Lithosphere and earth's crust. Section of the earth's crust Chemical composition of the Earth

Consists of many layers piled on top of each other. However, what we know best is the earth's crust and lithosphere. This is not surprising - after all, we not only live on them, but also draw from the depths most of the natural resources available to us. But the upper shells of the Earth still preserve millions of years of history of our planet and the entire solar system.

These two concepts appear so often in the press and literature that they have entered the everyday vocabulary of modern man. Both words are used to refer to the surface of the Earth or another planet - however, there is a difference between the concepts, based on two fundamental approaches: chemical and mechanical.

Chemical aspect - earth's crust

If you divide the Earth into layers based on differences in chemical composition, the top layer of the planet will be the earth's crust. This is a relatively thin shell, ending at a depth of 5 to 130 kilometers below sea level - the oceanic crust is thinner, and the continental crust, in mountainous areas, is thickest. Although 75% of the crust's mass is composed only of silicon and oxygen (not pure, bound in different substances), it has the greatest chemical diversity of all layers of the Earth.

The wealth of minerals also plays a role - various substances and mixtures created over billions of years of the planet’s history. The Earth's crust contains not only "native" minerals that were created by geological processes, but also massive organic heritage, such as oil and coal, as well as alien inclusions.

Physical aspect - lithosphere

Based on the physical characteristics of the Earth, such as hardness or elasticity, we will get a slightly different picture - the interior of the planet will be enveloped by the lithosphere (from the Greek lithos, “rocky, hard” and “sphaira” sphere). It is much thicker than the earth's crust: the lithosphere extends up to 280 kilometers deep and even covers the upper solid part of the mantle!

The characteristics of this shell fully correspond to the name - it is the only solid layer of the Earth, besides the inner core. Strength, however, is relative - the Earth's lithosphere is one of the most mobile in the solar system, which is why the planet has changed its appearance more than once. But significant compression, curvature and other elastic changes require thousands of years, if not more.

• An interesting fact is that the planet may not have a surface crust. So, the surface is its hardened mantle; The planet closest to the Sun lost its crust a long time ago as a result of numerous collisions.

To summarize, the Earth's crust is the upper, chemically diverse part of the lithosphere, the hard shell of the Earth. Initially they had almost the same composition. But when only the underlying asthenosphere and high temperatures affected the depths, the hydrosphere, atmosphere, meteorite remains and living organisms actively participated in the formation of minerals on the surface.

Lithospheric plates

Another feature that distinguishes the Earth from other planets is the diversity of different types of landscapes on it. Of course, water also played an incredibly important role, which we will talk about a little later. But even the basic forms of the planetary landscape of our planet differ from the same Moon. The seas and mountains of our satellite are pits from bombardment by meteorites. And on Earth they were formed as a result of hundreds and thousands of millions of years of movement of lithospheric plates.

You've probably already heard about plates - these are huge stable fragments of the lithosphere that drift along the fluid asthenosphere, like broken ice on a river. However, there are two main differences between the lithosphere and ice:

• The gaps between the plates are small and are quickly closed due to the molten substance erupting from them, and the plates themselves are not destroyed by collisions.
• Unlike water, there is no constant flow in the mantle, which could set a constant direction for the movement of the continents.

Thus, the driving force behind the drift of lithospheric plates is the convection of the asthenosphere, the main part of the mantle - hotter flows from the earth's core rise to the surface when cold ones fall back down. Considering that the continents differ in size, and the topography of their lower side mirrors the irregularities of the upper side, they also move unevenly and inconsistently.

Main plates

Over billions of years of movement of lithospheric plates, they repeatedly merged into supercontinents, after which they separated again. In the near future, in 200–300 million years, the formation of a supercontinent called Pangea Ultima is also expected. We recommend watching the video at the end of the article - it clearly shows how lithospheric plates have migrated over the past several hundred million years. In addition, the strength and activity of continental movement is determined by the internal heating of the Earth - the higher it is, the more the planet expands, and the faster and freer the lithospheric plates move. However, since the beginning of the Earth's history, its temperature and radius have been gradually decreasing.

• An interesting fact is that plate drift and geological activity do not necessarily have to be powered by the internal self-heating of the planet. For example, the satellite of Jupiter has many active volcanoes. But the energy for this is not provided by the satellite’s core, but by gravitational friction c, due to which Io’s interior heats up.

The boundaries of lithospheric plates are very arbitrary - some parts of the lithosphere sink under others, and some, like the Pacific plate, are completely hidden under water. Geologists today count 8 main plates that cover 90 percent of the entire Earth's area:

• Australian
• Antarctic
• African
• Eurasian
• Hindustan
• Pacific
• North American
• South American

Such a division appeared recently - for example, the Eurasian plate, 350 million years ago, consisted of separate parts, during the merger of which the Ural Mountains, one of the oldest on Earth, were formed. Scientists to this day continue to study faults and the ocean floor, discovering new plates and clarifying the boundaries of old ones.

Geological activity

Lithospheric plates move very slowly - they creep over each other at a speed of 1–6 cm/year, and move away by a maximum of 10–18 cm/year. But it is the interaction between the continents that creates the geological activity of the Earth, noticeable on the surface - volcanic eruptions, earthquakes and the formation of mountains always occur in the contact zones of lithospheric plates.

However, there are exceptions - so-called hot spots, which can also exist deep in lithospheric plates. In them, molten flows of asthenosphere matter break upward, melting the lithosphere, which leads to increased volcanic activity and regular earthquakes. Most often, this happens near those places where one lithospheric plate creeps onto another - the lower, depressed part of the plate sinks into the Earth's mantle, thereby increasing the pressure of magma on the upper plate. However, now scientists are inclined to believe that the “drowned” parts of the lithosphere are melting, increasing pressure in the depths of the mantle and thereby creating upward flows. This can explain the anomalous distance of some hot spots from tectonic faults.

• An interesting fact is that shield volcanoes, characterized by their flat shape, often form in hot spots. They erupt many times, growing due to flowing lava. This is also a typical alien volcano format. The most famous of them is on Mars, the highest point on the planet - its height reaches 27 kilometers!

Oceanic and continental crust of the Earth

Plate interactions also result in the formation of two different types of crust - oceanic and continental. Since the oceans, as a rule, are the junctions of different lithospheric plates, their crust is constantly changing - being broken or absorbed by other plates. At the site of faults, direct contact occurs with the mantle, from where hot magma rises. As it cools under the influence of water, it creates a thin layer of basalts, the main volcanic rock. Thus, the oceanic crust is completely renewed every 100 million years - the oldest areas, which are located in the Pacific Ocean, reach a maximum age of 156–160 million years.

Important! The oceanic crust is not all of the earth’s crust that is under water, but only its young sections at the junction of continents. Part of the continental crust is under water, in the zone of stable lithospheric plates.

