EARTH EVOLUTION
EARTH IN THE SOLAR SYSTEM
The Earth belongs to the terrestrial planets, which means that, unlike gas giants such as Jupiter, it has a solid surface. It is the largest of the four terrestrial planets in the solar system, both in terms of size and mass. In addition, the Earth has the highest density, the strongest surface gravity, and the strongest magnetic field among the four planets.
earth shape
Comparison of the sizes of the terrestrial planets (from left to right): Mercury, Venus, Earth, Mars.
Earth Movement
The Earth moves around the Sun in an elliptical orbit at a distance of about 150 million km with an average speed of 29.765 km/sec. The speed of the Earth's orbit is not constant: in July it begins to accelerate (after passing aphelion), and in January it starts to slow down again (after passing perihelion). The sun and the entire solar system revolve around the center of the Milky Way galaxy in an almost circular orbit at a speed of about 220 km/s. Carried away by the movement of the Sun, the Earth describes a helix in space.
At present, Earth's perihelion is around January 3rd and aphelion is around July 4th.
For the Earth, the radius of the Hill sphere (the sphere of influence of the earth's gravity) is approximately 1.5 million km. This is the maximum distance at which the influence of the Earth's gravity is greater than the influence of the gravitations of other planets and the Sun.
Earth structure Internal structure
General structure of the planet Earth
The Earth, like other terrestrial planets, has a layered internal structure. It consists of solid silicate shells (crust, extremely viscous mantle) and a metallic core. The outer part of the core is liquid (much less viscous than the mantle), while the inner part is solid.
The internal heat of the planet is most likely provided by the radioactive decay of the isotopes potassium-40, uranium-238 and thorium-232. All three elements have a half-life of over a billion years. At the center of the planet, the temperature may rise to 7,000 K, and the pressure may reach 360 GPa (3.6 thousand atm.).
The earth's crust is the upper part of the solid earth.
The earth's crust is divided into lithospheric plates of different sizes, moving relative to each other.
The mantle is a silicate shell of the Earth, composed mainly of rocks consisting of silicates of magnesium, iron, calcium, etc.
The mantle extends from depths of 5–70 km below the boundary with the Earth's crust to the boundary with the core at a depth of 2900 km.
The core consists of an iron-nickel alloy mixed with other elements.
Theory of tectonic plates Tectonic platforms
According to plate tectonic theory, the outer part of the Earth consists of the lithosphere, which includes the earth's crust and the hardened upper part of the mantle. Under the lithosphere is the asthenosphere, which makes up the inner part of the mantle. The asthenosphere behaves like an overheated and extremely viscous fluid.
The lithosphere is divided into tectonic plates and, as it were, floats on the asthenosphere. Plates are rigid segments that move relative to each other. These periods of migration are many millions of years. On faults between tectonic plates, earthquakes, volcanic activity, mountain building, and the formation of ocean depressions can occur.
Among the tectonic plates, the oceanic plates have the highest movement speed. So, the Pacific plate moves at a speed of 52 - 69 mm per year. The lowest speed is at the Eurasian plate - 21 mm per year.
supercontinent
A supercontinent is a continent in plate tectonics that contains almost all of the Earth's continental crust.
The study of the history of the movements of the continents has shown that with a frequency of about 600 million years, all continental blocks are collected into a single block, which then splits.
The formation of the next supercontinent in 50 million years is predicted by American scientists based on satellite observations of the movement of the continents. Africa will merge with Europe, Australia will continue to move north and unite with Asia, and the Atlantic Ocean, after some expansion, will disappear altogether.
Volcanoes
Volcanoes - geological formations on the surface of the earth's crust or the crust of another planet, where magma comes to the surface, forming lava, volcanic gases, stones.
The word "Vulcan" comes from the name of the ancient Roman god of fire, Vulcan.
The science that studies volcanoes is volcanology.
Volcanic activity
Volcanoes are divided depending on the degree of volcanic activity into active, dormant and extinct.
Among volcanologists there is no consensus on how to define an active volcano. The period of volcano activity can last from several months to several million years. Many volcanoes showed volcanic activity several tens of thousands of years ago, but are not currently considered active.
Often in the craters of volcanoes there are lakes of liquid lava. If the magma is viscous, then it can clog the vent, like a "cork". This leads to the strongest explosive eruptions, when the flow of gases literally knocks the “plug” out of the vent.
