Is it fair to say that the spread of the continental crust. Types of the earth's crust

Layer C cannot be considered as homogeneous. In it, either a change in the chemical composition, or phase transitions (or both) occurs.

As for layer B, which lies directly under the earth's crust, then, most likely, some heterogeneity also takes place here and it consists of such rocks as dunite, peridotites, eclogites.

When studying an earthquake that occurred 40 km from Zagreb (Yugoslavia), A. Mohorovichic in 1910 noticed that at a distance of more than 200 km from the source of the first, a longitudinal wave of a different type enters the seismogram than at closer distances. He explained this by the fact that in the Earth at a depth of about 50 km there is a boundary at which the speed suddenly increases. This research was continued by his son S. Mohorović, after Konrad, who in 1925 discovered another phase of longitudinal waves P* while studying waves from earthquakes in the eastern Alps. The corresponding shear wave phase S* was identified later. The P* and S* phases indicate the existence of at least one boundary, the "Konrad boundary" between the bottom of the sedimentary sequence and the Mohorović boundary.

Waves generated by earthquakes and artificial explosions and propagating in the earth's crust have been intensively studied in recent years. The methods of both refracted and reflected waves were used. The results of the research carried out are as follows. According to measurements carried out by different researchers, the values ​​of longitudinal V p and transverse V S velocities turned out to be equal: in granite - V p = 4.0 ÷ 5.7, V s = 2.1 ÷ 3.4, in basalt - V p = 5.4 ÷ 6.4, V s ≈ 3.2, V

gabbro - V p = 6.4 ÷ 6.7, V s ≈ 3.5, in dunite - V p = 7.4, V s = 3.8 and in eclogite - V p = 8.0, V s = 4.3

km/s.

In addition, indications were obtained in various areas of the existence of waves with different velocities and boundaries within the granite layer. On the other hand, there is no indication of the existence of a granite layer under the ocean floor beyond the shelves. In many continental areas, the base of the granite layer is the Konrad boundary.

At present, there are indications of additional clearly defined boundaries between the Konrad and Mohorovichic surfaces; for several continental regions, layers with longitudinal wave velocities from 6.5 to 7 and from 7 to 7.5 km/s are even indicated. It has been suggested that a "diorite" layer may exist (V p = 6.1

km/s) and the "gabbro" layer (V p = 7 km/s).

In many oceanic areas, the depth of the Moho boundary under the ocean floor is less than 10 km. For most continents, its depth increases with increasing distance from the coast and under high mountains can reach more than 50 km. These "roots" of mountains were first discovered from gravity data.

In most cases, determinations of velocities below the Moho boundary give the same figures: 8.1 - 8.2 km/s for longitudinal waves and about 4.7 km/s for transverse waves.

The Earth's crust [Sorokhtin, Ushakov, 2002, p. 39-52]

The Earth's crust is the upper layer of the rigid shell of the Earth - its lithosphere and differs from the subcrustal parts of the lithosphere in structure and chemical composition. The Earth's crust is separated from the underlying lithospheric mantle by the Mohorovichich boundary, on which the propagation velocities of seismic waves jump up to 8.0 - 8.2 km/s.

The surface of the earth's crust is formed due to the multidirectional effects of tectonic movements that create uneven terrain, the denudation of this relief through the destruction and weathering of the rocks that make it up, and due to the processes of sedimentation. As a result, constantly emerging and at the same time

the smoothing surface of the earth's crust turns out to be quite complex. The maximum contrast of the relief is observed only in places of the greatest modern tectonic activity of the Earth, for example, on the active continental margin of South America, where the difference in relief levels between the Peruano-Chile deep-water trench and the peaks of the Andes reaches 16-17 km. Significant height contrasts (up to 7-8 km) and a large dissection of the relief are observed in modern continental collision zones, for example, in the Alpine-Himalayan fold belt.

oceanic crust

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

The lower part of the sedimentary layer is usually composed of carbonate sediments deposited at depths of less than 4-4.5 km. At depths greater than 4-4.5 km, the upper part of the sedimentary layer is mainly composed of non-carbonate sediments - red deep-sea clays and siliceous silts. The second, or basaltic, layer of the oceanic crust in the upper part is composed of tholeiitic basaltic lavas. The total thickness of the basalt layer of the oceanic crust, according to seismic data, reaches 1.5, sometimes 2 km. According to seismic data, the thickness of the gabbro-serpentite (third) layer of the oceanic crust reaches 4.5-5 km. The thickness of the oceanic crust is usually reduced by the ridges of the mid-ocean ridges to 3-4 and even to 2-2.5 km directly under the rift valleys.

The total thickness of the oceanic crust without a sedimentary layer, thus, reaches 6.5-7 km. From below, the oceanic crust is underlain by crystalline rocks of the upper mantle, which form the subcrustal sections of the lithospheric plates. Beneath the crests of the mid-ocean ridges, the oceanic crust overlies directly above the chambers of basalt melts released from the hot mantle material (from the asthenosphere).

The area of ​​the oceanic crust is approximately equal to 306 million km 2, the average density of the oceanic crust (without precipitation) is close to 2.9 g / cm 3, therefore, the mass of the consolidated oceanic crust can be estimated as (5.8-6.2) 1024 g. The volume and mass of the sedimentary layer in the deep-water basins of the world ocean, according to A.P. Lisitsyn, is respectively 133 million km 3 and about 0.1 1024 g. The volume of precipitation concentrated on the shelves and continental slopes is somewhat larger - about 190 million km 3, which, in terms of mass (taking into account the compaction of sediments), is approximately

(0.4-0.45) 1024 g.

