Tectonics is the science of what? Global tectonics. Tectonics in architecture. Russia will run into Japan. Tectonic shifts change continents Tectonic plates interact through

The surface shell of the Earth consists of parts - lithospheric or tectonic plates. They are integral large blocks that are in continuous motion. This leads to the emergence of various phenomena on the surface of the globe, as a result of which the relief inevitably changes.

Plate tectonics

tectonic plates- these are the components of the lithosphere responsible for the geological activity of our planet. Millions of years ago, they were a single entity, making up the largest supercontinent called Pangea. However, as a result of high activity in the bowels of the Earth, this continent split into continents, which moved away from each other to the maximum distance.

According to scientists, in a few hundred years this process will go in the opposite direction, and the tectonic plates will again begin to combine with each other.

Rice. 1. Tectonic plates of the Earth.

Earth is the only planet in the solar system whose surface shell is broken into separate parts. The thickness of tectonic reaches several tens of kilometers.

According to tectonics, a science that studies lithospheric plates, huge areas of the earth's crust are surrounded on all sides by zones of increased activity. At the junctions of neighboring plates, natural phenomena occur, which most often cause large-scale catastrophic consequences: volcanic eruptions, strong earthquakes.

Movement of the Earth's tectonic plates

The main reason why the entire lithosphere of the globe is in continuous motion is thermal convection. Critically high temperatures reign in the central part of the planet. When heated, the upper layers of matter in the bowels of the Earth rise, while the upper layers, already cooled, sink towards the center. The continuous circulation of matter sets in motion parts of the earth's crust.

TOP 1 articlewho read along with this

The speed of movement of lithospheric plates is approximately 2-2.5 cm per year. Since their movement occurs on the surface of the planet, strong deformations occur in the earth's crust at the boundary of their interaction. As a rule, this leads to the formation of mountain ranges and faults. For example, on the territory of Russia, the mountain systems of the Caucasus, Urals, Altai and others were formed in this way.

Rice. 2. Greater Caucasus.

There are several types of lithospheric plate movement:

• divergent - two platforms diverge, forming an underwater mountain range or a hole in the ground.
• Convergent - two plates approach each other, while the thinner one sinks under the more massive one. At the same time, mountain ranges are formed.
• sliding - two plates move in opposite directions.

Africa is literally splitting into two parts. Large cracks in the ground have been recorded, stretching across much of Kenya. According to scientists, in about 10 million years the African continent as a whole will cease to exist.

Rice. 3. Cracks in Africa.

What have we learned?

When studying the topic “Tectonic Plates”, we learned that the surface of the planet consists of individual plates that are in continuous motion. We found out that it is thanks to the movement of these plates that the globe has such a diverse relief.

Topic quiz

Report Evaluation

Average rating: 4.4. Total ratings received: 281.

Clickable

According to modern theories of lithospheric plates the entire lithosphere is divided by narrow and active zones - deep faults - into separate blocks moving in the plastic layer of the upper mantle relative to each other at a speed of 2-3 cm per year. These blocks are called lithospheric plates.

Alfred Wegener first proposed the horizontal movement of crustal blocks in the 1920s as part of the “continental drift” hypothesis, but this hypothesis did not receive support at that time.

Only in the 1960s, studies of the ocean floor gave indisputable evidence horizontal movement of plates and processes of expansion of the oceans due to the formation (spreading) of the oceanic crust. The revival of ideas about the predominant role of horizontal movements occurred within the framework of the "mobilistic" direction, the development of which led to the development of the modern theory of plate tectonics. The main provisions of plate tectonics were formulated in 1967-68 by a group of American geophysicists - W. J. Morgan, C. Le Pichon, J. Oliver, J. Isaacs, L. Sykes in the development of earlier (1961-62) ideas of American scientists G. Hess and R. Digts on the expansion (spreading) of the ocean floor.

It is argued that scientists are not entirely sure what causes these very shifts and how the boundaries of tectonic plates were designated. There are countless different theories, but none of them fully explains all aspects of tectonic activity.

Let's at least find out how they imagine it now.

Wegener wrote: "In 1910, the idea of ​​moving the continents first occurred to me ... when I was struck by the similarity of the outlines of the coasts on both sides of the Atlantic Ocean." He suggested that in the early Paleozoic there were two large continents on Earth - Laurasia and Gondwana.

Laurasia was the northern mainland, which included the territories of modern Europe, Asia without India and North America. The southern mainland - Gondwana united the modern territories of South America, Africa, Antarctica, Australia and Hindustan.

Between Gondwana and Laurasia was the first sea - Tethys, like a huge bay. The rest of the Earth's space was occupied by the Panthalassa ocean.

About 200 million years ago, Gondwana and Laurasia were united into a single continent - Pangea (Pan - universal, Ge - earth)

Approximately 180 million years ago, the mainland of Pangea again began to be divided into constituent parts, which mixed up on the surface of our planet. The division took place as follows: first, Laurasia and Gondwana reappeared, then Laurasia divided, and then Gondwana also split. Due to the split and divergence of parts of Pangea, oceans were formed. The young oceans can be considered the Atlantic and Indian; old - Quiet. The Arctic Ocean became isolated with the increase in land mass in the Northern Hemisphere.

