The structure of the earth's crust. Earth's crust

Work No. 1, 2016-2017 academic year

buildings earth's crust continents and oceans

The outer shell of the earth is called the earth's crust. The lower boundary of the earth's crust was objectively established with the help of seismographic studies at the beginning of the 20th century. Croatian geophysicist A. Mohorovičić on the basis of an abrupt increase in the velocity of waves at a certain depth. This indicated an increase in the density of rocks and a change in their composition. The boundary is called the Mohorovicic (Moho) surface. Below this boundary, dense ultramafic rocks of the upper mantle, depleted in silica and enriched in magnesium (peridotites, dunites, etc.), actually occur. The depth of the Moho surface determines the thickness of the earth's crust, which is thicker under the continent than under the oceans.

In the study of the earth's crust, it was also discovered that its structure was not the same under the continents, including their underwater margins, by oceanic depressions.

Continental (mainland) crust consists of a thin discontinuous sedimentary layer; the second granite-metamorphic layer (granites, gneisses, crystalline schists, etc.) and the third, the so-called basalt layer, which most likely consists of dense metamorphic (granulites, eclogites) and igneous (gabbro) rocks. The maximum thickness of the continental crust is 70-75 km under high mountains - the Himalayas, Andes, etc.

oceanic crust thinner, and it does not have a granite-metamorphic layer. A thin layer of unconsolidated sediments overlies. Below the second layer there is a basalt layer, in the upper part of which basalt pillow lavas alternate with thin layers of sedimentary rocks, in the lower part there is a complex of parallel basaltic dikes. The third layer consists of igneous crystalline rocks of predominantly basic composition (gabbro, etc.). The thickness of the oceanic crust is 6-10 km.

In the transitional zones from the continents to the ocean floor - modern mobile belts - there are transitional subcontinental and suboceanic types of the earth's crust of medium thickness.

The bulk of the earth's crust is composed of igneous and metamorphic rocks, although their outcrops on the day surface are small. Of the igneous rocks, the most common are intrusive rocks - granites and effusive - basalts, of metamorphic rocks - gneisses, shales, quartzites, etc.

On the surface of the Earth due to many external factors various sediments accumulate, which then for several million years as a result diagenesis(compaction and physico-biochemical changes) are transformed into sedimentary rocks: clay, clastic, chemical, etc.

Internal relief-forming processes

Mountains, plains and uplands differ in height, the nature of the occurrence of rocks, the time and method of formation. Both internal and external forces of the Earth participated in their creation. All modern relief-forming factors are divided into two groups: internal ( endogenous) and external ( exogenous).

The energy basis of internal relief-forming processes is the energy coming from the depths of the earth - rotational, radioactive decay and the energy of geochemical accumulators. Rotational Energy associated with the release of energy when the Earth's rotation around its axis slows down due to the influence of friction (fractions of seconds per millennium). Energy of geochemical accumulators- this is the energy of the Sun accumulated over many millennia in the rocks, which is released when the rocks are immersed in the inner layers.

Exogenous (external forces) are called so because the main source of their energy is outside the Earth - this is energy directly coming from the Sun. For the manifestation of the action of exogenous forces, irregularities must be involved earth's surface, creating a potential difference and the possibility of moving particles under the action of gravity.

Internal forces tend to create irregularities, and external forces tend to level these irregularities.

Internal forces create structure(basis) of the relief, and external forces act as a sculptor, processing "roughness created by internal forces. Therefore, endogenous forces are sometimes called primary, and external forces are secondary. But this does not mean that external forces are weaker than internal ones. In geological history, the results of the manifestation of these forces are comparable.

We can observe the processes occurring inside the Earth in tectonic movements, earthquakes and volcanism. Tectonic movements are the whole set of horizontal and vertical movements of the lithosphere. They are accompanied by the appearance of faults and folds of the earth's crust.

For a long time science dominated "platform-geosynclinal" concept development of the earth's relief. Its essence lies in the allocation of calm and moving parts of the earth's crust, platforms and geosynclines. It is assumed that the evolution of the structure of the earth's crust proceeds from geosynclines to platforms. There are two major stages in the development of geosynclines.

The first (main in terms of duration) stage of subsidence with a marine regime, the accumulation of a thick (up to 15-20 km) strata of sedimentary and volcanic rocks, lava outpouring, metamorphism, and subsequently with folding. The second stage (shorter in duration) is folding and ruptures during a general uplift (mountain building), as a result of which mountains are formed. Mountains subsequently collapse under the influence of exogenous forces.

In recent decades, most scientists adhere to a different hypothesis - lithospheric plate hypotheses. Lithospheric plates- These are vast areas of the earth's crust that move along the asthenosphere at a speed of 2-5 cm / year. A distinction is made between continental and oceanic plates; when they interact, the thinner edge of the oceanic plate sinks under the edge of the continental plate. As a result, mountains, deep-sea trenches, island arcs (for example, the Kuril Trench and Kurile Islands, Atakama Trench and Andes Mountains). When continental plates collide, mountains are formed (for example, the Himalayas when the Indo-Australian and Eurasian plates collide). Plate movements can be caused by convective movements of the mantle matter. In places where this substance rises, faults form, and the plates begin to move. The magma that intrudes along the faults solidifies and builds up the edges of the diverging plates - this is how mid-ocean ridges, stretching along the bottom of all oceans and forming single system 60,000 km long. Their height reaches 3 km, and the width is greater than more speed extensions.
The number of lithospheric plates is not constant - they are connected and divided into parts during the formation of rifts, large linear tectonic structures, such as deep gorges in the axial part of the mid-ocean ridges. It is believed that in the Paleozoic, for example, modern southern continents were one continent gondwana, northern - Laurasia, and even earlier there was a single supercontinent - Pangea and one ocean.
Along with slow horizontal movements, vertical ones also occur in the lithosphere. When plates collide or when the load on the surface changes, for example, due to the melting of large ice sheets, uplift occurs ( Scandinavian Peninsula is still on the rise). Such fluctuations are called glacioisostatic.