The oceanic crust is formed in the rift zones of the mid-ocean ridges due to the separation of basalt melts from the hot mantle (from the asthenospheric layer of the Earth) occurring under them and their outpouring onto the surface of the ocean floor. Every year, in these zones, it rises from the asthenosphere, pours out onto the ocean floor and crystallizes at least 5.5-6 km 3 of basalt melts, which form the entire second layer of the oceanic crust (taking into account the gabbro layer, the volume of melts introduced into the crust increases to 12 km 3) . These grandiose tectonomagmatic processes, constantly developing under the crests of the mid-ocean ridges, are unparalleled on land and are accompanied by increased seismicity.

In rift zones located on the crests of mid-ocean ridges, the ocean floor is stretched and pushed apart. Therefore, all such zones are marked by frequent, but shallow-focus earthquakes with the dominance of discontinuous displacement mechanisms. In contrast, under island arcs and active continental margins, i.e. in zones of plate underthrust, stronger earthquakes usually occur with the dominance of compression and shear mechanisms. According to seismic data,

subsidence of the oceanic crust and lithosphere can be traced in the upper mantle and mesosphere to depths of about 600-700 km. According to tomography data, the subsidence of oceanic lithospheric plates has been traced to depths of about 1400-1500 km and, possibly, deeper - up to the surface of the earth's core.

The ocean floor has characteristic and rather contrasting banded magnetic anomalies, usually located parallel to the mid-ocean ridges (Fig. 7.8). The origin of these anomalies is associated with the ability of ocean floor basalts to be magnetized by the Earth's magnetic field during cooling, thereby remembering the direction of this field at the time of their outpouring onto the surface of the ocean floor.

The “conveyor” mechanism of ocean floor renewal with the constant subsidence of older sections of the oceanic crust and sediments accumulated on it into the mantle under island arcs explains why during the life of the Earth, oceanic depressions did not have time to be covered with sediments. Indeed, at the current rate of backfilling of oceanic depressions with terrigenous sediments carried from the land of 2.2 1016 g/year, the entire volume of these depressions, approximately equal to 1.37 1024 cm 3, would be completely filled up in approximately 1.2 billion years. Now it can be stated with great confidence that the continents and ocean basins have existed together for about 3.8 billion years and no significant backfilling of their depressions has occurred during this time. Moreover, after drilling in all oceans, we now know for certain that there are no sediments older than 160-190 Ma on the ocean floor. But this can be observed only in one case - in the case of the existence of an effective mechanism for removing sediment from the oceans. This mechanism, as is now known, is the process of dragging sediments under island arcs and active continental margins in the zones of plate movement.

continental crust

The continental crust, both in composition and structure, differs sharply from the oceanic. Its thickness varies from 20-25 km under island arcs and areas with a transitional type of crust to 80 km under the young folded belts of the Earth, for example, under the Andes or the Alpine-Himalayan belt. On average, the thickness of the continental crust under the ancient platforms is approximately 40 km, and its mass, including the subcontinental crust, reaches 2.25 1025 g. The relief of the continental crust is also characterized by maximum height differences, reaching 16-17 km from the foot of the continental slopes in deep-water trenches to the highest mountain peaks.

The structure of the continental crust is very heterogeneous, however, as in the oceanic crust, in its thickness, especially in ancient platforms, three layers are sometimes distinguished: the upper sedimentary and two lower layers composed of crystalline rocks. Under the young mobile belts, the structure of the crust is more complex, although its general dissection approaches two layers.

The thickness of the upper sedimentary layer of the continental crust varies widely - from zero on ancient shields to 10-12 and even 15 km on the passive margins of the continents and in the marginal foredeep of the platforms. The average thickness of sediments on stable Proterozoic platforms is usually close to 2-3 km. The sediments on such platforms are dominated by clay deposits and carbonates from shallow marine basins.

The upper part of the section of the consolidated continental crust is usually represented by ancient, mainly Precambrian rocks. Sometimes this part of the section of the hard crust is called the "granitic" layer, thereby emphasizing the predominance of rocks of the granitoid series in it and the subordination of basaltoids.

In deeper parts of the crust (approximately at depths of about 15-20 km), a scattered and unstable boundary is often traced, along which the propagation velocity of longitudinal waves increases by about 0.5 km/s. This so-called

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- border of Mohorovichich;

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 wedged 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 troughs of mountain structures.

2 - oh - medium "granite-gneiss" or "granite" - 50% granite and 40% gneiss 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", in composition close to basalt. Power from 15 - 20 to 35 km. The boundary between the "granite" and "basalt" layers is the Konrad 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 is from several hundred meters to 1 km.

2nd layer - basalts with interlayers of carbonate and siliceous rocks. Thickness is from 1 - 1.5 to 2.5 - 3 km.

The 3rd layer is the lower one, it has not been exposed by drilling. It is composed of basic igneous rocks of the gabrro type with subordinate, ultrabasic rocks (serpentinites, pyroxenites).

The subcontinental type of the earth's surface is similar in structure to the continental type, 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.

3rd layer - "basalt", at depths of 8 - 15 km., with a thickness of 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, Japanese, Mediterranean, Black, etc.). It is similar in structure to the oceanic, but is distinguished by an increased thickness of the sedimentary layer.

1st upper - 4 - 10 km or more, 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. by increasing the sediment layer.

A peculiar structure of the earth's crust is noted in the central rift zones of the mid-ocean ridges (mid-Atlantic). Here, under the second oceanic layer, there is a lens (or ledge) of low-velocity matter (V = 7.4 - 7.8 km / s). It is assumed that this is either a protrusion of an abnormally heated mantle, or a mixture of crustal and mantle matter.

The structure of the earth's crust

On the surface of the Earth, on the continents in different places, rocks of different ages are found.

