The study of the internal structure of planets, including our Earth, is extremely difficult task. We cannot physically “drill” the earth’s crust right down to the planet’s core, so all the knowledge we have gained on this moment- this is knowledge obtained “by touch”, and in the most literal way.
How seismic exploration works using the example of exploration oil fields. We “call” the earth and “listen” to what the reflected signal will bring us
The fact is that the simplest and reliable way to find out what is under the surface of the planet and is part of its crust is to study the speed of propagation seismic waves in the depths of the planet.
It is known that the speed of longitudinal seismic waves increases in denser media and, on the contrary, decreases in loose soils. Accordingly, knowing the parameters different types rocks and having calculated data on pressure, etc., “listening” to the response received, you can understand through which layers earth's crust the seismic signal passed through and how deep they are below the surface.
Studying the structure of the earth's crust using seismic waves
Seismic vibrations can be caused by two types of sources: natural And artificial. Natural sources of vibrations are earthquakes, the waves of which carry necessary information about the density of the rocks through which they penetrate.
Arsenal artificial sources vibrations are more extensive, but first of all, artificial vibrations are caused by an ordinary explosion, however, there are more “subtle” ways of working - generators of directed pulses, seismic vibrators, etc.
Conducting blasting operations and studying seismic wave velocities seismic survey- one of the most important branches of modern geophysics.
What did the study of seismic waves inside the Earth give? An analysis of their distribution revealed several jumps in the change in speed when passing through the bowels of the planet.
Earth's crust
The first jump, in which speeds increase from 6.7 to 8.1 km/s, according to geologists, is recorded base of the earth's crust. This surface is located in different places on the planet. various levels, from 5 to 75 km. The boundary between the earth's crust and the underlying shell, the mantle, is called "Mohorovicic surfaces", named after the Yugoslav scientist A. Mohorovicic who first established it.
Mantle
Mantle lies at depths of up to 2,900 km and is divided into two parts: upper and lower. The boundary between the upper and lower mantle is also recorded by a jump in the speed of propagation of longitudinal seismic waves (11.5 km/s) and is located at depths from 400 to 900 km.
The upper mantle has complex structure. In its upper part there is a layer located at depths of 100-200 km, where transverse seismic waves attenuate by 0.2-0.3 km/s, and the speed longitudinal waves, essentially do not change. This layer is named waveguide. Its thickness is usually 200-300 km.
The part of the upper mantle and crust that lies above the waveguide is called lithosphere, and the layer of reduced velocities itself - asthenosphere.
Thus, the lithosphere is a rigid, solid shell underlain by a plastic asthenosphere. It is assumed that processes occur in the asthenosphere that cause movement of the lithosphere.
The internal structure of our planet
Earth's core
At the base of the mantle there is a sharp decrease in the speed of propagation of longitudinal waves from 13.9 to 7.6 km/s. At this level lies the boundary between the mantle and Earth's core, deeper than which transverse seismic waves no longer propagate.
The radius of the core reaches 3500 km, its volume: 16% of the volume of the planet, and mass: 31% of the mass of the Earth.
Many scientists believe that the core is in a molten state. Its outer part is characterized by sharply reduced values of the velocities of longitudinal waves; in the inner part (with a radius of 1200 km) the velocities of seismic waves increase again to 11 km/s. The density of the core rocks is 11 g/cm 3, and it is determined by the presence of heavy elements. So heavy element maybe iron. Most likely, iron is integral part cores, since a core of pure iron or iron-nickel composition should have a density 8-15% higher than the existing core density. Therefore, oxygen, sulfur, carbon and hydrogen appear to be attached to the iron in the core.
Geochemical method for studying the structure of planets
There is another way to explore deep structure planets - geochemical method. Highlighting the different shells of the Earth and other planets terrestrial group physical parameters find quite clear geochemical confirmation based on the theory of heterogeneous accretion, according to which the composition of the cores of planets and their outer shells is, for the most part, initially different and depends on the early stage their development.