Silfra. reykjavik.
When viewed from space, it is not at all obvious that the Earth is teeming with life. To understand that it is here, you need to get close enough to the planet. But even from space, our planet still seems alive. Its surface is divided into seven continents, which are washed by huge oceans. Below these oceans, in the invisible depths of our planet, there is also life.
A dozen cold, hard plates slide slowly over the hot inner mantle, diving under each other and colliding from time to time. This process, called plate tectonics, is one of the defining characteristics of planet Earth. People mostly feel it when earthquakes occur and volcanoes erupt.
But plate tectonics is responsible for something more important than earthquakes and eruptions. New research suggests that Earth's tectonic activity may be important to another defining feature of our planet: life. Our Earth has a moving, ever-transforming outer crust, and this may be the main reason why the Earth is so amazing and no other planet can match its abundance.
One and a half billion years before the Cambrian explosion, back in the Archean era, there was almost no oxygen on Earth that we breathe now. Algae had already begun to use photosynthesis to produce oxygen, but most of that oxygen was consumed by iron-rich rocks, which used the oxygen to turn into rust.
According to research published in 2016, plate tectonics initiated a two-step process that led to higher oxygen levels. At the first stage, subduction caused the Earth's mantle to change and develop two types of crust - oceanic and continental. The continental version had fewer iron-rich minerals and more quartz-rich rocks that do not draw oxygen from the atmosphere.
Then over the next billion years - from 2.5 billion years ago to 1.5 billion years ago - the rocks pumped carbon dioxide into the air and oceans. The extra carbon dioxide helped the algae produce even more oxygen, enough to eventually cause the Cambrian explosion.
Tectonic plates on other planets
So tectonics is important for life?
The problem is that we have one sample. We have one planet, one place with water and slippery outer crust, one place that is teeming with life. Other planets or moons may have activity that resembles terrestrial tectonics, but it is not like what we see on Earth.
The Earth will eventually cool enough that plate tectonics will weaken, and the planet will eventually go into a frozen state. New supercontinents will rise and fall before they do, but at some point the earthquakes will stop. Volcanoes will be turned off forever. The earth will die like. Whether any forms of life will inhabit it by that time is a question.
The undeniable proof that the tectonic plates were in motion was the unprecedented flooding in the history of Pakistan in 2010. More than 1,600 people died, 20 million were injured, and a fifth of the country was under water. On the opposite side of the Indo-Australian Plate, the ocean floor is rising, as evidenced by buoy readings near Australia. The slope of the plate directs water to the east coast of Australia, so in January 2011 Australia experienced a "biblical flood", the flood area exceeded the combined area of France and Germany, the flood is recognized as the most destructive in the history of the country. Near station 55012 is station 55023, which in June 2010 already registered an unprecedented rise of the ocean floor by 400 (!!!) meters. Buoy 55023 first began showing seafloor uplift in April 2010, indicating not only the steady uplift of the eastern edge of the Indo-Australian Plate, but also the flexible parts of that plate that can bend when the plate's position changes. The slabs are heavy and when they topple they can buckle to the point where they become suspended, buckling under the weight of the rock no longer supported by the magma. In essence, a void is created under this part of the slab. Sudden rapid drop in water height June 25, 2010 . actually linked to a 7.1 magnitude quake in the Solomon Islands a day later. This activity, the rise of the plate, has become stronger, and this trend will only increase in the near future. Since the end of 2010, the Sunda Plate has been showing steady subsidence. All the countries that are on the plate - Myanmar, Thailand, Cambodia, Vietnam, Laos, China, Malaysia, the Philippines and Indonesia have experienced record floods this year. The photo shows the coast of cities on the island of Java in Indonesia - Jakarta, Semarang and Surabaya. The photo clearly shows that the ocean has swallowed the coastline and the coast goes under water.
The Earth Observatory, a division of NASA, admitted that when compared to images from a year ago, Pakistan's elevation above sea level has decreased.
The Indian plate is tilting, and Pakistan has lost several meters of height from this.
To the east of the Indonesian island of Java, in the sea between Java and Bali, a new island grew within a few days. Between eastern Java and Bali, where the Sunda Plate is under pressure as it is pushed down under the Indo-Australian Plate boundary, a new island has appeared. When the platform compresses, compressing, thin spots on it can give rise to deformation, this also reveals weak spots on the platform, which can deform in such a way that it has to rise.