Some areas of the continents are composed on the surface of the most ancient rocks of the Archean (AR) and Proterozoic (PT) age. They are highly metamorphosed: clays have turned into metamorphic schists, sandstones into crystalline quartzites, limestones into marbles. Among them are many granites. 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 mostly younger rocks - Paleozoic, Mesozoic, Cenozoic (Pz, Mz, Kz) age. These are mainly sedimentary rocks, although among them there are also rocks of igneous origin, which have erupted on the surface in the form of volcanic lava or have intruded and solidified at a certain depth. There are two categories of land areas: 1) platforms - plains: layers of sedimentary rocks lie quietly, almost horizontally, rare and small folds are observed in them. There are very few igneous, especially intrusive, rocks in such rocks; 2) folded zones (geosynclines) - mountains: sedimentary rocks are strongly crumpled into folds, riddled with deep cracks; igneous rocks intruded or erupted on the surface are often encountered. Differences between platforms or folded zones lie in the age of the lying or crumpled rocks. Therefore, platforms are old and young. Saying that the platforms could have been formed at different times, we thereby indicate a different age of the fold 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 that illuminate 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 the continents and oceans. It is larger under mountains and plains, thinner under oceanic islands and oceans. Therefore, two main types of the earth's crust are distinguished - continental (continental) and oceanic.

The average thickness of the continental crust is 42 km. But in the mountains it increases to 50-60 and even up to 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 are, as it were, superfluous heaps of masses. But these masses would have to create a stronger attraction, and in the oceans, where the attracting body is lighter water, gravity would have to weaken. But in reality there are no such differences. The force of gravity everywhere on the continents and oceans is approximately the same. Hence the conclusion is drawn: the continental and oceanic masses are balanced. They obey the law of isostasy (balance), which reads as follows: additional masses on the surface of the continents correspond to a lack of masses at depth, and vice versa - some heavy masses at depth must correspond to a lack of masses on the surface of the oceans.

Plan

1. Earth's crust (continental, oceanic, transitional).

2. The main components of the earth's crust are chemical elements, minerals, rocks, geological bodies.

3. Fundamentals of the classification of igneous rocks.

Earth's crust (continental, oceanic, transitional)

Based on the data of deep seismic soundings, a number of layers are distinguished in the thickness of the earth's crust, characterized by different rates of passage of elastic vibrations. Of these layers, three are considered basic. The uppermost of them is known as a sedimentary shell, the middle one is granite-metamorphic, and the lower one is basalt (Fig.).

Rice. . Diagram of the structure of the crust and upper mantle, including the solid lithosphere

and plastic asthenosphere

Sedimentary layer It is composed mainly of the softest, loose and denser (due to cementation of loose) rocks. Sedimentary rocks are usually arranged in layers. The thickness of the sedimentary layer on the Earth's surface is very variable and varies from a few meters to 10-15 km. There are areas where the sedimentary layer is completely absent.

Granite-metamorphic layer It is composed mainly of igneous and metamorphic rocks rich in aluminum and silicon. Places where there is no sedimentary layer and the granite layer comes to the surface are called crystal shields(Kola, Anabar, Aldan, etc.). The thickness of the granite layer is 20-40 km, in some places this layer is absent (at the bottom of the Pacific Ocean). According to the study of the speed of seismic waves, the density of rocks at the lower boundary from 6.5 km/sec to 7.0 km/sec changes dramatically. This boundary of the granite layer, which separates the granite layer from the basalt layer, is called Conrad borders.

Basalt layer stands out at the base of the earth's crust, is present everywhere, its thickness varies from 5 to 30 km. The density of matter in the basalt layer is 3.32 g/cm 3 , it differs in composition from granites and is characterized by a much lower silica content. At the lower boundary of the layer, there is an abrupt change in the velocity of the passage of longitudinal waves, which indicates a sharp change in the properties of the rocks. This boundary is taken as the lower boundary of the earth's crust and is called the Mohorovichic boundary, as discussed above.

In various parts of the globe, the earth's crust is heterogeneous both in composition and thickness. Types of the earth's crust - mainland or continental, oceanic and transitional. The oceanic crust occupies about 60%, and the continental crust about 40% of the earth's surface, which differs from the distribution of the areas of the oceans and land (71% and 29%, respectively). This is due to the fact that the boundary between the types of crust under consideration runs along the continental foot. Shallow seas, such as, for example, the Baltic and Arctic seas of Russia, belong to the World Ocean only from a geographical point of view. In the area of ​​the oceans, they distinguish ocean type, characterized by a thin sedimentary layer, under which there is a basalt layer. Moreover, the oceanic crust is much younger than the continental one - the age of the first is no more than 180 - 200 million years. The crust under the continent contains all 3 layers, has a large thickness (40-50 km) and is called mainland. The transitional crust corresponds to the underwater margin of the continents. In contrast to the continental, the granite layer is sharply reduced here and disappears into the ocean, and then the thickness of the basalt layer also decreases.

Sedimentary, granite-metamorphic and basalt layers together form a shell, which received the name sial - from the words silicium and aluminum. It is usually believed that in the sialic shell it is expedient to identify the concept of the earth's crust. It has also been established that throughout the geological history, the earth's crust absorbs oxygen, and by the present it consists of 91% of it by volume.

The main components of the earth's crust are chemical elements, minerals, rocks, geological bodies

The substance of the Earth consists of chemical elements. Within the stone shell, chemical elements form minerals, minerals form rocks, and rocks, in turn, form geological bodies. Our knowledge of the chemistry of the Earth, or otherwise geochemistry, catastrophically decreases with depth. Deeper than 15 km, our knowledge is gradually replaced by hypotheses.

American chemist F.W. Clark together with G.S. Washington, having begun analysis of various rocks (5159 samples) at the beginning of the last century, published data on the average contents of about ten of the most common elements in the earth's crust. Frank Clark proceeded from the position that the solid earth's crust to a depth of 16 km consists of 95% of igneous rocks and 5% of sedimentary rocks formed due to igneous rocks. Therefore, for the calculation, F. Clark used 6000 analyzes of various rocks, taking their arithmetic mean. Subsequently, these data were supplemented by average data on the contents of other elements. It turned out that the most common elements of the earth's crust are (wt.%): O - 47.2; Si - 27.6; Al - 8.8; Fe - 5.1; Ca - 3.6; Na, 2.64; Mg - 2.1; K - 1.4; H - 0.15, which is 99.79% in total. These elements (except hydrogen), as well as carbon, phosphorus, chlorine, fluorine, and some others, are called rock-forming or petrogenic.

