Work No. 1, 2016-2017 academic year

Structures of the earth's crust of 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 ultrabasic 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. Max Power continental crust 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 "created internal forces bumps. Therefore, endogenous forces are sometimes called primary, and external - secondary. But this does not mean that external forces are weaker than internal ones. Over 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 called the whole set of horizontal and vertical movements 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 - hypotheses lithospheric plates . 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 the Kuril Islands, the Atakama Trench and the Andes Mountains) are formed. 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 greater the width, the greater the speed of expansion.
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, the 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 surface loads change, for example due to the melting of large ice sheets, uplift occurs (the Scandinavian Peninsula is still uplifting). 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). The greatest force of an earthquake is reached directly above the source - in 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

Excited by energy sun rays and gravity, exogenous forces, 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 manifestation agents 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 water, rocks and soils contained in the air active substances(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 flows, rivers and streams for millions of years "bite" into the earth's surface, erode it (erosion), move and redeposit the washed-out 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 are distinguished: 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).

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

Besides water an important factor exogenous force 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 information provided in the table, guess which mountain system the number of altitudinal belts will be the greatest. 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.

In different countries they are called differently: ushkuyniki, 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 denser on the north side of the 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 the approximate height of the mountain, 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 true?

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 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 highest peak in the Caucasus.

10. Which of listed forms relief 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. Tropical lines and polar circles are boundaries...

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

4) belts of illumination.

13. Altitude Kilimanjaro volcano - 5895 m. Calculate its 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.

Earth is a cosmic body that is part of solar system. Considering the origin of the continents and oceans, it is worth touching on the issue of the origin of the planet.

How our planet was formed

The origin of the continents and oceans is the second question. The first is to explain the causes and method of the formation of the Earth. Its solution was dealt with by the pundits of antiquity. Many hypotheses have been put forward to explain their consideration - the prerogative of astronomy. One of the most common is the hypothesis of O.Yu. Schmidt, which states that our planet arose from a cold cloud of gas and dust. The particles that make up it, while rotating around the Sun, were in contact with each other. They stuck together, and the resulting lump increased in size, its density increased, and the structure changed.

There are other hypotheses explaining the appearance of planets. Some of them suggest that space bodies, including the Earth - the result of explosions in outer space high power, which led to the decay of stellar matter. Many scientists are still searching for the truth about the origin of the planet.

The structure of the earth's crust under the continents and oceans

Studying the origin of continents and oceans Grade 7 high school. Even students know that the top layer of the lithosphere is called the earth's crust. It is a kind of "cloak" that covers the seething bowels of the planet. If you compare it with others, it will seem like the thinnest film. Its average thickness is only 0.6% of the planet's radius.

The origin of the continents and depressions of the oceans that determine appearance Earth, it will become clearer if you first study the structure of the lithosphere. consists of continental and oceanic plates. The first consist of three layers (bottom-up): basalt, granite and sedimentary. Oceanic plates are devoid of the last two, so their thickness is much less.

Differences in the structure of plates

The question that geography studies (grade 7) is the origin of the continents and oceans, as well as the distinctive features of their structure. According to the vast majority of scientists, only oceanic plates originally arose on Earth. Under the influence of processes occurring in the bowels of the earth, the surface became folded, mountains appeared. The crust became thicker, ledges began to appear, which later turned into continents.

Further transformation of continents and oceanic depressions is not so unambiguous. Scholars are divided on this issue. According to one hypothesis, the continents do not move, according to another, they are constantly moving.

Recently, another hypothesis of the structure of the earth's crust has been substantiated. The basis for it was the theory of the movement of continents, the author of which was A. Wegener at the beginning of the 20th century. At one time, he failed to answer legitimate questions about the forces that make continents drift.

Lithospheric plates

The upper layer of the mantle, together with the earth's crust, is the lithosphere. The origin of continents and oceans is closely related to the theory of plates that are able to move, and are not shackled monolithically. many cracks reaching the mantle. They break the lithosphere into huge areas with a thickness of 60-100 km.

