In the process of the formation, and then the development of geology as a science, many hypotheses were proposed, each of which, from one point or another, considered and explained either individual problems or a complex of problems related to the development of the earth's crust or the Earth as a whole. These hypotheses are called geotectonic. Some of them, due to insufficient convincingness, quickly lost their significance in science, while others turned out to be more durable, again until new facts and ideas were accumulated, which formed the basis of new hypotheses that were more consistent with a given stage in the development of science. Despite the great success achieved in the study of the structure and development of the earth's crust, none of the modern hypotheses and theories (even recognized ones) is able to explain with sufficient reliability and fully all the conditions for the formation of the earth's crust.

The first scientific hypothesis, the uplift hypothesis, was formulated in the first half of the 19th century. on the basis of the ideas of the plutonists about the role of the internal forces of the Earth, which played a positive role in the fight against the erroneous ideas of the neptunists. In the 50s. XIX century. it was replaced by the more grounded hypothesis of contraction (condensed) by the French scientist Elie de Beaumont at the time. The contraction hypothesis was based on Laplace's cosmogonic hypothesis, which, as is known, recognized the primary hot state of the Earth and its subsequent gradual cooling.

The essence of the contraction hypothesis is that the cooling of the Earth causes it to contract with a subsequent decrease in its volume. As a result, the earth's crust, which hardened before the inner zones of the planet, is forced to wrinkle, which is why folded mountains are formed.

In the second half of the XIX century. American scientists J. Hall and J. Dan formulated the doctrine of geosynclines - special mobile zones of the earth's crust that eventually turn into folded mountain structures. This doctrine markedly strengthened the position of the contraction hypothesis. However, by the beginning of the XX century. In connection with the receipt of new data about the Earth, this hypothesis began to lose its significance, since it was unable to explain the periodicity of mountain-building movements and magmatism processes, ignored the extension processes, etc. In addition, ideas about the formation of a planet from cold particles arose in science , which deprived the hypothesis of its main support.

At the same time, the doctrine of geosynclines continued to be supplemented and developed. In this respect, a great contribution was made by Soviet scientists A. D. Arkhangelsky, N. S. Shatsky, M. V. Muratov, and others. and especially from the beginning of the XX century. the doctrine of relatively stable continental areas - platforms began to develop; among the domestic scientists who developed this doctrine, one must first of all name A. P. Karpinsky, A. D. Arkhangelsky, N. S. Shatsky, A. A. Bogdanov, A. L. Yanshin.

The study of geosynclines and platforms has become firmly established in geological science and retains its significance to the present day. However, it still does not have a solid theoretical basis.

The desire to supplement and eliminate shortcomings in the contraction hypothesis, or, conversely, to completely replace it, led to the appearance during the first half of the 20th century. a number of new geotectonic hypotheses. Let's note some of them.

Ripple hypothesis. It is based on the idea of ​​the alternation of the processes of compression and expansion of the Earth - processes that are very characteristic of the Universe as a whole. M.A.Usov and V.A.

Hypothesis of differentiation of subcrustal matter and migration of radioelements. Under the influence of gravitational differentiation and radiogenic heating, there is a periodic melting of liquid components from the atmosphere, which entails ruptures of the earth's crust, volcanism, mountain building and other phenomena. One of the authors of this hypothesis is the famous Soviet scientist V.V. Belousov.

Continental drift hypothesis. It was stated in 1912 by the German scientist A. Wegener and is fundamentally different from all other hypotheses. Based on the principles of mobilism - recognition of significant horizontal movements of vast continental masses. Most of the hypotheses proceeded from the principles of fixism - the recognition of a stable, fixed position of individual parts of the earth's crust relative to the underlying mantle (such are the hypotheses of contraction, differentiation of subcrustal matter and migration of radioelements, etc.).

According to A. Wegener, the granite layer of the earth's crust “floats” over the basalt layer. Under the influence of the rotation of the Earth, it turned out to be assembled into a single continent of Pangea. At the end of the Paleozoic era (about 200-300 million years ago), Pangea was split into separate blocks and began to drift until they took their present position. Under the influence of the drift of blocks of North and South America to the west, the Atlantic Ocean arose, and the resistance that these continents experienced as they moved along the basalt layer contributed to the emergence of mountains such as the Andes and Cordillera. For the same reasons, Australia and Antarctica moved apart and shifted south, etc.