Subsequently, these figures were repeatedly specified by various authors (Table).

Comparison of various estimates of the composition of the earth's crust of the continents,

The average mass fractions of chemical elements in the earth's crust were named at the suggestion of Academician A. E. Fersman clarks. The latest data on the chemical composition of the Earth's spheres are summarized in the following scheme (Fig.).

All matter of the earth's crust and mantle consists of minerals, diverse in form, structure, composition, abundance and properties. Currently, more than 4000 minerals have been isolated. It is impossible to give an exact figure because every year the number of mineral species is replenished with 50-70 names of mineral species. For example, about 550 minerals have been discovered on the territory of the former USSR (320 species are stored in the A.E. Fersman Museum), more than 90% of them in the 20th century.

The mineral composition of the earth's crust is as follows (vol.%): feldspars - 43.1; pyroxenes - 16.5; olivine - 6.4; amphiboles - 5.1; mica - 3.1; clay minerals - 3.0; orthosilicates - 1.3; chlorites, serpentines - 0.4; quartz - 11.5; cristobalite - 0.02; tridymite - 0.01; carbonates - 2.5; ore minerals - 1.5; phosphates - 1.4; sulfates - 0.05; iron hydroxides - 0.18; others - 0.06; organic matter - 0.04; chlorides - 0.04.

These figures are, of course, very relative. In general, the mineral composition of the earth's crust is the most varied and rich in comparison with the composition of deeper geospheres and meteorites, the substance of the Moon and the outer shells of other terrestrial planets. So, 85 minerals were found on the moon, and 175 in meteorites.

Natural mineral aggregates that make up independent geological bodies in the earth's crust are called rocks. The concept of "geological body" is a multi-scale concept, it includes volumes from a mineral crystal to continents. Each rock forms a three-dimensional body in the earth's crust (layer, lens, array, cover ...), characterized by a certain material composition and a specific internal structure.

The term "rock" was introduced into Russian geological literature at the end of the 18th century by Vasily Mikhailovich Severgin. The study of the earth's crust has shown that it is composed of various rocks, which by origin can be divided into 3 groups: igneous or igneous, sedimentary and metamorphic.

Before proceeding to the description of each of the groups of rocks separately, it is necessary to dwell on their historical relationships.

It is generally accepted that the original globe was a molten body. From this primary melt or magma, the solid earth's crust was formed by cooling, at the beginning it was composed entirely of igneous rocks, which should be considered as the historically most ancient group of rocks.

Only in a later phase of the development of the Earth could rocks of a different origin arise. This became possible after the emergence of all its outer shells: the atmosphere, hydrosphere, biosphere. Primary igneous rocks under their influence and solar energy were destroyed, the destroyed material was moved by water and wind, sorted and cemented again. This is how sedimentary rocks arose, which are secondary to igneous rocks, due to which they were formed.

Both igneous and sedimentary rocks served as the material for the formation of metamorphic rocks. As a result of various geological processes, large areas of the earth's crust were lowered, and sedimentary rocks accumulated within these areas. In the course of these subsidences, the lower parts of the sequence fall to ever greater depths into the region of high temperatures and pressures, into the region of penetration of various vapors and gases from the magma and circulation of hot water solutions, introducing new chemical elements into the rocks. The result of this is metamorphism.

The distribution of these breeds is not the same. It is estimated that the lithosphere is 95% composed of igneous and metamorphic rocks and only 5% is sedimentary rocks. On the surface, the distribution is somewhat different. Sedimentary rocks cover 75% of the earth's surface and only 25% are igneous and metamorphic rocks.

Types of the Earth's crust: oceanic, continental

The Earth's crust (the solid shell of the Earth above the mantle) consists of two types of crust and has two types of structure: continental and oceanic. The division of the Earth's lithosphere into the crust and upper mantle is rather conditional; the terms oceanic and continental lithosphere are often used.

Earth's continental crust

The continental crust of the Earth (the continental crust, the earth's crust of the continents) which consists of sedimentary, granite and basalt layers. The earth's crust of the continents has an average thickness of 35-45 km, the maximum thickness is up to 75 km (under mountain ranges).

The structure of the continental crust "American-style" is somewhat different. It contains layers of igneous, sedimentary and metamorphic rocks.

The continental crust has another name "sial" - because. granites and some other rocks contain silicon and aluminum - hence the origin of the term sial: silicon and aluminum, SiAl.

The average density of the crust of the continents is 2.6-2.7 g / cm³.

Gneiss is a (usually loose layered structure) metamorphic rock, composed of plagioclase, quartz, potassium feldspar, and the like.

Granite is "an acidic igneous intrusive rock. It consists of quartz, plagioclase, potassium feldspar and micas" (article "Granite", link - at the bottom of the page). Granites consist of feldspars, quartz. Granites have not been found on other bodies of the solar system.

Oceanic crust of the Earth

As far as is known, no granitic layer has been found in the Earth's crust at the bottom of the oceans; the sedimentary layer of the crust lies immediately on the basaltic layer. The oceanic type of crust is also called "sima", the rocks are dominated by silicon and magnesium - similar to sial, MgSi.

The thickness of the oceanic-type crust (thickness) is less than 10 kilometers, usually 3-7 kilometers. The average density of the sub-oceanic crust is about 3.3 g/cm³.

It is believed that the oceanic is formed in the mid-ocean ridges and absorbed in subduction zones (why, it is not very clear) - as a kind of transporter from the growth line in the mid-ocean ridge to the continent.

