Help on Tele2, tariffs, questions

The oceanic crust is primitive in its composition and, in essence, represents the upper differentiated layer of the mantle, overlain by a thin layer of pelagic sediments. The oceanic crust is usually divided into three layers, the first of which (upper) is sedimentary.

At the base of the sedimentary layer there are often thin metal-bearing sediments that are not consistent along the strike, with a predominance of iron oxides. The lower part of the sedimentary layer is usually composed of carbonate sediments deposited at depths less than 4-4.5 km. At great depths, carbonate sediments, as a rule, are not deposited, since the microscopic shells composing them single-celled organisms(foraminifera and colithopharid) at pressures above 400-450 atm easily dissolve in sea ​​water. For this reason, in oceanic depressions at depths greater than 4-4.5 km, the upper part of the sedimentary layer is composed mainly of carbon-free sediments - red deep-sea clays and siliceous silts. Near island arcs and volcanic islands in the section of sedimentary strata there are often lenses and layers of volcanogenic deposits, and near deltas large rivers- and terrigenous sediments. In the open oceans, the thickness of the sediment layer increases from the crests of mid-ocean ridges, where there is almost no precipitation, to their peripheral parts. The average thickness of sediments is small and, according to A.P. Lisitsyn, is close to 0.5 km, but near the continental margins of the Atlantic type and in areas of large river deltas it increases to 10-12 km. This is due to the fact that almost all terrigenous material transported from land, thanks to avalanche sedimentation processes, is deposited in coastal areas of the oceans and on the continental slopes of continents.

The second, or basaltic, layer of oceanic crust in the upper part is composed of basaltic lavas of tholeiitic composition (Fig. 5). Erupting underwater, these lavas take on bizarre shapes. corrugated pipes and pillows, which is why they are called pillow lavas. Below are dolerite dikes of the same tholeiitic composition, which are former supply channels through which basaltic magma in rift zones flowed onto the surface of the ocean floor. The basaltic layer of oceanic crust is exposed in many places on the ocean floor adjacent to the crests of mid-ocean ridges and the transform faults that feather them. This layer was studied in detail both by traditional methods of studying the ocean floor (dredging, sampling with soil tubes, photography), and with the help of underwater manned vehicles, allowing geologists to observe the geological structure of the objects under study and carry out targeted sampling of rocks. In addition, over the past 20 years, the surface of the basalt layer and its upper layers have been penetrated by numerous deep-sea drilling holes, one of which even penetrated the pillow lava layer and entered the dolerites of the dike complex. The total thickness of the basalt, or second, layer of the oceanic crust, judging by seismic data, reaches 1.5, sometimes 2 km.

Figure 5. Structure of the rift zone and oceanic crust:
1 - ocean level; 2—precipitation; 3—pillow basaltic lavas (layer 2a); 4—dike complex, dolerites (layer 2b); 5 - gabbro; 6 - layered complex; 7 - serpentinites; 8—lherzolites of lithospheric plates; 9 — asthenosphere; 10—isotherm 500 °C (beginning of serpentinization).

Frequent finds of gabbro tholeiitic inclusions within large transform faults indicate that the oceanic crust also includes these dense and coarse-crystalline rocks. The structure of ophiolite covers in the folded belts of the Earth, as is known, are fragments of ancient oceanic crust, thrust in these belts by former regions continents. Therefore, we can conclude that the dike complex in the modern oceanic crust (as well as in ophiolite nappes) is underlain by a layer of gabbro, which makes up top part third layer of oceanic crust (layer 3a). At some distance from the crests of the mid-ocean ridges, judging by seismic data, the lower part of this crustal layer can also be traced. Numerous findings in large transform faults of serpentinites, corresponding in composition to hydrated peridotites and ophiolite complexes similar in structure to serpentinites, suggest that the lower part of the oceanic crust is also composed of serpentinites. According to seismic data, the thickness of the gabbro-serpentinite (third) layer of the oceanic crust reaches 4.5-5 km. Under the crests of mid-ocean ridges, the thickness of the oceanic crust is usually reduced to 3-4 and even 2-2.5 km directly below the rift valleys.

