Lithosphere
The lithosphere is the outer solid shell of the Earth, which includes the entire earth's crust with part of the Earth's upper mantle and consists of sedimentary, igneous and metamorphic rocks. The lower boundary of the lithosphere is fuzzy and is determined by a sharp decrease in rock viscosity, a change in the propagation velocity of seismic waves, and an increase in the electrical conductivity of rocks. The thickness of the lithosphere on the continents and under the oceans varies and averages 25-200 and 5-100 km, respectively.
Consider in general terms the geological structure of the Earth. The third planet farthest from the Sun - the Earth has a radius of 6370 km, an average density of 5.5 g / cm3 and consists of three shells - the crust, mantle and core. The mantle and core are divided into inner and outer parts.
The Earth's crust is a thin upper shell of the Earth, which has a thickness of 40-80 km on the continents, 5-10 km under the oceans and makes up only about 1% of the Earth's mass. Eight elements - oxygen, silicon, hydrogen, aluminum, iron, magnesium, calcium, sodium - form 99.5% of the earth's crust. On the continents, the crust is three-layered: sedimentary rocks cover granitic rocks, and granitic rocks lie on basalt rocks. Under the oceans, the crust is of an "oceanic", two-layer type; sedimentary rocks lie simply on basalts, there is no granite layer. There is also a transitional type of the earth's crust (island-arc zones on the margins of the oceans and some areas on the continents, such as the Black Sea). The earth's crust has the greatest thickness in mountainous regions (under the Himalayas - over 75 km), the average - in the areas of platforms (under the West Siberian lowland - 35-40, within the boundaries of the Russian platform - 30-35), and the smallest - in the central regions of the oceans (5-7 km). The predominant part of the earth's surface is the plains of the continents and the ocean floor. The continents are surrounded by a shelf - a shallow-water strip up to 200 g deep and an average width of about 80 km, which, after a sharp steep bend of the bottom, passes into the continental slope (the slope varies from 15-17 to 20-30 °). The slopes gradually level off and turn into abyssal plains (depths 3.7-6.0 km). The greatest depths (9-11 km) have oceanic trenches, the vast majority of which are located on the northern and western margins of the Pacific Ocean.
The main part of the lithosphere consists of igneous igneous rocks (95%), among which granites and granitoids predominate on the continents, and basalts in the oceans.
The relevance of the ecological study of the lithosphere due to the fact that the lithosphere is the environment of all mineral resources, one of the main objects of anthropogenic activity (components of the natural environment), through significant changes in which the global ecological crisis develops. In the upper part of the continental crust, soils are developed, the importance of which for humans can hardly be overestimated. Soils - an organo-mineral product of many years (hundreds and thousands of years) of the general activity of living organisms, water, air, solar heat and light are one of the most important natural resources. Depending on climatic and geological and geographical conditions, soils have a thickness of 15-25 cm to 2-3 m.
Soils arose together with living matter and developed under the influence of the activities of plants, animals and microorganisms until they became a very valuable fertile substrate for humans. The bulk of organisms and microorganisms of the lithosphere is concentrated in soils, at a depth of no more than a few meters. Modern soils are a three-phase system (different-grained solid particles, water and gases dissolved in water and pores), which consists of a mixture of mineral particles (rock destruction products), organic substances (biota waste products of its microorganisms and fungi). Soils play a huge role in the circulation of water, substances and carbon dioxide.
Various minerals are associated with different rocks of the earth's crust, as well as with its tectonic structures: combustible, metal, construction, as well as those that are raw materials for the chemical and food industries.
Within the boundaries of the lithosphere, terrible ecological processes (shifts, mudflows, collapses, erosion) have periodically occurred and continue to occur, which are of great importance for the formation of ecological situations in a certain region of the planet, and sometimes lead to global ecological disasters.
The deep layers of the lithosphere, which are explored by geophysical methods, have a rather complex and still insufficiently studied structure, just like the mantle and core of the Earth. But it is already known that the density of rocks increases with depth, and if on the surface it averages 2.3-2.7 g / cm3, then at a depth of close to 400 km - 3.5 g / cm3, and at a depth of 2900 km ( boundary of the mantle and the outer core) - 5.6 g/cm3. In the center of the core, where the pressure reaches 3.5 thousand tons/cm2, it increases to 13-17 g/cm3. The nature of the increase in the deep temperature of the Earth has also been established. At a depth of 100 km, it is approximately 1300 K, at a depth of close to 3000 km -4800, and in the center of the earth's core - 6900 K.