Tectonic movements of the earth's crust of the Neogene-Quaternary time are called neotectonic. These movements were and are being manifested with varying intensity almost everywhere on Earth.

Tectonic movements are accompanied earthquakes(shocks and rapid vibrations of the earth's surface) and volcanism(introduction of magma into the earth's crust and outpouring it to the surface).

Earthquakes are characterized the depth of the focus (a place of displacement in the lithosphere, from which seismic waves propagate in all directions) and the strength of the earthquake, estimated by the degree of destruction caused by it in points on the Richter scale (from 1 to 12). greatest strength earthquakes reach directly above the focus - at the epicenter. In volcanoes, a magma chamber and a channel or cracks are distinguished along which lava rises.

Most earthquakes and active volcanoes are confined to the margins of the lithospheric plates - the so-called seismic belts. One of them encircles the Pacific Ocean along the perimeter, the other stretches through Central Asia from the Atlantic Ocean to the Pacific.

External relief-forming processes

Exogenous forces, excited by the energy of solar rays and gravity, on the one hand, destroy the forms created by endogenous forces, on the other hand, create new forms. In this process, there are:

1) destruction of rocks (weathering - it does not create landforms, but prepares the material);

2) removal of destroyed material, usually it is demolition down the slope (denudation); 3) redeposition (accumulation) of demolished material.

The most important agents of manifestation of external forces are air and water.

Distinguish physical, chemical and biogenic weathering.

physical weathering occurs due to uneven expansion and contraction of rock particles with temperature fluctuations. It is especially intense in transitional seasons and in areas with continental climate, large daily temperature ranges - in the highlands of the Sahara or in the mountains of Siberia, while often formed whole stone rivers - kurums. If water penetrates into the cracks of the rocks, and then, solidifying and expanding, increases these cracks, they speak of frosty weathering.

chemical weathering- this is the destruction of rocks and minerals under the action of active substances contained in the air, rocks and soils (oxygen, carbon dioxide, salts, acids, alkalis, etc.) as a result of chemical reactions. On the other hand, chemical weathering is favored by humid and warm conditions typical of coastal areas, humid tropics and subtropics.

Biogenic weathering is often reduced to chemical and physical impact on rocks of organisms.

Usually, several types of weathering are observed simultaneously, and when they talk about physical or chemical weathering, this does not mean that other forces are not involved in this - just the name is given by the leading factor.

Water is "the sculptor of the face of the earth" and one of the most powerful agents of relief reconstruction. flowing waters affect the relief, destroying rocks. Temporary and permanent water streams, rivers and streams for millions of years "bite" into the earth's surface, erode it (erosion), move and re-deposit washed particles. If it were not for the constant uplift of the earth's crust, only 200 million years would be enough for water to wash away all the areas protruding above the sea and the entire surface of our planet would represent a single boundless ocean. The most common erosional landforms are linear erosion forms: river valleys, ravines and beams.

To understand the processes of formation of such forms, it is important to realize the fact that erosion basis(the place where the water tends, the level at which the flow loses its energy - for rivers this is the mouth or confluence, or a rocky area in the channel) changes its position over time. Usually it decreases when the river erodes those rocks through which it flows, this occurs especially intensively with an increase in the water content of rivers or tectonic fluctuations.

Ravines and gullies are formed by temporary streams that appear after snow melts or heavy rains fall. They differ from each other in that ravines are constantly growing, cutting into loose rocks, narrow steep ruts, and beams - having a wide bottom and hollows that have ceased to develop, are occupied by meadows or forests.

Rivers create a wide variety of landforms. In river valleys, the following forms: root bank(river sediments do not participate in its structure), understand(part of the valley flooded in floods or floods), terraces(former floodplains that have risen above the water line as a result of a decrease in the erosion basis), old women(sections of the river separated from the former channel as a result of meandering).

In addition to natural factors (the presence of surface slopes, easily eroded soils, heavy rainfall, etc.), the formation of erosion forms is facilitated by irrational human activity - clear deforestation and plowing of slopes.

In addition to water, an important factor of exogenous forces is the wind. Usually it has less strength than water, but working with loose material can work wonders. The shapes created by the wind are called eolian. They predominate in dry areas, or where dry conditions have been in the past ( relic eolian forms). This is dunes(crescent-shaped sand hills) and dunes(oval-shaped hills), turned rocks.

Tasks

Exercise 1.

Based on the available information presented in the table, guess in which mountain system the number of altitudinal belts will be the largest. Justify your answer.

Task 2.

The ship at the point with coordinates 30 s. sh. 70 c. d. crashed, the radio operator transmitted the coordinates of his ship and asked for help. Two ships Nadezhda (30 S 110 E) and Vera (20 S 50 E) headed for the disaster area. Which ship will come faster to the aid of a sinking ship?

Task 3.

Where are: 1) horse latitudes; 2) roaring latitudes; 3) furious latitudes? What natural phenomena are characteristic of these places? Explain the origin of their names.

Task 4.

AT different countries they are called differently: ushkuiniki, corsairs, filibusters. When was their golden age? Where was main area their focus? In what areas did they hunt in Russia? Why exactly here? Name the most famous person in the world whose name is on the maps. What is interesting about this geographical feature?

Task 5.