As a result of this process, the heaviest ones were concentrated in the core ( iron-nickel) components, and in the outer shells - lighter silicate ( chondritic), enriched in the upper mantle with volatile substances and water.
The most important feature of the terrestrial planets (Earth) is that their outer shell, the so-called bark, consists of two types of substance: " mainland" - feldspathic and " oceanic" - basalt.
Continental crust of the Earth
The continental (continental) crust of the Earth is composed of granites or rocks similar to them in composition, that is, rocks with a large amount of feldspars. The formation of the “granite” layer of the Earth is due to the transformation of older sediments in the process of granitization.
The granite layer should be considered as specific shell of the Earth's crust - the only planet, in which the processes of differentiation of matter with the participation of water and having a hydrosphere, oxygen atmosphere and biosphere were widely developed. On the Moon and, probably, on the terrestrial planets, the continental crust is composed of gabbro-anorthosites - rocks consisting of large quantity feldspar, however, has a slightly different composition than in granites.
The oldest (4.0-4.5 billion years) surfaces of the planets are composed of these rocks.
Oceanic (basaltic) crust of the Earth
Oceanic (basaltic) crust The earth was formed as a result of stretching and is associated with zones of deep faults, which led to the penetration of the basalt centers of the upper mantle. Basaltic volcanism is superimposed on previously formed continental crust and is a relatively younger geological formation.
Manifestations of basaltic volcanism on all planets earth type, apparently similar. The widespread development of basalt “seas” on the Moon, Mars, and Mercury is obviously associated with stretching and the formation, as a result of this process, of permeability zones along which basaltic melts of the mantle rushed to the surface. This mechanism of manifestation of basaltic volcanism is more or less similar for all terrestrial planets.
The Earth's satellite, the Moon, also has a shell structure that generally replicates that of the Earth, although it has a striking difference in composition.
Heat flow of the Earth. It is hottest in the areas of faults in the earth's crust, and coldest in areas of ancient continental plates
Method for measuring heat flow to study the structure of planets
Another way to study the deep structure of the Earth is to study its heat flow. It is known that the Earth, hot from the inside, gives up its heat. The heating of deep horizons is evidenced by volcanic eruptions, geysers, and hot springs. Heat is the main energy source of the Earth.
The increase in temperature with depth from the Earth's surface averages about 15° C per 1 km. This means that at the boundary of the lithosphere and asthenosphere, located at approximately a depth of 100 km, the temperature should be close to 1500 ° C. It has been established that at this temperature the melting of basalts occurs. This means that the asthenospheric shell can serve as a source of magma of basaltic composition.
With depth, the temperature changes according to a more complex law and depends on the change in pressure. According to calculated data, at a depth of 400 km the temperature does not exceed 1600 ° C and at the boundary of the core and mantle is estimated at 2500-5000 ° C.
It has been established that heat release occurs constantly over the entire surface of the planet. Heat is the most important physical parameter. Some of their properties depend on the degree of heating of rocks: viscosity, electrical conductivity, magnetism, phase state. Therefore, according to thermal state one can judge the deep structure of the Earth.
Measuring the temperature of our planet on great depth- the task is technically complex, since only the first kilometers of the earth’s crust are available for measurements. However, the Earth's internal temperature can be studied indirectly through heat flow measurements.
Despite the fact that the main source of heat on Earth is the Sun, the total power of the heat flow of our planet is 30 times greater than the power of all power plants on Earth.
Measurements have shown that the average heat flow on continents and oceans is the same. This result is explained by the fact that in the oceans most of heat (up to 90%) comes from the mantle, where the process of transfer of matter by moving flows is more intense - convection.
Convection is a process in which heated fluid expands, becoming lighter, and rises, while cooler layers sink. Since the mantle substance is closer in its state to solid body, convection in it proceeds in special conditions, at low material flow rates.