The predominant part of the Earth's matter is in a solid state, but on the border of the earth's crust and upper mantle (depths of 100-150 km) lies a stratum of softened, pasty rocks. This thickness (100-150 km) is called the asthenosphere. Geophysicists believe that other parts of the Earth can also be in a rarefied state (due to decompaction, active radio decay of rocks, etc.), in particular, the zone of the outer core. The inner core is in the metallic phase, but today there is no consensus on its material composition.
Bibliography
For the preparation of this work, materials from the site http://ecosoft.iatp.org.ua/ were used.
The internal structure of the Earth includes three shells: the earth's crust, mantle and core. The shell structure of the Earth was established by remote methods based on measuring the propagation velocity of seismic waves, which have two components - longitudinal and transverse waves. Longitudinal (P) waves associated with tensile (or compressive) stresses oriented in the direction of their propagation. Transverse (S) waves cause oscillations of the medium, oriented at right angles to the direction of their propagation. These waves do not propagate in a liquid medium. The main values of the physical parameters of the Earth are given in fig. 5.1.
Earth's crust- a stony shell composed of a solid substance with an excess of silica, alkali, water and an insufficient amount of magnesium and iron. It separates from the upper mantle Mohorović border(Moho layer), on which there is a jump in the velocities of longitudinal seismic waves up to about 8 km/s. This boundary, established in 1909 by the Yugoslav scientist A. Mohorovic, 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 young folded mountains on the continents it increases to 80 km, and under mid-ocean ridges it decreases to 6-7 km (counting from the surface of the ocean floor) .
Mantle is the largest shell of the Earth in terms of volume and weight, extending from the sole of the earth's crust to borders Gutenberg, corresponding to a depth of approximately 2900 km and taken as the lower boundary of the mantle. The mantle is subdivided into lower(50% of the Earth's mass) and top(eighteen%). According to modern concepts, the composition of the mantle is fairly homogeneous 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 propagation velocities of longitudinal and transverse waves in the lower mantle increase to 13 and 7 km/s, respectively. 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 about the composition of the core. It is known that it is the most dense shell of the Earth. The core is also subdivided into two spheres: external, to a depth of 5150 km, which is in a liquid state, and internal - hard. In the outer core, the propagation velocity of longitudinal waves drops to 8 km/s, while transverse waves do not propagate at all, which is taken as proof of its liquid state. Deeper than 5150 km, the propagation velocity of longitudinal waves increases and transverse waves pass again. The inner core accounts for 2% of the mass of the Earth, the outer - 29%.
The outer "hard" shell of the Earth, including the earth's crust and the upper part of the mantle, forms lithosphere(Fig. 5.2). Its capacity is 50-200 km.
Rice. 5.1. Changes in physical parameters in the bowels of the Earth (according to S.V. Aplonov, 2001)
Rice. 5.2. The internal structure of the Earth and the propagation velocity of longitudinal (R) and transverse (S) seismic waves (according to S. V. Aplonov, 2001)
The lithosphere and the underlying mobile layers of the asthenosphere, where intraterrestrial movements of a tectonic nature are usually generated and realized, and earthquakes and molten magma are often located, are called tectonosphere.
The composition of the earth's crust. Chemical elements in the earth's crust form natural compounds - minerals, usually solids that have certain physical properties. The earth's crust contains more than 3,000 minerals, among which about 50 are rock-forming.
Regular natural combinations of minerals form rocks. The earth's crust is composed of rocks of different composition and origin. By origin, rocks are divided into igneous, sedimentary and metamorphic.
Igneous rocks formed by the solidification of magma. If this happens in the thickness of the earth's crust, then intrusive crystallized rocks, and when magma erupts onto the surface, effusive education. According to the content of silica (SiO2), the following groups of igneous rocks are distinguished: sour(> 65% - granites, liparites, etc.), medium(65-53% - syenites, andesites, etc.), main(52-45% - gabbro, basalts, etc.) and ultrabasic(<45% - перидотиты, дуниты и др.).