A. Wegener saw the confirmation of his hypothesis in the similarity of the contours and geological structure of the coasts on both sides of the Atlantic Ocean, in the similarity of the fossil organisms of the continents, far from each other, in the different structure of the earth's crust within the oceans and continents.

The appearance of A. Wegener's hypothesis aroused great interest, but it died out relatively quickly, since it was unable to explain many phenomena, and most importantly, the possibility of continental movement along the basalt layer. Nevertheless, as we will see below, mobilist views, but on a completely new basis, were revived and widely recognized in the second half of the 20th century.

Rotational hypothesis. It occupies a separate place among geotectonic hypotheses, since it sees the manifestation of tectonic processes on the Earth under the influence of extraterrestrial causes, namely the attraction of the Moon and the Sun, causing solid tides in the earth's crust and mantle, slowing down the Earth's rotation and changing its shape. The consequence of this is not only vertical, but also horizontal displacements of individual blocks of the earth's crust. The hypothesis is not widely accepted, since the vast majority of scientists believe that tectogenesis is the result of the manifestation of the Earth's internal forces. At the same time, the influence of extraterrestrial causes on the formation of the earth's crust, obviously, must also be taken into account.

The theory of new global tectonics, or tectonics of lithospheric plates. Since the beginning of the second half of the XX century. unfolded extensive geological and geophysical studies of the bottom of the World Ocean. Their result was the emergence of completely new ideas about the development of the oceans, such as, for example, the spreading of lithospheric plates and the formation of a young oceanic crust in rift valleys, the formation of continental crust in zones of underthrusting of lithospheric plates, etc. These ideas have led to the revival of mobilist ideas in geological science and to the emergence of the theory of new global tectonics, or tectonics of lithospheric plates.

The new theory is based on the idea that the entire lithosphere (i.e., the earth's crust together with the upper mantle layer) is divided by narrow tectonically active zones into separate rigid plates moving along the asthenosphere (a plastic layer in the upper mantle). The active tectonic zones characterized by high seismicity and volcanism are rift zones of mid-oceanic ridges, systems of island arcs and deep-sea trenches of the oceans, rift valleys on the continents. In the rift zones of the mid-oceanic ridges, plates are pushed apart and new oceanic crust is formed, and in deep-sea trenches, some plates are pushed under others and a continental crust is formed. A collision of plates is also possible - the result of this phenomenon is the formation of the Himalayan fold zone.

There are seven large lithospheric plates and a slightly larger number of small ones. These plates received the following names: 1) Pacific, 2) North American, 3) South American, 4) Eurasian, 5) African, 6) Indo-Australian and 7) Antarctic. Each of them includes one or more continents or parts of them and the oceanic crust, with the exception of the Pacific plate, which is almost entirely composed of oceanic crust. Simultaneously with the horizontal displacements of the plates, their rotations also took place.

The movement of lithospheric plates, according to this theory, is caused by convective flows of matter in the mantle, generated by heat released during the radioactive decay of elements and gravitational differentiation of matter in the interior of the Earth. However, the reasoning behind thermal convection in the mantle, according to many scientists, is insufficient. This also applies to the possibility of submersion of oceanic plates into the mantle at great depths and a number of other positions. The surface expression of convective movement is the rift zones of the mid-ocean ridges, where the relatively warmer mantle, rising to the surface, undergoes melting. It pours out in the form of basaltic lavas and solidifies. Further, basaltic magma is again introduced into these frozen rocks and pushes older basalts in both directions. This happens many times. At the same time, the ocean floor is growing, expanding. A similar process was named spreading... The growth rate of the ocean floor ranges from a few mm to 18 cm per year.

Other boundaries between lithospheric plates are convergent, that is, the earth's crust in these areas is absorbed. Such zones were called subduction zones. They are located on the edges of the Pacific Ocean and in the east of the Indian Ocean. The heavy and cold oceanic lithosphere, approaching the thicker and lighter continental one, goes under it, as if diving. If two oceanic plates come into contact, then the older one sinks, since it is heavier and colder than the younger plate.

The zones where subduction occurs are morphologically expressed by deep-sea trenches, and the plunging oceanic cold and elastic lithosphere itself is well established according to seismic tomography data. The dip angle of the oceanic plates is different, up to vertical, and the plates can be traced to the boundary of the upper and lower mantles at a depth of about 670 km.