Plate junctions coincide with oceanic ridges that run through the middle of the oceans. They look like huge trees. The border may be in the form of gorges running along the bottom of the ocean. Cracks also exist on the territory of the continents, they pass through mountain ranges (the Himalayas, the Urals, etc.). We can say that these are old scars on the body of the Earth. There are also relatively fresh faults, these include crevices in eastern Africa.

Found 7 huge blocks and dozens of small areas. The main number of plates capture the oceans and continents.

The movement of the plates of the lithosphere

Under the plates there is a rather soft and plastic mantle, which makes their drift possible. The hypothesis of the origin of the continents and oceans says that the blocks are set in motion due to the forces arising from the movement of the substance in the upper part of the mantle.

Strong currents directed from the center of the Earth cause ruptures in the lithosphere. You can see this type of faults on the continents, but most of them are located in the zone of mid-ocean ridges under the thickness ocean waters. In this place, the earth's crust is much thinner. Substances in the molten state rise from the depths of the mantle and, pushing apart the plates, increase the thickness of the lithosphere. And the edges of the plates are moved in opposite directions.

Pieces of the earth's crust move from the ridges at the bottom of the oceans to the troughs. The speed of their movement is 1-6 cm/year. These figures are due to satellite imagery made in different years. The plates in contact move towards, along or diverge. Their movement along the upper layer of the mantle resembles ice floes on the water.

When two plates move towards each other (oceanic and continental), then the first, having made a bend, goes under the second. The result is deep trenches, archipelagos, mountain ranges. Examples: the islands of Japan, the Andes, the Kuril Trench.

When continental plates collide, folding is formed as a result of crushing of the edges containing sedimentary layers. So the Himalayan mountains appeared at the junction of the Indo-Australian and Eurasian plates.

Continental evolution

Why does geography study the origin of continents and oceans? Because the understanding of these processes is necessary for the perception of other information related to this science. The theory of lithospheric plates suggests that at first one single continent appeared on the planet, the rest was occupied by the World Ocean. The deep faults of the crust that appeared led to its division into two continents. Laurasia is located in the northern hemisphere, and Gondwana is in the southern hemisphere.

All new cracks appeared in the earth's crust, they led to the division of these continents. The continents that exist now, as well as the oceans: the Indian and the Atlantic, arose. The basis of modern continents are platforms - aligned, very ancient and stable areas of the crust. In other words, these are plates that formed a long time ago by geological standards.

In places where sections of the earth's crust collided, mountains turned out. On individual continents, traces of the contact of several plates are visible. Their surface area gradually increased. In a similar way the Eurasian continent emerged.

Plate Movement Forecast

The theory of lithospheric plates involves calculations of their future movement. The calculations that were made by scientists indicate that:

• The Indian and Atlantic Oceans will expand.
• The African continent will be shifted towards the northern hemisphere.
• The Pacific will get smaller.
• The Australian mainland will overcome the equator and join the Eurasian one.

According to forecasts, this will happen no earlier than in 50 million years. However, these results need to be refined. The origin of continents and oceans, as well as their movement, is a very slow process.

In the mid-ocean ridges, new lithospheric plates are being formed. The resulting oceanic-type crust smoothly diverges away from the fault. In 15 or 20 million years, these blocks will reach the mainland and go under it into the mantle that created them. The cycle of lithospheric plates closes on this.

seismic belts

Studying the origin of continents and oceans Grade 7 of a comprehensive school. Knowing the basics will help students understand more complex questions in the subject. The joints between the plates of the lithosphere are called seismic belts. These places clearly demonstrate the processes occurring at the boundary of the plates. The vast majority of volcanic eruptions and earthquakes are confined to these areas. Now there are about 800 volcanoes on the planet.

The origin of continents and oceans must be known for forecasting natural Disasters and prospecting for minerals. There is an assumption that different ores are formed in the places of plate contact as a result of magma entering the crust.

abstract

The structure and origin of the continents

The structure and age of the earth's crust

The main elements of the relief of the surface of our planet are the continents and ocean trenches. This division is not accidental, it is due to profound differences in the structure of the earth's crust under the continents and oceans. Therefore, the earth's crust is divided into two main types: continental and oceanic crust.

