Using a map of lithospheric plate boundaries. The theory of lithospheric plates: who founded it and what is the largest? Plate tectonics concept

According to modern plate theories The entire lithosphere is divided into separate blocks by narrow and active zones - deep faults - 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.

The peculiarity of lithospheric plates is their rigidity and ability, in the absence of external influences, to maintain their shape and structure unchanged for a long time.

Lithospheric plates are mobile. Their movement along the surface of the asthenosphere occurs under the influence of convective currents in the mantle. Individual lithospheric plates can move apart, move closer together, or slide relative to each other. In the first case, tension zones with cracks along the boundaries of the plates appear between the plates, in the second - compression zones, accompanied by the pushing of one plate onto another (thrusting - obduction; thrusting - subduction), in the third - shear zones - faults along which sliding of neighboring plates occurs .

Where continental plates converge, they collide and mountain belts are formed. This is how, for example, the Himalaya mountain system arose on the border of the Eurasian and Indo-Australian plates (Fig. 1).

Rice. 1. Collision of continental lithospheric plates

When the continental and oceanic plates interact, the plate with the oceanic crust moves under the plate with the continental crust (Fig. 2).

Rice. 2. Collision of continental and oceanic lithospheric plates

As a result of the collision of continental and oceanic lithospheric plates, deep-sea trenches and island arcs are formed.

The divergence of lithospheric plates and the resulting formation of the oceanic crust is shown in Fig. 3.

The axial zones of mid-ocean ridges are characterized by rifts(from English rift - crevice, crack, fault) - a large linear tectonic structure of the earth's crust hundreds, thousands in length, tens and sometimes hundreds of kilometers wide, formed mainly during horizontal stretching of the crust (Fig. 4). Very large rifts are called rift belts, zones or systems.

Since the lithospheric plate is a single plate, each of its faults is a source of seismic activity and volcanism. These sources are concentrated within relatively narrow zones along which mutual movements and friction of adjacent plates occur. These zones are called seismic belts. Reefs, mid-ocean ridges and deep-sea trenches are mobile regions of the Earth and are located at the boundaries of lithospheric plates. This indicates that the process of formation of the earth's crust in these zones is currently occurring very intensively.

Rice. 3. Divergence of lithospheric plates in the zone among the oceanic ridge

Rice. 4. Rift formation scheme

Most of the faults of lithospheric plates occur at the bottom of the oceans, where the earth’s crust is thinner, but they also occur on land. The largest fault on land is located in eastern Africa. It stretches for 4000 km. The width of this fault is 80-120 km.

Currently, seven of the largest plates can be distinguished (Fig. 5). Of these, the largest in area is the Pacific, which consists entirely of oceanic lithosphere. As a rule, the Nazca plate, which is several times smaller in size than each of the seven largest ones, is also classified as large. At the same time, scientists suggest that in fact the Nazca plate is much larger than we see on the map (see Fig. 5), since a significant part of it went under neighboring plates. This plate also consists only of oceanic lithosphere.

Rice. 5. Earth's lithospheric plates

An example of a plate that includes both continental and oceanic lithosphere is, for example, the Indo-Australian lithospheric plate. The Arabian plate consists almost entirely of continental lithosphere.

The theory of lithospheric plates is important. First of all, it can explain why there are mountains in some places on Earth and plains in others. Using the theory of lithospheric plates, it is possible to explain and predict catastrophic phenomena that occur at plate boundaries.

Rice. 6. The shapes of the continents really seem compatible.

Continental drift theory

The theory of lithospheric plates originates from the theory of continental drift. Back in the 19th century. many geographers have noted that when looking at a map, one can notice that the coasts of Africa and South America seem compatible when approaching (Fig. 6).

The emergence of the hypothesis of continental movement is associated with the name of the German scientist Alfred Wegener(1880-1930) (Fig. 7), who most fully developed this idea.

Wegener wrote: “In 1910, the idea of moving 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 continent, which included the territories of modern Europe, Asia without India and North America. The southern continent - Gondwana united the modern territories of South America, Africa, Antarctica, Australia and Hindustan.

Between Gondwana and Laurasia there 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) (Fig. 8).