Age of oceanic crust (red corresponds to young crust, blue to old crust).

Earth's crust- the thin upper shell of the Earth, which has a thickness of 40-50 km on the continents, 5-10 km under the oceans and makes up only about 1% of the Earth’s mass.

Eight elements - oxygen, silicon, hydrogen, aluminum, iron, magnesium, calcium, sodium - form 99.5% of the earth's crust.

On continents, the crust is three-layered: sedimentary rocks cover granite rocks, and granite rocks overlie basaltic rocks. Under the oceans the crust is of the “oceanic”, two-layer type; sedimentary rocks simply lie on basalts, there is no granite layer. There is also a transitional type of the earth's crust (island-arc zones on the margins of the oceans and some areas on continents, for example).

The earth's crust is greatest in mountainous regions (under the Himalayas - over 75 km), average in platform areas (under the West Siberian Lowland - 35-40, within the Russian Platform - 30-35), and least in the central regions of the oceans (5-7 km).

The predominant part of the earth's surface is the plains of continents and the ocean floor. The continents are surrounded by a shelf - a shallow strip with a depth of up to 200 g and an average width of about SO km, which, after a sharp steep bend of the bottom, turns into a continental slope (the slope varies from 15-17 to 20-30° ). The slopes gradually level out and turn into abyssal plains (depths 3.7-6.0 km). The oceanic trenches have the greatest depths (9-11 km), the vast majority of which are located on the northern and western outskirts.

The earth's crust formed gradually: first a basalt layer was formed, then a granite layer; the sedimentary layer continues to form to this day.

The deep strata of the lithosphere, which are studied by geophysical methods, have a rather complex and still insufficiently studied structure, just like the mantle and core of the Earth. But it is already known that the density of rocks increases with depth, and if on the surface it averages 2.3-2.7 g/cm3, then at a depth of about 400 km it is 3.5 g/cm3, and at a depth of 2900 km ( boundary of the mantle and the outer core) - 5.6 g/cm3. In the center of the core, where the pressure reaches 3.5 thousand t/cm2, it increases to 13-17 g/cm3. The nature of the increase in the Earth's deep temperature has also been established. At a depth of 100 km it is approximately 1300 K, at a depth of approximately 3000 km -4800 K, and in the center of the earth's core - 6900 K.

The predominant part of the Earth's substance is in a solid state, but at the boundary of the earth's crust and the upper mantle (depths of 100-150 km) lies a layer of softened, pasty rocks. This thickness (100-150 km) is called the asthenosphere. Geophysicists believe that other parts of the Earth may also be in a rarefied state (due to decompression, active radio decay of rocks, etc.), in particular, the zone of the outer core. The inner core is in the metallic phase, but today there is no consensus regarding its material composition.

Earth's crust makes up the uppermost shell of the solid Earth and covers the planet with an almost continuous layer, changing its thickness from 0 in some areas of mid-ocean ridges and ocean faults to 70-75 km under high mountain structures (Khain, Lomise, 1995). The thickness of the crust on the continents, determined by the increase in the speed of passage of longitudinal seismic waves up to 8-8.2 km/s ( Mohorovicic border, or Moho border), reaches 30-75 km, and in oceanic depressions 5-15 km. First type of earth's crust was named oceanic,second- continental.

Ocean crust occupies 56% of the earth's surface and has a small thickness - 5–6 km. Its structure consists of three layers (Khain and Lomise, 1995).

First, or sedimentary, a layer no more than 1 km thick occurs in the central part of the oceans and reaches a thickness of 10–15 km at their periphery. It is completely absent from the axial zones of mid-ocean ridges. The composition of the layer includes clayey, siliceous and carbonate deep-sea pelagic sediments (Fig. 6.1). Carbonate sediments are distributed no deeper than the critical depth of carbonate accumulation. Closer to the continent there appears an admixture of clastic material carried from the land; these are the so-called hemipelagic sediments. The speed of propagation of longitudinal seismic waves here is 2–5 km/s. The age of sediments in this layer does not exceed 180 million years.

Second layer in its main upper part (2A) it is composed of basalts with rare and thin pelagic interlayers

Rice. 6.1. Section of the lithosphere of the oceans in comparison with the average section of ophiolitic allochthons. Below is a model for the formation of the main units of the section in the ocean spreading zone (Khain and Lomise, 1995). Legend: 1 –

pelagic sediments; 2 – erupted basalts; 3 – complex of parallel dikes (dolerites); 4 – upper (not layered) gabbros and gabbro-dolerites; 5, 6 – layered complex (cumulates): 5 – gabbroids, 6 – ultrabasites; 7 – tectonized peridotites; 8 – basal metamorphic aureole; 9 – basaltic magma change I–IV – successive change of crystallization conditions in the chamber with distance from the spreading axis

ical precipitation; basalts often have a characteristic pillow (in cross section) separation (pillow lavas), but covers of massive basalts also occur. In the lower part of the second layer (2B) parallel dolerite dikes are developed. The total thickness of the 2nd layer is 1.5–2 km, and the speed of longitudinal seismic waves is 4.5–5.5 km/s.

Third layer The oceanic crust consists of holocrystalline igneous rocks of basic and subordinate ultrabasic composition. In its upper part, rocks of the gabbro type are usually developed, and the lower part is made up of a “banded complex” consisting of alternating gabbro and ultra-ramafites. The thickness of the 3rd layer is 5 km. The speed of longitudinal waves in this layer reaches 6–7.5 km/s.

It is believed that the rocks of the 2nd and 3rd layers were formed simultaneously with the rocks of the 1st layer.

Oceanic crust, or rather ocean-type crust, is not limited in its distribution to the ocean floor, but is also developed in deep-sea basins of marginal seas, such as the Sea of ​​Japan, the South Okhotsk (Kuril) basin of the Sea of ​​Okhotsk, the Philippine, Caribbean and many others

seas. In addition, there are serious reasons to suspect that in the deep depressions of continents and shallow internal and marginal seas such as the Barents, where the thickness of the sedimentary cover is 10-12 km or more, it is underlain by oceanic-type crust; This is evidenced by the velocities of longitudinal seismic waves of the order of 6.5 km/s.

It was said above that the age of the crust of modern oceans (and marginal seas) does not exceed 180 million years. However, within the folded belts of the continents we also find much more ancient, up to the Early Precambrian, ocean-type crust, represented by the so-called ophiolite complexes(or simply ophiolites). This term belongs to the German geologist G. Steinmann and was proposed by him at the beginning of the 20th century. to designate the characteristic “triad” of rocks usually found together in the central zones of folded systems, namely serpentinized ultramafic rocks (analogous to layer 3), gabbro (analogous to layer 2B), basalts (analogous to layer 2A) and radiolarites (analogous to layer 1). The essence of this rock paragenesis has long been interpreted erroneously; in particular, gabbros and hyperbasites were considered intrusive and younger than basalts and radiolarites. Only in the 60s, when the first reliable information about the composition of the ocean crust was obtained, it became obvious that ophiolites are the ocean crust of the geological past. This discovery was of cardinal importance for a correct understanding of the conditions for the origin of the Earth's moving belts.