What is the thermal history of our planet? Its initial heating is probably associated with the heat generated by the collision of particles and their compaction in their own gravity field. The heat then resulted from radioactive decay. Under the influence of heat, a layered structure of the Earth and the terrestrial planets arose.
Radioactive heat is still being released in the Earth. There is a hypothesis according to which, at the border of the Earth’s molten core, the processes of fission of matter continue to this day with the release huge amount thermal energy that warms the mantle.
There are 2 main types of the earth's crust: continental and oceanic, and 2 transitional types - subcontinental and suboceanic (see figure).
1- sedimentary rocks;
2- volcanic rocks;
3- granite layer;
4- basalt layer;
5- Mohorovicic border;
6- upper mantle.
The continental type of the earth's crust has a thickness of 35 to 75 km, in the shelf area - 20 - 25 km, and pinches out on the continental slope. There are 3 layers of continental crust:
1st – upper, composed of sedimentary rocks with a thickness of 0 to 10 km. on platforms and 15 – 20 km. in tectonic deflections of mountain structures.
2nd – medium “granite-gneiss” or “granite” - 50% granites and 40% gneisses and other metamorphosed rocks. Its average thickness is 15–20 km. (in mountain structures up to 20 - 25 km.).
3rd – lower, “basalt” or “granite-basalt”, compositionally close to basalt. Power from 15 – 20 to 35 km. The boundary between the “granite” and “basalt” layers is the Conrad section.
According to modern data, the oceanic type of the earth’s crust also has a three-layer structure with a thickness of 5 to 9 (12) km, more often 6–7 km.
1st layer – upper, sedimentary, consists of loose sediments. Its thickness ranges from several hundred meters to 1 km.
2nd layer – basalts with interlayers of carbonate and silicon rocks. Thickness from 1 – 1.5 to 2.5 – 3 km.
The 3rd layer is the bottom one, not opened by drilling. It is composed of basic igneous rocks of the gabbro type with subordinate, ultrabasic rocks (serpentinites, pyroxenites).
The subcontinental type of earth's surface is similar in structure to the continental one, but does not have a clearly defined Conrad section. This type of crust is usually associated with island arcs - the Kuril, Aleutian and continental margins.
1st layer – upper, sedimentary – volcanic, thickness – 0.5 – 5 km. (on average 2 – 3 km.).
2nd layer – island arc, “granite”, thickness 5 – 10 km.
The 3rd layer is “basalt”, at depths of 8 – 15 km, with a thickness from 14 – 18 to 20 – 40 km.
The suboceanic type of the earth's crust is confined to the basin parts of the marginal and inland seas (Okhotsk, Japan, Mediterranean, Black, etc.). Its structure is similar to that of the ocean, but is distinguished by the increased thickness of the sedimentary layer.
1st upper – 4 – 10 or more km, located directly on the third oceanic layer with a thickness of 5 – 10 km.
The total thickness of the earth's crust is 10–20 km, in some places up to 25–30 km. due to an increase in the sedimentary layer.
A peculiar structure of the earth's crust is observed in the central rift zones of the mid-ocean ridges (Mid-Atlantic). Here, under the second oceanic layer, there is a lens (or protrusion) of low-speed material (V = 7.4 - 7.8 km / s). It is believed that this is either a protrusion of an abnormally heated mantle, or a mixture of crustal and mantle matter.
Structure of the earth's crust
On the surface of the Earth, on continents in different places, they are found rocks of different ages.
Some areas of the continents are composed on the surface of the most ancient rocks of Archean (AR) and Proterozoic (PT) age. They are highly metamorphosed: clays turned into metamorphic shales, sandstones into crystalline quartzites, limestones into marbles. There are many granites among them. The areas on the surface of which these most ancient rocks emerge are called crystalline massifs or shields (Baltic, Canadian, African, Brazilian, etc.).