Rice. 8. The existence of a single continent of Pangea (white - land, dots - shallow sea)

About 180 million years ago, the continent of Pangea again began to separate into its component parts, which mixed on the surface of our planet. The division occurred as follows: first Laurasia and Gondwana reappeared, then Laurasia split, and then Gondwana split. Due to the split and divergence of parts of Pangea, oceans were formed. The Atlantic and Indian oceans can be considered young oceans; old - Quiet. The Arctic Ocean became isolated as landmass increased in the Northern Hemisphere.

Rice. 9. Location and directions of continental drift during the Cretaceous period 180 million years ago

A. Wegener found many confirmations of the existence of a single continent of the Earth. He found the existence of remains of ancient animals—listosaurus—in Africa and South America especially convincing. These were reptiles, similar to small hippopotamuses, that lived only in freshwater bodies of water. This means that they could not swim huge distances in salty sea water. He found similar evidence in the plant world.

Interest in the hypothesis of continental movement in the 30s of the 20th century. decreased somewhat, but was revived again in the 60s, 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).

Consists of many layers piled on top of each other. However, what we know best is the earth's crust and lithosphere. This is not surprising - after all, we not only live on them, but also draw from the depths most of the natural resources available to us. But the upper shells of the Earth still preserve millions of years of history of our planet and the entire solar system.

These two concepts appear so often in the press and literature that they have entered the everyday vocabulary of modern man. Both words are used to refer to the surface of the Earth or another planet - however, there is a difference between the concepts, based on two fundamental approaches: chemical and mechanical.

Chemical aspect - earth's crust

If you divide the Earth into layers based on differences in chemical composition, the top layer of the planet will be the earth's crust. This is a relatively thin shell, ending at a depth of 5 to 130 kilometers below sea level - the oceanic crust is thinner, and the continental crust, in mountainous areas, is thickest. Although 75% of the crust's mass is composed only of silicon and oxygen (not pure, bound in different substances), it has the greatest chemical diversity of all layers of the Earth.

The wealth of minerals also plays a role - various substances and mixtures created over billions of years of the planet’s history. The Earth's crust contains not only "native" minerals that were created by geological processes, but also massive organic heritage, such as oil and coal, as well as alien inclusions.

Physical aspect - lithosphere

Based on the physical characteristics of the Earth, such as hardness or elasticity, we will get a slightly different picture - the interior of the planet will be enveloped by the lithosphere (from the Greek lithos, “rocky, hard” and “sphaira” sphere). It is much thicker than the earth's crust: the lithosphere extends up to 280 kilometers deep and even covers the upper solid part of the mantle!

The characteristics of this shell fully correspond to the name - it is the only solid layer of the Earth, besides the inner core. Strength, however, is relative - the Earth's lithosphere is one of the most mobile in the solar system, which is why the planet has changed its appearance more than once. But significant compression, curvature and other elastic changes require thousands of years, if not more.

An interesting fact is that the planet may not have a surface crust. So, the surface is its hardened mantle; The planet closest to the Sun lost its crust a long time ago as a result of numerous collisions.

To summarize, the Earth's crust is the upper, chemically diverse part of the lithosphere, the hard shell of the Earth. Initially they had almost the same composition. But when only the underlying asthenosphere and high temperatures affected the depths, the hydrosphere, atmosphere, meteorite remains and living organisms actively participated in the formation of minerals on the surface.

Lithospheric plates

Another feature that distinguishes the Earth from other planets is the diversity of different types of landscapes on it. Of course, water also played an incredibly important role, which we will talk about a little later. But even the basic forms of the planetary landscape of our planet differ from the same Moon. The seas and mountains of our satellite are pits from bombardment by meteorites. And on Earth they were formed as a result of hundreds and thousands of millions of years of movement of lithospheric plates.

You've probably already heard about plates - these are huge stable fragments of the lithosphere that drift along the fluid asthenosphere, like broken ice on a river. However, there are two main differences between the lithosphere and ice:

The gaps between the plates are small and are quickly closed due to the molten substance erupting from them, and the plates themselves are not destroyed by collisions.
Unlike water, there is no constant flow in the mantle, which could set a constant direction for the movement of the continents.

Thus, the driving force behind the drift of lithospheric plates is the convection of the asthenosphere, the main part of the mantle - hotter flows from the earth's core rise to the surface when cold ones fall back down. Considering that the continents differ in size, and the topography of their lower side mirrors the irregularities of the upper side, they also move unevenly and inconsistently.