A. Wegener found a lot of evidence for the existence of a single continent of the Earth. The existence in Africa and South America of the remains of ancient animals - leafosaurs seemed especially convincing to him. These were reptiles, similar to small hippos, that lived only in freshwater reservoirs. So, to swim huge distances on the salty sea ​​water they couldn't. He found similar evidence in the plant world.

Interest in the hypothesis of the movement of the continents in the 30s of the XX century. decreased slightly, but in the 60s it revived again, when, as a result of studies of the relief and geology of the ocean floor, data were obtained indicating the processes of expansion (spreading) of the oceanic crust and the “diving” of some parts of the crust under others (subduction).

The structure of the continental rift

The upper stone part of the planet is divided into two shells, which differ significantly in rheological properties: a rigid and brittle lithosphere and an underlying plastic and mobile asthenosphere.
The base of the lithosphere is an isotherm approximately equal to 1300°C, which corresponds to the melting temperature (solidus) of mantle material at lithostatic pressure existing at depths of a few hundreds of kilometers. The rocks lying in the Earth above this isotherm are quite cold and behave like a rigid material, while the underlying rocks of the same composition are quite heated and deform relatively easily.

The lithosphere is divided into plates, constantly moving along the surface of the plastic asthenosphere. The lithosphere is divided into 8 large plates, dozens of medium plates and many small ones. Between the large and medium slabs there are belts composed of a mosaic of small crustal slabs.

Plate boundaries are areas of seismic, tectonic, and magmatic activity; the inner areas of the plates are weakly seismic and are characterized by a weak manifestation of endogenous processes.
More than 90% of the Earth's surface falls on 8 large lithospheric plates:

Some lithospheric plates are composed exclusively of oceanic crust (for example, the Pacific Plate), others include fragments of both oceanic and continental crust.

Diagram of rift formation

There are three types of relative plate movements: divergence (divergence), convergence (convergence) and shear movements.

Divergent boundaries are boundaries along which plates move apart. The geodynamic setting in which the process of horizontal stretching of the earth's crust occurs, accompanied by the appearance of extended linearly elongated fissured or ravine-shaped depressions, is called rifting. These boundaries are confined to continental rifts and mid-ocean ridges in ocean basins. The term "rift" (from the English rift - gap, crack, gap) is applied to large linear structures of deep origin, formed during the stretching of the earth's crust. In terms of structure, they are graben-like structures. Rifts can be laid both on the continental and oceanic crust, forming a single global system oriented relative to the geoid axis. In this case, the evolution of continental rifts can lead to a break in the continuity of the continental crust and the transformation of this rift into an oceanic rift (if the expansion of the rift stops before the stage of break of the continental crust, it is filled with sediments, turning into an aulacogen).

The process of plate expansion in the zones of oceanic rifts (mid-ocean ridges) is accompanied by the formation of a new oceanic crust due to magmatic basaltic melts coming from the asthenosphere. Such a process of formation of a new oceanic crust due to the influx of mantle matter is called spreading (from the English spread - to spread, unfold).

The structure of the mid-ocean ridge. 1 - asthenosphere, 2 - ultrabasic rocks, 3 - basic rocks (gabbroids), 4 - complex of parallel dikes, 5 - ocean floor basalts, 6 - oceanic crust segments formed at different times (I-V as they age), 7 - near-surface igneous chamber (with ultrabasic magma in the lower part and basic in the upper part), 8 – sediments of the ocean floor (1-3 as they accumulate)

In the course of spreading, each stretching pulse is accompanied by the inflow of a new portion of mantle melts, which, while solidifying, build up the edges of the plates diverging from the MOR axis. It is in these zones that the formation of young oceanic crust occurs.

Collision of continental and oceanic lithospheric plates

Subduction is the process of subduction of an oceanic plate under a continental or other oceanic one. Subduction zones are confined to the axial parts of deep-sea trenches associated with island arcs (which are elements of active margins). Subduction boundaries account for about 80% of the length of all convergent boundaries.

When continental and oceanic plates collide, a natural phenomenon is the subduction of the oceanic (heavier) plate under the edge of the continental one; when two oceanic ones collide, the older one (that is, the cooler and denser) of them sinks.

The subduction zones have a characteristic structure: their typical elements are a deep-water trough - a volcanic island arc - a back-arc basin. A deep-water trench is formed in the zone of bending and underthrust of the subducting plate. As this plate sinks, it begins to lose water (which is found in abundance in sediments and minerals), the latter, as is known, significantly reduces the melting point of rocks, which leads to the formation of melting centers that feed island arc volcanoes. In the rear of a volcanic arc, some extension usually occurs, which determines the formation of a back-arc basin. In the zone of the back-arc basin, the extension can be so significant that it leads to the rupture of the plate crust and the opening of the basin with the oceanic crust (the so-called back-arc spreading process).

The volume of oceanic crust absorbed in subduction zones is equal to the volume of crust formed in spreading zones. This provision emphasizes the opinion about the constancy of the volume of the Earth. But such an opinion is not the only and definitively proven. It is possible that the volume of the plans changes pulsatingly, or there is a decrease in its decrease due to cooling.