Sedimentary rocks arise on the earth's surface due to the deposition of material in various ways. Some of them are formed as a result of the destruction of rocks. This is clastic, or plastic, rocks. The size of the fragments varies from boulders and pebbles to silty particles, which makes it possible to distinguish among them rocks of different granulometric composition - boulders, pebbles, conglomerates, sands, sandstones, etc. Organogenic rocks are created with the participation of organisms (limestone, coal, chalk, etc.). A significant place is occupied chemogenic rocks associated with the precipitation of a substance from solution under certain conditions.
metamorphic rocks are formed as a result of changes in igneous and sedimentary rocks under the influence of high temperatures and pressures in the bowels of the Earth. These include gneisses, schists, marble, etc.
About 90% of the volume of the earth's crust are crystalline rocks of igneous and metamorphic genesis. For the geographic envelope, a relatively thin and discontinuous layer of sedimentary rocks (stratisphere) plays an important role, which are in direct contact with various components of the geographic envelope. The average thickness of sedimentary rocks is about 2.2 km, the real thickness varies from 10-14 km in troughs to 0.5-1 km on the ocean floor. According to the studies of A.B. Ronov, the most common sedimentary rocks are clays and shale (50%), sands and sandstones (23.6%), carbonate formations (23.5%). An important role in the composition of the earth's surface is played by loess and loess-like loams of non-glacial regions, unsorted strata of moraines of glacial regions, and intrazonal accumulations of pebble-sand formations of water origin.
The structure of the earth's crust. According to the structure and thickness (Fig. 5.3), two main types of the earth's crust are distinguished - continental (continental) and oceanic. Differences in their chemical composition can be seen from Table. 5.1.
continental crust consists of sedimentary, granite and basalt layers. The latter is arbitrarily singled out because the velocities of seismic waves are equal to the velocities in basalts. The granite layer consists of rocks enriched in silicon and aluminum (SIAL), the rocks of the basalt layer are enriched in silicon and magnesium (SIAM). The contact between a granite layer with an average rock density of about 2.7 g/cm3 and a basalt layer with an average density of about 3 g/cm3 is known as the Konrad boundary (named after the German explorer W. Konrad, who discovered it in 1923).
oceanic crust two-layer. Its main mass is composed of basalts, on which lies a thin sedimentary layer. The thickness of the basalts exceeds 10 km; in the upper parts, layers of sedimentary Late Mesozoic rocks are reliably identified. The thickness of the sedimentary cover, as a rule, does not exceed 1-1.5 km.
Rice. 5.3. The structure of the earth's crust: 1 - basalt layer; 2 - granite layer; 3 - stratisphere and weathering crust; 4 - basalts of the ocean floor; 5 - areas with low biomass; 6 - areas with high biomass; 7 - ocean waters; 8 - sea ice; 9 - deep faults of continental slopes
The basalt layer on the continents and the ocean floor is fundamentally different. On the continents, these are contact formations between the mantle and the most ancient terrestrial rocks, as if the primary crust of the planet, which arose before or at the beginning of its independent development (possibly evidence of the "lunar" stage of the Earth's evolution). In the oceans, these are real basalt formations, mainly of the Mesozoic age, which arose due to underwater outpourings during the expansion of lithospheric plates. The age of the first should be several billion years, the second - no more than 200 million years.
Table 5.1. Chemical composition of the continental and oceanic crust (according to S.V. Aplonov, 2001)
| Content, % | ||
| oxides | continental crust | oceanic crust |
| SiO2 | 60,2 | 48,6 |
| TiО2 | 0,7 | 1.4 |
| Al2O3 | 15,2 | 16,5 |
| Fe2O3 | 2,5 | 2,3 |
| FeO | 3,8 | 6,2 |
| MNO | 0,1 | 0,2 |
| MgO | 3,1 | 6,8 |
| CaO | 5,5 | 12,3 |
| Na2O | 3,0 | 2,6 |
| K2O | 2,8 | 0,4 |
In some places there is transitional type the earth's crust, which is characterized by significant spatial heterogeneity. It is known in the marginal seas of East Asia (from the Bering Sea to the South China Sea), the Sunda Archipelago and some other regions of the globe.
The presence of different types of the earth's crust is due to differences in the development of individual parts of the planet and their age. This problem is extremely interesting and important from the point of view of the reconstruction of the geographic envelope. Previously, it was assumed that the oceanic crust is primary, and the continental crust is secondary, although it is many billions of years older than it. According to modern concepts, the oceanic crust arose due to the intrusion of magma along faults between continents.