8. structure of minerals and mineral aggregates. Genetic types of minerals. Bowen's reaction series. Polymorphism and isomorphism. Paragenesis of minerals. Pseudomorphism of minerals
A mineral is a natural substance consisting of one element or a regular combination of elements, formed as a result of natural processes occurring in the depths of the earth's crust or on the surface. Each mineral has a specific structure and has its own physical and chemical characteristics.
Reaction series (Bowen)
- Empirically established by Bowen, the sequence of crystallization of minerals from magma in the form of two reaction series:
1. a discontinuous series of femic minerals: olivine -> orthorhombic pyroxene -> monoclinic pyroxene -> amphibole -> biotite;
2. a continuous series of salic minerals: basic plagioclase -> medium plagioclase -> acid plagioclase -> potassium feldspar. Joint crystallization of minerals of two rows proceeds with the formation of a eutectic, and in this case the sequence of separation depends on the composition of the melt. The reaction series of crystallization of minerals proposed by Bowen may be violated depending on the composition of the melt, on temperature, pressure, and others. conditions.

9. Physical properties of minerals. The chemical composition of minerals
Color. For most minerals, the color changes depending on various impurities.
Line color. This is the color of the mineral in powder. The fact is that not all minerals in a piece and in powder have the same color. In order to obtain a powder, it is enough to draw a mineral over the unglazed surface of a porcelain plate. The color of the line is given only by those minerals whose hardness is lower than the hardness of a porcelain plate.
Transparency. According to the degree of transparency, minerals are divided into groups: (transparent lamellar gypsum, muscovite, halite), through which objects are clearly visible; translucent through which only the contours of objects are visible; translucent, which transmit light, and the contours of objects are indistinguishable; opaque, through which light cannot pass.
Shine. Distinguish between metallic and non-metallic luster.
Cleavage. Cleavage is understood as the ability of a mineral to split in certain directions, forming even or mirror-smooth shiny cleavage planes. There are several types of cleavage: very perfect, perfect, medium or clear and imperfect.
kink- this is the type of surface formed when the mineral is broken. A fracture can be: 1) even - most often in minerals with perfect cleavage (calcite, halite); 2) uneven - characterized by an uneven surface without shiny, jointed areas (apatite); 3) splintery - characteristic of fibrous minerals (fibrous gypsum, hornblende); 4) granular - inherent in minerals of a granular structure (olivine); 5) conchoidal - very characteristic of silicon oxide minerals (quartz, chalcedony, opal); 6) hooked (malachite, native copper); 7) earthy (kaolin, phosphorite).
Hardness. Hardness refers to the resistance that a mineral provides to another mineral or body that crashes into it. This is the most important feature, as it is the most constant.
Density. In the field, minerals are divided into three groups by density: light (up to 2.5), medium (2.5 - 4.0) and heavy (more than 4). The lungs include gypsum, graphite, opal, halite; to medium - quartz, corundum, limonite, calcite, magnesite; to heavy - pyrite, chalcopyrite, magnesite, gold, silver. The most common is the group of minerals of medium specific gravity.
Taste.
0 optical properties. Birefringence has a variety of calcite - Icelandic spar, Labrador has a blue tint on the cleavage planes.
The basis for the classification of minerals is the chemical composition of minerals. On this basis, such classes of minerals are distinguished - Silicates - Oxides - Hydroxides (hydroxides) - Carbonates - Sulfates - Sulfides - Phosphates - Halides - Native elements - Organic compounds

10. The most important diagnostic signs of minerals
The most important characteristics of minerals are their crystal structure and chemical composition. All other properties of minerals follow from them or are interconnected with them. The main properties of minerals that are diagnostic features and allow them to be determined are as follows:
-Crystal Shape and the shape of the faces - are primarily due to the structure of the crystal lattice.
-Hardness. Determined by the Mohs scale
-Shine- the light effect caused by the reflection of part of the light flux incident on the mineral. Depends on the reflectivity of the mineral.
-Cleavage- the ability of a mineral to split along certain crystallographic directions.
-kink- the specificity of the surface of the mineral on a fresh non-cleavage chip.
-Color- a sign that definitely characterizes some minerals (green malachite, blue lapis lazuli, red cinnabar), and is very misleading in a number of other minerals, the color of which can vary over a wide range depending on the presence of impurities of chromophore elements or specific defects in the crystal structure (fluorites , quartz, tourmaline).
-Dash color- the color of a mineral in a fine powder, usually determined by scratching the rough surface of a porcelain biscuit.
magnetism- depends on the content mainly of ferrous iron, is detected using a conventional magnet.
discoloration- a thin colored or multi-colored film that forms on the weathered surface of some minerals due to oxidation.
fragility- the strength of mineral grains (crystals), which is found during mechanical splitting. Fragility is sometimes linked or confused with hardness, which is incorrect. Other very hard minerals can easily split, i.e. be fragile (like a diamond)
These properties of minerals are easily determined in the field.

11. Rock-forming and ore-forming mineral
Rock-forming minerals- these are the constituent parts of rocks that differ from each other in chemical composition and physical properties.
Among the rock-forming minerals are:
-Characteristic, typomorphic minarals, having exclusively igneous, sedimentary or metamorphic origin.
- Minerals formed during various geological processes and found in rocks of any genesis.
The minerals contained in the composition of rocks are divided into rock-forming and secondary. The first, approximately 40 ... 50 minerals, are involved in the formation of rocks and determine their properties; minor ones are found in them only in the form of impurities. Among the rock-forming are primary and secondary.
The primary ones arose during the formation of rocks, the secondary ones - later as products of the modification of primary minerals.
Minerals have a number of characteristic properties that have a great influence on the technical properties of rocks, among which hardness, cleavage, fracture, luster, color, and density should be highlighted. These properties depend on the structure and strength of bonds in the crystal lattice.
An ore mineral is a mineral containing a metal. Only a few metals are found in elemental form in the native state. Mostly gold, platinum and silver. But the vast majority of metals are found in minerals in combination with other chemical elements. This is observed in sulfides: galena - an ore for lead, zinc, mercury, copper pyrite
- in oxides: hematite, magnetite, pyrolusite, cassiterite, rutile, chromite. They are an important raw material for obtaining metals.
- in carbonates: siderite (ferrous spar) FeCO 3 - ore for iron.
Many ores are complex in nature, as they contain two or more minerals with different metals. Thus, copper ore often contains a certain amount of silver and gold and significant amounts of iron.
Minerals play a very important role in human economic activity. Many minerals have great aesthetic appeal, not only when they are cut like gemstones, but also in their natural form. Collection material.
Many minerals are valuable as ore raw materials. This quality of minerals lies in their chemical composition, since it is the chemical composition that determines which elements can be extracted from a mineral by melting or otherwise destroying its structure. For example, chalcocite, galena and sphalerite (copper, lead and zinc sulfides), cassiterite (tin oxide) and many other minerals have such value.