The total thickness of the oceanic crust without the sedimentary layer thus reaches 6.5-7 km. Below, the oceanic crust is underlain by crystalline rocks of the upper mantle, which make up the subcrustal sections of lithospheric plates. Beneath the crests of mid-ocean ridges, the oceanic crust lies directly above pockets of basaltic melts released from the hot mantle (from the asthenosphere).

The area of ​​the oceanic crust is approximately equal to 3.0610 × 18 cm 2 (306 million km 2), the average density of the oceanic crust (without precipitation) is close to 2.9 g/cm 3, therefore, the mass of the consolidated oceanic crust can be estimated at (5.8 -6.2)x10 24 g. The volume and mass of the sedimentary layer in the deep-sea basins of the world ocean, according to A.P. Lisitsyn, is respectively 133 million km 3 and about 0.1 × 10 24 g. The volume of sediment concentrated on the shelves and continental slopes, somewhat larger - about 190 million km 3, which in terms of mass (taking into account the compaction of sediments) is approximately (0.4-0.45) 10 24 g.

The ocean floor, which is the surface of the oceanic crust, has a characteristic topography. In abyssal basins, the ocean floor lies at depths of about 66.5 km, while on the crests of mid-ocean ridges, sometimes dissected by steep gorges and rift valleys, ocean depths decrease to 2-2.5 km. In some places, the ocean floor reaches the surface of the Earth, for example, on the island. Iceland and in the Afar province (Northern Ethiopia). In front of the island arcs surrounding the western periphery Pacific Ocean, northeast Indian Ocean, in front of the arc of the Lesser Antilles and South Sandwich Islands in the Atlantic, as well as in front of the active margin of the continent in the Central and South America the oceanic crust bends and its surface sinks to depths of up to 9-10 km, going further under these structures and forming narrow and extensive deep-sea trenches in front of them.

The oceanic crust is formed in the rift zones of mid-ocean ridges due to the separation of basaltic melts from the hot mantle (from the asthenospheric layer of the Earth) occurring beneath them and their outpouring onto the surface of the ocean floor. Every year in these zones, at least 5.5-6 km 3 of basaltic melts rise from the asthenosphere, pour out onto the ocean floor and crystallize, forming the entire second layer of the oceanic crust (taking into account the gabbro layer, the volume of basaltic melts introduced into the crust increases to 12 km 3) . These enormous tectonomagmatic processes, constantly developing under the crests of mid-ocean ridges, have no equal on land and are accompanied by increased seismicity (Fig. 6).

Figure 6. Seismicity of the Earth; earthquake placement
Barazangi, Dorman, 1968

In rift zones located on the crests of mid-ocean ridges, stretching and spreading of the ocean floor occurs. Therefore, all such zones are marked by frequent but shallow-focus earthquakes with a predominance of rupture displacement mechanisms.

In contrast, under island arcs and active continental margins, i.e. in zones of plate underthrust, usually more strong earthquakes with the dominance of compression and shear mechanisms. According to seismic data, the subsidence of the oceanic crust and lithosphere can be traced in the upper mantle and mesosphere to depths of about 600-700 km (Fig. 7). According to tomography data, the subsidence of oceanic lithospheric plates has been traced to depths of about 1400-1500 km and, possibly, deeper - right up to the surface of the earth's core.

Figure 7. The structure of the plate underthrust zone in the Kuril Islands area:
1 - asthenosphere; 2 - lithosphere; 3 - oceanic crust; 4-5—sedimentary-volcanogenic strata; 6—ocean sediments; isolines show seismic activity in A 10 units (Fedotov et al., 1969); β is the angle of incidence of the Wadati-Benief zone; α is the angle of incidence of the plastic deformation zone.

The ocean floor is characterized by characteristic and fairly contrasting banded magnetic anomalies, usually located parallel to the crests of mid-ocean ridges (Fig. 8). The origin of these anomalies is associated with the ability of the basalts of the ocean floor, when cooling, to be magnetized by the Earth's magnetic field, thereby remembering the direction of this field at the moment of their outpouring onto the surface of the ocean floor. Taking into account now that the geomagnetic field has repeatedly changed its polarity over time, the English scientists F. Vine and D. Matthews, back in 1963, were the first to date individual anomalies and show that on different slopes of mid-ocean ridges these anomalies turn out to be approximately symmetrical in in relation to their ridges. As a result, they were able to reconstruct the basic patterns of plate movements in individual areas of the oceanic crust in the North Atlantic and show that the ocean floor is moving approximately symmetrically away from the crests of the mid-ocean ridges at speeds of the order of several centimeters per year. Subsequently, similar studies were carried out in all areas of the World Ocean, and everywhere this pattern was confirmed. Moreover, a detailed comparison of magnetic anomalies of the ocean floor with the geochronology of magnetization reversal of continental rocks, the age of which was known from other data, made it possible to extend the dating of the anomalies to the entire Cenozoic, and then to the late Mesozoic. As a result, a new and reliable paleomagnetic method for determining the age of the ocean floor was created.