Before going to 1886 in circumnavigation on this corvette, its captain wrote in his diary: The commander's job is to name his ship... "He managed to achieve his goal - oceanographic research, carried out during an expedition that lasted almost three years, glorified the corvette so much that later it became a tradition to name scientific research vessels after him.

What was the name of the corvette? What achievements of science and geographical discoveries four ships became famous, at different times wearing this proud name? What do you know about the captain whose diary excerpt is given in the assignment?

Tests

1 . According to the theory of lithospheric plate tectonics, the earth's crust and upper mantle are divided into large blocks. Russia is located on a lithospheric plate

1) African 2) Indo-Australian 3) Eurasian 4) Pacific

2. Specify wrong statement:

1) The sun is in the south at noon in the Northern Hemisphere;

2) lichens grow thicker with north side trunk;
3) the azimuth is measured from the south direction counterclockwise;
4) a device with which you can navigate is called a compass.

3. Determine approximate height mountains, if it is known that at its foot the air temperature was +16ºС, and at its top -8ºС:

1) 1.3 km; 2) 4 km; 3) 24 km; 4) 400 m.

4. Which statement about lithospheric plates is correct?

1) Mid-ocean ridges are confined to the zone of divergence of oceanic lithospheric plates

2) The boundaries of the lithospheric plates exactly coincide with the contours of the continents
3) The structure of continental and oceanic lithospheric plates is the same
4) When lithospheric plates collide, vast plains are formed

5. What is the numerical scale of the plan, on which the distance from the bus stop to the stadium, which is 750 m, is shown as a segment 3 cm long.

1) 1: 25 2) 1: 250 3) 1: 2500 4) 1: 25 000 5) 1: 250 000

6 . Which arrow on the fragment of the world map corresponds to the direction to the southeast?

7. The science that studies geographical names:

1) geodesy; 2) cartography; 3) toponymy; 4) topography.

8. Name the amazing "architects", as a result of whose indefatigable activity various landforms dominate the Earth. __________________________________________________________________

9. Specify the correct statement.

1) The East European Plain has a flat surface;

2) Altai Mountains are located on the mainland of Eurasia;

3) The Klyuchevskaya Sopka volcano is located on the Scandinavian Peninsula;

4) Mount Kazbek is the most high peak Caucasus.

10. Which of the following landforms is of glacial origin?

1) moraine ridge 2) dune 3) plateau 4) dune

11. What scientific hypothesis are Vladimir Vysotsky's lines devoted to?

“At first there was a word of sadness and longing,

The planet was born in the throes of creativity -

Huge pieces were torn from sushi to nowhere

And islands became somewhere"

1) the search for Atlantis; 2) the death of Pompeii; 3) continental drift;

4) the formation of the solar system.

12. The lines of the tropics and the arctic circles are the boundaries ...

1) climatic zones; 2) natural areas; 3) geographical areas;

4) belts of illumination.

13. The absolute height of the Kilimanjaro volcano is 5895 m. Calculate it relative height, if it was formed on a plain rising 500 m above sea level:

1) 5395 m; 2) 5805m; 3) 6395; 4) 11.79 m

14 . The speed of movement of lithospheric plates relative to each other

is 1-12

1) mm/year 2) cm/month 3) cm/year 4) m/year

15 . Arrange objects according to their geographic location from west to east:

1) the Sahara desert; 2) Atlantic Ocean; 3) the city of the Andes; 4) about. New Zealand.

1. Formation of continents and oceans

A billion years ago, the Earth was already covered with a solid shell, in which continental protrusions and oceanic depressions stood out. Then the area of the oceans was about 2 times the area of the continents. But the number of continents and oceans has changed significantly since then, and so has their location. Approximately 250 million years ago, there was one continent on Earth - Pangea. Its area was approximately the same as the area of all modern continents and islands combined. This supercontinent was washed by an ocean called Panthalassa and occupied all the rest of the space on Earth.

However, Pangea turned out to be a fragile, short-lived formation. Over time, the currents of the mantle inside the planet changed direction, and now, rising from the depths under Pangea and spreading into different sides, the substance of the mantle began to stretch the mainland, and not compress it, as before. Approximately 200 million years ago, Pangea split into 2 continents: Laurasia and Gondwana. The Tethys Ocean appeared between them (now it is the deep-water parts of the Mediterranean, Black, Caspian Seas and the shallow Persian Gulf).

The currents of the mantle continued to cover Laurasia and Gondwana with a network of cracks and break them up into many fragments that did not remain on certain place and gradually diverged in different directions. They were driven by currents within the mantle. Some researchers believe that it was these processes that caused the death of dinosaurs, but this question remains open for now. Gradually, between the diverging fragments - the continents - the space was filled with mantle matter, which rose from the bowels of the Earth. Cooling down, it formed the bottom of the future oceans. Over time, three oceans appeared here: the Atlantic, the Pacific, and the Indian. According to many scientists, the Pacific Ocean is the remnant of the ancient ocean of Panthalassa.

Later, new faults engulfed Gondwana and Laurasia. From Gondwana, the land first separated, which is now Australia and Antarctica. She began drifting to the southeast. Then it split into two unequal parts. The smaller one - Australia - rushed to the north, the larger one - Antarctica - to the south and took a place inside the South polar circle. The rest of Gondwana split into several plates, the largest of them being African and South American. These plates are now diverging from each other at a rate of 2 cm per year (see Lithospheric Plates).