Photo of Bali, Indonesia, port on the coast under water. This dive was sudden, within an hour. Similarly, on the northern coast of Java, the Semarang dive.
The sinking of the Sunda Plate has reached the stage where coastal cities such as Jakarta, Manila and Bangkok are in the news due to severe flooding problems. Bangkok, which is set to lose 12 meters of height from the sunda plate sinking, has declared "war" on rising water, which they attribute to rainfall runoff from the mountains, but in fact no rainwater not capable drain as the rivers are blocked by backflow from the sea. Local news frankly refers to downgrade, claiming that "sea level rise" is present in the Ayutthaya temple area, which is further inland from Bangkok. And the authorities in Manila, refusing to acknowledge what happened, are telling their rooftop population to just wait it out. Scientists warn of land flooding in Manila and Central Luzon caused by increased flooding. The flooding of land areas in Greater Manila and nearby provinces may be caused by geological movements associated with processes in the western Markina fault line valley.
In Thailand, more than 800 people have died from the floods and more than 3 million have been affected. The flood is already recognized as the worst in 100 years.
10.08. Residents of the island of Luzon report that they have never seen flooding of this magnitude, and the rivers in this region still hold high water levels, which for some reason do not go into the ocean.
The reality that the Sunda Plate, which also hosts Vietnam and Cambodia, is sinking, is starting to surface in the press. Press reports from Vietnam repeatedly mention that they are immersed in sea water"Torrential rains upstream and downstream over the past two days have caused Hue City to sink into seawater." "This year's event is anomalous," said Kirsten Mildren, a spokeswoman for the UN's regional Office for the Coordination of Humanitarian Affairs. "Here you are weeks or months in the water, and it just keeps getting worse."
30.09. In the Mekong River Valley in southern Vietnam and Cambodia, the most powerful ten years of flooding. More than 100 people died as a result.,
bridges and houses of hundreds of thousands of people were destroyed.
The buoy near the Mariana Trench plunged into the water by 15 !!! meters. The Mariana Plate is tilting and moving under the Philippine Plate, and the Mariana Trench is rolling up. The Marianas will tilt and move closer to the Philippine Islands by 47 miles.
A strip of land 800 m long and 50 m wide appeared in the sea near the Taman Peninsula. Clay layers rose 5 m above sea level.In this area, there is a weak point in the earth's crust and jerks of the plates occur in three directions, the earth has risen from compression.
In the south of Russia, seismic activity has sharply increased in recent years. In the zone of special attention are the Azov and Black Seas. Their coastlines are constantly changing. New islands appear, or, conversely, land areas go under water. Scientists have found that such phenomena are associated with the movement of tectonic plates. Recently, the line of the Azov coast began to change dramatically. Not a single plant, only cracked soil, rocks and sand. More recently, this land was deep under water, but literally overnight, a significant section of the bottom rose five meters up and a peninsula was formed. To understand what force lifted a piece of land weighing hundreds of tons, experts take soil samples every day. After all the measurements, the conclusion is the same - tectonic plates in the area began to actively move.
http://www.vesti.ru/doc.html?id=623831&cid=7
The latest earthquake patterns (monitor http://www.emsc-csem.org/Earthquake/) indicate that the platforms are released, so they move regularly generally- on the example of recent earthquakes at the boundaries of the Antarctic, Philippine and Caribbean plates. As a result, earthquake epicenters are often located on all sides of the platform contour. On the IRIS seismic monitor on November 13, 2011, earthquakes fringing the Antarctic Plate show a clear trend. The Antarctic Plate is moving!
A strong earthquake on November 8, 2011 at the border of the Philippine Plate indicates the movement of this plate. The quake hit exactly on the border of the Philippine Plate, and the next day there was another smaller quake on the opposite side of the plate. This the plate also moves.
The November 12-13, 2011 quakes fringing the Caribbean Plate show that the entire plate is moving under pressure at the junction near Venezuela, the islands of Trinidad and Tobago, being lifted off the Virgin Islands, and being severely crushed where Guatemala meets with Coconut Slab. Caribbean Plate moving, as one whole.
Plate tectonics
Definition 1
A tectonic plate is a moving part of the lithosphere that moves on the asthenosphere as a relatively rigid block.