When the ocean plate begins to bend sharply when approaching the continental plate, stresses arise in it, which, being discharged, provoke earthquakes. The hypocenters or earthquake foci clearly mark the friction boundary between the two plates and form an inclined seismic focal zone that plunges beneath the continental lithosphere to a depth of 700 km. These zones are called Benioff zones, after the American seismologist who studied them.

Submersion of the oceanic lithosphere leads to other important consequences. When the lithosphere reaches a depth of 100-200 km in the area of ​​high temperatures and pressures, fluids are released from it - special superheated mineral solutions that cause melting of rocks of the continental lithosphere and the formation of magma chambers that feed chains of volcanoes developed parallel to deep-sea trenches on active continental margins.

Thus, on the active continental margin, due to subduction, a highly dissected relief, high seismicity, and vigorous volcanic activity are observed.

In addition to the phenomenon of subduction, there is the so-called obduction, that is, the thrust of the oceanic lithosphere onto the continental one, an example of which is the huge tectonic cover on the eastern edge of the Arabian Peninsula, composed of typical oceanic crust.

A collision should also be mentioned, or collisions, two continental plates, which, due to the relative lightness of the material that compose them, cannot submerge under each other, but collide, forming a mountain-fold belt with a very complex internal structure.

The main provisions of plate tectonics are as follows:

1.First prerequisite Plate tectonics is the division of the upper part of the solid Earth into two shells that differ significantly in rheological properties (viscosity) - the rigid and fragile lithosphere and the more plastic and mobile asthenosphere. As already mentioned, these two shells are identified using seismological or magnetotelluric data.

2.Second position plate tectonics, to which it owes its name, is that the lithosphere is naturally subdivided into a limited number of plates, currently seven large and as many small. The basis for their identification and the boundaries between them is the location of earthquake foci.

3.Third provision plate tectonics concerns the nature of their mutual movement. There are three types of such displacements and, accordingly, the boundaries between the plates: 1) divergent boundaries, along which the plates move apart - spreading; 2) convergent borders, on which there is a convergence of plates, usually expressed by the thrust of one plate under another; if the ocean plate moves under the continental plate, this process is called subduction, if the ocean plate is advancing on the continental - obduction; if two continental plates collide, also usually with one under the other, - collision; 3)transform boundaries, along which there is a horizontal sliding of one plate relative to the other along the plane of the vertical transform fault.

In nature, the boundaries of the first two types prevail.

At divergent boundaries, in spreading zones, new oceanic crust is continuously born; therefore these boundaries are also called constructive. This crust moves by the asthenospheric current towards the subduction zones, where it is absorbed at depth; this gives reason to call such boundaries destructive.

Fourth position plate tectonics lies in the fact that during their movements, the plates obey the laws of spherical geometry, or rather Euler's theorem, according to which any movement of two conjugate points on a sphere is performed along a circle drawn relative to an axis passing through the center of the Earth.

5.Fifth position Plate tectonics states that the volume of oceanic crust absorbed in subduction zones is equal to the volume of crust originating in spreading zones.

6.Sixth position plate tectonics sees the main cause of plate movement in the mantle convection. This convection in the classic 1968 model. is purely thermal and general mantle, and the way of its effect on lithospheric plates is that these plates, which are in viscous adhesion to the asthenosphere, are carried away by the flow of the latter and move in the manner of a conveyor belt from the spreading axes to the subduction zones. In general, the scheme of mantle convection, leading to a plate tectonic model of the movements of the lithosphere, consists in the fact that ascending branches of convective cells are located under the mid-ocean ridges, descending branches under subduction zones, and horizontal segments of these cells.

The theory of new global tectonics, or tectonics of lithospheric plates, is especially popular abroad: it is also recognized by many Soviet scientists who do not limit themselves to general recognition, but work a lot to clarify its main provisions, supplementing, deepening and developing them. The Soviet scientist-mobilist A.V. Paves, developing this theory, came, however, to the conclusion that giant rigid lithospheric plates do not exist at all, and the lithosphere, due to the fact that it is penetrated by horizontal, inclined and vertical mobile zones, consists of separate plates ("lithoplastin"), moving differentially. This is a fundamentally new look at one of the main, but controversial provisions of this theory.

Note that a certain part of mobilist scientists (both abroad and domestic) in their views show an extremely negative attitude to the classical doctrine of geosynclines. in fact, they completely reject it, regardless of the fact that many of the provisions of this doctrine are based on reliable facts and observations established and carried out during geological studies of continents.