The dreams of scientists about the practical verification of ideas on the structure of the lithosphere, based on remote geophysical data, came true in the second half of the 20th century, when deep and ultra-deep drilling on land and the bottom of the World Ocean became possible. Among the most famous projects is the Kola super-deep well, drilled to a depth of 12,066 m (drilling was stopped in 1986) within the Baltic Shield in order to reach the boundary between the granite and basalt layers of the earth's crust, and, if possible, its sole - the Moho horizon. The Kola super-deep well disproved many established ideas about the structure of the Earth's interior. The location of the Konrad horizon in this region at a depth of about 4.5 km, which was assumed by geophysical sounding, was not confirmed. The velocity of compressional waves changed (did not increase, but fell) at the level of 6842 m, where the volcanogenic-sedimentary rocks of the Early Proterozoic changed to amphibolite-gneiss rocks of the Late Archean. The "culprit" of the change was not the composition of the rocks, but their special state - hydrogenous decompaction, first discovered in the natural state in the Earth's thickness. Thus, another explanation of the change in the speeds and directions of geophysical waves became possible.
Structural elements of the earth's crust. The Earth's crust has been formed for at least 4 billion years, during which it has become more complex under. the influence of endogenous (mainly under the influence of tectonic movements) and exogenous (weathering, etc.) processes. Manifested with different intensity and at different times, tectonic movements formed the structures of the earth's crust, which form relief planets.
Large landforms are called morphostructures(e.g. mountain ranges, plateaus). Relatively small landforms form morphosculptures(for example, karst).
The main planetary structures of the Earth - continents and oceans. AT within the continents, large structures of the second order are distinguished - folded belts and platforms, which are clearly expressed in modern relief.
Platforms - these are tectonically stable sections of the earth's crust, usually of a two-tier structure: the lower one, formed by the most ancient rocks, is called foundation, upper, composed mainly of sedimentary rocks of a later age - sedimentary cover. The age of platforms is estimated by the time of formation of the foundation. Platform sections where the foundation is submerged under the sedimentary cover are called slabs(for example, Russian plate). The places where the rocks of the platform foundation come to the day surface are called shields(for example, the Baltic Shield).
At the bottom of the oceans, tectonically stable areas are distinguished - thalassocratons and mobile tectonically active bands - georiftogenals. The latter spatially correspond to mid-ocean ridges with alternating uplifts (in the form of seamounts) and subsidences (in the form of deep-water depressions and trenches). Together with volcanic manifestations and local uplifts of the ocean floor, oceanic geosynclines create specific structures of island arcs and archipelagos, expressed on the northern and western margins of the Pacific Ocean.
Contact zones between continents and oceans are divided into two types: active and passive. The first are the centers of the strongest earthquakes, active volcanism and a significant scope of tectonic movements. Morphologically, they are expressed by the conjugation of marginal seas, island arcs, and deep ocean trenches. The most typical are all the margins of the Pacific Ocean ("Pacific Ring of Fire") and the northern part of the Indian Ocean. The latter are an example of a gradual change of continents through the shelves and continental slopes to the ocean floor. These are the margins of most of the Atlantic Ocean, as well as the Arctic and Indian Oceans. We can also talk about more complex contacts, especially in the regions of development of transitional types of the earth's crust.
Dynamics of the lithosphere. Ideas about the mechanism of formation of terrestrial structures are being developed by scientists of various directions, which can be combined into two groups. Representatives fixism they proceed from the statement about the fixed position of the Continents on the surface of the Earth and the predominance of vertical Movements in tectonic deformations of the layers of the earth's crust. Supporters mobilism the primary role is given to horizontal movements. The main ideas of mobilism were formulated by A. Wegener (1880-1930) as continental drift hypothesis. New data obtained in the second half of the 20th century made it possible to develop this direction to the modern theory neomobilism, explaining the dynamics of processes in the earth's crust by the drift of large lithospheric plates.
According to the theory of neomobilism, the lithosphere consists of plates (their number, according to various estimates, ranges from 6 to several dozen), which move in a horizontal direction at a speed of several millimeters to several centimeters per year. Lithospheric plates are drawn into motion as a result of thermal convection in the upper mantle. However, recent studies, in particular deep drilling, show that the asthenosphere layer is not continuous. If, however, the discreteness of the asthenosphere is recognized, then the established ideas about convective cells and the structure of the movement of crustal blocks, which underlie the classical models of geodynamics, should also be rejected. P. N. Kropotkin, for example, believes that it is more correct to speak of forced convection, which is associated with the movement of matter in the Earth's mantle under the influence of an alternate increase and decrease in the Earth's radius. Intensive mountain building in the last tens of millions of years, in his opinion, was due to the progressive compression of the Earth, which amounted to about 0.5 mm per year, or 0.5 km per million years, possibly with the general tendency of the Earth to expand.