Remark 1
Plate tectonics is the science that studies the structure and dynamics of the earth's surface. It has been established that the upper dynamic zone of the Earth is fragmented into plates moving along the asthenosphere. Plate tectonics describes the direction in which lithospheric plates move, as well as the features of their interaction.
The entire lithosphere is divided into larger and smaller plates. Tectonic, volcanic and seismic activity is manifested along the edges of the plates, which leads to the formation of large mountain basins. Tectonic movements can change the relief of the planet. At the place of their connection, mountains and hills are formed, at the places of divergence, depressions and cracks in the ground are formed.
Currently, the movement of tectonic plates continues.
Movement of tectonic plates
Lithospheric plates move relative to each other at an average rate of 2.5 cm per year. When moving, the plates interact with each other, especially along the boundaries, causing significant deformations in the earth's crust.
As a result of the interaction of tectonic plates, massive mountain ranges and associated fault systems were formed (for example, the Himalayas, the Pyrenees, the Alps, the Urals, the Atlas, the Appalachians, the Apennines, the Andes, the San Andreas fault system, etc.).
The friction between the plates causes most of the planet's earthquakes, volcanic activity, and the formation of oceanic pits.
The composition of tectonic plates includes two types of lithosphere: continental crust and oceanic crust.
The tectonic plate can be of three types:
- continental Plate,
- ocean Plate,
- mixed board.
Theories of tectonic plate movement
In the study of the movement of tectonic plates, special merit belongs to A. Wegener, who suggested that Africa and the eastern part of South America were previously a single continent. However, after the break that happened many million years ago, parts of the earth's crust began to shift.
According to Wegener's hypothesis, tectonic platforms with different masses and rigid structures were located on the plastic asthenosphere. They were in an unstable state and moved all the time, as a result of which they collided, entered each other, and zones of plate separation and joints were formed. At the collision sites, areas with increased tectonic activity formed, mountains formed, volcanoes erupted and earthquakes occurred. The displacement occurred at a rate of up to 18 cm per year. Magma penetrated the faults from the deep layers of the lithosphere.
Some researchers believe that the magma that came to the surface gradually cooled down and formed a new bottom structure. The unused earth's crust, under the influence of plate drift, sank into the bowels and again turned into magma.
Wegener's research touched upon the processes of volcanism, the study of the stretching of the surface of the ocean floor, as well as the viscous-liquid internal structure of the earth. The works of A. Wegener became the foundation for the development of the theory of lithospheric plate tectonics.
Schmelling's research proved the existence of convective movement inside the mantle and leading to the movement of lithospheric plates. The scientist believed that the main reason for the movement of tectonic plates is thermal convection in the planet's mantle, in which the lower layers of the earth's crust heat up and rise, and the upper layers cool down and gradually descend.
The main position in the theory of plate tectonics is occupied by the concept of a geodynamic setting, a characteristic structure with a certain ratio of tectonic plates. In the same geodynamic setting, the same type of magmatic, tectonic, geochemical and seismic processes are observed.
The theory of plate tectonics does not fully explain the relationship between plate movements and processes occurring in the depths of the planet. A theory is needed that could describe the internal structure of the earth itself, the processes taking place in its depths.
Provisions of modern plate tectonics:
- the upper part of the earth's crust includes the lithosphere, which has a fragile structure, and the asthenosphere, which has a plastic structure;
- the main cause of plate movement is convection in the asthenosphere;
- the modern lithosphere consists of eight large tectonic plates, about ten medium plates and many small ones;
- small tectonic plates are located between large ones;
- magmatic, tectonic and seismic activity are concentrated at plate boundaries;
- the movement of tectonic plates obeys Euler's rotation theorem.
Types of tectonic plate movements
There are different types of tectonic plate movements:
- divergent movement - two plates diverge, and an underwater mountain range or an abyss in the ground forms between them;
- convergent movement - two plates converge and a thinner plate moves under a larger plate, resulting in the formation of mountain ranges;
- sliding motion - plates move in opposite directions.
Depending on the type of movement, divergent, convergent and sliding tectonic plates are distinguished.
Convergence leads to subduction (one plate is on top of another) or to collision (two plates are crushed and mountain ranges are formed).
Divergence leads to spreading (divergence of plates and formation of oceanic ridges) and rifting (formation of a break in the continental crust).
The transform type of movement of tectonic plates implies their movement along the fault.