Figure 8. Anomaly map magnetic field in the area of ​​the underwater Reykjanes Ridge in the North Atlantic
(Heirtzler et al., 1966). Positive anomalies are indicated in black; AA—zero anomaly of the rift zone.

The use of this method led to the confirmation of previously expressed ideas about the comparative youth of the ocean floor: the paleomagnetic age of all oceans without exception turned out to be only Cenozoic and Late Mesozoic (Fig. 9). Subsequently, this conclusion was brilliantly confirmed by deep-sea drilling at many points on the ocean floor.

It turned out that the age of the basins of the young oceans (Atlantic, Indian and Arctic) coincides with the age of their bottom, while the age of the ancient Pacific Ocean significantly exceeds the age of its bottom. Indeed, the Pacific Ocean basin has existed at least since the late Proterozoic (maybe earlier), and the age of the most ancient sections of the bottom of this ocean does not exceed 160 million years, while most of it was formed only in the Cenozoic, i.e. younger than 67 million years.

Figure 9. Map of the age of the ocean floor in millions of years
from Larson, Pitman et al., 1985

The “conveyor” mechanism of renewal of the ocean floor with the constant immersion of older sections of the oceanic crust and sediments accumulated on it into the mantle under island arcs explains why, during the life of the Earth, ocean basins never had time to be filled with sediments. Indeed, at the current rate of filling ocean basins with terrigenous sediments carried from land, 2.210 × 16 g/year, the entire volume of these basins, approximately equal to 1.3710 × 24 cm 3, would be completely filled in approximately 1.2 billion years. Now we can say with great confidence that the continents and ocean basins have existed together for about 3.8 billion years and no significant filling of their depressions has occurred during this time. Moreover, after drilling in all oceans, we now know for sure that there is no sediment on the ocean floor older than 160-190 million years. But this can only be observed in one case - if there is an effective mechanism for removing sediment from the oceans. This mechanism, as is now known, is the process of sediments being pulled under island arcs and active continental margins in plate subduction zones, where these sediments are melted and reattached in the form of granitoid intrusions to the continental crust forming in these zones. This process of melting terrigenous sediments and reattaching their material to the continental crust is called sediment recycling.

Concept of the earth's crust.

Earth's crust

3) the top layer is sedimentary. Its thickness on average is about 3 km. In some areas the thickness of precipitation reaches 10 km (for example, in the Caspian lowland). In some areas of the Earth there is no sedimentary layer at all and a granite layer comes to the surface.

Such areas are called shields (for example, Ukrainian Shield, Baltic Shield).

weathering crust.

Conrad surface

On continental shoals or shelves, the crust is about 25 km thick and is generally similar to the continental crust. However, a layer of basalt may fall out. IN East Asia in the region of island arcs (Kuril Islands, Aleutian Islands, Japanese Islands, etc.) the earth's crust is of a transitional type. Finally, the crust of the mid-ocean ridges is very complex and has so far been little studied.

There is no Moho boundary here, and mantle material rises along faults into the crust and even to its surface.

The concept of isostasy

isothermal layer

geothermal gradient geothermal stage

Read also:

The Earth's shell includes the earth's crust and the upper part of the mantle.

The surface of the earth's crust has large irregularities, the main of which are the protrusions of the continents and their depressions - huge oceanic depressions. The existence and relative position of continents and ocean basins is associated with differences in the structure of the earth's crust.