According to the modern structure of the earth's crust, in the central parts of the oceans, the boundaries of the lithospheric plates are mid-ocean ridges with rift (fault) zones along their axes. Along the periphery of the oceans, in the transition zones between the continents and the bed of the ocean basin, geosynclinal mobile belts with folded-volcanic island arcs and deep-water trenches along their outer margins. There are three options for the interaction of lithospheric plates: discrepancy, or spreading; collision, accompanied, depending on the type of contacting plates, by subduction, eduction or collision; horizontal slip one plate relative to another.
Concerning the problem of the emergence of oceans and continents, it should be noted that at present it is most often solved by recognizing the fragmentation of the earth's crust into a number of plates, the separation of which caused the formation of huge depressions occupied by ocean waters. The diagram of the geological structure of the ocean floor is shown in fig. 5.4. The scheme of magnetic field reversals of ocean floor basalts shows amazing regularities of the symmetrical arrangement of similar formations on both sides of the spreading zone and their gradual ageing towards the continents (Fig. 5.5). Not only for the sake of fairness, we note the existing opinion about the sufficient antiquity of the oceans - deep ocean sediments, as well as relics of the basaltic oceanic crust in the form of ophiolites, are widely represented in the geological history of the Earth for the last 2.5 billion years. Blocks of the ancient oceanic crust and lithosphere, imprinted in a deeply submerged foundation of sedimentary basins - a kind of failures of the earth's crust, according to S.V. Aplonov, testify to the unrealized possibilities of the planet - "failed oceans".
Rice. 5.4. Scheme of the geological structure of the bed of the Pacific Ocean and its continental framing (according to A. A. Markushev, 1999): / - continental volcanism (a- separate volcanoes, b - trap fields); II - island volcanoes and continental margins (a - underwater, b- ground); III- volcanoes of underwater ridges (a) and oceanic islands (b); IV- marginal sea volcanoes (a - underwater, b - ground); V- spreading structures of the development of modern tholeiite-basalt underwater volcanism; VI- deep water trenches; VII- lithospheric plates (numbers in circles): 1 - Burmese; 2 - Asian; 3 - North American; 4 - South American; 5 - Antarctic; 6 - Australian; 7- Solomon; 8- Bismarck; 9 - Philippine; 10 - Mariana; 11 - Juan de Fuca; 12 - Caribbean; 13 - Coconut; 14 - Nazca; 15 - Skosha; 16 - Pacific; VIII- the main volcanoes and trap fields: 1 - Baker; 2 - Lassen Peak; 3-5- traps {3 - Colombia, 4 - Patagonia, 5 - Mongolia); 6 - Tres Virgines; 7 - Paricutin; 8 - Popocatepetl; 9 - Mont Pele; 10 - Cotopaxi; 11 - Taravera; 12 - Kermadec; 13 - Maunaloa (Hawaiian archipelago); 14- Krakatoa; 75- Taal; 16- Fujiyama; 17 - Theologian; 18 - Katmai. The age of basalts is given according to drilling data
Rice. 5.5. Age (million years) of the bottom of the Atlantic Ocean, determined by the magnetostratigraphic scale (according to E. Zeibol and V. Berger, 1984)
Formation of the modern appearance of the Earth. AT Throughout the history of the Earth, the location and configuration of continents and oceans have constantly changed. According to geological data, the continents of the Earth united four times. Reconstruction of the stages of their formation over the past 570 million years (in the Phanerozoic) indicates the existence of the last supercontinent - Pangaea with a fairly thick, up to 30-35 km continental crust, formed 250 million years ago, which broke up into gondwana, occupying the southern part of the globe, and Laurasia, united the northern continents. The collapse of Pangea led to the opening of the body of water, initially in the form paleo-pacific ocean and ocean Tethys, and later (65 million years ago) - modern oceans. We are now watching the continents drift apart. It is difficult to imagine what will be the location of modern continents and oceans in the future. According to S. V. Aplonov, it is possible to unite them into the fifth supercontinent, the center of which will be Eurasia. V. P. Trubitsyn believes that in a billion years the continents may again gather at the South Pole.