Crustal structures of the oceans

Areas of continuous distribution oceanic crust expressed in the relief of the Earth oceanicdepressions. Within the ocean basins, two largest elements are distinguished: oceanic platforms And oceanic orogenic belts. Ocean platforms(or tha-lassocratons) in the bottom topography have the appearance of extensive abyssal flat or hilly plains. TO oceanic orogenic belts These include mid-ocean ridges that have a height above the surrounding plain of up to 3 km (in some places they rise in the form of islands above ocean level). Along the axis of the ridge, a zone of rifts is often traced - narrow grabens 12-45 km wide at a depth of 3-5 km, indicating the dominance of crustal extension in these areas. They are characterized by high seismicity, sharply increased heat flow, and low density of the upper mantle. Geophysical and geological data indicate that the thickness of the sedimentary cover decreases as it approaches the axial zones of the ridges, and the oceanic crust experiences a noticeable uplift.

The next major element of the earth's crust is transition zone between continent and ocean. This is the area of ​​maximum dissection of the earth's surface, where there are island arcs, characterized by high seismicity and modern andesitic and andesite-basaltic volcanism, deep-sea trenches and deep-sea depressions of marginal seas. The sources of earthquakes here form a seismofocal zone (Benioff-Zavaritsky zone), plunging under the continents. The transition zone is most

clearly manifested in the western part of the Pacific Ocean. It is characterized by an intermediate type of structure of the earth's crust.

Continental crust(Khain, Lomise, 1995) is distributed not only within the continents themselves, i.e., land, with the possible exception of the deepest depressions, but also within the shelf zones of continental margins and individual areas within ocean basins-microcontinents. Nevertheless, the total area of ​​development of the continental crust is less than that of the oceanic crust, accounting for 41% of the earth's surface. The average thickness of the continental crust is 35-40 km; it decreases towards the margins of continents and within microcontinents and increases under mountain structures to 70-75 km.

All in all, continental crust, like the oceanic one, has a three-layer structure, but the composition of the layers, especially the lower two, differs significantly from those observed in the oceanic crust.

1. sedimentary layer, commonly referred to as the sedimentary cover. Its thickness varies from zero on shields and smaller uplifts of platform foundations and axial zones of folded structures to 10 and even 20 km in platform depressions, forward and intermountain troughs of mountain belts. True, in these depressions the crust underlying the sediments and usually called consolidated, may already be closer in nature to oceanic than to continental. The composition of the sedimentary layer includes various sedimentary rocks of predominantly continental or shallow marine, less often bathyal (again within deep depressions) origin, and also, far

not everywhere, covers and sills of basic igneous rocks forming trap fields. The speed of longitudinal waves in the sedimentary layer is 2.0-5.0 km/s with a maximum for carbonate rocks. The age range of the sedimentary cover rocks is up to 1.7 billion years, i.e., an order of magnitude higher than the sedimentary layer of modern oceans.

2. Upper layer of consolidated crust protrudes onto the day surface on shields and arrays of platforms and in the axial zones of folded structures; it was discovered to a depth of 12 km in the Kola well and to a much smaller depth in wells in the Volga-Ural region on the Russian Plate, on the US Midcontinent Plate and on the Baltic Shield in Sweden. A gold mine in South India passed through this layer up to 3.2 km, in South Africa - up to 3.8 km. Therefore, the composition of this layer, at least its upper part, is generally well known; the main role in its composition is played by various crystalline schists, gneisses, amphibolites and granites, and therefore it is often called granite-gneiss. The speed of longitudinal waves in it is 6.0-6.5 km/s. In the foundation of young platforms, which have a Riphean-Paleozoic or even Mesozoic age, and partly in the internal zones of young folded structures, the same layer is composed of less strongly metamorphosed (greenschist facies instead of amphibolite) rocks and contains fewer granites; that's why it is often called here granite-metamorphic layer, and typical longitudinal velocities in it are of the order of 5.5-6.0 km/s. The thickness of this crustal layer reaches 15-20 km on platforms and 25-30 km in mountain structures.

3. The lower layer of the consolidated crust. It was initially assumed that there was a clear seismic boundary between the two layers of the consolidated crust, which was named the Conrad boundary after its discoverer, a German geophysicist. The drilling of the wells just mentioned has cast doubt on the existence of such a clear boundary; sometimes, instead, seismicity detects not one, but two (K 1 and K 2) boundaries in the crust, which gave grounds to distinguish two layers in the lower crust (Fig. 6.2). The composition of the rocks composing the lower crust, as noted, is not sufficiently known, since it has not been reached by wells, and is exposed fragmentarily on the surface. Based

Rice. 6.2. Structure and thickness of the continental crust (Khain, Lomise, 1995). A - main types of section according to seismic data: I-II - ancient platforms (I - shields, II

Syneclises), III - shelves, IV - young orogens. K 1 , K 2 -Conrad surfaces, M-Mohorovicic surface, velocities are indicated for longitudinal waves; B - histogram of the distribution of thickness of the continental crust; B - generalized strength profile

General considerations, V.V. Belousov came to the conclusion that the lower crust should be dominated, on the one hand, by rocks at a higher stage of metamorphism and, on the other hand, by rocks of a more basic composition than in the upper crust. That's why he called this layer of cortex gra-nullite-mafic. Belousov's assumption is generally confirmed, although outcrops show that not only basic, but also acidic granulites are involved in the composition of the lower crust. Currently, most geophysicists distinguish the upper and lower crust on another basis - by their excellent rheological properties: the upper crust is hard and brittle, the lower crust is plastic. The speed of longitudinal waves in the lower crust is 6.4-7.7 km/s; belonging to the crust or mantle of the lower layers of this layer with velocities exceeding 7.0 km/s is often controversial.

Between the two extreme types of the earth's crust - oceanic and continental - there are transitional types. One of them - suboceanic crust - developed along the continental slopes and foothills and, possibly, underlies the bottom of the basins of some not very deep and wide marginal and internal seas. The suboceanic crust is a continental crust thinned to 15-20 km and penetrated by dikes and sills of basic igneous rocks.

bark It was exposed by deep-sea drilling at the entrance to the Gulf of Mexico and exposed on the Red Sea coast. Another type of transitional cortex is subcontinental- is formed in the case when the oceanic crust in ensimatic volcanic arcs turns into continental, but has not yet reached full “maturity”, having a reduced, less than 25 km, thickness and a lower degree of consolidation, which is reflected in lower velocities of seismic waves - no more than 5.0-5.5 km/s in the lower crust.