Main plates

Over billions of years of movement of lithospheric plates, they repeatedly merged into supercontinents, after which they separated again. In the near future, in 200–300 million years, the formation of a supercontinent called Pangea Ultima is also expected. We recommend watching the video at the end of the article - it clearly shows how lithospheric plates have migrated over the past several hundred million years. In addition, the strength and activity of continental movement is determined by the internal heating of the Earth - the higher it is, the more the planet expands, and the faster and freer the lithospheric plates move. However, since the beginning of the Earth's history, its temperature and radius have been gradually decreasing.

An interesting fact is that plate drift and geological activity do not necessarily have to be powered by the internal self-heating of the planet. For example, the satellite of Jupiter has many active volcanoes. But the energy for this is not provided by the satellite’s core, but by gravitational friction c, due to which Io’s interior heats up.

The boundaries of lithospheric plates are very arbitrary - some parts of the lithosphere sink under others, and some, like the Pacific plate, are completely hidden under water. Geologists today count 8 main plates that cover 90 percent of the entire Earth's area:

Australian
Antarctic
African
Eurasian
Hindustan
Pacific
North American
South American

Such a division appeared recently - for example, the Eurasian plate, 350 million years ago, consisted of separate parts, during the merger of which the Ural Mountains, one of the oldest on Earth, were formed. Scientists to this day continue to study faults and the ocean floor, discovering new plates and clarifying the boundaries of old ones.

Geological activity

Lithospheric plates move very slowly - they creep over each other at a speed of 1–6 cm/year, and move away by a maximum of 10–18 cm/year. But it is the interaction between the continents that creates the geological activity of the Earth, noticeable on the surface - volcanic eruptions, earthquakes and the formation of mountains always occur in the contact zones of lithospheric plates.

However, there are exceptions - so-called hot spots, which can also exist deep in lithospheric plates. In them, molten flows of asthenosphere matter break upward, melting the lithosphere, which leads to increased volcanic activity and regular earthquakes. Most often, this happens near those places where one lithospheric plate creeps onto another - the lower, depressed part of the plate sinks into the Earth's mantle, thereby increasing the pressure of magma on the upper plate. However, now scientists are inclined to believe that the “drowned” parts of the lithosphere are melting, increasing pressure in the depths of the mantle and thereby creating upward flows. This can explain the anomalous distance of some hot spots from tectonic faults.

An interesting fact is that shield volcanoes, characterized by their flat shape, often form in hot spots. They erupt many times, growing due to flowing lava. This is also a typical alien volcano format. The most famous of them is on Mars, the highest point on the planet - its height reaches 27 kilometers!

Oceanic and continental crust of the Earth

Plate interactions also result in the formation of two different types of crust - oceanic and continental. Since the oceans, as a rule, are the junctions of different lithospheric plates, their crust is constantly changing - being broken or absorbed by other plates. At the site of faults, direct contact occurs with the mantle, from where hot magma rises. As it cools under the influence of water, it creates a thin layer of basalts, the main volcanic rock. Thus, the oceanic crust is completely renewed every 100 million years - the oldest areas, which are located in the Pacific Ocean, reach a maximum age of 156–160 million years.

Important! The oceanic crust is not all of the earth’s crust that is under water, but only its young sections at the junction of continents. Part of the continental crust is under water, in the zone of stable lithospheric plates.

The Earth's lithospheric plates are huge blocks. Their foundation is formed by strongly folded granite metamorphosed igneous rocks. The names of lithospheric plates will be given in the article below. From above they are covered with a three- to four-kilometer “cover.” It is formed from sedimentary rocks. The platform has a topography consisting of isolated mountain ranges and vast plains. Next, the theory of the movement of lithospheric plates will be considered.

The emergence of a hypothesis

The theory of the movement of lithospheric plates appeared at the beginning of the twentieth century. Subsequently, she was destined to play a major role in planetary exploration. The scientist Taylor, and after him Wegener, put forward the hypothesis that over time, lithospheric plates drift in a horizontal direction. However, in the thirties of the 20th century, a different opinion took hold. According to him, the movement of lithospheric plates was carried out vertically. This phenomenon was based on the process of differentiation of the planet's mantle matter. It came to be called fixism. This name was due to the fact that the permanently fixed position of sections of the crust relative to the mantle was recognized. But in 1960, after the discovery of a global system of mid-ocean ridges that encircle the entire planet and reach land in some areas, there was a return to the hypothesis of the early 20th century. However, the theory took on a new form. Block tectonics has become a leading hypothesis in sciences studying the structure of the planet.