Faults also covered Laurasia. It split into two plates - North American and Eurasian, which make up most of the Eurasian continent. The emergence of this continent is the greatest cataclysm in the life of our planet. Unlike all other continents, which are based on one fragment ancient continent, Eurasia includes 3 parts: Eurasian (part of Laurasia), Arabian (protrusion of Gondwana) and Indostan (part of Gondwana) lithospheric plates. Approaching each other, they almost destroyed the ancient Tethys ocean. Africa is also involved in the formation of the image of Eurasia, the lithospheric plate of which, although slowly, is approaching the Eurasian one. The result of this convergence are the mountains: the Pyrenees, the Alps, the Carpathians, the Sudetes and the Ore Mountains (see Lithospheric Plates).

The convergence of the Eurasian and African lithospheric plates is still going on, this is reminiscent of the activity of the volcanoes Vesuvius and Etna, disturbing the tranquility of the inhabitants of Europe.

The convergence of the Arabian and Eurasian lithospheric plates led to crushing and crushing into folds of rocks that fell on their way. This was accompanied by strong volcanic eruptions. As a result of the convergence of these lithospheric plates, the Armenian Highland and the Caucasus arose.

The convergence of the Eurasian and Hindustan lithospheric plates made the entire continent shudder from indian ocean to the Arctic, while Hindustan itself, which originally broke away from Africa, suffered little. The result of this rapprochement was the emergence of the highest highlands in the world of Tibet, surrounded by even higher chains of mountains - the Himalayas, the Pamirs, the Karakorum. It is not surprising that it is here, in the place of the strongest compression of the earth's crust of the Eurasian lithospheric plate, that the highest peak of the Earth is located - Everest (Chomolungma), rising to a height of 8848 m.

The "march" of the Hindustan lithospheric plate could lead to a complete split of the Eurasian plate, if there were no parts inside it that could withstand pressure from the south. Acted as a worthy "defender" Eastern Siberia, but the lands located to the south of it were folded into folds, crushed and moved.

So, the struggle between continents and oceans has been going on for hundreds of millions of years. The main participants in it are the continental lithospheric plates. Every mountain range, island arc, deepest ocean trench is the result of this struggle.

2. Structure of continents and oceans

Continents and oceans are the largest elements in the structure of the Earth's crust. Speaking of oceans, one should keep in mind the structure of the crust within the areas occupied by the oceans.

The composition of the earth's crust is different between continental and oceanic. This, in turn, leaves an imprint on the features of their development and structure.

The boundary between the mainland and the ocean is drawn at the foot of the continental slope. The surface of this foot is an accumulative plain with large hills, which are formed due to underwater landslides and alluvial fans.

In the structure of the oceans, sections are distinguished according to the degree of tectonic mobility, which is expressed in manifestations of seismic activity. On this basis, distinguish:

seismically active areas(oceanic mobile belts),

aseismic areas (ocean basins).

Mobile belts in the oceans are represented by mid-ocean ridges. Their length is up to 20,000 km, their width is up to 1,000 km, and their height reaches 2–3 km from the bottom of the oceans. In the axial part of such ridges, rift zones are almost continuously traced. They are marked with high values heat flow. Mid-ocean ridges are considered as stretching areas of the earth's crust or spreading zones.

The second group of structural elements is ocean basins or thalassocratons. These are flat, slightly hilly areas of the seabed. The thickness of the sedimentary cover here is no more than 1000 m.

Another major element of the structure is the transition zone between the ocean and the mainland (continent), some geologists call it a mobile geosynclinal belt. This is the area of maximum dissection of the earth's surface. This includes:

1-island arcs, 2 - deep-water trenches, 3 - deep-water basins of marginal seas.

Island arcs are long (up to 3000 km) mountain structures formed by a chain of volcanic structures with modern manifestation basaltic andesite volcanism. An example of island arcs is the Kurile-Kamchatka ridge, the Aleutian Islands, etc. From the ocean side, island arcs are replaced by deep-water trenches, which are deep-water depressions 1500–4000 km long and 5–10 km deep. The width is 5–20 km. The bottoms of the gutters are covered with sediments, which are brought here by turbidity streams. The slopes of the gutters are stepped with different angles tilt. No deposits were found on them.

The boundary between the island arc and the slope of the trench represents a zone of concentration of earthquake sources and is called the Wadati-Zavaritsky-Benioff zone.

Considering the signs of modern oceanic margins, geologists, relying on the principle of actualism, conduct a comparative historical analysis of similar structures that formed in more ancient periods. These signs include:

· marine type sediments with a predominance of deep-sea sediments,

linear shape of structures and bodies of sedimentary strata,

· abrupt change thickness and material composition of sedimentary and volcanic strata in a cross strike of folded structures,

· high seismicity,

· a specific set of sedimentary and igneous formations and the presence of indicator formations.

Of these signs, the last one is one of the leading ones. Therefore, we define what a geological formation is. First of all, it is a real category. In the hierarchy of the matter of the earth's crust, you know the following sequence:

A geological formation is a more complex stage of development following a rock. It is a natural association of rocks, connected by the unity of the material composition and structure, which is due to the commonality of their origin or location. Geological formations are distinguished in groups of sedimentary, igneous and metamorphic rocks.

For the formation of stable associations of sedimentary rocks, the main factors are the tectonic setting and climate. Examples of formations and the conditions for their formation will be considered in the analysis of the development of structural elements of continents.

There are two types of regions on the continents.

Type I coincides with mountainous regions, in which sedimentary deposits are folded into folds and broken up by various faults. Sedimentary sequences are intruded by igneous rocks and metamorphosed.

Type II coincides with flat areas, on which deposits occur almost horizontally.

The first type is called a folded region or folded belt. The second type is called a platform. These are the main elements of the continents.

Folded areas are formed at the site of geosynclinal belts or geosynclines. A geosyncline is a mobile extended area of a deep trough of the earth's crust. It is characterized by the accumulation of thick sedimentary strata, prolonged volcanism, a sharp change in direction tectonic movements with the formation of folded structures.