Some researchers identify two more types of ocean crust as special types, which were already discussed above; this is, firstly, the oceanic crust of the internal uplifts of the ocean thickened to 25-30 km (Iceland, etc.) and, secondly, the ocean-type crust, “built on” with a thick, up to 15-20 km, sedimentary cover (Caspian Basin and etc.).

Mohorovicic surface and composition of the upper manatii. The boundary between the crust and the mantle, usually seismically quite clearly expressed by a jump in longitudinal wave velocities from 7.5-7.7 to 7.9-8.2 km/s, is known as the Mohorovicic surface (or simply Moho and even M), named the Croatian geophysicist who established it. In the oceans, this boundary corresponds to the transition from a banded complex of the 3rd layer with a predominance of gabbroids to continuous serpentinized peridotites (harzburgites, lherzolites), less often dunites, in places protruding onto the bottom surface, and in the rocks of Sao Paulo in the Atlantic off the coast of Brazil and on o. Zabargad in the Red Sea, rising above the surface

the sea's fury. The tops of the oceanic mantle can be observed in places on land as part of the bottoms of ophiolite complexes. Their thickness in Oman reaches 8 km, and in Papua New Guinea, perhaps even 12 km. They are composed of peridotites, mainly harzburgites (Khain and Lomise, 1995).

The study of inclusions in lavas and kimberlites from pipes shows that beneath the continents, the upper mantle is mainly composed of peridotites, both here and under the oceans in the upper part these are spinel peridotites, and below are garnet ones. But in the continental mantle, according to the same data, in addition to peridotites, eclogites, i.e., deeply metamorphosed basic rocks, are present in minor quantities. Eclogites may be metamorphosed relics of oceanic crust, dragged into the mantle during the process of underthrusting this crust (subduction).

The upper part of the mantle is secondarily depleted in a number of components: silica, alkalis, uranium, thorium, rare earths and other incoherent elements due to the melting of basaltic rocks of the earth's crust from it. This “depleted” (“depleted”) mantle extends under the continents to a greater depth (encompassing all or almost all of its lithospheric part) than under the oceans, giving way deeper to the “undepleted” mantle. The average primary composition of the mantle should be close to spinel lherzolite or a hypothetical mixture of peridotite and basalt in a 3:1 ratio, named by the Australian scientist A.E. Ringwood pyrolite.

At a depth of about 400 km, a rapid increase in the speed of seismic waves begins; from here to 670 km

erased Golitsyn layer, named after the Russian seismologist B.B. Golitsyn. It is also distinguished as the middle mantle, or mesosphere - transition zone between the upper and lower mantle. The increase in the rates of elastic vibrations in the Golitsyn layer is explained by an increase in the density of the mantle material by approximately 10% due to the transition of some mineral species to others, with a more dense packing of atoms: olivine into spinel, pyroxene into garnet.

Lower mantle(Hain, Lomise, 1995) begins at a depth of about 670 km. The lower mantle should be composed mainly of perovskite (MgSiO 3) and magnesium wustite (Fe, Mg)O - products of further alteration of the minerals composing the middle mantle. The Earth's core in its outer part, according to seismology, is liquid, and the inner part is solid again. Convection in the outer core generates the Earth's main magnetic field. The composition of the core is accepted by the overwhelming majority of geophysicists as iron. But again, according to experimental data, it is necessary to allow for some admixture of nickel, as well as sulfur, or oxygen, or silicon, in order to explain the reduced core density compared to that determined for pure iron.

According to seismic tomography data, core surface is uneven and forms protrusions and depressions with an amplitude of up to 5-6 km. At the boundary of the mantle and the core, a transition layer with the index D is distinguished (the crust is designated by the index A, the upper mantle - B, the middle - C, the lower - D, the upper part of the lower mantle - D"). The thickness of layer D" in some places reaches 300 km.

Lithosphere and asthenosphere. Unlike the crust and mantle, distinguished by geological data (by material composition) and seismological data (by the jump in seismic wave velocities at the Mohorovicic boundary), the lithosphere and asthenosphere are purely physical, or rather rheological, concepts. The initial basis for identifying the asthenosphere is a weakened, plastic shell. underlying a more rigid and fragile lithosphere, there was a need to explain the fact of isostatic balance of the crust, discovered when measuring gravity at the foot of mountain structures. It was initially expected that such structures, especially those as grand as the Himalayas, would create an excess of gravity. However, when in the middle of the 19th century. corresponding measurements were made, it turned out that such attraction was not observed. Consequently, even large unevenness in the relief of the earth's surface is somehow compensated, balanced at depth so that at the level of the earth's surface there are no significant deviations from the average values ​​of gravity. Thus, the researchers came to the conclusion that there is a general tendency of the earth’s crust to balance at the expense of the mantle; this phenomenon is called isostasia(Hain, Lomise, 1995) .

There are two ways to implement isostasy. The first is that mountains have roots immersed in the mantle, i.e. isostasy is ensured by variations in the thickness of the earth's crust and the lower surface of the latter has a relief opposite to the relief of the earth's surface; this is the hypothesis of the English astronomer J. Airy

(Fig. 6.3). On a regional scale, it is usually justified, since mountain structures actually have thicker crust and the maximum thickness of the crust is observed at the highest of them (Himalayas, Andes, Hindu Kush, Tien Shan, etc.). But another mechanism for the implementation of isostasy is also possible: areas of increased relief should be composed of less dense rocks, and areas of lower relief should be composed of more dense ones; This is the hypothesis of another English scientist, J. Pratt. In this case, the base of the earth's crust may even be horizontal. The balance of continents and oceans is achieved by a combination of both mechanisms—the crust under the oceans is both much thinner and noticeably denser than under the continents.

Most of the Earth's surface is in a state close to isostatic equilibrium. The greatest deviations from isostasy—isostatic anomalies—are found in island arcs and associated deep-sea trenches.

In order for the desire for isostatic equilibrium to be effective, i.e., under additional load, the crust would sink, and when the load is removed, it would rise, it is necessary that there be a sufficiently plastic layer under the crust, capable of flowing from areas of increased geostatic pressure to areas low pressure. It was for this layer, initially identified hypothetically, that the American geologist J. Burrell proposed the name asthenosphere, which means “weak shell”. This assumption was confirmed only much later, in the 60s, when seismic

Rice. 6.3. Schemes of isostatic equilibrium of the earth's crust:

A - by J. Erie, b - by J. Pratt (Khain, Koronovsky, 1995)

logs (B. Gutenberg) discovered the existence at some depth under the crust of a zone of decrease or absence of increase, natural with an increase in pressure, in the speed of seismic waves. Subsequently, another method of establishing the asthenosphere appeared—the method of magnetotelluric sounding, in which the asthenosphere manifests itself as a zone of reduced electrical resistance. In addition, seismologists have identified another sign of the asthenosphere - increased attenuation of seismic waves.