Other areas on the continents are occupied by rocks of predominantly younger age - Paleozoic, Mesozoic, Cenozoic (Pz, Mz, Kz). These are mainly sedimentary rocks, although among them there are also rocks of igneous origin, erupted on the surface in the form of volcanic lava or embedded and frozen at some depth. There are two categories of land areas: 1) platforms - plains: layers of sedimentary rocks lie calmly, almost horizontally, with rare and small folds observed in them. There is very little igneous, especially intrusive, rock in such rocks; 2) folded zones (geosynclines) - mountains: sedimentary rocks are strongly folded, penetrated by deep cracks; Intruded or erupted igneous rocks are often encountered. The differences between platforms or folded zones lie in the age of the resting or folded rocks. Therefore, there are ancient and young platforms. Saying that the platforms could have formed in different time, we thereby indicate different ages of folded zones.
Maps depicting the location of platforms and folded zones of different ages and some other features of the structure of the earth's crust are called tectonic. They serve as a complement to geological maps, which represent the most objective geological documents illuminating the structure of the earth's crust.
Types of the earth's crust
The thickness of the earth's crust is not the same under continents and oceans. It is larger under mountains and plains, thinner under oceanic islands and oceans. Therefore, there are two main types of the earth's crust - continental and oceanic.
Average thickness continental crust is 42 km. But in the mountains it increases to 50-60 and even 70 km. Then they talk about “the roots of the mountains.” The average thickness of the oceanic crust is about 11 km.
Thus, the continents represent, as it were, unnecessary accumulations of masses. But these masses should create a stronger attraction, and in the oceans, where the attracting body is lighter water, the force of gravity should weaken. But in reality there are no such differences. The force of gravity is approximately the same everywhere on the continents and oceans. This leads to the conclusion: continental and oceanic masses are balanced. They obey the law of isostasy (equilibrium), which reads like this: additional masses on the surface of the continents correspond to a lack of masses at depth, and vice versa - the lack of masses on the surface of the oceans must correspond to some heavy masses at depth.
What is the earth's crust
This hard shell of the Earth, on which we walk, on which oceans splash and baobab trees grow.
It was formed due to the fact that our planet (being initially hot fireball) still slow cooled down, becoming covered with a “brown crust”. Now only its “fiery” core, which sometimes appears outward with volcanic eruptions, reminds us of our planet’s formidable past.
What is the earth's crust made of?
This is how you look at it. From a geographical (more precisely from a geomorphological) point of view, it consists of:
And here from the point of view of geochemistry, the earth's crust is formed:
- silicon (17%);
- oddly enough, oxygen (53%);
- aluminum (6%) and a dozen other elements.
In general, scientists have argued a lot and heatedly about this. After all, how can we say what the surface of the Earth consists of when the entire periodic table is scattered and floating on it?
Determination of the composition of the earth's crust
The first attempt to analyze this “earth cocktail” was made by an American Frank Clark. He did what for many years analyzed the composition he came across rocks, and when I had analyzed enough, I decided that it was possible to summarize the data and obtain the composition “ average earth's crust" Many scientists found this idea controversial, and new debates began.
But a Swiss researcher came to Frank's aid. Victor Goldshmit who assumed that “those who passed” (during ice age) across the Earth's surface, glaciers tore off and mixed upper layer rocks, the chemical composition of which interested scientists.
Therefore, it is possible to analyze "glacial" clays settled, for example, in the Barents Sea, and understand what exactly the glacier “attached” along the way. Imagine the public's surprise when the results obtained by Goldschmit coincided with the results of Clark's work.
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The Earth's crust is, first of all, the outer shell of the Earth, what we stand on. It lies to a depth of more than seventy kilometers, and its composition includes more than forty different substances. For example, the fundamental elements of its composition are silicon and oxygen (26% and 49%, respectively). They are followed (by volume) by aluminum (7.3%), iron (4.5%), calcium (3.4%), sodium (2.7%), magnesium (2.3%). Plus many other elements that have an extremely small percentage of the total mass of the crust.
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Back in school, I (like, most likely, many of you) were told about the what does our planet consist of?. It was then that I remembered that what we walk on is called earth's crust. In my children's consciousness associations immediately arose with the bark of trees, but in fact their compositions have nothing in common with each other. So What exactly does the earth's crust consist of?