Basic provisions

It was determined that large lithospheric plates exist. Their number is limited. There are also smaller lithospheric plates of the Earth. The boundaries between them are drawn according to the concentration in the earthquake foci.

The names of lithospheric plates correspond to the continental and oceanic regions located above them. There are only seven blocks with a huge area. The largest lithospheric plates are the South and North American, Euro-Asian, African, Antarctic, Pacific and Indo-Australian.

The blocks floating on the asthenosphere are distinguished by their solidity and rigidity. The above areas are the main lithospheric plates. In accordance with the initial ideas, it was believed that continents make their way through the ocean floor. In this case, the movement of lithospheric plates was carried out under the influence of an invisible force. As a result of the studies, it was revealed that the blocks float passively along the mantle material. It is worth noting that their direction is first vertical. Mantle material rises upward under the crest of the ridge. Then propagation occurs in both directions. Accordingly, the divergence of lithospheric plates is observed. This model represents the ocean floor as a giant one. It comes to the surface in the rift regions of mid-ocean ridges. Then it hides in deep-sea trenches.

The divergence of lithospheric plates provokes the expansion of ocean floors. However, the volume of the planet, despite this, remains constant. The fact is that the birth of new crust is compensated by its absorption in areas of subduction (underthrust) in deep-sea trenches.

Why do lithospheric plates move?

The reason is thermal convection of the planet's mantle material. The lithosphere is stretched and rises, which occurs above the ascending branches of convective currents. This provokes the movement of lithospheric plates to the sides. As the platform moves away from the mid-ocean rifts, the platform becomes denser. It becomes heavier, its surface sinks down. This explains the increase in ocean depth. As a result, the platform sinks into deep-sea trenches. As the heated mantle decays, it cools and sinks, forming basins that are filled with sediment.

Plate collision zones are areas where the crust and platform experience compression. In this regard, the power of the first increases. As a result, the upward movement of lithospheric plates begins. It leads to the formation of mountains.

Research

The study today is carried out using geodetic methods. They allow us to draw a conclusion about the continuity and ubiquity of processes. Collision zones of lithospheric plates are also identified. The lifting speed can be up to tens of millimeters.

Horizontally large lithospheric plates float somewhat faster. In this case, the speed can be up to ten centimeters over the course of a year. So, for example, St. Petersburg has already risen by a meter over the entire period of its existence. Scandinavian Peninsula - by 250 m in 25,000 years. Mantle material moves relatively slowly. However, as a result, earthquakes and other phenomena occur. This allows us to conclude about the high power of material movement.

Using the tectonic position of plates, researchers explain many geological phenomena. At the same time, during the study it became clear that the complexity of the processes occurring with the platform was much greater than it seemed at the very beginning of the hypothesis.

Plate tectonics could not explain changes in the intensity of deformation and movement, the presence of a global stable network of deep faults and some other phenomena. The question of the historical beginning of the action also remains open. Direct signs indicating plate tectonic processes have been known since the late Proterozoic period. However, a number of researchers recognize their manifestation from the Archean or Early Proterozoic.

Expanding Research Opportunities

The advent of seismic tomography led to the transition of this science to a qualitatively new level. In the mid-eighties of the last century, deep geodynamics became the most promising and youngest direction of all existing geosciences. However, new problems were solved using not only seismic tomography. Other sciences also came to the rescue. These include, in particular, experimental mineralogy.

Thanks to the availability of new equipment, it became possible to study the behavior of substances at temperatures and pressures corresponding to the maximum at the depths of the mantle. The research also used isotope geochemistry methods. This science studies, in particular, the isotopic balance of rare elements, as well as noble gases in various earthly shells. In this case, the indicators are compared with meteorite data. Geomagnetism methods are used, with the help of which scientists try to uncover the causes and mechanism of reversals in the magnetic field.

Modern painting

The platform tectonics hypothesis continues to satisfactorily explain the process of crustal development over at least the last three billion years. At the same time, there are satellite measurements, according to which the fact is confirmed that the main lithospheric plates of the Earth do not stand still. As a result, a certain picture emerges.