The asthenosphere also plays a leading role in the movements of the lithosphere. The flow of asthenospheric matter carries along lithospheric plates and causes their horizontal movements. The rise of the surface of the asthenosphere leads to the rise of the lithosphere, and in the extreme case, to a break in its continuity, the formation of a separation and subsidence. The latter also leads to the outflow of the asthenosphere.

Thus, of the two shells that make up the tectonosphere: the asthenosphere is an active element, and the lithosphere is a relatively passive element. Their interaction determines the tectonic and magmatic “life” of the earth’s crust.

In the axial zones of mid-ocean ridges, especially on the East Pacific Rise, the top of the asthenosphere is located at a depth of only 3-4 km, i.e., the lithosphere is limited only to the upper part of the crust. As we move towards the periphery of the oceans, the thickness of the lithosphere increases due to

the lower crust, and mainly the upper mantle and can reach 80-100 km. In the central parts of the continents, especially under the shields of ancient platforms, such as the East European or Siberian, the thickness of the lithosphere is already measured at 150-200 km or more (in South Africa 350 km); according to some ideas, it can reach 400 km, i.e. here the entire upper mantle above the Golitsyn layer should be part of the lithosphere.

The difficulty of detecting the asthenosphere at depths of more than 150-200 km has raised doubts among some researchers about its existence beneath such areas and led them to an alternative idea that the asthenosphere as a continuous shell, i.e., the geosphere, does not exist, but there is a series of disconnected “asthenolenses” " We cannot agree with this conclusion, which could be important for geodynamics, since it is these areas that demonstrate a high degree of isostatic balance, because these include the above examples of areas of modern and ancient glaciation - Greenland, etc.

The reason that the asthenosphere is not easy to detect everywhere is obviously a change in its viscosity laterally.

The main structural elements of the continental crust

On continents, two structural elements of the earth's crust are distinguished: platforms and mobile belts (Historical Geology, 1985).

Definition:platform- a stable, rigid section of the continental crust, having an isometric shape and a two-story structure (Fig. 6.4). Lower (first) structural floor – crystalline foundation, represented by highly dislocated metamorphosed rocks, intruded by intrusions. The upper (second) structural floor is gently lying sedimentary cover, weakly dislocated and unmetamorphosed. Exits to the day surface of the lower structural floor are called shield. Areas of the foundation covered by sedimentary cover are called stove. The thickness of the sedimentary cover of the plate is a few kilometers.

Example: on the East European Platform there are two shields (Ukrainian and Baltic) and the Russian plate.

Structures of the second floor of the platform (case) There are negative (deflections, syneclises) and positive (anteclises). Syneclises have the shape of a saucer, and anteclises have the shape of an inverted saucer. The thickness of sediments is always greater on the syneclise, and less on the anteclise. The dimensions of these structures in diameter can reach hundreds or a few thousand kilometers, and the fall of the layers on the wings is usually a few meters per 1 km. There are two definitions of these structures.

Definition: syneclise is a geological structure, the fall of the layers of which is directed from the periphery to the center. Anteclise is a geological structure, the fall of the layers of which is directed from the center to the periphery.

Definition: syneclise - a geological structure in the core of which younger sediments emerge, and along the edges

Rice. 6.4. Platform structure diagram. 1 - folded foundation; 2 - platform case; 3 faults (Historical Geology, 1985)

- more ancient. Anteclise is a geological structure, in the core of which more ancient sediments emerge, and at the edges - younger ones.

Definition: trough is an elongated (elongated) geological body that has a concave shape in cross section.

Example: on the Russian plate of the East European platform stand out anteclises(Belarusian, Voronezh, Volga-Ural, etc.), syneclises(Moscow, Caspian, etc.) and troughs (Ulyanovsk-Saratov, Transnistria-Black Sea, etc.).

There is a structure of the lower horizons of the cover - av-lacogene.

Definition: aulacogen - a narrow, elongated depression extending across the platform. Aulacogens are located in the lower part of the upper structural floor (cover) and can reach a length of up to hundreds of kilometers and a width of tens of kilometers. Aulacogens are formed under conditions of horizontal extension. Thick layers of sediments accumulate in them, which can be crushed into folds and are similar in composition to the formations of miogeosynclines. Basalts are present in the lower part of the section.

Example: Pachelma (Ryazan-Saratov) aulacogen, Dnieper-Donets aulacogen of the Russian plate.

History of the development of platforms. The history of development can be divided into three stages. First– geosynclinal, on which the formation of the lower (first) structural element (foundation) occurs. Second- aulacogenic, on which, depending on the climate, accumulation occurs

red-colored, gray-colored or carbon-bearing sediments in av-lacogenes. Third– slab, on which sedimentation occurs over a large area and the upper (second) structural floor (slab) is formed.

The process of precipitation accumulation usually occurs cyclically. Accumulates first transgressive maritime terrigenous formation, then - carbonate formation (maximum transgression, Table 6.1). During regression under arid climate conditions, salt-bearing red-flowered formation, and in conditions of a humid climate - paralytic coal-bearing formation. At the end of the sedimentation cycle, sediments are formed continental formations. At any moment the stage can be interrupted by the formation of a trap formation.

Table 6.1. Sequence of slab accumulation

formations and their characteristics.

End of table 6.1.

For movable belts (folded areas) characteristic:

linearity of their contours;

the enormous thickness of accumulated sediments (up to 15-25 km);

consistency composition and thickness of these deposits along strike folded area and sudden changes across its strike;

presence of peculiar formations- rock complexes formed at certain stages of development of these areas ( slate, flysch, spilito-keratophyric, molasse and other formations);

intense effusive and intrusive magmatism (large granite intrusions-batholiths are especially characteristic);

strong regional metamorphism;

7) strong folding, an abundance of faults, including

thrusts indicating the dominance of compression. Folded areas (belts) arise in place of geosynclinal areas (belts).

Definition: geosyncline(Fig. 6.5) - a mobile region of the earth’s crust, in which thick sedimentary and volcanogenic strata initially accumulated, then they were crushed into complex folds, accompanied by the formation of faults, the introduction of intrusions and metamorphism. There are two stages in the development of a geosyncline.