Figure 1. Types of tectonic plate movements. Author24 - online exchange of student papers
Earth's lithospheric plates are huge blocks. Their foundation is formed by highly folded granite metamorphosed igneous rocks. The names of the lithospheric plates will be given in the article below. From above they are covered with a three-four-kilometer "cover". It is formed from sedimentary rocks. The platform has a relief consisting of individual mountain ranges and vast plains. Next, the theory of the movement of lithospheric plates will be considered.
The emergence of the 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 the exploration of the planet. The scientist Taylor, and after him Wegener, put forward the hypothesis that over time there is a drift of lithospheric plates in a horizontal direction. However, in the thirties of the 20th century, a different opinion was established. 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 became known as fixism. Such a 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 come out on land in some areas, there was a return to the hypothesis of the early 20th century. However, the theory has taken on a new form. Block tectonics has become the leading hypothesis in the sciences that study the structure of the planet.
Key points
It was determined that there are large lithospheric plates. 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 sources of earthquakes.
The names of the 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.
Blocks floating in the asthenosphere are characterized by solidity and rigidity. The above areas are the main lithospheric plates. In accordance with the initial ideas, it was believed that the continents make their way through the ocean floor. At the same time, the movement of lithospheric plates was carried out under the influence of an invisible force. As a result of the research, it was revealed that the blocks float passively over the material of the mantle. It is worth noting that their direction is vertical at first. The mantle material rises under the crest of the ridge. Then there is a spread in both directions. Accordingly, there is a divergence of lithospheric plates. This model represents the ocean floor as a giant. It comes to the surface in the rift areas of the mid-ocean ridges. Then hides in deep-sea trenches.
The divergence of lithospheric plates provokes the expansion of oceanic beds. However, the volume of the planet, despite this, remains constant. The fact is that the birth of a new crust is compensated by its absorption in subduction (underthrust) areas in deep-sea trenches.
Why does lithospheric plates move?
The reason is the thermal convection of the planet's mantle material. The lithosphere is stretched and uplifted, which occurs over ascending branches from 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 compacted. It becomes heavier, its surface sinks down. This explains the increase in ocean depth. As a result, the platform plunges into deep-sea trenches. When attenuating from the heated mantle, it cools and sinks with the formation of basins, which are filled with sediments.
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 conclude that the processes are continuous and ubiquitous. Collision zones of lithospheric plates are also revealed. 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 during the 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. The mantle material moves relatively slowly. However, earthquakes and other phenomena occur as a result. This allows us to draw a conclusion about the high power of moving the material.
Using the tectonic position of the plates, researchers explain many geological phenomena. At the same time, during the study, it turned out that the complexity of the processes occurring with the platform is much greater than it seemed at the very beginning of the appearance of the hypothesis.
Plate tectonics could not explain changes in the intensity of deformations 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. 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 young direction of all the existing geosciences. However, the solution of new problems was carried out 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 methods of isotope geochemistry were also used in the studies. 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. Methods of geomagnetism are used, with the help of which scientists are trying to uncover the causes and mechanism of reversals in a magnetic field.
Modern painting
The platform tectonics hypothesis continues to satisfactorily explain the process of crustal development during at least the last three billion years. At the same time, there are satellite measurements, according to which the fact that the main lithospheric plates of the Earth do not stand still is confirmed. As a result, a certain picture emerges.
There are three most active layers in the cross section of the planet. The thickness of each of them is several hundred kilometers. It is assumed that the main role in global geodynamics is assigned to them. In 1972, Morgan substantiated the hypothesis put forward in 1963 by Wilson about ascending mantle jets. 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 the crust is considered. In accordance with the concept set forth by Artyushkov in his work "Geodynamics", the main source of energy is the gravitational differentiation of matter. This process is noted in the lower mantle.
After the heavy components (iron, etc.) are separated from the rock, a lighter mass of solids remains. She descends into the core. The location of the lighter layer under the heavy one is unstable. In this regard, the accumulating material is collected periodically into fairly large blocks that float into the upper layers. The size of such formations is about a hundred kilometers. This material was the basis for the formation of the upper
The lower layer is probably an 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 are uplifted in the lower mantle along the channels. In them, the temperature of the mass is quite high. At the same time, the viscosity is significantly reduced. The increase in temperature is facilitated by the release of a large amount of potential energy in the process of lifting matter into the region of gravity at a distance of about 2000 km. In the course of movement along such a channel, a strong heating of light masses occurs. In this regard, the substance enters the mantle, having a sufficiently high temperature and significantly less weight in comparison with the surrounding elements.