The subduction of the subducting plate into the mantle is traced by earthquake foci that occur at the contact of the plates and inside the subducting plate (which is colder and therefore more fragile than the surrounding mantle rocks). This seismic focal zone is called the Benioff-Zavaritsky zone. In subduction zones, the process of formation of a new continental crust begins. A much rarer process of interaction between the continental and oceanic plates is the process of obduction - thrusting of a part of the oceanic lithosphere onto the edge of the continental plate. It should be emphasized that in the course of this process, the oceanic plate is stratified, and only its upper part is advancing - the crust and several kilometers of the upper mantle.

Collision of continental lithospheric plates

When continental plates collide, the crust of which is lighter than the substance of the mantle and, as a result, is not able to sink into it, the process of collision proceeds. In the course of collision, the edges of colliding continental plates are crushed, crushed, and systems of large thrusts are formed, which leads to the growth of mountain structures with a complex fold-thrust structure. A classic example such a process is the collision of the Hindustan plate with the Eurasian one, accompanied by the growth of the grandiose mountain systems of the Himalayas and Tibet. The collision process replaces the subduction process, completing the closure of the ocean basin. At the same time, at the beginning of the collision process, when the edges of the continents have already approached, the collision is combined with the subduction process (the remains of the oceanic crust continue to sink under the edge of the continent). Collision processes are characterized by large-scale regional metamorphism and intrusive granitoid magmatism. These processes lead to the creation of a new continental crust (with its typical granite-gneiss layer).

The main cause of plate movement is mantle convection, caused by mantle heat and gravity currents.

The source of energy for these currents is the temperature difference between the central regions of the Earth and the temperature of its near-surface parts. At the same time, the main part of the endogenous heat is released at the boundary of the core and mantle during the process of deep differentiation, which determines the decay of the primary chondritic substance, during which the metal part rushes to the center, increasing the core of the planet, and the silicate part is concentrated in the mantle, where it further undergoes differentiation.

The rocks heated in the central zones of the Earth expand, their density decreases, and they float, giving way to descending colder and therefore heavier masses, which have already given up part of the heat in near-surface zones. This process of heat transfer goes on continuously, resulting in the formation of ordered closed convective cells. At the same time, in the upper part of the cell, the flow of matter occurs in an almost horizontal plane, and it is this part of the flow that determines the horizontal movement of the matter of the asthenosphere and the plates located on it. In general, the ascending branches of convective cells are located under the zones of divergent boundaries (MOR and continental rifts), while the descending branches are located under the zones of convergent boundaries. Thus, the main reason for the movement of lithospheric plates is "drag" by convective currents. In addition, a number of other factors act on the plates. In particular, the surface of the asthenosphere turns out to be somewhat elevated above the zones of ascending branches and more lowered in the zones of subsidence, which determines the gravitational "sliding" of the lithospheric plate located on an inclined plastic surface. Additionally, there are processes of pulling the heavy cold oceanic lithosphere in the subduction zones into the hot, and as a result less dense, asthenosphere, as well as hydraulic wedging by basalts in the MOR zones.

The main driving forces of plate tectonics are applied to the bottom of the intraplate parts of the lithosphere: the forces of mantle “drag” (English drag) FDO under the oceans and FDC under the continents, the magnitude of which depends primarily on the speed of the asthenospheric current, and the latter is determined by the viscosity and thickness of the asthenospheric layer. Since the thickness of the asthenosphere under the continents is much less and the viscosity is much higher than under the oceans, the magnitude of the FDC force is almost an order of magnitude inferior to that of the FDO. Under the continents, especially their ancient parts (continental shields), the asthenosphere almost wedges out, so the continents seem to be “sitting aground”. Since most of the lithospheric plates modern Earth include both oceanic and continental parts, it should be expected that the presence of a continent in the composition of the plate in the general case should “slow down” the movement of the entire plate. This is how it actually happens (the fastest moving are the almost purely oceanic plates Pacific, Cocos and Nasca; the slowest are the Eurasian, North American, South American, Antarctic and African, a significant part of the area of ​​​​which is occupied by continents). Finally, at convergent plate boundaries, where the heavy and cold edges of lithospheric plates (slabs) sink into the mantle, their negative buoyancy creates the FNB force (negative buoyance). The action of the latter leads to the fact that the subducting part of the plate sinks in the asthenosphere and pulls the entire plate along with it, thereby increasing the speed of its movement. Obviously, the FNB force acts episodically and only in certain geodynamic settings, for example, in the cases of the collapse of slabs through the 670 km section described above.

Thus, the mechanisms that set the lithospheric plates in motion can be conventionally assigned to the following two groups: 1) associated with the forces of the mantle “dragging” (mantle drag mechanism) applied to any points of the bottom of the plates, in the figure - the forces of FDO and FDC; 2) associated with the forces applied to the edges of the plates (edge-force mechanism), in the figure - the forces FRP and FNB. The role of this or that driving mechanism, as well as these or those forces, is evaluated individually for each lithospheric plate.

The totality of these processes reflects the general geodynamic process, covering areas from the surface to deep zones of the Earth. At present, two-cell closed-cell mantle convection is developing in the Earth's mantle (according to the through-mantle convection model) or separate convection in the upper and lower mantle with the accumulation of slabs under subduction zones (according to the two-tier model). The probable poles of the rise of the mantle matter are located in northeast Africa (approximately under the junction zone of the African, Somali and Arabian plates) and in the area of ​​Easter Island (under the middle ridge of the Pacific Ocean - the East Pacific Rise). The mantle subsidence equator runs approximately along a continuous chain of convergent plate boundaries along the periphery of the Pacific and eastern Indian Oceans. convection) or (according to an alternative model) convection will become through the mantle due to the collapse of slabs through the 670 km section. This may lead to the collision of the continents and the formation of a new supercontinent, the fifth in the history of the Earth.