2 barks
I think everyone imagines a picture from a geography textbook with a cross-section of the earth. on it the earth's crust is the topmost layer, but in some places there is still an ocean on top of it - the hydrosphere. Indeed, a question that seems simple at first glance hides many difficulties to answer. For example, earth's crust bThere are two types:
- Oceanic.
- Continental.
Let's try to figure it out their differences and composition, because that’s what interests you.
What is the oceanic crust made of?
As the name suggests - oceanic crust covered by the ocean, or rather, the hydrosphere. The age of even the oldest components is much younger than age continental crust, although for us 156 million years sounds impressive.
Here is its composition:
Composition of the continental crust
Continental crust, in its turn, covered not by the ocean, but by the atmosphere, but that’s not exactly what I’m talking about now. It is much older than the oceanic crust, its age can reach 4 billion years! This is the age of minerals that includes one of layers of continental crust - “granite”. You and I can see it, and probably everyone has encountered it more than once, because the “granite” layer is most mountains, not covered sedimentary rocks. Accordingly, the composition of the continental crust looks like this:
- Sedimentary rocks.
- "Granite layer"
- Basalt covers.
- Mantle.
It happens that some scientists distinguish another layer - Moho section, which is boundary between other layers.
It would be nice for everyone to know all this, because not having an idea of what you walk on every day is like not knowing anything about a person close to you.
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Since my school days, I remember that one of the components of the Earth is the earth's crust. But it, in turn, is also divided into components. I want to answer the question of exactly what parts the Earth’s crust is divided into.
The mantle as one of the components of the earth's crust
The Earth's mantle can be called that part that is located higher than the core, but is located under the crust itself. It contains large quantity earth substance. Its location is determined from approximately 20 to 3000 kilometers below the earth's surface. The mantle consists of rocks that have complex and incomprehensible names, but are its important components:
- peridotites;
- perovskites;
- eclogites.
We can say with confidence that all processes that occur in the Earth’s mantle affect its surface. These factors also explain earthly cataclysms, as well as the formation of new ore deposits.
Basalt part
It is the bottom layer of which it consists top part surface of the earth. It can be called a product of magma. Located above the mantle. We can say that the basalt layer is the place where all minerals accumulate. And minerals form combinations various elements from the periodic table. It contains huge reserves of magnesium, iron and calcium. The layer is intermediate between the mantle and the granite layer.
Granite part
This layer is about 10-40 kilometers. The composition of the layer can be considered magma or igneous rock. This rock formed a hard layer due to volcanic eruptions and the solidification of magma that came out of the volcano. This all happened at a very high temperature and pressure in the earth's thickness.
Sedimentary part
The layer that is located above granite and basalt. Its thickness reaches 20 kilometers. The layer is formed due to the fact that on land they are deposited various substances, and eventually they create sedimentary rocks. Seismic waves in this place reach a speed of four and a half kilometers per second. For the most part, sediment predominates on land more than in water.
These are all the main parts that make up the earth's crust.
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Clear concepts and definitions of the subject " The world“I would never need them, I thought, until my little brother came up to me with a notebook and asked for help with his homework. The assignment required me to draw a cross-section of the Earth with all the components of the earth’s crust. I was already getting ready to draw, when I suddenly realized, that everything flew out of my head. I know that there is a core in the center of the Earth, and everything else is like a fog. “Well, let’s figure it out,” I told my brother and began searching for information.
What is the Earth made of?
If you imagine a globe, then the earth’s crust is like a protective shell along its contour, which is continuous throughout its entire length. Transfer this mentally to the Earth and you will understand that there is an earth’s crust. In almost all textbooks the earth's crust is called hard shell Earth, that's how it is.