12. genetic types of rocks, their texture, structure, material composition
According to the genetic classification, rocks are divided into three large groups: 1) igneous (igneous), 2) sedimentary and 3) metamorphic.
1) Igneous rocks formed from molten magma that rose from the depths of the Earth and solidified when it cooled. deep rocks are massive, dense and consist of closely intergrown more or less large crystals; they have high density, high compressive strength and frost resistance, low water absorption and high thermal conductivity. Deep rocks have a granular crystalline structure, also called granite.
- Erupted rocks formed on the surface of the earth in the absence of pressure and with the rapid cooling of magma. in most cases, the erupted rocks consist of individual well-formed crystals interspersed in the main cryptocrystalline mass; such a structure is called porphyritic. In those cases when the outflowing rocks solidified in a thick layer, their structure was similar to deep rocks. If the layer was comparatively thin, then cooling occurred rapidly and their mass turned out to be glassy, ​​and the upper layers of the erupted lava became porous due to the vigorous release of gases from the magma with a decrease in pressure. Clastic rocks were formed during the rapid cooling of crushed lava ejected during volcanic eruptions (pumice, volcanic ash.
2)Sedimentary rocks formed during the deposition of substances from any medium, mainly water. According to the nature of formation and composition, sedimentary rocks are divided into three groups: chemical, organogenic and mechanical.
-Chemical sediments are rocks formed during the precipitation of mineral substances from aqueous solutions with their subsequent compaction and cementation (gypsum, anhydrite, calcareous tuffs, etc.).
-Organogenic rocks were formed as a result of the deposition of the remains of some algae and animal organisms, followed by their compaction and cementation (most limestones, chalk, diatomites, etc.).
-Mechanical deposits formed as a result of sedimentation or accumulation of loose products during the physical and chemical decomposition of rocks. Some of them were further cemented with clay, ferruginous compounds, carbonates or other carbon cements, forming cemented sedimentary rocks - conglomerates, breccias.
3)Metamorphic (species igneous) rocks were formed as a result of more or less deep transformation of igneous or sedimentary rocks under the influence of high temperature and pressure, and sometimes chemical influences.
Under these conditions, recrystallization of minerals can occur without their melting; the resulting rocks are usually denser than the original sedimentary ones. In the process of metamorphism, the structure of rocks changed. In most cases, metamorphic rocks are characterized by a schistose structure.

13. igneous rocks, their classification by chemical and miner. composition, according to the conditions of education. The concept of intrusive, vein and effusive analogues. Structure and texture
The formation of igneous rocks is closely connected with the most complex problems of the origin of magmas and the structure of the Earth.
Depending on the conditions of education
Deep - these are rocks formed during the solidification of magma at different depths in the earth's crust.
- Erupted rocks were formed during volcanic activity, outpouring of magma from the depths and hardening on the surface.
At the heart of chemical classification lies the percentage of silica (SiO 2) in the rock. 1. ultra-acidic, 2. acidic, 3.medium, 4.basic 5.ultrabasic rocks.
Intrusive. The rocks are full-crystalline, with clearly visible crystals. They form batholiths, laccoliths, stocks, sills, and other intrusive bodies.
Effusive. Dense or almost dense porphyritic. Compose lava flows, but also subvolcanic intrusions.
Residential. Porphyritic or finely to microcrystalline. Compose veins, sills, marginal parts of intrusions, small intrusions
Structure- an essential feature that determines the physical and mechanical properties of the rock. The most durable are uniformly granular rocks, while rocks of the same mineral composition, but coarse-grained porphyritic structure, are destroyed faster both under mechanical action and under sharp temperature fluctuations (see Prakt Tetr)
Texture All intrusive rocks have a full-crystalline structure, massive or spotty texture, while effusive rocks have a predominantly glassy, ​​porphyritic, cryptocrystalline structure, massive, slag, amygdaloidal texture.
According to the genetic classification, rocks are divided into three large groups: igneous, sedimentary and metamorphic.

14. sedimentary rocks, their classification by origin and material composition. Structures and texture of sedimentary rocks
sedimentary rock It is formed under conditions of redeposition of weathering products and destruction of various rocks, chemical and mechanical precipitation from water, and plant life.
Origin classification:
1) clastic rocks - products of predominantly physical weathering of parent rocks and minerals with subsequent transfer of material and its deposition in other areas;
2) colloid-sedimentary rocks - the result of predominantly chemical decomposition with the transition of a substance into a colloidal state (colloidal solutions);
3) chemogenic rocks - sediments that fall out of aqueous, mostly true, solutions - the waters of the seas, oceans, lakes and other basins chemically, i.e. as a result of chemical reactions or supersaturation of solutions caused by various reasons;
4) biochemical rocks, including rocks formed in the course of chemical reactions with the participation of microorganisms, and rocks that can have a dual origin: chemical and biogenic;
5) organogenic rocks formed with the participation of living organisms;
Classification by composition, structure (notebook practical).
Texture: -layered - the rock consists of heterogeneous in composition, color, density of layers with more or less well-defined boundaries between them
- porous - rock with an abundance of large holes, caverns, unfilled with secondary minerals