The thickness of the earth's crust varies from 5 to 70 km, it differs sharply under the continents and the ocean floor. The most powerful earth's crust under the mountainous areas of the continents is 50-70 km, under the plains its thickness decreases to 30-40 km, and under the ocean floor it is only 5-15 km.

Earth's crust continents consists of three powerful layers, differing in their composition and density. The upper layer is composed of relatively loose sedimentary rocks, the middle one is called granite, and the lower one is called basalt. The names "granite" and "basalt" come from the similarity of these layers in composition and density with granite and basalt.

The earth's crust under the oceans differs from the mainland not only in its thickness, but also in the absence of a granite layer. Thus, under the oceans there are only two layers - sedimentary and basalt. There is a granite layer on the shelf; the crust of the continental type is developed here. The change of the continental-type crust to the oceanic occurs in the zone of the continental slope, where the granite layer becomes thinner and breaks off. The oceanic crust is still very poorly studied in comparison with the earth's crust of the continents.

The age of the Earth is now estimated at approximately 4.2-6 billion years according to astronomical and radiometric data. The age of the oldest rocks of the continental crust studied by man is up to 3.98 billion years (southwestern part of Greenland), and the rocks of the basalt layer are over 4 billion years old. Undoubtedly, these breeds are not primary substance Earth. The prehistory of these ancient rocks lasted many hundreds of millions, and perhaps even billions of years. Therefore, the age of the Earth is approximately estimated at 6 billion years.

The structure and development of the earth's crust of the continents

The largest structures of the earth's crust of the continents are geosynclinal folded belts and ancient platforms. They are very different from each other in their structure and history. geological development.

Before proceeding to the description of the structure and development of these main structures, it is necessary to talk about the origin and essence of the term "geosyncline". This term comes from the Greek words "geo" - Earth and "synclino" - deflection. It was first used by the American geologist D. Dan more than 100 years ago, while studying the Appalachian mountains. He established that the marine Paleozoic deposits that make up the Appalachians have a maximum thickness in the central part of the mountains, much greater than on their slopes. Dan explained this fact quite correctly. During the period of sedimentation in the Paleozoic era, on the site of the Appalachian Mountains there was a sagging depression, which he called the geosyncline. In its central part, the sagging was more intense than on the wings, which is evidenced by the large thickness of the deposits. Dan confirmed his findings with a drawing depicting the Appalachian geosyncline. Considering that sedimentation in the Paleozoic took place in marine conditions, he deposited down from the horizontal line - the estimated sea level - all the measured thicknesses of deposits in the center and on the slopes of the Appalachian Mountains. The figure turned out to be a clearly expressed large depression at the site of the modern Appalachian Mountains.

At the beginning of the 20th century, the famous French scientist E. Og proved that geosynclines played a big role in the history of the Earth's development. He established that folded mountain ranges formed at the site of geosynclines. E. Og divided all the areas of the continents into geosynclines and platforms; he developed the foundations of the theory of geosynclines. Huge contribution This doctrine was introduced by Soviet scientists A. D. Arkhangelsky and N. S. Shatsky, who established that the geosynclinal process not only occurs in individual troughs, but also covers vast areas of the earth's surface, which they called geosynclinal regions. Later, huge geosynclinal belts began to be distinguished, within which several geosynclinal regions are located. In our time, the theory of geosynclines has grown into a substantiated theory of the geosynclinal development of the earth's crust, in the creation of which Soviet scientists play a leading role.

Geosynclinal fold belts are mobile sections of the earth's crust, geological history which was characterized by intense sedimentation, multiple folding processes and strong volcanic activity. Thick strata of sedimentary rocks accumulated here, igneous rocks formed, and earthquakes often occurred. Geosynclinal belts occupy vast areas of the continents, located between ancient platforms or along their edges in the form of wide strips. Geosynclinal belts arose in the Proterozoic, they have a complex structure and a long history of development. There are 7 geosynclinal belts: Mediterranean, Pacific, Atlantic, Ural-Mongolian, Arctic, Brazilian and Intra-African.

Ancient platforms are the most stable and inactive parts of the continents. In contrast to geosynclinal belts, ancient platforms experienced slow oscillatory movements, sedimentary rocks, usually of small thickness, accumulated within them, there were no folding processes, and volcanism and earthquakes were rare. Ancient platforms form parts of the continents that are the backbones of all continents. These are the most ancient parts of the continents, formed in the Archean and early Proterozoic.