Lithosphere. Earth's crust. 4.5 billion years ago, the Earth was a ball consisting of some gases. Gradually, heavy metals such as iron and nickel sank to the center and condensed. Light rocks and minerals floated to the surface, cooled and hardened.
The internal structure of the Earth.
It is customary to divide the body of the Earth into three main parts - lithosphere(earth crust) mantle and core.
The core is the center of the earth , the average radius of which is about 3500 km (16.2% of the volume of the Earth). As suggested, it consists of iron with an admixture of silicon and nickel. The outer part of the core is in a molten state (5000 °C), the inner, apparently, is solid (subnucleus). The movement of matter in the core creates a magnetic field on Earth that protects the planet from cosmic radiation.
The core is changing mantle , which extends almost 3000 km (83% of the Earth's volume). It is believed that it is solid, at the same time plastic and red-hot. The mantle is made up of three layers: Golitsyn layer, Gutenberg layer and substrate. The upper part of the mantle, called magma , contains a layer with reduced viscosity, density and hardness - the asthenosphere, on which sections of the earth's surface are balanced. The boundary between the mantle and the core is called the Gutenberg layer.
Lithosphere
Lithosphere - the upper shell of the "solid" Earth, including the earth's crust and the upper part of the underlying upper mantle of the Earth.
Earth's crust - the upper shell of the "solid" Earth. The thickness of the earth's crust is from 5 km (under the oceans) to 75 km (under the continents). The earth's crust is heterogeneous. It distinguishes 3 layers – sedimentary, granite, basalt. The granite and basalt layers are so named because they contain rocks similar in physical properties to granite and basalt.
Compound the earth's crust: oxygen (49%), silicon (26%), aluminum (7%), iron (5%), calcium (4%); the most common minerals are feldspar and quartz. The boundary between the earth's crust and mantle is called moho surface .
Distinguish continental and oceanic earth's crust. Oceanic different from the continental (mainland) lack of granite layer and much lower power (from 5 to 10 km). Thickness continental crust on the plains 35-45 km, in the mountains 70-80 km. On the border of the continents and oceans, in the areas of the islands, the thickness of the earth's crust is 15-30 km, the granite layer is wedged out.
The position of the layers in the continental crust indicates different time of its formation . The basalt layer is the oldest, younger than it is granite, and the youngest is the upper, sedimentary, developing at the present time. Each layer of the crust was formed over a long period of geological time.
Lithospheric plates
The earth's crust is in constant motion. The first hypothesis about continental drift(i.e. the horizontal movement of the earth's crust) put forward at the beginning of the twentieth century A. Wegener. On its basis, created theory of lithospheric plates . According to this theory, the lithosphere is not a monolith, but consists of seven large and several smaller plates "floating" on the asthenosphere. The boundary regions between lithospheric plates are called seismic belts - these are the most "restless" areas of the planet.
The earth's crust is divided into stable and mobile sections.
Stable areas of the earth's crust - platforms- are formed at the site of geosynclines that have lost their mobility. The platform consists of a crystalline basement and a sedimentary cover. Depending on the age of the foundation, ancient (Precambrian) and young (Paleozoic, Mesozoic) platforms are distinguished. Ancient platforms lie at the base of all continents.
Mobile, highly dissected parts of the earth's surface are called geosynclines ( folded areas ). In their development, there are two stages : at the first stage, the earth's crust experiences subsidence, sedimentary rocks accumulate and metamorphize. Then the uplift of the earth's crust begins, the rocks are crushed into folds. There were several epochs of intensive mountain building on Earth: Baikal, Caledonian, Hercynian, Mesozoic, Cenozoic. In accordance with this, different areas of folding are distinguished.
Archived: three lessons in geography on the topic "Lithosphere"
"lithosphere_plate"
The lithospheric plate is a large stable area of the earth's crust, part of the lithosphere. According to the theory of plate tectonics, lithospheric plates are limited by zones of seismic, volcanic and tectonic activity - plate boundaries.
The division of the earth's crust into plates is not unambiguous, and as geological knowledge accumulates, new plates are distinguished, and some plate boundaries are recognized as non-existent.
A. Wegener came up with the idea of a possible movement of the continents when he carefully examined the geographical map of the world. He was struck by the amazing similarity of the outlines of the coasts of South America and Africa.