In the cross section of the planet there are three most active layers. The thickness of each of them is several hundred kilometers. It is assumed that they are entrusted with playing the main role in global geodynamics. In 1972, Morgan substantiated the hypothesis of ascending mantle jets put forward in 1963 by Wilson. This theory explained the phenomenon of intraplate magnetism. The resulting plume tectonics has become increasingly popular over time.

Geodynamics

With its help, the interaction of rather complex processes that occur in the mantle and crust is examined. In accordance with the concept outlined by Artyushkov in his work “Geodynamics”, gravitational differentiation of matter acts as the main source of energy. This process is observed in the lower mantle.

After the heavy components (iron, etc.) are separated from the rock, a lighter mass of solids remains. It descends into the core. The placement of a lighter layer under a heavier one is unstable. In this regard, the accumulating material is periodically collected into fairly large blocks that float to the upper layers. The size of such formations is about one hundred kilometers. This material was the basis for the formation of the upper

The lower layer probably represents undifferentiated primary substance. During the evolution of the planet, due to the lower mantle, the upper mantle grows and the core increases. It is more likely that blocks of light material rise in the lower mantle along the channels. The mass temperature in them is quite high. The viscosity is significantly reduced. The increase in temperature is facilitated by the release of a large amount of potential energy during the rise of matter into the gravity region at a distance of approximately 2000 km. In the course of movement along such a channel, strong heating of light masses occurs. In this regard, the substance enters the mantle at a fairly high temperature and significantly less weight in comparison with the surrounding elements.

Due to the reduced density, light material floats to the upper layers to a depth of 100-200 kilometers or less. As the pressure decreases, the melting point of the components of the substance decreases. After primary differentiation at the core-mantle level, secondary differentiation occurs. At shallow depths, the light substance partially undergoes melting. During differentiation, denser substances are released. They sink into the lower layers of the upper mantle. The released lighter components, accordingly, rise upward.

The complex of movements of substances in the mantle associated with the redistribution of masses having different densities as a result of differentiation is called chemical convection. The rise of light masses occurs with a periodicity of approximately 200 million years. However, penetration into the upper mantle is not observed everywhere. In the lower layer, the channels are located at a fairly large distance from each other (up to several thousand kilometers).

Lifting blocks

As mentioned above, in those zones where large masses of light heated material are introduced into the asthenosphere, partial melting and differentiation occurs. In the latter case, the release of components and their subsequent ascent are noted. They pass through the asthenosphere quite quickly. When reaching the lithosphere, their speed decreases. In some areas, the substance forms accumulations of anomalous mantle. They lie, as a rule, in the upper layers of the planet.

Anomalous mantle

Its composition approximately corresponds to normal mantle matter. The difference between the anomalous cluster is a higher temperature (up to 1300-1500 degrees) and a reduced speed of elastic longitudinal waves.

The entry of matter under the lithosphere provokes isostatic uplift. Due to the increased temperature, the anomalous cluster has a lower density than the normal mantle. In addition, there is a slight viscosity of the composition.

In the process of reaching the lithosphere, the anomalous mantle is quite quickly distributed along the base. At the same time, it displaces the denser and less heated substance of the asthenosphere. As the movement progresses, the anomalous accumulation fills those areas where the base of the platform is in an elevated state (traps), and it flows around deeply submerged areas. As a result, in the first case there is an isostatic rise. Above submerged areas, the crust remains stable.

Traps

The cooling process of the upper mantle layer and crust to a depth of about one hundred kilometers occurs slowly. Overall, it takes several hundred million years. In this regard, heterogeneities in the thickness of the lithosphere, explained by horizontal temperature differences, have a fairly large inertia. In the event that the trap is located near the upward flow of an anomalous accumulation from the depths, a large amount of substance is captured by a very heated substance. As a result, a fairly large mountain element is formed. In accordance with this scheme, high uplifts occur in the area of epiplatform orogenesis in

Description of processes

In the trap, the anomalous layer is compressed by 1-2 kilometers during cooling. The crust located on top sinks. Sediment begins to accumulate in the formed trough. Their severity contributes to even greater subsidence of the lithosphere. As a result, the depth of the basin can be from 5 to 8 km. At the same time, when the mantle compacts in the lower part of the basalt layer in the crust, a phase transformation of the rock into eclogite and garnet granulite can be observed. Due to the heat flow escaping from the anomalous substance, the overlying mantle is heated and its viscosity decreases. In this regard, there is a gradual displacement of the normal accumulation.