On modern continents, from 10 to 16 ancient platforms are distinguished. The largest are East European, Siberian, North American, South American, African-Arabian, Hindustan, Australian and Antarctic.

Geosynclinal fold belts

Geosynclinal folded belts are divided into large and small, differing in their size and history of development. There are two small belts, they are located in Africa (Intra-African) and in South America (Brazilian). Their geosynclinal development continued throughout Proterozoic era. Large belts began their geosynclinal development later - from the late Proterozoic. Three of them - the Ural-Mongolian, Atlantic and Arctic - completed their geosynclinal development at the end of the Paleozoic era, and inside the Mediterranean and Pacific belts, vast territories where geosynclinal processes continue are still preserved. Each geosynclinal belt has its own specific features structure and geological development, but there are also general patterns in their structure and development.

Most large parts geosynclinal belts are geosynclinal folded areas, within which smaller structures are distinguished - geosynclinal troughs and geoanticlinal uplifts (geoanticlines). Troughs are the main elements of each geosynclinal region - areas of intense bowing, sedimentation and volcanism. Within the geosynclinal region there may be two, three or more such troughs. Geosynclinal troughs are separated from each other by uplifted areas - geoanticlines, where erosion processes mainly took place. Several geosynclinal troughs and geoanticlinal uplifts located between them form a geosynclinal system.

An example is the vast Mediterranean belt, stretching across the entire eastern hemisphere from west coast Europe and Northwest Africa up to and including the islands of Indonesia. Within this belt, several geosynclinal folded regions are distinguished: Western European, Alpine, North African, Indochinese, etc. In each of these folded regions, many geosynclinal systems are distinguished. There are especially many of them in the complexly constructed Alpine folded region: geosynclinal systems of the Pyrenees, Alps, Carpathians, Crimean-Caucasian, Himalayan, etc.

In the complex and long history of the development of geosynclinal folded areas, two stages are distinguished - the main and final (orogenic).

main stage characterized by processes of deep subsidence of the earth's crust in geosynclinal troughs, which are the main areas of sedimentation. At the same time, uplift occurs in neighboring geoanticlines, they become places of erosion and removal of detrital material. Sharply differentiated processes of subsidence in geosynclines and uplift in geoanticlines lead to fragmentation of the earth's crust and to the emergence of numerous deep ruptures in it, called deep faults. A colossal mass of volcanic material rises along these faults from great depths, which forms on the surface of the earth's crust - on land or on the ocean floor - numerous volcanoes pouring out lava and spewing volcanic ash and a mass of rock fragments during explosions. Thus, at the bottom of geosynclinal seas, along with marine sediments - sands and clays - volcanic material also accumulates, which either forms huge strata of effusive rocks, or is interbedded with layers of sedimentary rocks. This process occurs continuously during the long-term subsidence of geosynclinal troughs, as a result of which many kilometers of volcanic-sedimentary rocks are accumulated, which are combined under the name of a volcanic-sedimentary formation. This process occurs unevenly, depending on the magnitude of the movements of the earth's crust in geosynclinal areas. During periods of calmer subsidence, deep faults “heal” and do not supply volcanic material. In these periods of time, smaller carbonate (limestones and dolomites) and terrigenous (sands and clays) formations accumulate. In deep areas of geosynclinal troughs, thin material is deposited, from which a clayey formation is formed.

The process of accumulation of powerful geosynclinal formations is always accompanied by movements of the earth's crust - subsidence in geosynclinal troughs and uplifts in geoanticlinal areas. As a result of these movements, the layers of accumulated thick sediments undergo various deformations and acquire a complex folded structure. Folding processes are most strongly manifested at the end of the main stage of development of geosynclinal areas, when the subsidence of geosynclinal troughs stops and a general uplift begins, which first embraces the geoanticlinal areas and the marginal parts of the troughs, and then their central parts. This leads to intense folding into folds of all layers formed in geosynclinal troughs. The sea recedes, sedimentation stops and the layers crumpled into complex folds are above sea level; a complex folded mountainous region arises. By this time - by the end of the main geosynclinal stage - the introduction of large granite intrusions is timed, with which the formation of many deposits of metallic minerals is associated.