First stage(actually geosynclinal) characterized by a predominance of subsidence. High precipitation rate in a geosyncline - this is result of stretching of the earth's crust and its deflection. IN first half firststages Sandy-clayey and clayey sediments usually accumulate (as a result of metamorphism, they then form black clayey shales, released in slate formation) and limestones. Subduction may be accompanied by ruptures through which mafic magma rises and erupts under submarine conditions. The resulting rocks after metamorphism, together with accompanying subvolcanic formations, give spilite-keratophyric formation. At the same time, siliceous rocks and jasper are usually formed.

oceanic

Rice. 6.5. Scheme of the geosync structure

linali on a schematic cross-section through the Sunda Arc in Indonesia (Structural Geology and Plate Tectonics, 1991). Legend: 1 – sediments and sedimentary rocks; 2 – volcano-

nic breeds; 3 – basement conti-metamorphic rocks

Specified formations accumulate simultaneously, But in different areas. Accumulation spilito-keratophyric formation usually occurs in the inner part of the geosyncline - in eugeosynclines. For eugeo-synclines Characterized by the formation of thick volcanogenic strata, usually of basic composition, and the introduction of intrusions of gabbro, diabase and ultrabasic rocks. In the marginal part of the geosyncline, along its border with the platform, there are usually located miogeosynclines. Mainly terrigenous and carbonate strata accumulate here; There are no volcanic rocks, and intrusions are not typical.

In the first half of the first stage Most of the geosyncline is sea ​​with significantdepths. Evidence is provided by the fine granularity of sediments and the rarity of faunal finds (mainly nekton and plankton).

TO mid first stage due to different rates of subsidence, areas are formed in different parts of the geosyncline relative rise(intrageoantic-linali) And relative descent(intrageosynclines). At this time, the intrusion of small intrusions of plagiogranites may occur.

In second half of the first stage As a result of the appearance of internal uplifts, the sea in the geosyncline becomes shallower. now this archipelago, separated by straits. Due to shallowing, the sea is advancing on adjacent platforms. Limestones, thick sandy-clayey rhythmically built strata, accumulate in the geosyncline, forming flysch for-216

mation; there is an outpouring of lavas of intermediate composition that make up porphyritic formation.

TO end of the first stage intrageosynclines disappear, intrageoanticlines merge into one central uplift. This is a general inversion; she matches main phase of folding in a geosyncline. Folding is usually accompanied by the intrusion of large synorogenic (simultaneous with folding) granite intrusions. Rocks are crushed into folds, often complicated by thrusts. All this causes regional metamorphism. In place of intrageosynclines there arise synclinorium- complexly constructed structures of the synclinal type, and in place of intrageoanticlines - anticlinoria. The geosyncline “closes”, turning into a folded area.

In the structure and development of a geosyncline, a very important role belongs to deep faults - long-lived ruptures that cut through the entire earth's crust and go into the upper mantle. Deep faults determine the contours of geosynclines, their magmatism, and the division of the geosyncline into structural-facial zones that differ in the composition of sediments, their thickness, magmatism and the nature of the structures. Inside a geosyncline they sometimes distinguish middle massifs, limited by deep faults. These are blocks of more ancient folding, composed of rocks from the foundation on which the geosyncline was formed. In terms of the composition of sediments and their thickness, the middle massifs are similar to platforms, but they are distinguished by strong magmatism and folding of rocks, mainly along the edges of the massif.

The second stage of geosyncline development called orogenic and is characterized by a predominance of uplifts. Sedimentation occurs in limited areas along the periphery of the central uplift - in marginal deflections, arising along the border of the geosyncline and the platform and partially overlapping the platform, as well as in intermountain troughs that sometimes form inside the central uplift. The source of sediment is the destruction of the constantly rising central rise. First halfsecond stage this rise probably has a hilly topography; when it is destroyed, marine and sometimes lagoonal sediments accumulate, forming lower molasse formation. Depending on climatic conditions, this may be coal-bearing paralic or salty thickness. At the same time, the introduction of large granite intrusions - batholiths - usually occurs.

In the second half of the stage the rate of uplift of the central uplift sharply increases, which is accompanied by its splits and collapse of individual sections. This phenomenon is explained by the fact that, as a result of folding, metamorphism, and the introduction of intrusions, the folded region (no longer a geosyncline!) becomes rigid and reacts to the ongoing uplift with rifts. The sea is leaving this area. As a result of the destruction of the central uplift, which at that time was a mountainous country, continental coarse clastic strata accumulate, forming upper molasse formation. The splitting of the arched part of the uplift is accompanied by ground volcanism; usually these are lavas of acidic composition, which, together with

subvolcanic formations give porphyry formation. Fissure alkaline and small acidic intrusions are associated with it. Thus, as a result of the development of the geosyncline, the thickness of the continental crust increases.

By the end of the second stage, the folded mountain area that arose on the site of the geosyncline is destroyed, the territory gradually levels out and becomes a platform. The geosyncline turns from an area of ​​sediment accumulation into an area of ​​destruction, from a mobile territory into a sedentary, rigid, leveled territory. Therefore, the range of movements on the platform is small. Usually the sea, even shallow, covers vast areas here. This territory no longer experiences such strong subsidence as before, therefore the thickness of the sediments is much less (on average 2-3 km). The subsidence is repeatedly interrupted, so frequent breaks in sedimentation are observed; then weathering crusts can form. There are no energetic uplifts accompanied by folding. Therefore, the newly formed thin, usually shallow-water sediments on the platform are not metamorphosed and lie horizontally or slightly inclined. Igneous rocks are rare and are usually represented by terrestrial outpourings of basaltic lavas.

In addition to the geosynclinal model, there is a model of lithospheric plate tectonics.

Model of plate tectonics

Plate tectonics(Structural Geology and Plate Tectonics, 1991) is a model that was created to explain the observed pattern of distribution of deformations and seismicity in the outer shell of the Earth. It is based on extensive geophysical data acquired in the 1950s and 1960s. The theoretical foundations of plate tectonics are based on two premises.

The outermost layer of the Earth, called lithosphere, lies directly on a layer called actenosphere, which is less durable than the lithosphere.

The lithosphere is divided into a number of rigid segments, or plates (Fig. 6.6), which are constantly moving relative to each other and whose surface area is also constantly changing. Most tectonic processes with intense energy exchange operate at the boundaries between plates.

Although the thickness of the lithosphere cannot be measured with great precision, researchers agree that within plates it varies from 70-80 km under the oceans to a maximum of over 200 km under some parts of the continents, with an average of about 100 km. The asthenosphere underlying the lithosphere extends down to a depth of about 700 km (the maximum depth for the distribution of sources of deep-focus earthquakes). Its strength increases with depth, and some seismologists believe that its lower limit is

Rice. 6.6. Earth's lithospheric plates and their active boundaries. Double lines indicate divergent boundaries (spreading axes); lines with teeth - convergent grains P.PIT

single lines - transform faults (slip faults); areas of the continental crust that are subject to active faulting are speckled (Structural geology and plate tectonics, 1991)

Tsa is located at a depth of 400 km and coincides with a slight change in physical parameters.