Obviously, the most correct way in creating a truly global theory of the Earth is not opposition, but the identification of unity and interconnection between everything positive, reflected in the classical doctrine of geosynclines, and everything new that is revealed in the theory of new global tectonics.

This is a modern geological theory about the movement of the lithosphere, according to which the earth's crust consists of relatively integral blocks - lithospheric plates, which are in constant motion relative to each other. At the same time, in the expansion zones (mid-ocean ridges and continental rifts), as a result of seafloor spreading, a new oceanic crust is formed, and the old one is absorbed in subduction zones. Plate tectonics theory explains the occurrence of earthquakes, volcanic activity and mountain building processes, mostly associated with plate boundaries.

For the first time, the idea of ​​the movement of crustal blocks was expressed in the theory of continental drift, proposed by Alfred Wegener in the 1920s. This theory was initially rejected. The revival of the idea of ​​movements in the solid shell of the Earth ("mobilism") took place in the 1960s, 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 pushing of some parts of the crust under others ( subduction). Combining these ideas with the old theory of continental drift gave rise to the modern theory of plate tectonics, which soon became a generally accepted concept in the earth sciences.

In the theory of plate tectonics, the key position is occupied by the concept of geodynamic setting - a characteristic geological structure with a certain ratio of plates. In the same geodynamic setting, the same tectonic, magmatic, seismic and geochemical processes occur.

Current state of plate tectonics

Over the past decades, plate tectonics has changed its fundamentals significantly. Now they can be formulated as follows:

The upper part of the solid Earth is divided into a fragile lithosphere and a plastic asthenosphere. Convection in the asthenosphere is the main cause of plate movement.

The modern lithosphere is divided into 8 large plates, dozens of medium plates, and many small ones. Small slabs are located in belts between large slabs. Seismic, tectonic and magmatic activity is concentrated at plate boundaries.

Lithospheric plates in the first approximation are described as rigid bodies, and their motion obeys Euler's theorem of rotation.

There are three main types of relative plate movements.

1) divergence (divergence), expressed by rifting and spreading;

2) convergence (convergence) expressed by subduction and collision;

3) shear displacements along transform geological faults.

Spreading in the oceans is compensated by subduction and collision along their periphery, and the Earth's radius and volume are constant up to the thermal contraction of the planet (in any case, the average temperature of the Earth's interior slowly decreases over billions of years).

The movement of lithospheric plates is caused by their entrainment by convective currents in the asthenosphere.

There are two fundamentally different types of the earth's crust - continental crust (older) and oceanic crust (less than 200 million years old). Some lithospheric plates are composed exclusively of oceanic crust (for example, the largest Pacific plate), others consist of a block of continental crust soldered into the oceanic crust.

More than 90% of the Earth's surface in the modern era is covered by 8 largest lithospheric plates:

1. Australian plate.

2. Antarctic plate.

3. African plate.

4. Eurasian plate.

5. Hindustan plate.

6. Pacific plate.

7. North American Plate.

8. South American Plate.

Medium-sized plates include the Arabian Plate, as well as the Cocos Plate and the Juan de Fuca Plate, remnants of the huge Faralon Plate, which formed a significant part of the Pacific Ocean floor, but has now disappeared in the subduction zone beneath the Americas.

A tectonic plate or lithospheric plate is a piece of the lithosphere that moves as a relatively rigid block on the asthenosphere (upper mantle). The word tectonics comes from the ancient Greek τέκτων, τέκτωνος: builder.

Plate tectonics is a theory that explains the structure and dynamics of the earth's surface. It establishes that the lithosphere (the uppermost dynamic zone of the Earth) is fragmented into a series of plates that move along the asthenosphere. This theory also describes the movement of the plates, their directions and interactions. The terrestrial lithosphere is divided into large plates and other small ones. Seismic, volcanic and tectonic activity is concentrated at the edges of the plates. This leads to the formation of large mountain ranges and basins.

Earth is the only planet in the solar system with active tectonic plates, although there is evidence that Mars, Venus, and some of the moons such as Europa were tectonically active in ancient times.

Tectonic plates move relative to each other at a rate of 2.5 cm per year, which roughly corresponds to the rate at which nails grow. As they move on the planet's surface, the plates interact with each other along their boundaries, causing severe deformations in the earth's crust and lithosphere. This results in the formation of large mountain ranges (for example, mountain ranges of the Himalayas, Alps, Pyrenees, Atlas, Urals, Apennines, Appalachians, Andes, among many others) and associated large fault systems (for example, the San Andreas fault system). Frictional contact between the edges of the plates is responsible for most earthquakes. Other related phenomena are volcanoes (especially notorious in the Pacific fire belt) and ocean pits.