Geosynclinal folded areas enter the second, orogenic stage of their development, following uplifts that occurred at the end of the main stage. At the orogenic stage, the processes of uplift and the formation of large mountain ranges and massifs continue. In parallel with the formation of mountain ranges, large depressions are formed, separated by mountain ranges. In these depressions, called intermontane, there is an accumulation of coarse clastic rocks - conglomerates and coarse sands, called the molasse formation. In addition to intermontane depressions, the molasse formation also accumulates in the marginal parts of the platforms adjacent to the formed mountain ranges. Here, at the orogenic stage, the so-called marginal troughs arise, in which not only the molasse formation is accumulated, but also the salt-bearing or coal-bearing formation, depending on climatic conditions and sedimentation conditions. The orogenic stage is accompanied by folding processes and the intrusion of large granite intrusions. The geosynclinal region gradually turns into a very complexly built folded mountainous region. The end of the orogenic stage marks the end of geosynclinal development - the processes of mountain building, folding, and subsidence of intermountain depressions cease. The mountainous country enters the platform stage, which is accompanied by a gradual smoothing of the relief and a slow accumulation of calmly occurring rocks of the platform cover over complexly folded, but leveled from the surface, geosynclinal deposits. A platform is formed, the folded base (foundation) of which is rocks crumpled into folds, formed in geosynclinal conditions. Sedimentary rocks of the platform cover are actually platform rocks.

The process of development of geosynclinal regions from the time of the formation of the first geosynclinal troughs to their transformation into platform regions continued for tens and hundreds of millions of years. As a result of this long process, many geosynclinal regions within geosynclinal belts and even entire geosynclinal belts have completely turned into platform territories. The platforms that formed inside the geosynclinal belts were called young, since their folded base was formed much later than that of the ancient platforms. According to the time of foundation formation, three main types of young platforms are distinguished: with a Precambrian, Paleozoic and Mesozoic folded base. The foundation of the first platforms was formed at the end of the Proterozoic after the Baikal folding, which resulted in the formation of folded structures - Baikalids. The foundation of the second platforms was formed at the end of the Paleozoic after the Hercynian folding, which resulted in the formation of folded structures - Hercynides. The foundation of the third type of platforms was formed at the end of the Mesozoic after the Mesozoic folding, which resulted in the formation of folded structures - mesozoids.

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Within the areas of Baikal and Paleozoic folding, which formed as folded areas many hundreds of millions of years ago, large areas are covered with a fairly thick platform cover (hundreds of meters and a few kilometers). Within the areas of Mesozoic folding, which formed as folded areas much later (the time of manifestation of folding is from 100 to 60 million years), the platform cover could be formed in relatively small areas, and folded mesozoic structures are exposed here on large areas of the Earth's surface.

Finishing the description of the structure and development of geosynclinal folded belts, it is necessary to characterize them modern structure. It was already noted earlier that both small belts - Brazilian and Intra-African, as well as three of the large belts - Ural-Mongolian, Atlantic and Arctic - have long completed their geosynclinal development. In our time, the geosynclinal regime continues to persist over large areas of the Mediterranean and Pacific belts. The modern geosynclinal regions of the Pacific belt are at the main stage, they have retained mobility to the present day, subsidence and uplift are intensively manifested here. individual sections, modern folding processes, earthquakes, volcanism. A different picture is observed within the Mediterranean belt, where the modern Alpine geosynclinal region was covered by young Cenozoic Alpine folding and is now at the orogenic stage. Here are the highest mountain ranges on Earth (Himalayas, Karakorum, Pamir, etc.), which are still suppliers of coarse clastic material to nearby intermountain depressions. In the Alpine geosynclinal region, earthquakes are still quite frequent, and individual volcanoes sometimes manifest their effect. The geosynclinal regime ends here.