Boundaries between plates are divided into three types:

divergent;

convergent;

transform (with displacements along strike).

At divergent plate boundaries, represented mainly by rifts, new formation of the lithosphere occurs, which leads to the spreading of the ocean floor (spreading). At convergent plate boundaries, the lithosphere is submerged into the asthenosphere, i.e., it is absorbed. At transform boundaries, two lithospheric plates slide relative to each other, and lithosphere matter is neither created nor destroyed on them .

All lithospheric plates continuously move relative to each other. It is assumed that the total area of ​​all slabs remains constant over a significant period of time. At a sufficient distance from the edges of the plates, horizontal deformations inside them are insignificant, which allows the plates to be considered rigid. Since displacements along transform faults occur along their strike, plate movement should be parallel to modern transform faults. Since all this happens on the surface of a sphere, then, in accordance with Euler’s theorem, each section of the plate describes a trajectory equivalent to rotation on the spherical surface of the Earth. For the relative movement of each pair of plates at any given time, an axis, or pole of rotation, can be determined. As you move away from this pole (up to the corner

distance of 90°), spreading rates naturally increase, but the angular velocity for any given pair of plates relative to their pole of rotation is constant. Let us also note that, geometrically, the poles of rotation are unique for any pair of plates and are in no way connected with the pole of rotation of the Earth as a planet.

Plate tectonics is an effective model of crustal processes because it fits well with known observational data, provides elegant explanations for previously unrelated phenomena, and opens up possibilities for prediction.

Wilson cycle(Structural Geology and Plate Tectonics, 1991). In 1966, Professor Wilson of the University of Toronto published a paper in which he argued that continental drift occurred not only after the early Mesozoic breakup of Pangea, but also in pre-Pangean times. The cycle of opening and closing of oceans relative to adjacent continental margins is now called Wilson cycle.

In Fig. Figure 6.7 provides a schematic explanation of the basic concept of the Wilson cycle within the framework of ideas about the evolution of lithospheric plates.

Rice. 6.7, but represents beginning of the Wilson cycle– the initial stage of continental breakup and formation of the accretionary plate margin. Known to be tough

Rice. 6.7. Scheme of the Wilson cycle of ocean development within the framework of the evolution of lithospheric plates (Structural Geology and Plate Tectonics, 1991)

the lithosphere covers a weaker, partially molten zone of the asthenosphere - the so-called low-velocity layer (Figure 6.7, b) . As the continents continue to separate, a rift valley (Fig. 6.7, 6) and a small ocean (Fig. 6.7, c) develop. These are the stages of early ocean opening in the Wilson cycle.. The African Rift and the Red Sea are suitable examples. With the continuation of the drift of separated continents, accompanied by the symmetrical accretion of new lithosphere on the margins of plates, shelf sediments accumulate at the continent-ocean boundary due to erosion of the continent. Fully formed ocean(Fig. 6.7, d) with a median ridge at the plate boundary and a developed continental shelf is called ocean of the Atlantic type.

From observations of oceanic trenches, their relationship to seismicity, and reconstruction from patterns of oceanic magnetic anomalies around the trenches, it is known that the oceanic lithosphere is dismembered and subducted into the mesosphere. In Fig. 6.7, d shown ocean with stove, which has simple margins of lithosphere accretion and absorption, – this is the initial stage of ocean closure V Wilson cycle. The dismemberment of the lithosphere in the vicinity of the continental margin leads to the transformation of the latter into an Andean-type orogen as a result of tectonic and volcanic processes occurring at the absorbing plate boundary. If this dismemberment occurs at a considerable distance from the continental margin towards the ocean, then an island arc like the Japanese Islands is formed. Oceanic absorptionlithosphere leads to a change in the geometry of the plates and in the end

ends to complete disappearance of the accretionary plate margin(Fig. 6.7, f). During this time, the opposite continental shelf may continue to expand, becoming an Atlantic-type semi-ocean. As the ocean shrinks, the opposite continental margin is eventually drawn into the plate absorption mode and participates in the development Andean-type accretionary orogen. This is the early stage of the collision of two continents (collisions) . At the next stage, due to the buoyancy of the continental lithosphere, the absorption of the plate stops. The lithospheric plate breaks off below, under a growing Himalayan-type orogen, and advances final orogenic stageWilson cyclewith a mature mountain belt, representing the seam between the newly united continents. Antipode Andean-type accretionary orogen is Himalayan-type collisional orogen.

The earth's crust in the scientific sense is the uppermost and hardest geological part of the shell of our planet.

Scientific research allows us to study it thoroughly. This is facilitated by repeated drilling of wells both on continents and on the ocean floor. The structure of the earth and the earth's crust in different parts of the planet differs both in composition and characteristics. The upper boundary of the earth's crust is the visible relief, and the lower boundary is the zone of separation of the two environments, which is also known as the Mohorovicic surface. It is often referred to simply as the “M boundary.” It received this name thanks to the Croatian seismologist Mohorovicic A. For many years he observed the speed of seismic movements depending on the depth level. In 1909, he established the existence of a difference between the earth's crust and the hot mantle of the earth. The M boundary lies at the level where the speed of seismic waves increases from 7.4 to 8.0 km/s.

Chemical composition of the Earth

Studying the shells of our planet, scientists have made interesting and even stunning conclusions. The structural features of the earth's crust make it similar to the same areas on Mars and Venus. More than 90% of its constituent elements are represented by oxygen, silicon, iron, aluminum, calcium, potassium, magnesium, and sodium. Combining with each other in various combinations, they form homogeneous physical bodies - minerals. They can be included in rocks in different concentrations. The structure of the earth's crust is very heterogeneous. Thus, rocks in a generalized form are aggregates of more or less constant chemical composition. These are independent geological bodies. They mean a clearly defined area of ​​the earth's crust, which has the same origin and age within its boundaries.

Rocks by group

1. Igneous. The name speaks for itself. They arise from cooled magma flowing from the mouths of ancient volcanoes. The structure of these rocks directly depends on the rate of lava solidification. The larger it is, the smaller the crystals of the substance. Granite, for example, was formed in the thickness of the earth's crust, and basalt appeared as a result of the gradual outpouring of magma onto its surface. The variety of such breeds is quite large. Looking at the structure of the earth's crust, we see that it consists of 60% igneous minerals.