The formation and movement of plates is associated with the mixing of the mantle substance due to the temperature difference in its upper and lower parts.
There are three types of plate boundaries: divergent, convergent, and transform.
There are three types of plate boundaries: divergent, convergent, and transform.
Formation of mountains and mid-ranges
Plate displacement during earthquakes
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"Storage. belt"
Horst - an elevated, usually elongated section of the earth's crust, formed as a result of tectonic movements.
Graben - a section of the earth's crust, lowered relative to the surrounding area along tectonic faults.
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"Ancient Continents"
ancient continents
Geography of continents and oceans
The history of the formation of the Earth's relief
Since the formation of the Earth - 4.6 billion years ago - the appearance of its surface has changed many times: the continents and oceans have acquired different sizes and shapes. The current geographical position of the continents and oceans, the features of their relief are the result of a long geological development of the Earth.
Pangea, 200 million years ago
Pangea is the name given Alfred Wegener proto-continent that arose in the Paleozoic era.
Ancient continent and ocean
In the process of the formation of Pangea from more ancient continents, mountain systems arose at the places of their collision, some of which have existed to this day, for example, the Urals or the Appalachians. These early mountains are much older than such relatively young mountain systems as the Alps in Europe, the Cordillera in North America, the Andes in South America or the Himalayas in Asia. Due to the erosion that lasts for many millions of years, the Urals and the Appalachians are run-in low mountains.
The giant ocean that washed Pangea is called
Panthalassa .
About 200 million years ago, Pangea began to split and first broke up into two continents: Laurasia and Gondwana.
Further splits divided Laurasia into North America and Eurasia, and Gondwana into the southern continents: Africa, South America, India, Australia and Antarctica.
Due to the divergence of the lithospheric plates, the continents moved away from each other and eventually occupied their present position. Between the continents, the depressions of the Atlantic, Indian and Arctic oceans expanded.
What awaits the continents in the future?
The black lines on the maps are the boundaries of giant plates, slowly and steadily spreading the continents. Now scientists can foresee the geography of the future: the latest map tells about the planet of tomorrow. Look - the Atlantic Ocean has become even wider, and Africa has split.
Presumably, our continents will collide again and form a new supercontinent, which has already been given a name - Pangea Ultima. The term Pangea Ultima and the very theory of the appearance of the mainland was coined by the American geologist Christopher Scotese, who, using various methods for calculating the movement of lithospheric plates, found that the merger could occur somewhere in 200 million years.
The last Pangea, as this continent is sometimes called in Russia, will be almost entirely covered with deserts, and in the northwest and southeast there will be huge mountain ranges.
The lithosphere is the stone shell of the Earth. From the Greek "lithos" - a stone and "sphere" - a ball
The lithosphere is the outer solid shell of the Earth, which includes the entire earth's crust with part of the Earth's upper mantle and consists of sedimentary, igneous and metamorphic rocks. The lower boundary of the lithosphere is fuzzy and is determined by a sharp decrease in rock viscosity, a change in the propagation velocity of seismic waves, and an increase in the electrical conductivity of rocks. The thickness of the lithosphere on the continents and under the oceans varies and averages 25 - 200 and 5 - 100 km, respectively.
Consider in general terms the geological structure of the Earth. The third planet farthest from the Sun - the Earth has a radius of 6370 km, an average density of 5.5 g / cm3 and consists of three shells - bark, robes and i. The mantle and core are divided into inner and outer parts.
The Earth's crust is a thin upper shell of the Earth, which has a thickness of 40-80 km on the continents, 5-10 km under the oceans and makes up only about 1% of the Earth's mass. Eight elements - oxygen, silicon, hydrogen, aluminum, iron, magnesium, calcium, sodium - form 99.5% of the earth's crust.
According to scientific research, scientists were able to establish that the lithosphere consists of:
- Oxygen - 49%;
- Silicon - 26%;
- Aluminum - 7%;
- Iron - 5%;
- Calcium - 4%
- The composition of the lithosphere includes many minerals, the most common are feldspar and quartz.
On the continents, the crust is three-layered: sedimentary rocks cover granitic rocks, and granitic rocks lie on basalt rocks. Under the oceans, the crust is "oceanic", two-layered; sedimentary rocks lie simply on basalts, there is no granite layer. There is also a transitional type of the earth's crust (island-arc zones on the outskirts of the oceans and some areas on the continents, such as the Black Sea).