Geosynclines are divided into:

The continental type of the earth's crust is oceanic. Therefore, the ocean floor itself includes the depressions of the ocean floor located behind the continental slope. These huge depressions differ from the continents not only in the structure of the earth's crust, but also in their tectonic structures. The most extensive areas ocean floor are deep-water plains located at depths of 4-6 km and ...

And depressions with sharp elevation changes, measured in hundreds of meters. All these features of the structure of the axial strip of the median ridges should obviously be understood as a manifestation of intense blocky tectonics, and the axial depressions are grabens, and on both sides of them the median ridge is broken into raised and lowered blocks by ruptures. The whole set of structural features that characterize ...

The primary basalt layer of the Earth was formed. Archaean was characterized by the formation of primary large water bodies (seas and oceans), the appearance of the first signs of life in aquatic environment, education ancient relief Earth, similar to the relief of the moon. Several epochs of folding occurred in the Archaean. Formed shallow ocean with many volcanic islands. An atmosphere has formed containing vapors...

The water in the South Equatorial Current is 22 ... 28 ° С, in the East Australian in winter from north to south it changes from 20 to 11 ° С, in summer - from 26 to 15 ° С. The Circumpolar Antarctic, or West Wind Current, enters the Pacific Ocean south of Australia and New Zealand and moves in a sublatitudinal direction toward the coast South America, where its main branch deviates to the north and, passing along the coasts ...

Continents and oceans are the largest elements in the structure of the Earth's crust. Speaking of oceans, one should keep in mind the structure of the crust within the areas occupied by the oceans.

The composition of the earth's crust is different between continental and oceanic. This, in turn, leaves an imprint on the features of their development and structure.

In the structure of the oceans, sections are distinguished according to the degree of tectonic mobility, which is expressed in manifestations of seismic activity. On this basis, distinguish:

seismically active areas (oceanic mobile belts),
aseismic regions (ocean basins).

Mobile belts in the oceans are represented by mid-ocean ridges. Their length is up to 20,000 km, width - up to 1,000 km, height reaches 2-3 km from the bottom of the oceans. In the axial part of such ridges, one can almost continuously trace rift zones. They are marked by high values of heat flux. Mid-ocean ridges are considered as areas of stretching of the earth's crust or zone spreading.

The second group of structural elements - ocean basins or thalassocratons. These are flat, slightly hilly areas of the seabed. The thickness of the sedimentary cover here is no more than 1000 m.

Another major element of the structure is the transition zone between the ocean and the mainland (continent), some geologists call it mobile geosynclinal belt. This is the area of maximum dissection of the earth's surface. This includes:

1-island arcs, 2 - deep-sea trenches, 3 - deep-water basins of marginal seas.

island arcs- these are extended (up to 3000 km) mountain structures formed by a chain of volcanic structures with a modern manifestation of basaltic andesite volcanism. An example of island arcs is the Kuril-Kamchatka ridge, the Aleutian Islands, etc. From the ocean side, island arcs are replaced deep sea trenches, which are deep depressions with a length of 1500-4000 km, a depth of 5-10 km. The width is 5-20 km. The bottoms of the gutters are covered with sediments, which are brought here by turbidity streams. The slopes of the gutters are stepped with different angles of inclination. No deposits were found on them.

The boundary between the island arc and the slope of the trench represents the zone of concentration of earthquake sources and is called the zone Wadati-Zavaritsky-Benioff.

marine type of sediments with a predominance of deep-sea sediments,
linear form of structures and bodies of sedimentary strata,
a sharp change in the thickness and material composition of sedimentary and volcanic strata in a cross-strike of folded structures,
high seismicity,
a specific set of sedimentary and igneous formations and the presence of indicator formations.

Chem. element→ mineral → rock → geological formation

There are two types of regions on the continents.

I the type coincides with mountainous regions, in which sedimentary deposits are folded into folds and broken up by various faults. Sedimentary sequences are intruded by igneous rocks and metamorphosed.

II the type coincides with flat areas, on which deposits occur almost horizontally.

The first type is called a folded region or folded belt. The second type is called a platform. These are the main elements of the continents.

Folded areas are formed at the site of geosynclinal belts or geosynclines. Geosyncline- this is a mobile extended area of deep deflection of the earth's crust. It is characterized by the accumulation of thick sedimentary strata, prolonged volcanism, and a sharp change in the direction of tectonic movements with the formation of folded structures.

Geosynclines are divided into:

1. Eugeosinklinal - represents the inner part of the mobile belt,

2. Miogeosyncline - the outer part of the mobile belt.

They are distinguished by the manifestation of volcanism, the accumulation of sedimentary formations, folded and discontinuous deformations.

There are two stages in the formation of the geosyncline. In turn, in each of the stages, the stages are distinguished, which are characterized by: certain type tectonic movements and geological formations. Let's consider them.

stages	Stages of tectonic movements	Traffic sign	Formations in:
stages	Stages of tectonic movements	Traffic sign	Miogeosynclines	Eugeosynclines
	1. *Early geosynclinal* Lowering - relief irregularities are formed, by the end of the stage, a partial inversion i.e. relative descent and rise individual sections geosynclines 2.Late geosynclinal Shallowing of the sea, formation of island arcs and marginal seas	↓ ↔ → ←	Slate (black shale) sandy-clayey Flysch - rhythmic interbedding of sandy-silty sediments and limestones	Basaltic volcanism with siliceous sediments Differentiated: basalt-andesite-rhyolitic lavas and tuffs
	1.Early orogenic The formation of a central uplift and marginal deflections, the speed of movement is low. The sea is shallow 2.orogenic A sharp rise in the central rise with splits into blocks. Intermountain depressions in the middle massifs	→ ← → ←	Thin molasses -fine clastic rocks + saline and coal-bearing strata Rough molasse continental coarse sediments	Intrusion of granite batholiths Porphyritic: terrestrial alkaline andesite-iolite volcanism, stratovolcanoes