Geosynclinal folded areas are the main sources of extraction of the most important minerals. Among them, ores of various metals play the greatest role: copper, lead, zinc, gold, silver, tin, tungsten, molybdenum, nickel, cobalt, etc. large deposits coal, oil and gas fields.

ancient platforms

Main Feature The structure of all platforms is the presence of two structural floors that are sharply different from each other, called the foundation and the platform cover. The foundation has a complex structure, it is formed by highly folded and metamorphosed rocks, cut through by various intrusions. The platform cover rests almost horizontally on the eroded basement surface with a sharp angular unconformity. It is formed by layers of sedimentary rocks.

Ancient and young platforms differ in the time of formation of the folded basement. At the ancient platforms, the basement rocks were formed in the Archean, Early and Middle Proterozoic, and the rocks of the platform cover began to accumulate from the Late Proterozoic and continued to form during the Paleozoic, Mesozoic and Cenozoic eras. On the young platforms, the foundation was formed later than on the ancient ones; accordingly, the accumulation of the rocks of the platform cover began later.

Ancient platforms are covered with a sedimentary cover, but in some places where this cover is absent, the foundation comes to the surface. The areas of the foundation exit are called shields, and the territories covered with a cover are called slabs. There are two types of platform depressions on the slabs. Some of them - syneclises - are flat and extensive depressions. Others - aulacogenes - are narrow, long, laterally limited by faults, deep troughs. In addition, there are areas on the slabs where the foundation is raised, but does not come to the surface. These are anteclises, they usually separate adjacent syneclises.

The basement is exposed in the northwest within the Baltic Shield, and most of the section is located on the Russian plate. On the Russian plate, a wide and gentle Moscow syneclise is visible, central part which is located in the vicinity of Moscow. Further to the southeast, in the regions of Kursk and Voronezh, the Voronezh anteclise is located. Here the foundation is raised and covered with a low-powered platform cover. Even further south, within Ukraine, there is a narrow but very deep Dnieper-Donetsk aulacogen. Here, the basement is submerged to a very great depth along large faults located on both sides of the aulacogen.

The foundation rocks of the ancient platforms were formed over a very long time (Archean - early Proterozoic). They were repeatedly subjected to the processes of folding and metamorphism, as a result of which they became strong - crystalline. They are crumpled into extremely complex folds, have a large thickness, and igneous rocks (effusive and intrusive) are widespread in their composition. All these signs indicate that the basement rocks were formed in geosynclinal conditions. Folding processes ended in the Early Proterozoic, they completed the geosynclinal mode of development.

A new stage has begun - a platform one, which continues to this day.

The rocks of the platform cover, which began to accumulate from the Late Proterozoic, differ sharply in structure and composition from the crystalline basement rocks. They are not folded, not metamorphosed, have small thicknesses, and igneous rocks are rarely found in their composition. Usually, the rocks that make up the platform cover lie horizontally and are of sedimentary marine or continental origin. They form different from geosynclinal platform formations. These formations covering plates and filling depressions - syneclises and aulacogenes - are represented by alternating clays, sands, sandstones, marls, limestones, dolomites, which form layers that are very consistent in composition and thickness. A characteristic platform formation is also writing chalk, which forms layers of several tens of meters. Sometimes there are volcanic rocks, called the trap formation. In continental conditions, in a warm, humid climate, a powerful coal-bearing formation accumulated (alternation of sandstones and clayey rocks with interlayers and lenses of coal), and in dry, hot climates, a formation of red sandstones and clays or a salt-bearing formation (clays and sandstones with interlayers and lenses of salts) .

The sharply different structure of the basement and platform cover testifies to two major stages in the development of ancient platforms: geosynclinal (formation of the basement) and platform (accumulation of the platform cover). The platform stage was preceded by the geosynclinal stage.

The structure of the ocean floor

Despite the fact that oceanological research has greatly increased over the past two decades and is being widely carried out at the present time, the geological structure of the ocean floor remains poorly understood.

It is known that within the shelf the structures of the continental crust continue, and in the zone of the continental slope, the continental type of the earth's crust is replaced by the oceanic one. 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 of the ocean floor are deep-water plains located at depths of 4-6 km and separated by underwater heights. Particularly large deep-water plains are found in the Pacific Ocean. Along the edges of these vast plains are deep-sea trenches - narrow and very long troughs, stretched for hundreds and thousands of kilometers.