Plate movements obey the laws of spherical geometry and can be described on the basis of Euler's theorem. Euler's rotation theorem states that any rotation of three-dimensional space has an axis. Thus, rotation can be described by three parameters: the coordinates of the rotation axis (for example, its latitude and longitude) and the angle of rotation. Based on this position, the position of the continents in past geological epochs can be reconstructed. An analysis of the movements of the continents led to the conclusion that every 400-600 million years they unite into a single supercontinent, which is further disintegrated. As a result of the split of such a supercontinent Pangea, which occurred 200-150 million years ago, modern continents were formed.

Plate tectonics is the first general geological concept that could be tested. Such a check has been made. In the 70s. deep-sea drilling program was organized. As part of this program, several hundred wells were drilled by the Glomar Challenger drillship, which showed good agreement of ages estimated from magnetic anomalies with ages determined from basalts or from sedimentary horizons. The distribution scheme of uneven-aged sections of the oceanic crust is shown in Fig.:

The age of the oceanic crust according to magnetic anomalies (Kenneth, 1987): 1 - areas of lack of data and dry land; 2–8 - age: 2 - Holocene, Pleistocene, Pliocene (0–5 Ma); 3 - Miocene (5–23 Ma); 4 - Oligocene (23–38 Ma); 5 - Eocene (38–53 Ma); 6 - Paleocene (53–65 Ma) 7 - Cretaceous (65–135 Ma) 8 - Jurassic (135–190 Ma)

At the end of the 80s. completed another experiment to test the movement of lithospheric plates. It was based on baseline measurements relative to distant quasars. Points were selected on two plates, at which, using modern radio telescopes, the distance to quasars and their declination angle were determined, and, accordingly, the distances between points on two plates were calculated, i.e., the baseline was determined. The accuracy of the determination was a few centimeters. Several years later, the measurements were repeated. Very good convergence of results calculated from magnetic anomalies with data determined from baselines was obtained.

Scheme illustrating the results of measurements of the mutual displacement of lithospheric plates, obtained by the method of interferometry with an extra long baseline - ISDB (Carter, Robertson, 1987). The movement of the plates changes the length of the baseline between radio telescopes located on different plates. The map of the Northern Hemisphere shows the baselines from which the ISDB measured enough data to make a reliable estimate of the rate of change in their length (in centimeters per year). The numbers in parentheses indicate the amount of plate displacement calculated from the theoretical model. In almost all cases, the calculated and measured values ​​are very close.

Thus, lithospheric plate tectonics has been tested over the years by a number of independent methods. It is recognized by the world scientific community as the paradigm of geology at the present time.

Knowing the position of the poles and the speed of the current movement of lithospheric plates, the speed of expansion and absorption of the ocean floor, it is possible to outline the path of movement of the continents in the future and imagine their position for a certain period of time.

Such a forecast was made by American geologists R. Dietz and J. Holden. In 50 million years, according to their assumptions, the Atlantic and Indian oceans will expand at the expense of the Pacific, Africa will shift to the north, and due to this, the Mediterranean Sea will gradually be liquidated. The Strait of Gibraltar will disappear, and the “turned” Spain will close the Bay of Biscay. Africa will be split by the great African faults and the eastern part of it will shift to the northeast. The Red Sea will expand so much that it will separate the Sinai Peninsula from Africa, Arabia will move to the northeast and close the Persian Gulf. India will increasingly move towards Asia, which means that the Himalayan mountains will grow. California will separate from North America along the San Andreas Fault, and a new ocean basin will begin to form in this place. Significant changes will occur in the southern hemisphere. Australia will cross the equator and come into contact with Eurasia. This forecast requires significant refinement. Much here is still debatable and unclear.

sources

http://www.pegmatite.ru/My_Collection/mineralogy/6tr.htm

http://www.grandars.ru/shkola/geografiya/dvizhenie-litosfernyh-plit.html

http://kafgeo.igpu.ru/web-text-books/geology/platehistory.htm

http://stepnoy-sledopyt.narod.ru/geologia/dvizh/dvizh.htm

And let me remind you, but here are some interesting ones and this one. Look at and The original article is on the website InfoGlaz.rf Link to the article from which this copy is made -