Continental crust. It consists of several layers. Upper - sedimentary layer rocks. The thickness of this layer is up to 10-15 km. Beneath it lies a granite layer. The rocks that compose it, in their own way physical properties similar to granite. The thickness of this layer is from 5 to 15 km. Beneath the granite layer is a basalt layer, consisting of basalt and rocks whose physical properties resemble basalt. The thickness of this layer is from 10 km to 35 km. Thus, the total thickness of the continental crust reaches 30-70 km.

Oceanic crust. It differs from the continental crust in that it does not have a granite layer or it is very thin, so the thickness of the oceanic crust is only 6-15 km.

For determining chemical composition Only the upper parts of the earth's crust are accessible - to a depth of no more than 15-20 km. 97.2% of the total composition of the earth's crust is made up of: oxygen - 49.13%, aluminum - 7.45%, calcium - 3.25%, silicon - 26%, iron - 4.2%, potassium - 2.35 %, magnesium - 2.35%, sodium - 2.24%.

Other elements of the periodic table account for from tenths to hundredths of a percent.

Most scientists believe that oceanic-type crust first appeared on our planet.

Under the influence of processes occurring inside the Earth, folds, that is, mountainous areas, formed in the earth's crust. The thickness of the bark increased. This is how continental protrusions were formed, that is, the continental crust began to form.

IN last years in connection with studies of the earth's crust of oceanic and continental types, a theory of the structure of the earth's crust was created, which is based on the idea of lithospheric plates. The theory in its development was based on the hypothesis of continental drift, created at the beginning of the 20th century by the German scientist A. Wegener.

Types of the earth's crust Wikipedia
Site search:

Hypotheses explaining the origin and development of the earth's crust

Concept of the earth's crust.

Earth's crust is a complex of surface layers solid Earth. In the scientific geographical literature there is no single idea about the origin and paths of development of the earth's crust.

There are several concepts (hypotheses) that reveal the mechanisms of formation and development of the earth’s crust, the most substantiated of which are the following:

1. The theory of fixism (from the Latin fixus - motionless, unchanging) states that the continents have always remained in the places that they currently occupy. This theory denies any movement of continents and large parts of the lithosphere.

2. The theory of mobilism (from the Latin mobilis - mobile) proves that the blocks of the lithosphere are in constant motion. This concept has become especially firmly established in recent years in connection with the acquisition of new scientific data from the study of the bottom of the World Ocean.

3. The concept of continental growth at the expense of the ocean floor believes that the original continents formed in the form of relatively small massifs that now make up ancient continental platforms. Subsequently, these massifs grew due to the formation of mountains on the ocean floor adjacent to the edges of the original land cores. The study of the ocean floor, especially in the zone of mid-ocean ridges, has given reason to doubt the correctness of the concept of continental growth due to the ocean floor.

4. The theory of geosynclines states that the increase in land size occurs through the formation of mountains in geosynclines. The geosynclinal process, as one of the main ones in the development of the continental crust, forms the basis of many modern scientific explanations the process of origin and development of the earth's crust.

5. Rotation theory bases its explanation on the proposition that since the figure of the Earth does not coincide with the surface of a mathematical spheroid and is rearranged due to uneven rotation, zonal stripes and meridional sectors on a rotating planet are inevitably tectonically unequal. They react with varying degrees of activity to tectonic stresses caused by intraterrestrial processes.

There are two main types of earth's crust: oceanic and continental. A transitional type of the earth's crust is also distinguished.

Oceanic crust. Thickness of the oceanic crust in modern times geological epoch ranges from 5 to 10 km. It consists of the following three layers:

1) top thin layer marine sediments (thickness no more than 1 km);

2) middle basalt layer (thickness from 1.0 to 2.5 km);

3) bottom layer gabbro (thickness about 5 km).

Continental (continental) crust. The continental crust has a more complex structure and greater thickness than the oceanic crust. Its thickness averages 35-45 km, and in mountainous countries it increases to 70 km. It also consists of three layers, but differs significantly from the ocean:

1) lower layer composed of basalts (thickness about 20 km);

2) the middle layer occupies the main thickness of the continental crust and is conventionally called granite. It is composed mainly of granites and gneisses. This layer does not extend under the oceans;

3) the top layer is sedimentary. Its thickness on average is about 3 km.

In some areas the thickness of precipitation reaches 10 km (for example, in the Caspian lowland). In some areas of the Earth there is no sedimentary layer at all and a granite layer comes to the surface. Such areas are called shields (for example, Ukrainian Shield, Baltic Shield).