Tectonic plates are made up of two different types of lithosphere: continental crust, and oceanic crust, which is relatively thin. The upper part of the lithosphere is known as the earth's crust, again of two types (continental and oceanic). This means that the lithospheric plate can be a continental plate, an oceanic plate, or both, if so, it is called a mixed plate.

The movements of tectonic plates, in turn, determine the type of tectonic plates:

• Divergent motion: This is when two plates separate and produce a chasm in the ground or an underwater mountain range.
• Convergent motion: When two slabs come together, the thinner slab sinks under the thicker one. This creates ridges.
• Sliding movement: two plates slide in opposite directions.

Convergent tectonic plate

Divergent tectonic plate

Sliding tectonic plate

Tectonic plates of the world

Currently, there are tectonic plates on the Earth's surface in the world with more or less definite boundaries, which are divided into large and small (or secondary) plates.

Tectonic plates of the world

Major tectonic plates

• Australian plate
• Antarctic plate
• African plate
• Eurasian plate
• Hindustan plate
• Pacific plate
• North American Plate
• South American Plate

Medium-sized plates include the Arabian Plate, as well as the Cocos Plate and the Juan de Fuca Plate, remnants of the huge Faralon Plate, which formed a significant part of the Pacific Ocean floor, but has now disappeared in the subduction zone beneath the Americas.

Small tectonic plates

• Amurian
• Apulian or Adriatic plate
• Altiplano slab
• Anatolian plate
• Burma plate
• Bismarck North
• Bismarck of the South
• Chiloe
• Futuna
• Thick slab
• Juan Fernandez
• Kermadeca
• Manus plate
• Maoke
• Nubia
• Okhotsk plate
• Okinawan
• Panama
• Sandwich plate
• Shetland
• Tonga plate
• Probe
• Carolina
• Plate of the Mariana Islands
• New hebrides
• Northern Andes plate
• Balmoral reef
• Strip of the sea
• Plate of the Aegean or Greek Sea
• Moluccas plate
• Sea of ​​Solomon plateau
• Iranian plate
• Niuafou plate
• Rivera stove
• Somali plate
• Wood board
• Yangtze plate

Lithospheric plates- large rigid blocks of the Earth's lithosphere, limited by seismically and tectonically active fault zones.

The plates, as a rule, are separated by deep faults and move along the viscous layer of the mantle relative to each other at a speed of 2-3 cm per year. At the points of convergence of the continental plates, they collide, mountain belts ... When the continental and oceanic plates interact, the plate with the oceanic crust moves under the plate with the continental crust, resulting in the formation of deep-sea trenches and island arcs.

The movement of lithospheric plates is associated with the movement of matter in the mantle. In some parts of the mantle, there are powerful streams of heat and matter, rising from its depths to the surface of the planet.

More than 90% of the Earth's surface is covered 13 th largest lithospheric plates.

The rift– a huge rift in the earth's crust, formed when it is stretched horizontally (that is, where the flows of heat and matter diverge). An outpouring of magma occurs in the rifts, new faults, horsts, and grabens appear. Mid-ocean ridges are being formed.

The first continental drift hypothesis (i.e. horizontal movement of the earth's crust) put forward at the beginning of the twentieth century A. Wegener... Based on it, theory of lithospheric or m. According to this theory, the lithosphere is not a monolith, but consists of large and small plates "floating" on the asthenosphere. The border areas between lithospheric plates are called seismic belts - these are the most "restless" areas of the planet.

The earth's crust is divided into stable (platforms) and mobile areas (folded areas - geosynclines).

- powerful underwater mountain structures within the ocean floor, most often occupying the middle position. Near the mid-oceanic ridges, lithospheric plates move apart and a young basaltic oceanic crust appears. The process is accompanied by intense volcanism and high seismicity.

Continental rift zones are, for example, the East African rift system, the Baikal rift system. Rifts, like mid-ocean ridges, are characterized by seismic activity and volcanism.

Plate tectonics- a hypothesis assuming that the lithosphere is broken up into large plates that move horizontally along the mantle. Near the mid-oceanic ridges, lithospheric plates move apart and grow due to matter rising from the bowels of the Earth; in deep-sea trenches, one plate moves under the other and is absorbed by the mantle. In places where the plates collide, folded structures are formed.