Structure of the earth's crust
It is unreasonable to believe that the earth's crust will lie in a cast layer consisting of a single rock. Years of formation developed the earth's crust, and scientists were able to identify its components:
- sedimentary rocks;
- "granite" layer;
- "basalt" layer;
The sedimentary layer is the topmost layer of the earth's crust. It is the thinnest, formed by rocks that weather from the surface of the Earth. In some areas such a layer does not exist at all, it can be so thin. Let me consider the composition of the layers.
Composition of the layers of the earth's crust
The Earth's crust is the thinnest part of the shell that protects our Earth. Let me look at what percentage this part consists of:
- oxygen - 49.1%;
- silicon - 26.0%;
- aluminum - 7.5%;
- iron - 4.2%;
- calcium - 3.3%;
- potassium - 2.4%;
- magnesium - 2.4%;
- sodium - 2.4%;
- other elements - 2.9%.
All these substances interact with each other, forming new elements. They can even form new rocks.
I’ll also describe a small one, but interesting fact for those interested in planets. The Earth's crust is in many ways similar to the crust of other planets, or more precisely, it is not they that are similar, but their structure.
I hope I helped you deal with this issue!
By modern ideas Geology Our planet consists of several layers - geospheres. They differ in physical properties, chemical composition and In the center of the Earth there is a core, followed by the mantle, then the earth's crust, hydrosphere and atmosphere.
In this article we will look at the structure of the earth's crust, which is the upper part of the lithosphere. It is an outer solid shell whose thickness is so small (1.5%) that it can be compared to a thin film on the scale of the entire planet. However, despite this, it is the upper layer of the earth’s crust that is of great interest to humanity as a source of minerals.
The earth's crust is conventionally divided into three layers, each of which is remarkable in its own way.
- The top layer is sedimentary. It reaches a thickness of 0 to 20 km. Sedimentary rocks are formed due to the deposition of substances on land, or their settling at the bottom of the hydrosphere. They are part of the earth's crust, located in it in successive layers.
- The middle layer is granite. Its thickness can vary from 10 to 40 km. This is an igneous rock that formed a solid layer as a result of eruptions and subsequent solidification of magma in the earth's thickness during high blood pressure and temperature.
- The lower layer, which is part of the structure of the earth's crust, is basalt, also of magmatic origin. It contains higher amounts of calcium, iron and magnesium, and its mass is greater than that of granite rock.
The structure of the earth's crust is not the same everywhere. The oceanic crust and the continental crust have especially striking differences. Under the oceans the earth's crust is thinner, and under the continents it is thicker. Greatest thickness it has in mountainous areas.
The composition includes two layers - sedimentary and basalt. Below the basalt layer is the Moho surface, and behind it is the upper mantle. ocean floor has the most complex relief forms. Among all their diversity special place occupy huge mid-ocean ridges, in which young basaltic oceanic crust is born from the mantle. Magma has access to the surface through deep fault- a rift that runs along the center of the ridge along the peaks. Outside, the magma spreads, thereby constantly pushing the walls of the gorge to the sides. This process is called “spreading”.
The structure of the earth's crust is more complex on continents than under the oceans. The continental crust occupies a much smaller area than the oceanic crust - up to 40% of the earth's surface, but has a much greater thickness. Below it reaches a thickness of 60-70 km. The continental crust has a three-layer structure - a sedimentary layer, granite and basalt. In areas called shields, a granite layer is on the surface. As an example, it is made of granite rocks.
The underwater extreme part of the continent - the shelf, also has a continental structure of the earth's crust. It also includes the islands of Kalimantan, New Zealand, New Guinea, Sulawesi, Greenland, Madagascar, Sakhalin, etc. As well as internal and marginal seas: Mediterranean, Azov, Black.
It is possible to draw a boundary between the granite layer and the basalt layer only conditionally, since they have a similar speed of passage of seismic waves, which is used to determine the density of the earth’s layers and their composition. The basalt layer is in contact with the Moho surface. The sedimentary layer can have different thicknesses, depending on the landform located on it. In the mountains, for example, it is either absent or has a very small thickness, due to the fact that loose particles move down the slopes under the influence external forces. But it is very powerful in foothill areas, depressions and basins. So, in it reaches 22 km.