Horizontal offsets

When uplifts form as anomalous mantle enters the crust on the continents and oceans, the potential energy stored in the upper layers of the planet increases. To discharge excess substances they tend to move apart. As a result, additional stresses are formed. They are associated with different types of movement of plates and crust.

The expansion of the ocean floor and the floating of continents are a consequence of the simultaneous expansion of the ridges and the subsidence of the platform into the mantle. Underneath the former are large masses of highly heated anomalous matter. In the axial part of these ridges the latter is located directly under the crust. The lithosphere here has significantly less thickness. At the same time, the anomalous mantle spreads in an area of high pressure - in both directions from under the ridge. At the same time, it quite easily tears the ocean crust. The crevice is filled with basaltic magma. It, in turn, is melted from the anomalous mantle. In the process of solidification of magma, a new one is formed. This is how the bottom grows.

Process Features

Beneath the median ridges, the anomalous mantle has reduced viscosity due to increased temperature. The substance can spread quite quickly. In this regard, the growth of the bottom occurs at an increased rate. The oceanic asthenosphere also has relatively low viscosity.

The main lithospheric plates of the Earth float from ridges to subsidence sites. If these areas are located in the same ocean, then the process occurs at a relatively high speed. This situation is typical for the Pacific Ocean today. If expansion of the bottom and subsidence occur in different areas, then the continent located between them drifts in the direction where the deepening occurs. Under continents, the viscosity of the asthenosphere is higher than under the oceans. Due to the resulting friction, significant resistance to movement appears. The result is a reduction in the rate at which seafloor expansion occurs unless there is compensation for mantle subsidence in the same area. Thus, expansion in the Pacific Ocean is faster than in the Atlantic.

December 10th, 2015

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The first suggestion about the horizontal movement of crustal blocks was made by Alfred Wegener in the 1920s within the framework of the “continental drift” hypothesis, but this hypothesis did not receive support at that time.

Only in the 1960s did studies of the ocean floor provide conclusive evidence of horizontal plate movements and ocean expansion processes due to the formation (spreading) of oceanic crust. The revival of ideas about the predominant role of horizontal movements occurred within the framework of the “mobilistic” trend, the development of which led to the development of the modern theory of plate tectonics. The main principles 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. Digtsa about the expansion (spreading) of the ocean floor.

It is argued that scientists are not entirely sure what causes these shifts and how the boundaries of tectonic plates are defined. There are countless different theories, but none completely 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 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.

Between Gondwana and Laurasia there 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)

A. Wegener found many confirmations of the existence of a single continent of the Earth. What seemed especially convincing to him was the existence in Africa and South America of the remains of ancient animals - listosaurs. These were reptiles, similar to small hippopotamuses, that lived only in freshwater bodies of water. This means that they could not swim huge distances in salty sea water. He found similar evidence in the plant world.

Structure of the continental rift

The upper rocky part of the planet is divided into two shells, significantly different 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 the mantle material at lithostatic pressure existing at depths of the first hundreds of kilometers. Rocks in the Earth above this isotherm are quite cold and behave like rigid materials, while 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 internal regions of the plates are weakly seismic and characterized by 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.

Rift formation scheme

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

Divergent boundaries are boundaries along which plates move apart. The geodynamic situation in which the process of horizontal stretching of the earth's crust occurs, accompanied by the appearance of extended linearly elongated slot or ditch-like 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 form on both 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 rupture of the continental crust, it is filled with sediments, turning into an aulacogen).

The process of plate separation in zones of oceanic rifts (mid-ocean ridges) is accompanied by the formation of new oceanic crust due to magmatic basaltic melt coming from the asthenosphere. This process of formation of new oceanic crust due to the influx of mantle material 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 – basalts of the ocean floor, 6 – segments of the oceanic crust formed at different times (I-V as they become more ancient), 7 – near-surface igneous chamber (with ultrabasic magma in the lower part and basic magma in the upper), 8 – sediments of the ocean floor (1-3 as they accumulate)

During spreading, each extension pulse is accompanied by the arrival of a new portion of mantle melts, which, when solidified, build up the edges of 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 pushing 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 the continental and oceanic plates collide, a natural phenomenon is the displacement of the oceanic (heavier) plate under the edge of the continental one; When two oceans collide, the more ancient (that is, cooler and denser) of them sinks.