The bottom depth in them reaches 10-11 km, and the width does not exceed 2-5 km. These are the deepest areas on the surface of the Earth. On the outskirts of these trenches are chains of islands called island arcs. These are the Aleutian and Kuril arcs, the islands of Japan, the Philippine, Samoa, Tonga, etc.

At the bottom of the ocean there are many different underwater hills. Some of them form real underwater mountain ranges and chains of mountains, others rise from the bottom in the form of individual hills and mountains, and others appear above the surface of the ocean in the form of islands.

Of exceptional importance in the structure of the ocean floor are the mid-ocean ridges, which got their name because they were first discovered in the middle of the Atlantic Ocean. They are traced at the bottom of all oceans, forming a single system of uplifts at a distance of more than 60 thousand km. This is one of the most grandiose tectonic zones of the Earth. Starting in the waters of the North Arctic Ocean, it stretches in a wide ridge (700-1000 km) in the middle part of the Atlantic Ocean and, skirting Africa, passes into the Indian Ocean. Here, this system of underwater ridges forms two branches. One goes to the Red Sea; the other goes around Australia from the south and continues in the southern part Pacific Ocean to the coast of America. In the system of mid-ocean ridges, earthquakes often occur and underwater volcanism is highly developed.

The present meager geological data on the structure of oceanic depressions do not yet allow us to solve the problem of their origin. So far, we can only say that different oceanic depressions have different origins and ages. The most ancient age has a depression of the Pacific Ocean. Most researchers believe that it originated in the Precambrian and its bed is a remnant of the oldest primary earth's crust. The basins of other oceans are younger, most scientists believe that they were formed on the site of pre-existing continental masses. The most ancient of them is the depression indian ocean, it is assumed that it arose in the Paleozoic era. The Atlantic Ocean arose at the beginning of the Mesozoic, and the Arctic Ocean - at the end of the Mesozoic or at the beginning of the Cenozoic.

Literature

1. Allison A., Palmer D. Geology. - M., 1984

2. Vologdin A.G. Earth and life. - M., 1996

3. Voitkevich G.V. Geological chronology of the Earth. - M., 1994

4. Dobrovolsky V.V. Yakushova A.F. Geology. - M., 2000

It is different, and the dependence of the composition of the crust on the nature of the relief and internal structure territory. The results of geophysical research and deep drilling made it possible to identify two main and two transitional types of the earth's crust. Basic types mark such global structural elements crusts as continents and oceans. These structures are perfectly expressed on the Earth, and they are characterized by continental and oceanic types of crust.

The continental crust is developed under the continents and, as already mentioned, has a different thickness. Within the platform areas corresponding to the continental ones, this is 35-40 km, in young mountain structures - 55-70 km. The maximum thickness of the earth's crust - 70-75 km - is established under the Andes. Two strata are distinguished in the continental crust: the upper one is sedimentary and the lower one is consolidated crust. The consolidated crust contains two layers of different speeds: the upper granite-metamorphic layer, composed of granites and gneisses, and the lower granulite-mafic layer, composed of highly metamorphosed gabbro-type basic rocks or ultrabasic igneous rocks. Granite-metamorphic layer studied by cores ultra-deep wells; granulite-basite - according to geophysical data and the results of dredging, which still makes its existence hypothetical.

In the lower part of the upper layer, a zone of weakened rocks is found, which differs little from it in composition and seismic characteristics. The reason for its occurrence is the metamorphism of rocks and their decompaction due to the loss of constitutional water. It is likely that the rocks of the granulite-mafic layer are all the same rocks, but even more highly metamorphosed.

Oceanic crust is characteristic of. It differs from the continental one in thickness and composition. Its thickness ranges from 5 to 12 km, averaging 6-7 km. From top to bottom, three layers are distinguished in the oceanic crust: the upper layer of loose marine sedimentary rocks up to 1 km thick; middle, represented by interbedding of basalts, carbonate and siliceous rocks, 1-3 km thick; the lower one, composed of basic rocks of the gabbro type, often metamorphosed to amphibolites, and ultrabasic amphibolites, thickness 3.5-5 km. The first two layers were drilled, the third one was characterized by dredging material.