Which differs in composition and physical properties- it is denser and contains mainly refractory elements. The crust and mantle are separated by the Mohorovicic boundary, or Moho for short, where there is a sharp increase in seismic wave velocities. WITH outside Most of the crust is covered by the hydrosphere, and the smaller part is exposed to the atmosphere.
There is a crust on most terrestrial planets, the Moon and many satellites of the giant planets. In most cases it consists of basalts. The Earth is unique in that it has two types of crust: continental and oceanic.
The mass of the earth's crust is estimated at 2.8 × 1019 tons (of which 21% is oceanic crust and 79% is continental). Bark makes up only 0.473% total mass Earth.
General information about the internal structure of the earth
The first ideas about the existence of the earth's crust were expressed by the English physicist W. Gilbert in 1600. They proposed dividing the interior of the Earth into two unequal parts: the crust or shell and the solid core.
The development of these ideas is contained in the works of L. Descartes, G. Leibniz, J. Buffon, M.V. Lomonosov and many other foreign and domestic scientists. In the beginning, the study of the earth's crust was focused on studying the earth's crust of the continents. Therefore, the first models of the crust reflected the structural features of the continental type crust.
In the first half of the 20th century, the study of the structure of the subsoil began to be carried out using seismology and seismicity. Analyzing the nature of seismic waves from the earthquake in Croatia in 1909, seismologist A. Mohorovicic, as already indicated, identified a clearly visible seismic boundary at a depth of about 50 km, which he defined as the base of the earth's crust (Mohorovicic, Moho, or M surface).
In 1925, V. Conrad recorded another interface surface inside the crust above the Mohorovicic boundary, which also received his name - the Conrad surface, or K surface. Scientists proposed calling the upper layer of the crust with a thickness of about 12 km the granite m layer, and the lower layer with a thickness of 25 km - basalt. The first two-layer model of the structure of the earth's crust appeared. Further studies made it possible to measure the thickness of the cortex in different areas continents. It was found that in lowland areas it is 35 ÷ 45 km, and in mountainous areas it increases to 50 ÷ 60 km (the maximum crustal thickness of 75 km was recorded in the Pamirs). This thickening of the earth’s crust was called by B. Gutenberg “ roots of the mountains" It was also established that the granite layer has a speed of 5 ÷ 6 km/s, characteristic of granites, and the lower layer has a speed of 6 ÷ 7 km/s, characteristic of basalts. The earth's crust, consisting of granite and basalt layers, was called the consolidated crust, on which another, upper, sedimentary layer is located. Its thickness varied within 0 ÷ 5-6 km (the maximum thickness of the sedimentary layer reaches 20 ÷ 25 km).
Thus, information about internal structure The lands are obtained primarily from geophysical surveys.
According to modern geophysical (seismological) data, three main regions are distinguished in the volume of the Earth: crust, mantle and core.
The crust is separated from the mantle by a sharp seismic boundary, an increase in the speed of longitudinal seismic waves is observed (up to 8.2 km/s), as well as an increase in the density of the substance - from 2.9 to 5.6 g/cm 3 . This boundary was named the Moho boundary (or simply the M boundary) in honor of its discoverer, the Yugoslav geophysicist Mohorovicic. The outer thickness of the Earth, located above the M boundary, began to be called the Earth’s crust.
According to seismic studies, two types of deep structure of the earth’s crust are distinguished, differing in thickness and structure:
- continental type - thickness 30-50 km to 60-80 km.
- oceanic type - thickness 5-10 km.
Continental type crust
The continental crust in its most complete form is divided into 3 main geophysical “layers”, which differ in elastic properties and density characteristics of rocks:
- "Sedimentary layer"(“sedimentary cover”, “unconsolidated strata”) is composed of horizontally or gently lying non-metamorphosed strata of sedimentary and volcanogenic rocks of Phanerozoic, less often - Upper Proterozoic age. In almost 40% of the territory of Russia there is no sedimentary layer - it is pinched out (washed away) in areas occupied by ancient shields. Within the fold belts it is developed sporadically, in fragments.