On continents, as a result of the weathering of rocks, a geological formation is formed, called weathering crust.

The granite layer is separated from the basalt layer Conrad surface , at which the speed of seismic waves increases from 6.4 to 7.6 km/sec.

Border between earth's crust and the mantle (both on continents and oceans) passes along Mohorovicic surface (Moho line). The speed of seismic waves on it increases abruptly to 8 km/hour.

In addition to the two main types - oceanic and continental - there are also areas of mixed (transitional) type.

On continental shoals or shelves, the crust is about 25 km thick and is generally similar to the continental crust. However, a layer of basalt may fall out. In East Asia, in the region of island arcs (Kuril Islands, Aleutian Islands, Japanese Islands, etc.), the earth's crust is of a transitional type. Finally, the crust of the mid-ocean ridges is very complex and has so far been little studied. There is no Moho boundary here, and mantle material rises along faults into the crust and even to its surface.

The concept of "earth's crust" should be distinguished from the concept of "lithosphere". The concept of "lithosphere" is broader than the "earth's crust". To the lithosphere modern science includes not only the earth's crust, but also the uppermost mantle to the asthenosphere, that is, to a depth of approximately 100 km.

The concept of isostasy . A study of the distribution of gravity showed that all parts of the earth's crust - continents, mountainous countries, plains - are balanced on the upper mantle. This balanced position is called isostasy (from the Latin isoc - even, stasis - position). Isostatic equilibrium is achieved due to the fact that the thickness of the earth's crust is inversely proportional to its density. Heavy oceanic crust is thinner than lighter continental crust.

Isostasy is, in essence, not even an equilibrium, but a desire for equilibrium, continuously disrupted and restored again. For example, the Baltic Shield, after the melting of continental ice of the Pleistocene glaciation, rises by about 1 meter per century. The area of ​​Finland is constantly increasing due to the seabed. The territory of the Netherlands, on the contrary, is decreasing. The zero equilibrium line currently runs slightly south of 60 0 N latitude. Modern St. Petersburg is approximately 1.5 m higher than St. Petersburg during the time of Peter the Great. As data from modern scientific research, even the heaviness of large cities turns out to be sufficient for isostatic fluctuations of the territory beneath them. Consequently, the earth's crust in areas of large cities is very mobile. In general, the relief of the earth's crust is a mirror image of the Moho surface, the base of the earth's crust: elevated areas correspond to depressions in the mantle, lower areas correspond to more high level its upper limit. Thus, under the Pamirs the depth of the Moho surface is 65 km, and in the Caspian lowland it is about 30 km.

Thermal properties of the earth's crust . Daily fluctuations in soil temperature extend to a depth of 1.0 - 1.5 m, and annual fluctuations in temperate latitudes in countries with a continental climate to a depth of 20-30 m. At the depth where the influence of annual temperature fluctuations due to heating ceases earth's surface The sun is a layer of constant soil temperature. It is called isothermal layer . Below the isothermal layer deep into the Earth, the temperature rises, and this is caused by the internal heat of the earth's bowels. In the formation of climates internal heat does not participate, but it serves as the energetic basis of all tectonic processes.

The number of degrees by which the temperature increases for every 100 m of depth is called geothermal gradient . The distance in meters, when lowered by which the temperature increases by 1 0 C is called geothermal stage . The magnitude of the geothermal step depends on the topography, thermal conductivity of rocks, proximity of volcanic sources, circulation groundwater etc. On average, the geothermal step is 33 m. In volcanic areas, the geothermal step can be only about 5 m, and in geologically quiet areas (for example, on platforms) it can reach 100 m.

⇐ Previous234567891011Next ⇒

The earth consists of several shells: atmosphere, hydrosphere, biosphere, lithosphere.

