is the habitat of many living things, which makes it possible to consider the lithosphere inextricably linked with the biosphere. Thanks to the soil, gas exchange occurs between the atmosphere and the earth's crust, as well as the atmosphere and the hydrosphere. Feature chemical reactions in the soil is the possibility of simultaneous occurrence of biological, physical and chemical processes.
All chemical reactions in soil are based on oxygen and water. The structure of humus includes such minerals as: quartz, clay and limestone. Characteristic feature soil as part of the lithosphere is that it contains 92 chemical elements.