Due to the reduced density, light material floats into the upper layers to a depth of 100-200 kilometers or less. With decreasing pressure, the melting point of the components of the substance decreases. After the primary differentiation at the "core-mantle" level, the secondary one occurs. At shallow depths, light matter is partially subjected to melting. During differentiation, denser substances are released. They sink into the lower layers of the upper mantle. The released lighter components rise accordingly.
The complex of motions of substances in the mantle, associated with the redistribution of masses with different densities as a result of differentiation, is called chemical convection. The rise of light masses occurs at intervals of about 200 million years. At the same time, intrusion into the upper mantle is not observed everywhere. In the lower layer, the channels are located at a sufficiently large distance from each other (up to several thousand kilometers).
Boulder lifting
As mentioned above, in those zones where large masses of light heated material are introduced into the asthenosphere, its partial melting and differentiation occur. In the latter case, the separation of components and their subsequent ascent are noted. They quickly pass through the asthenosphere. When they reach the lithosphere, their speed decreases. In some areas, matter 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 accumulation is a higher temperature (up to 1300-1500 degrees) and a reduced speed of elastic longitudinal waves.
The influx of matter under the lithosphere provokes isostatic uplift. Due to the elevated temperature, the anomalous cluster has a lower density than the normal mantle. In addition, there is a small viscosity of the composition.
In the process of entering the lithosphere, the anomalous mantle is rather quickly distributed along the sole. At the same time, it displaces the denser and less heated matter of the asthenosphere. In the course of movement, the anomalous accumulation fills those areas where the sole of the platform is in an elevated state (traps), and it flows around deeply submerged areas. As a result, in the first case, an isostatic uplift is noted. Above submerged areas, the crust remains stable.
Traps
The process of cooling the upper mantle layer and the crust to a depth of about a hundred kilometers is slow. In general, it takes several hundred million years. In this regard, inhomogeneities in the thickness of the lithosphere, explained by horizontal temperature differences, have a rather large inertia. In the event that the trap is located not far from the upward flow of the anomalous accumulation from the depth, a large amount of the substance is captured very heated. As a result, a rather large mountain element is formed. In accordance with this scheme, high uplifts occur in the area of epiplatform orogeny in
Description of processes
In the trap, the anomalous layer undergoes compression by 1–2 kilometers during cooling. The bark located on top is immersed. Precipitation begins to accumulate in the formed trough. Their heaviness 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, during the compaction of the mantle in the lower part of the basalt layer, a phase transformation of the rock into eclogite and garnet granulite can be observed in the crust. Due to the heat flow leaving the anomalous substance, the overlying mantle is heated and its viscosity decreases. In this regard, a gradual displacement of the normal cluster is observed.
Horizontal offsets
During the formation of uplifts in the process of the anomalous mantle reaching the crust on the continents and oceans, there is an increase in the potential energy stored in the upper layers of the planet. To dump excess substances, they tend to disperse to the sides. 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 the continents are the result of the simultaneous expansion of the ridges and the sinking of the platform into the mantle. Under the first are large masses of highly heated anomalous matter. In the axial part of these ridges, the latter is directly under the crust. The lithosphere here has a much smaller thickness. At the same time, the anomalous mantle spreads in the area of high pressure - in both directions from under the ridge. At the same time, it quite easily breaks the ocean's crust. The crevice is filled with basaltic magma. It, in turn, is melted out of 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 mid-ridges, the anomalous mantle has reduced viscosity due to elevated temperatures. The substance is able to spread quite quickly. As a result, the growth of the bottom occurs at an increased rate. The oceanic asthenosphere also has a relatively low viscosity.
The main lithospheric plates of the Earth float from the ridges to the places of immersion. If these areas are in the same ocean, then the process occurs at a relatively high speed. This situation is typical today for the Pacific Ocean. If the expansion of the bottom and the subsidence occurs in different areas, then the continent located between them drifts in the direction where the deepening occurs. Under the continents, the viscosity of the asthenosphere is higher than under the oceans. Due to the resulting friction, there is a significant resistance to movement. As a result, the rate at which the bottom expands is reduced if there is no compensation for the mantle subsidence in the same area. Thus, the expansion in the Pacific is faster than in the Atlantic.