Subduction zones have a characteristic structure: their typical elements are a deep-sea trench - a volcanic island arc - a back-arc basin. A deep-sea trench is formed in the zone of bending and underthrusting of the subducting plate. As this plate sinks, it begins to lose water (found in abundance in sediments and minerals), the latter, as is known, significantly reduces the melting temperature of rocks, which leads to the formation of melting centers that feed volcanoes of island arcs. In the rear of a volcanic arc, some stretching usually occurs, which determines the formation of a back-arc basin. In the back-arc basin zone, stretching can be so significant that it leads to rupture of the plate crust and the opening of a basin with 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 emerging in spreading zones. This position emphasizes the idea that the volume of the Earth is constant. But this opinion is not the only and definitively proven one. It is possible that the volume of the plane changes pulsatingly, or that it decreases due to cooling.

The immersion of the subducting plate into the mantle is traced by the foci of earthquakes that occur at the contact of the plates and inside the subducting plate (colder and, therefore, more fragile than the surrounding mantle rocks). This seismofocal zone is called the Benioff-Zavaritsky zone. In subduction zones, the process of formation of new continental crust begins. A much rarer process of interaction between the continental and oceanic plates is the process of obduction - the pushing of part of the oceanic lithosphere onto the edge of the continental plate. It should be emphasized that during this process, the ocean plate is separated, and only its upper part - the crust and several kilometers of the upper mantle - moves forward.

Collision of continental plates

When continental plates collide, the crust of which is lighter than the mantle material and, as a result, is not able to sink into it, a collision process occurs. During the 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 of such a process is the collision of the Hindustan plate with the Eurasian plate, 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. Moreover, at the beginning of the collision process, when the edges of the continents have already moved closer together, the collision is combined with the process of subduction (the remnants of the oceanic crust continue to sink under the edge of the continent). Large-scale regional metamorphism and intrusive granitoid magmatism are typical for collision processes. These processes lead to the creation of a new continental crust (with its typical granite-gneiss layer).

The main reason for plate movement is mantle convection, caused by mantle thermogravitational currents.

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

Rocks heated in the central zones of the Earth expand, their density decreases, and they float up, giving way to sinking colder and therefore heavier masses that have already given up some of the heat in the near-surface zones. This process of heat transfer occurs continuously, resulting in the formation of ordered closed convective cells. In this case, in the upper part of the cell, the flow of matter occurs almost in a 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 “dragging” by convective currents. In addition, a number of other factors act on the slabs. In particular, the surface of the asthenosphere turns out to be somewhat elevated above the zones of ascending branches and more depressed 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 drawing heavy cold oceanic lithosphere in subduction zones into the hot, and as a consequence 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 base of the intraplate parts of the lithosphere - the mantle drag forces FDO under the oceans and FDC under the continents, the magnitude of which depends primarily on the speed of the asthenospheric flow, 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 greater than under the oceans, the magnitude of the FDC force is almost an order of magnitude lower than the FDO value. Under the continents, especially their ancient parts (continental shields), the asthenosphere almost pinches out, so the continents seem to be “stranded.” Since most lithospheric plates of the modern Earth include both oceanic and continental parts, it should be expected that the presence of a continent in the plate should, in general, “slow down” the movement of the entire plate. This is how it actually happens (the fastest moving almost purely oceanic plates are the Pacific, Cocos and Nazca; the slowest are the Eurasian, North American, South American, Antarctic and African plates, a significant part of whose area 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 (an index in the designation of force - from the English 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 sporadically and only in certain geodynamic settings, for example in the cases of slab failure across the 670 km divide described above.

Thus, the mechanisms that set lithospheric plates in motion can be conditionally classified into the following two groups: 1) associated with the forces of mantle drag mechanism applied to any points of the base of the plates, in the figure - forces FDO and FDC; 2) associated with forces applied to the edges of the slabs (edge-force mechanism), in the figure - FRP and FNB forces. The role of one or another driving mechanism, as well as certain forces, is assessed individually for each lithospheric plate.