• 1)_The first hypothesis arose in the second half of the 18th century and was called the uplift hypothesis. It was proposed by M. V. Lomonosov, German scientists A. von Humboldt and L. von Buch, Scot J. Hutton. The essence of the hypothesis is as follows - mountain uplifts are caused by the rise of molten magma from the depths of the Earth, which on its way had a pushing effect on the surrounding layers, leading to the formation of folds, abysses of various sizes. Lomonosov was the first to distinguish two types of tectonic movements - slow and fast, causing earthquakes.
• 2) In the middle of the 19th century, this hypothesis was replaced by the contraction hypothesis of the French scientist Elie de Beaumont. It was based on the cosmogonic hypothesis of Kant and Laplace about the origin of the Earth as an initially hot body with subsequent gradual cooling. This process led to a decrease in the volume of the Earth, and as a result, the Earth's crust was compressed, and folded mountain structures arose similar to giant "wrinkles".
• 3) In the middle of the 19th century, the Englishman D. Airy and the priest from Calcutta D. Pratt discovered a pattern in the positions of gravity anomalies - high in the mountains, the anomalies turned out to be negative, i.e., a mass deficit was detected, and in the oceans the anomalies were positive. To explain this phenomenon, a hypothesis was proposed, according to which the earth's crust floats on a heavier and more viscous substrate and is in isostatic equilibrium, which is disturbed by the action of external radial forces.
• 4) The cosmogonic hypothesis of Kant-Laplace was replaced by the hypothesis of O. Yu. Schmidt about the initial solid, cold and homogeneous state of the Earth. There was a need for a different approach in explaining the formation of the earth's crust. Such a hypothesis was proposed by V. V. Belousov. It's called radio migration. The essence of this hypothesis:
• 1. The main energy factor is radioactivity. The heating of the Earth with subsequent compaction of matter occurred due to the heat of radioactive decay. radioactive elements on early stages The development of the Earth was distributed evenly, and therefore the heating was strong and ubiquitous.
• 2. Heating of the primary substance and its compaction led to the separation of magma or its differentiation into basalt and granite. The latter concentrated radioactive elements. As a lighter granitic magma “floated up” to the upper part of the Earth, while the basalt magma sank down. At the same time, there was also a temperature difference.

Modern geotectonic hypotheses are developed using the ideas of mobilism. This idea is based on the concept of the predominance of horizontal movements in the tectonic movements of the earth's crust.

• 5) For the first time, to explain the mechanism and sequence of geotectonic processes, the German scientist A. Wegener proposed the hypothesis of horizontal continental drift.
• 1. The similarity of the outlines of the coasts of the Atlantic Ocean, especially in the southern hemisphere (near South America and Africa).
• 2. Similarity of the geological structure of the continents (coincidence of some regional tectonic strikes, similarity in composition and age of rocks, etc.).

hypothesis of lithospheric plate tectonics or new global tectonics. The main points of this hypothesis are:

• 1. The earth's crust with the upper part of the mantle forms the lithosphere, which is underlain by the plastic asthenosphere. The lithosphere is divided into large blocks (plates). The boundaries of the plates are rift zones, deep-water trenches, which are adjacent to faults that penetrate deep into the mantle - these are the Benioff-Zavaritsky zones, as well as zones of modern seismic activity.
• 2. Lithospheric plates move horizontally. This movement is determined by two main processes - pushing the plates apart or spreading, submerging one plate under another - subduction or pushing one plate onto another - obduction.
• 3. Basalts from the mantle periodically enter the pull apart zone. Evidence of the separation is provided by strip magnetic anomalies in basalts.
• 4. In the regions of island arcs, zones of accumulation of sources of deep-focus earthquakes are distinguished, which reflect zones of subsidence of a plate with basaltic oceanic crust under the continental crust, i.e., these zones reflect subduction zones. In these zones, due to crushing and melting, part of the material subsides, while the other part penetrates into the continent in the form of volcanoes and intrusions, thereby increasing the thickness of the continental crust.

Plate tectonics is a modern geological theory about the movement of the lithosphere. According to this theory, global tectonic processes are based on horizontal movement of relatively integral blocks of the lithosphere - lithospheric plates. Thus, plate tectonics considers the movements and interactions of lithospheric plates. Alfred Wegener first proposed the horizontal movement of crustal blocks in the 1920s as part of the “continental drift” hypothesis, but this hypothesis did not receive support at that time. Only in the 1960s, studies of the ocean floor provided indisputable evidence of the horizontal movement of plates and the processes of expansion of the oceans due to the formation (spreading) of the oceanic crust. The revival of ideas about the predominant role of horizontal movements occurred within the framework of the "mobilistic" direction, the development of which led to the development of the modern theory of plate tectonics. The main provisions of plate tectonics were formulated in 1967-68 by a group of American geophysicists - W. J. Morgan, C. Le Pichon, J. Oliver, J. Isaacs, L. Sykes in the development of earlier (1961-62) ideas of American scientists G. Hess and R. Digts on the expansion (spreading) of the ocean floor. 1). The upper stone part of the planet is divided into two shells, which differ significantly in rheological properties: a rigid and brittle lithosphere and an underlying plastic and mobile asthenosphere. 2). The lithosphere is divided into plates, constantly moving along the surface of the plastic asthenosphere. The lithosphere is divided into 8 large plates, dozens of medium plates and many small ones. Between the large and medium slabs there are belts composed of a mosaic of small crustal slabs. 3). There are three types of relative plate movements: divergence (divergence), convergence (convergence) and shear movements. 4). The volume of oceanic crust absorbed in subduction zones is equal to the volume of crust formed in spreading zones. This provision emphasizes the opinion about the constancy of the volume of the Earth. 5). The main cause of plate movement is mantle convection, caused by mantle heat and gravity currents.