The time from the beginning of the origin of the geosyncline to the completion of its development is called the stage of folding (tectonic epoch). In the history of the formation of the earth's crust, several tectonic epochs are distinguished:

1. Precambrian, unites several epochs, among which we single out Baikal stage of folding, ended in the early Cambrian.

2. Caledonianfolding - occurred in the early Paleozoic, was maximally manifested at the end of the Silurian. The Scandinavian mountains, Western Sayan, etc.

3. Hercynianfolding - occurred in the late Paleozoic. It includes folded structures Western Europe, Ural, Appalachians, etc.

4. Mesozoic(Cimmerian) - covers the entire MZ . The Cordillera, Verkhoyansk-Chukotka folded regions were formed.

5. Alpinefolding - manifested itself in Cenozoic era and continues now. The Andes, Alps, Himalayas, Carpathians, etc.

After the completion of folding, a section of the earth's crust may again be involved in the next geosynclinal cycle. But in most cases, after the completion of mountain building, the epigeosynclinal stage of development of the folded area begins. Tectonic movements become slow oscillatory (huge areas experience slow subsidence or rise), as a result of which powerful strata of sedimentary formations accumulate. Magmatic activity takes on new forms. In this case, we are talking about the platform stage of development. And large areas of the earth's crust with a stable tectonic development regime are called platforms.

Platform features:

1-marine shallow, lagoonal and terrestrial types of sediments;

2-slope occurrence of layers,

3-aged on large areas composition and thickness of deposits,

4-lack of metamorphism of sedimentary strata, etc.

Common in the structure of the platforms - there are always two floors: 1 - lower folded and metamorphosed, broken through by intrusions - called the foundation; 2 - upper, represents horizontally or gently sloping thick sedimentary strata, called a cover.

By the time of formation, the platforms are divided into ancient and young. The age of the platforms is determined by the age of the folded basement.

Ancient platforms are those in which the folded foundation is represented by granite-gneisses of the Archean-Proterozoic age. Otherwise, they are also called cratons.

The largest ancient platforms:

1-North American, 2-South American, 3-African-Arabian, 4-East European, 5-Siberian, 6-Australian, 7-Antarctic, 8-Indostan.

There are two types of structures on platforms - shields and slabs.

Shield- this is the section of the platform on which the folded foundation comes to the surface. In these areas, vertical uplift predominates.

Plate- part of the platform covered by a sedimentary cover. Slow vertical subsidence prevails here. In the structure of the plates, anteclises and syneclises are distinguished. Their formation is due to the uneven structure of the surface of the folded foundation.

Anteclises- areas of the sedimentary cover formed above the ledges of the folded basement. Signs of anteclise: reduction in the thickness of the sedimentary cover, breaks and wedging out of layers towards the anteclise dome.

syneclise- large depressions above the areas of immersion of the surface of the folded foundation.

Both forms are characterized by gently sloping (not >5 o) occurrence of layers and isometric forms in plan. Along with this, on the plates allocate aulacogens are graben-like deflections. They appear at an early stage of development of the platform cover and represent a system of stepped deep faults, along which the basement rocks subside and the thickness of the sedimentary rocks of the cover increases.

The junction zones of geosynclinal and platform areas are of two types.

edge seam- a linear zone of deep faults along the edge of the platform, arising from mountain building processes in the adjacent geosyncline.

Edge (forward) deflection - a linear zone on the border of the platform and the geosynclinal belt, formed as a result of the lowering of the edge blocks of the platform and part of the geosyncline wing. In the section, the marginal trough is an asymmetric synclinal shape, in which the wing from the side of the platform is flat, and the wing adjacent to the folded belt is steep.

The platform formation process can be divided into two stages.

The first stage is the beginning of the subsidence of the folded orogenic area and its transformation into the foundation of the platform. The second stage covers the process of formation of the sedimentary cover, which occurs cyclically. Each cycle is divided into stages, which are characterized by their own tectonic regime and a set of geological formations.

Stages of tectonic movements	Sign	formations
1. Immersion of the foundation sections along the faults - the initiation and development of aulacogen with the accumulation of sediments in it		Basal, lagoonal-continental in aulacogenes
2. Slab - immersion of a significant part of the platform		Transgressive marine terrigenous (sands, clays - often bituminous, clay-carbonate)
3 Maximum transgression		Carbonate (limestones, dolomites with interlayers of sandy-argillaceous rocks)
4 Shallowing of the sea - the beginning of the regression		Salt-bearing, coal or red
5 General lift - continental mode		Continental

In the development of platforms, epochs of tectonic activation are distinguished, in which the fragmentation of platforms along faults and the revival of several types of magmatism took place. Let's point out 2 main ones.

1. Fissure eruptions with the formation of thick covers of basic rocks - the formation of a trap formation (Siberian platform).

2. Intrusions of alkaline - ultrabasic formation (kimberlite) with explosion pipes. Diamond deposits in South Africa and Yakutia are associated with this formation.

On some platforms, such processes of tectonic activity are accompanied by uplifting of crustal blocks and mountain building. Unlike folded regions, they are called regions epiplatform orogeny, or lumpy.

MAIN STRUCTURAL ELEMENTS OF THE EARTH'S CRUST: The largest structural elements of the earth's crust are continents and oceans.