15. metamorphic rocks: mineral composition, structure, texture. Facies of metamorphism
metamorphic rocks- the result of the transformation of rocks of different genesis, leading to a change in the primary structure, texture and mineral composition in accordance with the new physical and chemical environment. The main factors of metamorphism are endogenous heat, all-round pressure, chemical action of gases and fluids. The gradual increase in the intensity of the factors of metamorphism makes it possible to observe all the transitions from primary sedimentary or igneous rocks to the metamorphic rocks formed from them.
STRUCTURE: Metamorphic rocks have a full crystalline structure. The sizes of crystalline grains, as a rule, increase with increasing temperatures of metamorphism.
TEXTURE: - slate texture, due to the mutually parallel arrangement of mineral grains of prismatic or lamellar forms;
- gneissic, or gneissic texture, characterized by alternating strips of different mineral composition;
- in the case of alternating bands consisting of grains of light and colored minerals, the texture is called banded. Externally, these textures resemble the layering of sedimentary rocks, but their origin is not associated with the process of accumulation of sediments, but with recrystallization and reorientation of mineral grains under conditions of oriented pressure. All metamorphic rocks have a dense texture. Since metamorphic rocks similar in composition, structures and textures can be formed due to the change in both igneous and sedimentary rocks,. Facia metamorphism - a set of metamorphic rocks of various compositions that meet certain conditions of formation in relation to the main factors of metamorphism (temperature, lithostatic pressure and partial pressures of volatile components in fluids) involved in metamorphic reactions between minerals .
Types of facies by the name of the main rocks:
1. greenschist and glaucophane shale (low temperature, medium and high pressures); 2. epidote-amphibolite and amphibolite (medium temperature, medium and high pressures); 3. granulite and eclogite (high temperature and pressure); 4. sanidinite and pyroxene hornfelsic (very high temperature and very low pressure).

17. Exogenous processes. Weathering. Exogenous (external) processes occurring on the earth's surface or at shallow depths in the earth's crust are called. These processes are carried out, for example, by flowing waters, glaciers, wind, etc. The activities of these processes include two major types of work: the destruction of rocks and their accumulation (accumulation). The nature of the work performed is determined, on the one hand, by the speed of movement and the mass of the geological agent, and on the other hand, by the nature of the rock formations. So, the higher the speed of movement and the mass of the geological agent, the more active the destruction of rocks and the transportation of debris. With a decrease in velocity, the accumulation process begins, and at the beginning the largest particles settle on the surface, and then smaller ones. The main energy sources of exogenous processes are solar radiation and gravity. Since solar radiation over the earth's surface is distributed zonally and unevenly, its arrival varies according to the seasons of the year, then the activity of external processes is subject to the same laws. The work of external forces leads to such a change in the earth's surface, which is aimed at changing the forms created by internal processes. Ultimately, such a change leads to the redistribution of rocks and the leveling of the relief. That is, the protrusions of land created by internal forces are destroyed and lowered, and the fragments of rocks carried away from them accumulate in the oceans and reduce their depth.
weathering called the totality of processes of physical and chemical destruction of rocks and minerals. An important role is played by living organisms. There are two main types of weathering: physical and chemical. . physical weathering leads to successive crushing of rocks into smaller fragments. It can be divided into two groups of processes: thermal and mechanical weathering. Thermal weathering occurs as a result of sharp diurnal temperature changes, leading to the expansion of rocks when heated and contraction when cooled. Thus, the intensity of destruction of rocks is affected by: the magnitude of the daily temperature difference; mineral composition of rocks; coloring of rocks; the size of the mineral grains that make up the rocks. The most intense temperature weathering occurs on exposed high-mountain peaks and slopes, as well as in the desert zone, where, in conditions of low humidity and lack of vegetation, the daily temperature difference on the surface of rocks can exceed 60 ° C. In this case, the process desquamation(peeling) of rock ledges, expressed in the layer-by-layer separation of scales and rock plates parallel to the surface of the ledge.
mechanical weathering It is carried out by freezing water, as well as living organisms and newly formed mineral crystals. The maximum value of water freezing in the pores and cracks of rocks, which at the same time increases in volume by 9 - 10% and wedges the rock into separate fragments. Such weathering is called frosty. It is most active at frequent (daily) temperature transitions through 0°C, observed in high and temperate latitudes and above the snow line in the mountains. Plant roots, burrowing animals, and mineral crystals growing in the pores and cracks of rocks also have a wedging effect on rocks. chemical weathering leads to a change in the mineral composition of rocks or their complete dissolution. The most important factors here are water, as well as the oxygen, carbonic and organic acids contained in it. The greatest activity of chemical weathering processes is observed in humid and hot climates.
As a result of weathering, a special genetic type of deposits is formed on the earth's surface - eluvium- a layer of loose undisplaced weathering products. The composition and thickness of the eluvium are determined by the composition of primary rocks and the time factor, as well as the nature of weathering processes, which, first of all, depends on the climate. Consequently, seasonal rhythm and latitudinal zonality are observed in the development of weathering processes. weathering bark called the totality of eluvial formations of the upper part of the earth's crust.

Origin of the Earth. As you already know. Earth is a small cosmic body, part of the solar system. How was our planet born? Even scientists of the ancient world tried to answer this question. There are many different hypotheses. You will get acquainted with them when studying astronomy in high school.

From modern views on the origin of the Earth, the most common hypothesis is O. Yu. Schmidt about the formation of the Earth from a cold gas-dust cloud. The particles of this cloud, revolving around the Sun, collided, "stick together", forming clots that grew like a snowball.

There are also hypotheses for the formation of planets as a result of cosmic catastrophes - powerful explosions caused by the decay of stellar matter. Scientists continue to look for new ways to solve the problem of the origin of the Earth.