The source of energy for these currents is the temperature difference between the central regions of the Earth and the temperature of its near-surface parts. At the same time, the main part of the endogenous heat is released at the boundary of the core and mantle during the process of deep differentiation, which determines the decay of the primary chondritic substance, during which the metal part rushes to the center, increasing the core of the planet, and the silicate part is concentrated in the mantle, where it further undergoes differentiation. 6). Plate movements obey the laws of spherical geometry and can be described on the basis of Euler's theorem. Euler's rotation theorem states that any rotation of three-dimensional space has an axis. Thus, rotation can be described by three parameters: the coordinates of the rotation axis (for example, its latitude and longitude) and the angle of rotation.

Geographical consequences of the movement of Lith plates (Seismic activity increases, faults form, ridges appear, and so on). In the theory of plate tectonics, the key position is occupied by the concept of the geodynamic setting - a characteristic geological structure with a certain ratio of plates. In the same geodynamic setting, the same type of tectonic, magmatic, seismic, and geochemical processes occur.

tectonic fault lithospheric geomagnetic

Beginning with the Early Proterozoic, the rate of movement of lithospheric plates consistently decreased from 50 cm/yr to its current value of about 5 cm/yr.

decline average speed plate movements will continue, until the moment when, due to the increase in the power of oceanic plates and their friction against each other, it does not stop at all. But this will happen, apparently, only after 1-1.5 billion years.

To determine the velocities of the movement of lithospheric plates, data on the location of banded magnetic anomalies on the ocean floor are usually used. These anomalies, as has now been established, appear in the rift zones of the oceans due to the magnetization of the basalt erupted on them by the magnetic field that existed on Earth at the time of the basalt outpouring.

But, as you know, the geomagnetic field from time to time changed direction to the exact opposite. This led to the fact that the basalts that erupted into different periods reversals of the geomagnetic field turned out to be magnetized in opposite directions.

But due to the expansion of the ocean floor in the rift zones of the mid-ocean ridges, the older basalts always turn out to be moved to greater distances from these zones, and together with the ocean floor, the ancient magnetic field of the Earth “frozen” into the basalts also moves away from them.

Rice.

The expansion of the oceanic crust together with differently magnetized basalts usually develops strictly symmetrically on both sides of the rift fault. Therefore, the magnetic anomalies associated with them are also located symmetrically along both slopes of the mid-ocean ridges and the abyssal basins surrounding them. Such anomalies can now be used to determine the age of the ocean floor and its expansion rate in rift zones. However, for this it is necessary to know the age of individual reversals of the Earth's magnetic field and compare these reversals with the magnetic anomalies observed on the ocean floor.

The age of magnetic reversals was determined from detailed paleomagnetic studies of well-dated sequences of basaltic sheets and sedimentary rocks of the continents and ocean floor basalts. As a result of comparing the geomagnetic time scale obtained in this way with magnetic anomalies on the ocean floor, it was possible to determine the age of the oceanic crust in most of the waters of the World Ocean. All oceanic plates that formed earlier than the Late Jurassic have already subsided into the mantle under modern or ancient zones of plate underthrust, and, consequently, no magnetic anomalies older than 150 million years have been preserved on the ocean floor.

The above conclusions of the theory make it possible to quantitatively calculate the motion parameters at the beginning of two adjacent plates, and then for the third, taken in tandem with one of the previous ones. In this way, one can gradually involve the main of the identified lithospheric plates in the calculation and determine the mutual displacements of all plates on the Earth's surface. Abroad, such calculations were performed by J. Minster and his colleagues, and in Russia by S.A. Ushakov and Yu.I. Galushkin. It turned out that with maximum speed the ocean floor is moving apart in the southeastern part of the Pacific Ocean (near Easter Island). In this place, up to 18 cm of new oceanic crust grows annually. In terms of geological scale, this is a lot, since in just 1 million years a strip of a young bottom up to 180 km wide is formed in this way, while approximately 360 km3 of basalt lavas are poured out at each kilometer of the rift zone in the same time! According to the same calculations, Australia is moving away from Antarctica at a rate of about 7 cm/year, and South America is moving away from Africa at a rate of about 4 cm/year. The pushing away of North America from Europe is slower - 2-2.3 cm/year. The Red Sea expands even more slowly - by 1.5 cm/year (correspondingly, less basalt is poured out here - only 30 km3 per linear kilometer of the Red Sea rift in 1 million years). On the other hand, the rate of "collision" between India and Asia reaches 5 cm/year, which explains the intense neotectonic deformations developing before our eyes and the growth of the mountain systems of the Hindu Kush, the Pamirs and the Himalayas. These deformations create a high level of seismic activity in the entire region (the tectonic impact of the collision of India with Asia affects far beyond the plate collision zone itself, extending all the way to Lake Baikal and the regions of the Baikal-Amur Mainline). The deformations of the Greater and Lesser Caucasus are caused by the pressure of the Arabian Plate on this region of Eurasia, however, the rate of convergence of the plates here is much less - only 1.5-2 cm / year. Therefore, the seismic activity of the region is also less here.

Modern geodetic methods, including space geodesy, high-precision laser measurements, and other methods have established the velocities of lithospheric plates, and it has been proven that oceanic plates move faster than those that include a continent, and the thicker the continental lithosphere, the lower the plate movement speed.