Within the oceans and continents, smaller structural elements are distinguished, firstly, these are stable structures - platforms that can be both in the oceans and on the continents. They are characterized, as a rule, by a leveled, calm relief, which corresponds to the same position of the surface at depth, only under the continental platforms it is at a depth of 30-50 km, and under the oceans 5-8 km, since oceanic crust much thinner than continental.

in the oceans like structural elements, mid-ocean mobile belts are distinguished, represented by mid-ocean ridges with rift zones in their axial part, crossed by transform faults and which are currently zones spreading, i.e. extensions ocean floor and buildup of newly formed oceanic crust.

On the continents, as structural elements of the highest rank, stable areas are distinguished - platforms and epiplatform orogenic belts that formed in the Neogene-Quaternary time in stable structural elements of the earth's crust after a period of platform development. Such belts include modern mountain structures of the Tien Shan, Altai, Sayan, Western and Eastern Transbaikalia, East Africa and others. also in the Neogene-Quaternary time, they make up epigeosynclinal orogenic belts, such as the Alps, Carpathians, Dinarids, the Caucasus, Kopetdag, Kamchatka, etc.

The structure of the Earth's crust of continents and oceans: The Earth's crust is the outer solid shell of the Earth (geosphere). Below the crust is the mantle, which differs in composition and physical properties- it is denser, contains mainly refractory elements. The crust and mantle are separated by the Mohorovichic boundary, on which there is a sharp increase in seismic wave velocities.

The mass of the earth's crust is estimated at 2.8 1019 tons (of which 21% is oceanic crust and 79% is continental). The crust makes up only 0.473% of the total mass of the Earth.

Oceanic th bark: The oceanic crust consists mainly of basalts. According to the theory of plate tectonics, it continuously forms at mid-ocean ridges, diverges from them, and is absorbed into the mantle in subduction zones (the place where oceanic crust sinks into the mantle). Therefore, the oceanic crust is relatively young. Ocean. the crust has a three-layer structure (sedimentary - 1 km, basalt - 1-3 km, igneous rocks - 3-5 km), its total thickness is 6-7 km.

Continental crust: The continental crust has a three-layer structure. The upper layer is represented by a discontinuous cover of sedimentary rocks, which is widely developed, but rarely has a large thickness. Most of the bark is folded under upper bark- a layer consisting mainly of granites and gneisses, having a low density and ancient history. Studies show that most of these rocks were formed very long ago, about 3 billion years ago. Below is the lower crust, consisting of metamorphic rocks - granulites and the like. The average thickness is 35 km.

Chemical composition of the Earth and the earth's crust. Minerals and rocks: definition, principles and classification.

The chemical composition of the Earth: consists mainly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8% ), calcium (1.5%) and aluminum (1.4%); the remaining elements account for 1.2%. Due to mass segregation inner space, presumably composed of iron (88.8%), a small amount of nickel (5.8%), sulfur (4.5%)

The chemical composition of the earth's crust: The earth's crust is slightly more than 47% oxygen. The most common rock-constituting minerals of the earth's crust almost entirely consist of oxides; the total content of chlorine, sulfur and fluorine in rocks is usually less than 1%. The main oxides are silica (SiO2), alumina (Al2O3), iron oxide (FeO), calcium oxide (CaO), magnesium oxide (MgO), potassium oxide (K2O) and sodium oxide (Na2O). Silica serves mainly as an acid medium and forms silicates; the nature of all major volcanic rocks is associated with it.

Minerals: - natural chemical compounds arising from certain physical and chemical processes. Most minerals are crystalline solids. The crystalline form is due to the structure of the crystal lattice.

According to the prevalence, minerals can be divided into rock-forming - forming the basis of most rocks, accessory - often present in rocks, but rarely making up more than 5% of the rock, rare, the occurrences of which are single or few, and ore, widely represented in ore deposits.

Holy Island of minerals: hardness, crystal morphology, color, luster, transparency, cohesion, density, solubility.

Rocks: a natural collection of minerals of a more or less constant mineralogical composition, forming an independent body in the earth's crust.

By origin, rocks are divided into three groups: igneous(effusive (frozen at depth) and intrusive (volcanic, erupted)), sedimentary and metamorphic(rocks formed in the thickness of the earth's crust as a result of changes in sedimentary and igneous rocks due to changes in physico-chemical conditions). Igneous and metamorphic rocks make up about 90% of the volume of the earth's crust, however, on the modern surface of the continents, their areas of distribution are relatively small. The remaining 10% are sedimentary rocks, which occupy 75% of the earth's surface area.

The structure of the planet on which we live has long occupied the minds of scientists. Many naive judgments and brilliant conjectures were made, but no one could prove the correctness or fallacy of any hypothesis with convincing facts until very recently. And even today, despite the colossal successes of Earth science, primarily due to the development of geophysical methods for studying its interior, there is no single and final opinion on the structure of the inner parts of the globe.

True, all experts agree on one thing: the Earth consists of several concentric layers, or shells, inside of which there is a spherical core. Latest Methods made it possible to measure with great accuracy the thickness of each of these nested spheres, but what they are and what they consist of has not yet been fully established.

Some properties of the inner parts of the Earth are known for certain, while others can only be guessed at. So, using the seismic method, it was possible to establish the speed of passage through the planet elastic vibrations(seismic waves) caused by an earthquake or explosion. The magnitude of this velocity is, in general, very high (several kilometers per second), but in a denser medium it increases, in a loose medium it sharply decreases, and in a liquid medium such oscillations quickly die out.

Seismic waves can travel through the Earth in less than half an hour. However, having reached the interface between layers with different densities, they are partially reflected and return to the surface, where the time of their arrival can be recorded by sensitive instruments.