The suboceanic crust is developed under the deep basins of the marginal and inland seas (Chernoe, etc.), and is also found in some deep depressions on land (the central part of the Caspian Sea). The thickness of the suboceanic crust is 10-25 km, and it is increased mainly due to the sedimentary layer, which lies directly on the lower layer of the oceanic crust.

The subcontinental crust is characteristic of the arcs (Aleutian, Kurile, South Antilles, etc.) and the margins of the continents. In structure, it is close to the continental crust, but has a smaller thickness - 20-30 km. A feature of the subcontinental crust is the indistinct boundary between the layers of consolidated rocks.

Thus, various types of the earth's crust distinctly divide the earth into oceanic and continental blocks. high position continents is explained by a more powerful and less dense earth's crust, and the submerged position of the ocean floor is explained by a thinner, but denser and heavier crust. The shelf area is underlain by the continental crust and is the underwater end of the continents.

Structural elements of the cortex. In addition to dividing into such planetary structural elements as oceans and continents, the earth's crust (and) reveals regions (tectonically active) and aseismic (calm). Calm are inner regions continents and ocean beds - continental and oceanic platforms. Between the platforms there are narrow seismic zones, which are marked by tectonic movements. These zones correspond to mid-ocean ridges and junctions of island arcs or marginal mountain ranges and deep sea trenches at the edge of the ocean.

In the oceans, the following structural elements are distinguished:

• mid-ocean ridges - mobile belts with axial rifts like grabens;
• oceanic platforms are calm areas of abyssal basins with uplifts complicating them.

On the continents, the main structural elements are:

• mountain structures (orogens), which, like mid-ocean ridges, can show tectonic activity;
• Platforms are mostly tectonically calm vast territories with a thick cover of sedimentary rocks.

Mountain structures are divided and bordered by low areas - intermountain troughs and depressions, which are filled with products of the destruction of the ridges. For example, the Greater Caucasus is bordered by the West Kuban, East Kuban and Terek-Kaspisky foredeeps, and is separated from the Small one by the Rionskaya and Kura intermountain depressions.

But not all ancient mountain structures were involved in repeated mountain building. Most of them, after leveling, slowly sank, were flooded by the sea, and the thickness of the sea layered on the relics of the mountain ranges. This is how the platforms were formed. AT geological structure platforms, there are always two structural-tectonic floors: the lower one, composed of the metamorphosed remains of the former mountains, which is the foundation, and the upper one, represented by sedimentary rocks.

Platforms with a Precambrian basement are considered ancient, while platforms with a Paleozoic and Early Mesozoic basement are considered young. Young platforms are located between the ancient ones or border them. For example, between the ancient East European and Siberian platforms there is a young one, and on the southern and southeastern outskirts of the East European platform, the young Scythian and Turan platforms begin. Within the platforms, there are large structures of anticlinal and synclinal profile, called anteclises and syneclises.

So, platforms are ancient denuded orogens, not affected by later (young) orogeny movements.

As opposed to calm platform regions, there are tectonically active geosynclinal regions on Earth. The geosynclinal process can be compared to the work of a huge deep-seated cauldron, where ultrabasic and basic and lithosphere material is “boiled” new light continental crust, which, surfacing, builds up continents in marginal () and welds them together in intercontinental (Mediterranean) geosynclines. This process ends with the formation of folded mountain structures, in the arched part of which there is still long time can work. Over time, the growth of mountains stops, volcanism fades, the earth's crust enters a new cycle of its development: the alignment of the mountain structure begins.

Thus, where the mountain ranges are now located, there used to be geosynclines. Large structures of anticline and synclinal profile in geosynclinal regions are called anticlinoria and synclinoria.

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 the oceanic crust is much thinner than the continental one.

In the oceans, as 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 bark is only 0.473% total weight 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 crust is folded under the upper crust, a layer composed mainly of granites and gneisses, of low density and ancient history. Studies show that most of these rocks were formed very long ago, about 3 billion years ago. Below is lower cortex, consisting of metamorphic rocks - granulites and the like. The average thickness is 35 km.

Chemical composition Earth and 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.