Last week, the public was stirred by the news that the Crimean peninsula is moving towards Russia, not only thanks to the political will of the population, but also according to the laws of nature. What are lithospheric plates and on which of them is Russia territorially located? What makes them move and where? Which territories still want to "join" Russia, and which ones threaten to "escape" to the USA?

"And we're going somewhere"

Yes, we are all going somewhere. While you are reading these lines, you are moving slowly: if you are in Eurasia, then east at a speed of about 2-3 centimeters per year, if in North America, then at the same speed west, and if somewhere at the bottom of the Pacific Ocean (how did you get there?), then it takes you to the northwest by 10 centimeters a year.

If you sit back in your chair and wait about 250 million years, you will find yourself on a new supercontinent that will unite all the earth's land - on the mainland Pangea Ultima, named so in memory of the ancient supercontinent Pangea, which existed just 250 million years ago.

Therefore, the news that "Crimea is moving" can hardly be called news. Firstly, because Crimea, together with Russia, Ukraine, Siberia and the European Union, is part of the Eurasian lithospheric plate, and all of them have been moving together in one direction for the last hundred million years. However, Crimea is also part of the so-called Mediterranean mobile belt, it is located on the Scythian plate, and most of the European part of Russia (including the city of St. Petersburg) - on the East European platform.

And this is where confusion often arises. The fact is that in addition to huge sections of the lithosphere, such as the Eurasian or North American plates, there are completely different smaller "tiles". If very conditionally, then the earth's crust is composed of continental lithospheric plates. They themselves consist of ancient and very stable platforms.and mountain building zones (ancient and modern). And already the platforms themselves are divided into slabs - smaller sections of the crust, consisting of two "layers" - the foundation and the cover, and shields - "single-layer" outcrops.

The cover of these non-lithospheric plates consists of sedimentary rocks (for example, limestone, composed of many shells of marine animals that lived in the prehistoric ocean above the surface of Crimea) or igneous rocks (thrown from volcanoes and solidified lava masses). A fslab foundations and shields most often consist of very old rocks, mainly of metamorphic origin. This is the name of igneous and sedimentary rocks that have sunk into the depths of the earth's crust, where, under the influence of high temperatures and enormous pressure, a variety of changes occur with them.

In other words, most of Russia (with the exception of Chukotka and Transbaikalia) is located on the Eurasian lithospheric plate. However, its territory is "divided" between the West Siberian plate, the Aldan shield, the Siberian and East European platforms and the Scythian plate.

Probably, the director of the Institute of Applied Astronomy (IPA RAS), Doctor of Physical and Mathematical Sciences Alexander Ipatov, said about the movement of the last two plates. And later, in an interview with Indicator, he clarified: “We are engaged in observations that allow us to determine the direction of movement of the plates of the earth's crust. The plate on which the Simeiz station is located moves at a speed of 29 millimeters per year to the northeast, that is, to where Russia And the plate where Peter is located is moving, one might say, towards Iran, to the south-southwest."However, this is not such a discovery, because this movement has been around for several decades, and it itself began back in the Cenozoic era.

Wegener's theory was received with skepticism - mainly because he could not offer a satisfactory mechanism to explain the movement of the continents. He believed that the continents move, breaking through the earth's crust, like icebreakers through ice, due to the centrifugal force from the rotation of the Earth and tidal forces. His opponents said that the continents-"icebreakers" in the process of movement would change their appearance beyond recognition, and centrifugal and tidal forces are too weak to serve as a "motor" for them. One critic calculated that if the tidal force were strong enough to move the continents so fast (Wegener estimated their speed at 250 centimeters per year), it would stop the rotation of the Earth in less than a year.

By the end of the 1930s, the theory of continental drift was rejected as unscientific, but by the middle of the 20th century it had to be returned to: mid-ocean ridges were discovered and it turned out that new crust was continuously forming in the zone of these ridges, due to which the continents were "moving apart" . Geophysicists have studied the magnetization of rocks along the mid-ocean ridges and found "stripes" with multidirectional magnetization.

It turned out that the new oceanic crust "records" the state of the Earth's magnetic field at the time of formation, and scientists have received an excellent "ruler" to measure the speed of this conveyor. So, in the 1960s, the theory of continental drift returned for the second time, for good. And this time, scientists were able to understand what moves the continents.

Ice floes in the boiling ocean

"Imagine an ocean where ice floes float, that is, there is water in it, there is ice, and, let's say, wooden rafts are also frozen into some ice floes. Ice is lithospheric plates, rafts are continents, and they float in the substance of the mantle," explains Corresponding Member of the Russian Academy of Sciences Valery Trubitsyn, chief researcher at the Institute of Physics of the Earth named after O.Yu. Schmidt.

Back in the 1960s, he put forward the theory of the structure of giant planets, and at the end of the 20th century he began to create a mathematically substantiated theory of continental tectonics.

The intermediate layer between the lithosphere and the hot iron core in the center of the Earth - the mantle - consists of silicate rocks. The temperature in it varies from 500 degrees Celsius in the upper part to 4000 degrees Celsius at the border of the core. Therefore, from a depth of 100 kilometers, where the temperature is already more than 1300 degrees, the mantle substance behaves like a very thick resin and flows at a speed of 5-10 centimeters per year, says Trubitsyn.