- Granite (granulite-metamorphic) layer, is represented by highly dislocated and in varying degrees metamorphosed sedimentary, effusive and intrusive rocks, predominantly acidic, i.e. granitoid composition. On shields and significant areas of folded belts it faces earth's surface. The velocities of longitudinal seismic waves are from 5.5 to 6.3 km/s. The thickness in the areas of development of the typical continental crust is 10-20 km, occasionally up to 25 km.
- Basalt (more correctly, granulite-basalt layer) is not exposed anywhere and consists, according to indirect data, of deeply metamorphosed rocks of granulite facies and igneous rocks of essentially basic and partially ultrabasic compositions with longitudinal wave velocities from 6.5 to 7.3 km/s (on average 6.8-7 km/s ). Power from 15 to 25-30km.
The transition from the overlying granite-metamorphic layer to the granulite-basalt layer in a number of areas occurs sharply, abruptly according to the so-called. Conrad surfaces (K surfaces), and in others, the velocities of longitudinal waves (and rock densities) increase smoothly with depth and a clear separation of these layers is impossible.
Below the granulite-basalt layer lies the upper mantle.
In addition to the so-called typical, classical section of the continental crust, there are areas with an anomalous structure.
For example, within some island arcs (the zone of the Kuril and Commander Islands) the crust of the subcontinental type with a thickness of 15-25 km is widespread with an unclear separation of granite-metamorphic and granulite-basalt layers.
Deep-water depressions of both internal seas (Black Sea, South Caspian) and marginal seas (Sea of Japan, South Okhotsk), as well as some ultra-deep depressions within the suboceanic type, in which there is a thick thickness of sedimentary rocks (3-5 to 15-25 km) - according to seismic data, it is directly underlain by a granulite-basalt layer with a thickness of 5 to 15 km. There is no granite-metamorphic layer.
The transition of a continent into a depression is accompanied by a change in the type of crust, and the transition occurs both within a narrow zone and over a wide strip. The transition is accompanied by alternating sections with various types bark. Example - complexly built transition zone between the Asian continent and the bed of the Pacific Ocean.
Oceanic crust
Oceanic crust forms the bed of the Pacific, Atlantic and Indian Oceans, where the depth exceeds 3-4 km. According to seismic and geological data, it consists of 3 layers.
Sedimentary layer thickness from zero - the first tens of meters to 0.5-1 km (on average 0.2-0.5 km). As drilling in the oceans has shown, the most ancient sediment horizons in the oceans are no older than the Middle-Late Jurassic (about 170 million years), and on most of the ocean floors they range in age from the Cretaceous to the Cenozoic or are only Cenozoic in age. The sedimentation rate during this period is 1-5 mm/thousand. years.
Basalt layer 1.5-2.0 km thick, the upper part of which was exposed by drilling, composed of lavas and volcanic glasses; dikes of basic rocks are found in the lower part of the layer. In age, the rocks of the upper part of the second layer are close to the age of the lower horizons of the sedimentary layer (from the Cenozoic to the Middle Jurassic). In general, the age of the upper part of the second layer naturally becomes older from the intraoceanic rift ridges to the peripheral parts of the oceans. The thickness of the layer rocks also increases in the same direction.
Gabbro-serpentinite layer- has a thickness of 3-4 km, the rocks of this layer have not been exposed by drilling, but in a number of places, fragments of intrusive rocks of basic and ultrabasic compositions have been lifted by dredges from fault zones in the oceans. Until recently, this layer was compared with the granulite-basalt layer of the continental crust. The velocities of longitudinal waves for this layer are 6.5-7 km/sec. The third layer is underlain by rocks of the upper mantle and the transition layer between them is even thinner than under the continents.