The fact that another layer is located under the upper hard shell of our planet was guessed back in ancient times. The first to say this was the ancient Greek philosopher Empedocles, who lived in the 5th century BC. Watching the eruption famous volcano Etna, he saw molten lava and came to the conclusion that under the solid cold shell of the earth's surface there is a layer of molten magma. A brave scientist died while trying to get into the mouth of a volcano in order to get to know its device better.

The idea of the fiery-liquid structure of the deep earth's interior was most vividly developed in mid-eighteenth century in theory German philosopher I. Kant and the French astronomer P. Laplace. This theory lasted until the end of the 19th century, although no one was able to measure at what depth the cold solid crust ends and liquid magma begins. In 1910, the Yugoslav geophysicist A. Mohorovicic did this by applying the seismic method. Studying the earthquake in Croatia, he found that at a depth of 60-70 kilometers the speed of seismic waves changes dramatically. Above this section, which was later called the Mohorovichic (or simply "Moho") boundary, the speed of the waves does not exceed 6.5-7 kilometers per second, while below it increases abruptly to 8 kilometers per second.

Thus, it turned out that directly under the lithosphere (crust) there is not molten magma at all, but, on the contrary, a hundred-kilometer layer, even denser than the crust. It is underlain by the asthenosphere (weakened layer), the substance of which is in a softened state.

Some researchers believe that the asthenosphere is a mixture of solid granules with a liquid melt.

Judging by the speed of propagation of seismic waves, under the asthenosphere, up to a depth of 2900 kilometers, there are superdense layers.

What is this multi-layered inner shell (mantle), located between the Moho surface and the core, is difficult to say. On the one hand, it has signs solid body(seismic waves propagate rapidly in it), on the other hand, the mantle has an undoubted fluidity.

It should be noted that the physical conditions in this part of the bowels of our planet are completely unusual. There reign heat and colossal pressure of the order of hundreds of thousands of atmospheres. The well-known Soviet scientist, academician D. Shcherbakov believes that the substance of the mantle, although solid, has plasticity. Perhaps it can be compared to a shoe pitch, which, under the blows of a hammer, breaks into fragments with sharp edges. However, over time, even in the cold, it begins to spread like a liquid and flow down a slight slope, and upon reaching the edge of the surface, drip down.

The central part of the Earth, its core, is fraught with more puzzles. What is it, liquid or solid? What substances does it consist of? Seismic methods have established that the core is heterogeneous and is divided into two main layers - outer and inner. According to some theories, it consists of iron and nickel, according to others - from super-densified silicon. Recently, the idea has been put forward that the central part of the core is iron-nickel, and the outer part is silicon.

It is clear that the most well known of all the geospheres are those that are accessible to direct observation and research: the atmosphere, the hydrosphere, and the crust. The mantle, although it comes close to the earth's surface, does not appear to be exposed anywhere. Therefore, even about her chemical composition there is no consensus. True, Academician A. Yanshin believes that some rare minerals from the so-called mer-richbite-redderite group, previously known only as part of meteorites and recently found in the Eastern Sayans, are mantle outcrops. But this hypothesis still requires careful testing.

The earth's crust of the continents has been studied by geologists with sufficient completeness. Big role this was played by deep drilling. The upper layer of the continental crust is formed by sedimentary rocks. As the name itself indicates, they are of water origin, that is, the particles that formed this layer of the earth's crust settled from the water suspension. The vast majority of sedimentary rocks were formed in ancient seas, less often they owe their origin to freshwater reservoirs. In very rare cases, sedimentary rocks have arisen as a result of weathering directly on land.

The main sedimentary rocks are sands, sandstones, clays, limestones, and sometimes rock salt. The thickness of the sedimentary layer of the crust is different in different parts earth's surface. In some cases, it reaches 20-25 kilometers, but in some places there is no precipitation at all. In these places, the next layer of the earth's crust comes out to the "day surface" - granite.

It got this name because it is composed of both granites themselves and rocks close to them - granitoids, gneisses and micaceous schists.

The granite layer reaches a thickness of 25-30 kilometers and is usually covered from above by sedimentary rocks. The lowest layer of the earth's crust - basalt - is no longer available for direct study, since it does not come out anywhere on the day surface and deep wells it is not reached. The structure and properties of the basalt layer are judged solely on the basis of geophysical data. It is assumed with a high degree of certainty that this lower layer of the crust consists of igneous rocks close to basalts originating from cooled volcanic lava. The thickness of the basalt layer reaches 15–20 kilometers.

Until recently, it was believed that the structure of the earth's crust is the same everywhere, and only in the mountains it rises, forming folds, and under the oceans it sinks, forming giant bowls. One of the results of the scientific and technological revolution was rapid development in the middle of the 20th century a number of sciences, including marine geology. In this branch of human knowledge, many cardinal discoveries have been made that radically changed the previous ideas about the structure of the crust under the ocean bed. It was found that if under the marginal seas and near the continents, that is, in the shelf area, the crust is still to some extent similar to the continental one, then the oceanic crust is completely different. Firstly, it has a very small thickness: from 5 to 10 kilometers. Secondly, under the ocean floor, it consists not of three, but only of two layers - sedimentary 1-2 kilometers thick and basalt. The granite layer, so characteristic of the continental crust, continues towards the ocean only to the continental slope, where it breaks off.

These discoveries sharply intensified the interest of geologists in the study of the ocean. There was a hope to discover outcrops of mysterious basalt on the seabed, and maybe even mantles. The prospects of underwater drilling, with which you can get to deep layers through a relatively thin and easily overcome layer of sediments.

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