As a result, in the mantle, as in a pot of boiling water, convective cells appear - areas where hot matter rises from one edge, and cooled down from the other.

"There are about eight of these large cells in the mantle and many more small ones," the scientist says. Mid-ocean ridges (for example, in the center of the Atlantic) are the place where the material of the mantle rises to the surface and where new crust is born. In addition, there are subduction zones, places where a plate begins to "creep" under the neighboring one and sinks down into the mantle. Subduction zones are, for example, the western coast of South America. This is where the most powerful earthquakes occur.

“In this way, the plates take part in the convective circulation of the mantle substance, which temporarily becomes solid while on the surface. Plunging into the mantle, the plate substance heats up and softens again,” explains the geophysicist.

In addition, separate jets of matter rise to the surface from the mantle - plumes, and these jets have every chance to destroy humanity. After all, it is the mantle plumes that are the cause of the appearance of supervolcanoes (see). Such points are in no way connected with lithospheric plates and can remain in place even when the plates move. When the plume exits, a giant volcano arises. There are many such volcanoes, they are in Hawaii, in Iceland, a similar example is the Yellowstone caldera. Supervolcanoes can generate eruptions thousands of times more powerful than most ordinary volcanoes like Vesuvius or Etna.

"250 million years ago, such a volcano on the territory of modern Siberia killed almost all life, only the ancestors of dinosaurs survived," says Trubitsyn.

Agreed - dispersed

Lithospheric plates consist of relatively heavy and thin basaltic oceanic crust and lighter, but much thicker continents. A plate with a continent and oceanic crust "frozen" around it can move forward, while the heavy oceanic crust sinks under its neighbor. But when continents collide, they can no longer sink under each other.

For example, about 60 million years ago, the Indian plate broke away from what later became Africa and went north, and about 45 million years ago it met with the Eurasian plate, the Himalayas, the highest mountains on Earth, grew at the point of collision.

The movement of the plates will sooner or later bring all the continents into one, as leaves converge into one island in a whirlpool. In the history of the Earth, the continents have united and broken up approximately four to six times. The last supercontinent Pangea existed 250 million years ago, before it was the supercontinent Rodinia, 900 million years ago, before it - two more. "And already, it seems, the unification of the new continent will soon begin," the scientist clarifies.

He explains that the continents act as a thermal insulator, the mantle beneath them begins to heat up, updrafts occur, and therefore the supercontinents break apart again after a while.

America will "take away" Chukotka

Large lithospheric plates are drawn in textbooks, anyone can name them: Antarctic plate, Eurasian, North American, South American, Indian, Australian, Pacific. But at the boundaries between the plates there is a real chaos of many microplates.

For example, the boundary between the North American Plate and the Eurasian Plate does not run along the Bering Strait at all, but much to the west, along the Chersky Ridge. Chukotka thus turns out to be part of the North American Plate. At the same time, Kamchatka is partly located in the zone of the Okhotsk microplate, and partly in the zone of the Bering Sea microplate. And Primorye is located on the hypothetical Amur Plate, the western edge of which rests on Baikal.

Now the eastern edge of the Eurasian plate and the western edge of the North American plate are "spinning" like gears: America is turning counterclockwise, and Eurasia is turning clockwise. As a result, Chukotka may finally come off "along the seam", and in this case, a giant circular seam may appear on Earth, which will pass through the Atlantic, the Indian, Pacific and Arctic Oceans (where it is still closed). And Chukotka itself will continue to move "in the orbit" of North America.

Speedometer for the lithosphere

Wegener's theory has been resurrected, not least because scientists have the ability to accurately measure the displacement of continents. Now satellite navigation systems are used for this, but there are other methods. All of them are needed to build a single international coordinate system - the International Terrestrial Reference Frame (ITRF).

One of these methods is very long baseline radio interferometry (VLBI). Its essence lies in simultaneous observations with the help of several radio telescopes in different parts of the Earth. The difference in signal acquisition time makes it possible to determine offsets with high accuracy. Two other ways to measure speed are laser ranging observations using satellites and Doppler measurements. All these observations, including with the help of GPS, are carried out at hundreds of stations, all these data are brought together, and as a result, we get a picture of continental drift.

For example, Crimean Simeiz, where a laser sounding station is located, as well as a satellite station for determining coordinates, "moves" to the northeast (in azimuth about 65 degrees) at a speed of about 26.8 millimeters per year. Zvenigorod, near Moscow, is moving about a millimeter a year faster (27.8 millimeters a year) and keeps its course to the east - about 77 degrees. And, say, the Hawaiian volcano Mauna Loa is moving northwest twice as fast - 72.3 millimeters per year.

Lithospheric plates can also be deformed, and their parts can "live their own lives", especially at the boundaries. Although the scale of their independence is much more modest. For example, Crimea is still moving independently to the northeast at a speed of 0.9 millimeters per year (and at the same time growing by 1.8 millimeters), and Zvenigorod is moving somewhere to the southeast at the same speed (and down - by 0 .2 millimeters per year).

Trubitsyn says that this independence is partly due to the "personal history" of different parts of the continents: the main parts of the continents, the platforms, may be fragments of ancient lithospheric plates that "merged" with their neighbors. For example, the Ural Range is one of the seams. Platforms are relatively rigid, but parts around them can deform and move at will.