2. Sedimentary. These are rocks that were the result of the gradual deposition of fragments of certain minerals on land and the ocean floor. These can be loose components (sand, pebbles), cemented components (sandstone), remains of microorganisms (coal, limestone), or products of chemical reactions (potassium salt). They make up up to 75% of the entire earth's crust on the continents.
According to the physiological method of formation, sedimentary rocks are divided into:

• Clastic. These are the remains of various rocks. They were destroyed under the influence of natural factors (earthquake, typhoon, tsunami). These include sand, pebbles, gravel, crushed stone, clay.
• Chemical. They are gradually formed from aqueous solutions of certain mineral substances (salt).
• Organic or biogenic. Consist of the remains of animals or plants. These are oil shale, gas, oil, coal, limestone, phosphorites, chalk.

3. Metamorphic rocks. Other components can be converted into them. This occurs under the influence of changing temperature, high pressure, solutions or gases. For example, you can get marble from limestone, gneiss from granite, and quartzite from sand.

Minerals and rocks that humanity actively uses in its life are called minerals. What are they?

These are natural mineral formations that affect the structure of the earth and the earth's crust. They can be used in agriculture and industry, both in their natural form and through processing.

Types of useful minerals. Their classification

Depending on their physical state and aggregation, minerals can be divided into categories:

1. Solid (ore, marble, coal).
2. Liquid (mineral water, oil).
3. Gaseous (methane).

Characteristics of individual types of minerals

According to the composition and features of application, they are distinguished:

1. Combustibles (coal, oil, gas).
2. Ore. They include radioactive (radium, uranium) and noble metals (silver, gold, platinum). There are ores of ferrous (iron, manganese, chromium) and non-ferrous metals (copper, tin, zinc, aluminum).
3. Nonmetallic minerals play a significant role in such a concept as the structure of the earth's crust. Their geography is vast. These are non-metallic and non-combustible rocks. These are building materials (sand, gravel, clay) and chemicals (sulfur, phosphates, potassium salts). A separate section is devoted to precious and ornamental stones.

The distribution of minerals on our planet directly depends on external factors and geological patterns.

Thus, fuel minerals are primarily mined in oil, gas and coal basins. They are of sedimentary origin and form on the sedimentary covers of platforms. Oil and coal rarely occur together.

Ore minerals most often correspond to the basement, overhangs, and folded areas of platform plates. In such places they can create huge belts.

Core

The earth's shell, as is known, is multi-layered. The core is located in the very center, and its radius is approximately 3,500 km. Its temperature is much higher than that of the Sun and is about 10,000 K. Accurate data on the chemical composition of the core has not been obtained, but it presumably consists of nickel and iron.

The outer core is in a molten state and has even greater power than the inner one. The latter is subject to enormous pressure. The substances of which it consists are in a permanent solid state.

Mantle

The Earth's geosphere surrounds the core and makes up about 83 percent of the entire surface of our planet. The lower boundary of the mantle is located at a huge depth of almost 3000 km. This shell is conventionally divided into a less plastic and dense upper part (it is from this that magma is formed) and a lower crystalline one, the width of which is 2000 kilometers.

Composition and structure of the earth's crust

In order to talk about what elements make up the lithosphere, we need to give some concepts.

The earth's crust is the outermost shell of the lithosphere. Its density is less than half the average density of the planet.

The earth's crust is separated from the mantle by the boundary M, which was already mentioned above. Since the processes occurring in both areas mutually influence each other, their symbiosis is usually called the lithosphere. It means "stone shell". Its power ranges from 50-200 kilometers.

Below the lithosphere is the asthenosphere, which has a less dense and viscous consistency. Its temperature is about 1200 degrees. A unique feature of the asthenosphere is the ability to violate its boundaries and penetrate the lithosphere. It is the source of volcanism. Here there are molten pockets of magma, which penetrates the earth's crust and pours out to the surface. By studying these processes, scientists were able to make many amazing discoveries. This is how the structure of the earth's crust was studied. The lithosphere was formed many thousands of years ago, but even now active processes are taking place in it.

Structural elements of the earth's crust

Compared to the mantle and core, the lithosphere is a hard, thin and very fragile layer. It is made up of a combination of substances, in which more than 90 chemical elements have been discovered to date. They are distributed heterogeneously. 98 percent of the mass of the earth's crust is made up of seven components. These are oxygen, iron, calcium, aluminum, potassium, sodium and magnesium. The oldest rocks and minerals are over 4.5 billion years old.

By studying the internal structure of the earth's crust, various minerals can be identified.
A mineral is a relatively homogeneous substance that can be found both inside and on the surface of the lithosphere. These are quartz, gypsum, talc, etc. Rocks are made up of one or more minerals.

Processes that form the earth's crust

The structure of the oceanic crust

This part of the lithosphere mainly consists of basaltic rocks. The structure of the oceanic crust has not been studied as thoroughly as the continental one. Plate tectonic theory explains that the oceanic crust is relatively young, and the most recent parts of it can be dated to the Late Jurassic.
Its thickness practically does not change over time, since it is determined by the amount of melts released from the mantle in the zone of mid-ocean ridges. It is significantly influenced by the depth of sedimentary layers on the ocean floor. In the most extensive areas it ranges from 5 to 10 kilometers. This type of earth's shell belongs to the oceanic lithosphere.

Continental crust

The lithosphere interacts with the atmosphere, hydrosphere and biosphere. In the process of synthesis, they form the most complex and reactive shell of the Earth. It is in the tectonosphere that processes occur that change the composition and structure of these shells.
The lithosphere on the earth's surface is not homogeneous. It has several layers.

1. Sedimentary. It is mainly formed by rocks. Clays and shales predominate here, and carbonate, volcanic and sandy rocks are also widespread. In sedimentary layers you can find minerals such as gas, oil and coal. All of them are of organic origin.
2. Granite layer. It consists of igneous and metamorphic rocks that are closest in nature to granite. This layer is not found everywhere; it is most pronounced on the continents. Here its depth can be tens of kilometers.
3. The basalt layer is formed by rocks close to the mineral of the same name. It is denser than granite.

Depth and temperature changes in the earth's crust

The surface layer is heated by solar heat. This is the heliometric shell. It experiences seasonal temperature fluctuations. The average thickness of the layer is about 30 m.

Below is a layer that is even thinner and more fragile. Its temperature is constant and approximately equal to the average annual temperature characteristic of this region of the planet. Depending on the continental climate, the depth of this layer increases.
Even deeper in the earth's crust is another level. This is a geothermal layer. The structure of the earth's crust allows for its presence, and its temperature is determined by the internal heat of the Earth and increases with depth.

The temperature rise occurs due to the decay of radioactive substances that are part of rocks. First of all, these are radium and uranium.

Geometric gradient - the magnitude of the temperature increase depending on the degree of increase in the depth of the layers. This parameter depends on various factors. The structure and types of the earth's crust influence it, as well as the composition of rocks, the level and conditions of their occurrence.

The heat of the earth's crust is an important energy source. Its study is very relevant today.