The earth's crust is thickest in mountainous regions.(under the Himalayas - over 75 km), the middle one - in the areas of the platforms (under the West Siberian lowland - 35-40, within the boundaries of the Russian platform - 30-35), and the smallest - in the central regions of the oceans (5-7 km). The predominant part of the earth's surface is the plains of the continents and the ocean floor.
The continents are surrounded by a shelf - a shallow-water strip up to 200 g deep and an average width of about 80 km, which, after a sharp steep bend of the bottom, passes into the continental slope (the slope varies from 15-17 to 20-30 °). The slopes gradually level off and turn into abyssal plains (depths 3.7-6.0 km). The greatest depths (9-11 km) have oceanic trenches, the vast majority of which are located on the northern and western margins of the Pacific Ocean.
The main part of the lithosphere consists of igneous igneous rocks (95%), among which granites and granitoids predominate on the continents, and basalts in the oceans.
Blocks of the lithosphere - lithospheric plates - move along the relatively plastic asthenosphere. The section of geology on plate tectonics is devoted to the study and description of these movements.
To designate the outer shell of the lithosphere, the now obsolete term sial was used, which comes from the name of the main elements of rocks Si (lat. Silicium - silicon) and Al (lat. Aluminum - aluminum).
Lithospheric plates
It is worth noting that the largest tectonic plates are very clearly visible on the map and they are:
- Pacific- the largest plate of the planet, along the boundaries of which constant collisions of tectonic plates occur and faults form - this is the reason for its constant decrease;
- Eurasian- covers almost the entire territory of Eurasia (except Hindustan and the Arabian Peninsula) and contains the largest part of the continental crust;
- Indo-Australian- It includes the Australian continent and the Indian subcontinent. Due to constant collisions with the Eurasian plate, it is in the process of breaking;
- South American- consists of the South American mainland and part of the Atlantic Ocean;
- North American- consists of the North American continent, part of northeastern Siberia, the northwestern part of the Atlantic and half of the Arctic Oceans;
- African- consists of the African continent and the oceanic crust of the Atlantic and Indian oceans. It is interesting that the plates adjacent to it move in the opposite direction from it, therefore the largest fault of our planet is located here;
- Antarctic Plate- consists of the mainland Antarctica and the nearby oceanic crust. Due to the fact that the plate is surrounded by mid-ocean ridges, the rest of the continents are constantly moving away from it.
Movement of tectonic plates in the lithosphere
Lithospheric plates, connecting and separating, change their outlines all the time. This allows scientists to put forward the theory that about 200 million years ago the lithosphere had only Pangea - a single continent, which subsequently split into parts, which began to gradually move away from each other at a very low speed (an average of about seven centimeters per year ).
It is interesting! There is an assumption that due to the movement of the lithosphere, in 250 million years a new continent will form on our planet due to the union of moving continents.
When the oceanic and continental plates collide, the edge of the oceanic crust sinks under the continental one, while on the other side of the oceanic plate its boundary diverges from the plate adjacent to it. The boundary along which the movement of the lithospheres occurs is called the subduction zone, where the upper and plunging edges of the plate are distinguished. It is interesting that the plate, plunging into the mantle, begins to melt when the upper part of the earth's crust is squeezed, as a result of which mountains are formed, and if magma also breaks out, then volcanoes.
In places where tectonic plates come into contact with each other, there are zones of maximum volcanic and seismic activity: during the movement and collision of the lithosphere, the earth's crust collapses, and when they diverge, faults and depressions form (the lithosphere and the Earth's relief are connected to each other). This is the reason that the largest landforms of the Earth are located along the edges of the tectonic plates - mountain ranges with active volcanoes and deep-sea trenches.
Problems of the lithosphere
The intensive development of industry has led to the fact that man and the lithosphere have recently become extremely difficult to get along with each other: pollution of the lithosphere is acquiring catastrophic proportions. This happened due to the increase in industrial waste in combination with household waste and fertilizers and pesticides used in agriculture, which negatively affects the chemical composition of the soil and living organisms. Scientists have calculated that about one ton of garbage falls per person per year, including 50 kg of hardly decomposable waste.
Today, pollution of the lithosphere has become an urgent problem, since nature is not able to cope with it on its own: the self-purification of the earth's crust is very slow, and therefore harmful substances gradually accumulate and eventually negatively affect the main culprit of the problem - man.