Biosphere- a special shell of the earth, an area of ​​vital activity of living organisms. It includes the lower part of the atmosphere, the entire hydrosphere and the upper part of the lithosphere. Lithosphere is the hardest shell of the earth:

Structure:

Earth's crust

mantle (Si, Ca, Mg, O, Fe)

outer core

inner core

center of the earth - temperature 5-6 thousand o C

Core composition – Ni\Fe; core density – 12.5 kg/cm 3 ;

Kimberlites- (from the name of the city of Kimberley in South Africa), magmatic ultrabasic brecciated rock of effusive appearance, producing explosion tubes. It consists mainly of olivine, pyroxenes, pyrope-almandine garnet, picroilmenite, phlogopite, less commonly zircon, apatite and other minerals included in the fine-grained groundmass, usually altered by post-volcanic processes to a serpentine-carbonate composition with perovskite, chlorite, etc. d.

Eclogite- metamorphic rock consisting of pyroxene with a high content of jadeite end-member (omphacite) and grossular-pyrope-almandine garnet, quartz and rutile. The chemical composition of eclogites is identical to igneous rocks of basic composition - gabbro and basalts.

Structure of the earth's crust

Layer thickness = 5-70 km; highlands - 70 km, seabed - 5-20 km, average 40-45 km. Layers: sedimentary, granite-gneiss (not in the oceanic crust), granite-bosite (basalt)

The earth's crust is a complex of rocks that lie above the Mohorovicic boundary. Rocks are regular aggregates of minerals. The latter consist of various chemical elements. The chemical composition and internal structure of minerals depend on the conditions of their formation and determine their properties. In turn, the structure and mineral composition of rocks indicate the origin of the latter and make it possible to determine the rocks in the field.

There are two types of the earth's crust - continental and oceanic, which differ sharply in composition and structure. The first, lighter, forms elevated areas - continents with their underwater margins, the second occupies the bottom of the oceanic depressions (2500-3000m). The continental crust consists of three layers - sedimentary, granite-gneiss and granulite-mafic, with a thickness of 30-40 km on the plains to 70-75 km under young mountains. The oceanic crust, up to 6-7 km thick, has a three-layer structure. Under a thin layer of loose sediments lies the second oceanic layer, consisting of basalts, the third layer is composed of gabbro with subordinate ultrabasites. The continental crust is enriched in silica and light elements - Al, sodium, potassium, C, compared to the oceanic crust.

Continental (mainland) crust characterized by great thickness - on average 40 km, in some places reaching 75 km. It consists of three "layers". On top lies a sedimentary layer formed by sedimentary rocks of various compositions, ages, genesis and degrees of dislocation. Its power varies from zero (on shields) to 25 km (in deep depressions, for example, Caspian). Below lies the “granite” (granite-metamorphic) layer, consisting mainly of acidic rocks, similar in composition to granite. The greatest thickness of the granite layer is observed under young high mountains, where it reaches 30 km or more. Within the flat areas of the continents, the thickness of the granite layer decreases to 15-20 km. Under the granite layer lies the third, “basalt” layer, which also received its name conventionally: seismic waves pass through it at the same speeds with which, under experimental conditions, they pass through basalts and rocks close to them. The third layer, 10-30 km thick, is composed of highly metamorphosed rocks of predominantly basic composition. Therefore, it is also called granulite-mafic.

Oceanic crust differs sharply from the continental one. Over most of the ocean floor, its thickness ranges from 5 to 10 km. Its structure is also peculiar: under a sedimentary layer with a thickness ranging from several hundred meters (in deep-sea basins) to 15 km (near continents) lies a second layer composed of pillow lavas with thin layers of sedimentary rocks. The lower part of the second layer is composed of a peculiar complex of parallel dikes of basaltic composition. The third layer of oceanic crust, 4-7 km thick, is represented by crystalline igneous rocks of predominantly basic composition (gabbro). Thus, the most important specific feature of the oceanic crust is its low thickness and the absence of a granite layer.

Earth's crust- the outer solid shell of the Earth (geosphere), part of the lithosphere, with a width from 5 km (under the ocean) to 75 km (under the continents). Below the crust is the mantle, which differs in composition and physical properties - it is more compacted and contains mainly refractory elements. The crust and mantle are divided by the Mohorovicic feature, or the Moho layer, where a sharp acceleration of seismic waves occurs.

There are continental (continental) and oceanic crust, as well as its transitional types: subcontinental and suboceanic crust.