The combination of these processes reflects the general geodynamic process, covering areas from the surface to the deep zones of the Earth. Currently, two-cell mantle convection with closed cells is developing in the Earth's mantle (according to the model of through-mantle convection) 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 mantle material are located in northeastern Africa (approximately under the junction zone of the African, Somali and Arabian plates) and in the Easter Island region (under the middle ridge of the Pacific Ocean - the East Pacific Rise). The equator of subsidence of mantle matter passes approximately along a continuous chain of convergent plate boundaries along the periphery of the Pacific and eastern Indian Oceans. The modern regime of mantle convection, which began approximately 200 million years ago with the collapse of Pangea and gave rise to modern oceans, will in the future be replaced by a single-cell regime (according to the model of through-mantle convection 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 a collision of 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 based on 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 rotation angle. Based on this position, the position of the continents in past geological eras 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 subsequently undergoes disintegration. As a result of the split of such a supercontinent Pangea, which occurred 200-150 million years ago, modern continents were formed.

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

Age of the ocean crust based on magnetic anomalies (Kennet, 1987): 1 - areas of missing data and land; 2–8 - age: 2 - Holocene, Pleistocene, Pliocene (0–5 million years); 3 - Miocene (5–23 million years); 4 - Oligocene (23–38 million years); 5 - Eocene (38–53 million years); 6 - Paleocene (53–65 million years) 7 - Cretaceous (65–135 million years) 8 - Jurassic (135–190 million years)

At the end of the 80s. Another experiment to test the movement of lithospheric plates was completed. It was based on measuring baselines relative to distant quasars. Points were selected on two plates at which, using modern radio telescopes, the distance to the quasars and their declination angle were determined, and, accordingly, the distances between the points on the two plates were calculated, i.e., the base line was determined. The accuracy of the determination was a few centimeters. After several years, the measurements were repeated. A very good agreement was obtained between the results calculated from magnetic anomalies and the data determined from the baselines

Diagram illustrating the results of measurements of the mutual movement of lithospheric plates obtained by the very long baseline interferometry method - 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 baselines from which sufficient data have been obtained using the ISDB method 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, 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 modern movement of lithospheric plates, the speed of spreading 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.

This 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 thanks to this the Mediterranean Sea will gradually be eliminated. The Strait of Gibraltar will disappear, and a “turned” Spain will close the Bay of Biscay. Africa will be split by the great African faults and its eastern part 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 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 clarification. Much here still remains 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

Let me remind you, but here are the 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 was made -

Together with part of the upper mantle, it consists of several very large blocks called lithospheric plates. Their thickness varies - from 60 to 100 km. Most plates include both continental and oceanic crust. There are 13 main plates, of which 7 are the largest: American, African, Indo-, Amur.

The plates lie on a plastic layer of the upper mantle (asthenosphere) and slowly move relative to each other at a speed of 1-6 cm per year. This fact was established by comparing images taken from artificial Earth satellites. They suggest that the configuration in the future may be completely different from the present one, since it is known that the American lithospheric plate is moving towards the Pacific, and the Eurasian plate is moving closer to the African, Indo-Australian, and also the Pacific. The American and African lithospheric plates are slowly moving apart.

The forces that cause the divergence of lithospheric plates arise when the material of the mantle moves. Powerful upward flows of this substance push the plates apart, tearing apart the earth's crust, forming deep faults in it. Due to underwater outpourings of lavas, strata are formed along faults. By freezing, they seem to heal wounds - cracks. However, the stretching increases again, and ruptures occur again. So, gradually increasing, lithospheric plates diverge in different directions.

There are fault zones on land, but most of them are in the ocean ridges, where the earth's crust is thinner. The largest fault on land is located in the east. It stretches for 4000 km. The width of this fault is 80-120 km. Its outskirts are dotted with extinct and active ones.

Along other plate boundaries, plate collisions are observed. It happens in different ways. If plates, one of which has oceanic crust and the other continental, come closer together, then the lithospheric plate, covered by the sea, sinks under the continental one. In this case, arcs () or mountain ranges () appear. If two plates that have continental crust collide, the edges of these plates are crushed into folds of rock, and mountainous regions are formed. This is how they arose, for example, on the border of the Eurasian and Indo-Australian plates. The presence of mountainous areas in the internal parts of the lithospheric plate suggests that once there was a boundary of two plates that were firmly fused with each other and turned into a single, larger lithospheric plate. Thus, we can draw a general conclusion: the boundaries of lithospheric plates are mobile areas to which volcanoes, zones, mountain areas, mid-ocean ridges, deep-sea depressions and trenches are confined. It is at the border of lithospheric plates that they are formed, the origin of which is associated with magmatism.