Continental (mainland) crust consists of several layers. The top is a layer of sedimentary rocks. The thickness of this layer is up to 10-15 km. Beneath it lies a granite layer. The rocks that make it up are similar in their physical properties to granite. The thickness of this layer is from 5 to 15 km. Under the granite layer there is a basalt layer consisting of basalt and rocks, physical characteristics which resemble basalt. The thickness of this layer is from 10 km to 35 km. Consequently, the total thickness of the continental crust reaches 30-70 km.

Oceanic crust differs from the continental crust in that it does not have a granite layer, or it is very thin, therefore the thickness of the oceanic crust is only 6-15 km.

To determine the chemical composition of the earth's crust, only its upper parts are available - to a depth of less than 15-20 km. 97.2% of the total composition of the earth's crust is made up of: oxygen - 49.13%, aluminum - 7.45%, calcium - 3.25%, silicon - 26%, iron - 4.2%, potassium - 2.35 %, magnesium - 2.35%, sodium - 2.24%.

Other elements of the periodic table account for from 10ths to hundredths of a percent.

Sources:

In the structure of the Earth, researchers distinguish 2 types of the earth's crust - continental and oceanic.

What is the continental crust?

Continental crust, also called continental, is characterized by the presence of 3 different layers in its structure. The upper one is represented by sedimentary rocks, the second one is granite or gneisses, the third one consists of basalt, granulites and other metamorphic rocks.

Continental crust

The thickness of the continental crust is about 35-45 km, sometimes reaching 75 km (usually in areas mountain ranges). The type of crust in question covers approximately 40% of the Earth's surface. In terms of volume, it corresponds to approximately 70% of the Earth's crust.

The age of the continental crust reaches 4.4 billion years.

What is the oceanic crust?

Main mineral forming oceanic crust, - basalt. But besides this, its structure includes:

1. sedimentary rocks;
2. layered intrusions.

According to the prevailing scientific concept, the oceanic crust is constantly formed due to tectonic processes. It is much younger than the mainland, the age of its oldest sections is about 200 million years.

The thickness of the oceanic crust is about 5-10 km, depending on the specific measurement site. It can be noted that over time it remains almost unchanged. A common approach among scientists is that the oceanic crust should be considered as belonging to the oceanic lithosphere. In turn, its thickness largely depends on age.

Comparison

The main difference between the continental crust and the oceanic crust is, obviously, their location. The first contains continents, land, the second - oceans and seas.

The continental crust is represented mainly by sedimentary rocks, granites and granulites. Oceanic - mainly basalt.

The continental crust is much thicker and older. It is inferior to the oceanic one in terms of the area covering the earth's surface, but superior in terms of the volume it occupies throughout the entire earth's crust.

It can be noted that in some cases the oceanic crust is capable of being layered on top of the continental crust in the process of obduction.

Having determined what the difference is between the continental and oceanic crust, we will record the conclusions in a small table.

Table

I think that any person understands that one of the components of our planet is the crust. But few people know that there is a difference between the earth's crust on continents and in the oceans. I want to clarify what the differences are and why.

Oceanic crust

It is one of the types of ordinary earth's crust and is located within the oceans. But oceanic crust sometimes tends to creep directly onto the continental crust. The thickness of this crust is approximately seven kilometers, and it consists of the following layers:

• ocean sediments;
• basalt covers;
• mantle.

At the root of the oceanic crust there are most often formations that are obtained as a result of the crystallization of various melts, or they may initially be rocks that are found in the mantle. I would like to note that there are places where the thickness of the crust within the ocean is greater than usual. This occurs in areas where islands are located.

Continental crust

This crust is also part of the earth's crust and, accordingly, predominates in continental areas. Unlike the oceanic crust, the composition of the continental crust is characterized by a granite layer, sedimentary and other various layers. The thickness differs significantly from the crust in the oceans - it ranges from 35 to 45 kilometers, and sometimes 75 kilometers in mountainous areas. Despite the fact that the continental crust makes up almost 70 percent of the total volume of the earth's crust, it covers less than half of the entire surface of the planet (this is due to the fact that there is more water than land).

I want to note important fact that the continental crust is much older than the oceanic crust. If the second age is approximately 200 million years, then the continental age is approximately two and a half billion years old (but this includes approximately seven percent of the crust). That is, as a result, we can say that the main difference between one crust and another is in thickness (continental is larger), age (continental is also larger), composition (basaltic base in oceanic) and, of course, in location ( oceans and continents).