The structure of the continental and oceanic crust. The earth's crust is the uppermost part of the lithosphere. It is like a thin "veil", under which the restless earth's bowels are hidden. Compared to other geospheres, the earth's crust seems to be a thin film in which the globe is wrapped. On average, the thickness of the earth's crust is only 0.6% of the length of the earth's radius.

The appearance of our planet is determined by the protrusions of the continents and the depressions of the oceans filled with water. To answer the question of how they formed, one must know the differences in the structure of the earth's crust. You can see these differences in Figure 8.

1. What are the three layers that make up the earth's crust?
2. How thick is the crust on the continents? Under the oceans?
3. Highlight two features that distinguish the continental crust from the oceanic.

How to explain the differences in the structure of the earth's crust? Most scientists believe that oceanic-type crust first formed on our planet. Under the influence of processes occurring inside the Earth, folds, i.e., mountainous areas, formed on its surface. The thickness of the crust increased, ledges of the continents formed. There are a number of hypotheses regarding the further development of continents and ocean basins. Some scientists argue that the continents are motionless, while others, on the contrary, speak of their constant movement.

In recent years, a theory of the structure of the earth's crust has been created, based on the concept of lithospheric plates and on the hypothesis of continental drift, created at the beginning of the 20th century. German scientist A. Wegener. However, at that time he could not find an answer to the question of the origin of the forces that move the continents.

Rice. 8. The structure of the earth's crust on the continents and under the oceans

Plates of the lithosphere. According to the theory of lithospheric plates, the earth's crust, together with part of the upper mantle, is not a monolithic shell of the planet. It is broken by a complex network of deep cracks that go to great depths and reach the mantle. These giant cracks divide the lithosphere into several very large blocks (plates) with a thickness of 60 to 100 km. The boundaries between the plates run along the mid-ocean ridges - giant swellings on the body of the planet or along deep-sea trenches - gorges on the ocean floor. There are such cracks and on land. They pass through mountain belts like the Alysh-Himalayan, Ural, etc. These mountain belts are like "seams in the place of healed old wounds on the body of the planet." On land there are also "fresh wounds" - the famous East African faults.

There are seven huge slabs and dozens of smaller slabs. Most plates include both continental and oceanic crust (Fig. 9).

Rice. 9. Plates of the lithosphere

The plates lie on a relatively soft, plastic layer of the mantle, along which they slide. The forces that cause the movement of plates arise when matter moves in the upper mantle (Fig. 10). Powerful upward flows of this substance break the earth's crust, forming deep faults in it. These faults are found on land, but most of them are in the mid-ocean ridges at the bottom of the oceans, where the earth's crust is thinner. Here, molten matter rises from the bowels of the Earth and pushes the plates apart, building up the earth's crust. The edges of the faults move away from each other.

Rice. 10. Proposed movement of lithospheric plates: 1. Atlantic Ocean. 2. Mid-ocean ridge. 3. Immersion of plates in the mantle. 4. Ocean trench. 5. Andes. 6. Rise of matter from the mantle

Plates slowly move from the line of underwater ridges to the lines of trenches at a speed of 1 to 6 cm per year. This fact was established as a result of a comparison of images taken from artificial earth satellites. Neighboring plates approach, diverge or slide one relative to the other (see Fig. 10). They float on the surface of the upper mantle, like pieces of ice on the surface of water.

If plates, one of which has oceanic crust and the other continental crust, approach each other, then the plate covered by the sea bends, as it were, dives under the continent (see Fig. 10). In this case, deep-sea trenches, island arcs, and mountain ranges arise, for example, the Kuril Trench. Japanese islands, Andes. If two plates approach the continental crust, then their edges, together with all the sedimentary rocks accumulated on them, are crushed into folds. This is how the Himalayas were formed, for example, on the border of the Eurasian and Indo-Australian plates.

Rice. 11. Changing the outlines of the continents at different times

According to the theory of lithospheric plates, the Earth once had one continent surrounded by an ocean. Over time, deep faults arose on it and two continents formed - in the Southern Hemisphere Gondwana, and in the Northern Hemisphere - Laurasia (Fig. 11). Subsequently, these continents were also broken by new faults. Formed modern continents and new oceans - the Atlantic and Indian. At the base of modern continents lie the oldest relatively stable and leveled sections of the earth's crust - platforms, that is, plates formed in the distant geological past of the Earth. When the plates collided, mountain structures arose. Some continents have preserved traces of the collision of several plates. Their area gradually increased. So, for example, Eurasia was formed.

The doctrine of lithospheric plates makes it possible to look into the future of the Earth. It is assumed that in about 50 million years the Atlantic and Indian oceans will expand, the Pacific will decrease in size. Africa will move north. Australia will cross the equator and come into contact with Eurasia. However, this is only a forecast that needs to be clarified.

Scientists came to the conclusion that in places of rupture and stretching of the earth's crust in the middle ridges, a new oceanic crust is formed, which gradually spreads in both directions from the deep fault that gave rise to it. At the bottom of the ocean, it's like a giant conveyor belt. It transports young blocks of lithospheric plates from their place of origin to the continental margins of the oceans. The speed of movement is small, the path is long. Therefore, these blocks reach the coast in 15–20 Ma. Having passed this path, the plate descends into a deep-water trench and, “diving” under the continent, plunges into the mantle from which it was formed in the central parts of the median ridges. Thus the circle of life of each lithospheric plate closes.

Map of the structure of the earth's crust. Ancient platforms, folded mountainous areas, the position of mid-ocean ridges, fault zones on land and the ocean floor, ledges of crystalline rocks on the continents are shown on the thematic map "The structure of the earth's crust".

Seismic belts of the Earth. The boundary regions between the lithospheric plates are called seismic belts. These are the most restless mobile areas of the planet. Most active volcanoes are concentrated here, at least 95% of all earthquakes occur. Seismic areas stretched for thousands of kilometers and coincide with areas of deep faults on land, in the ocean - with mid-ocean ridges and deep-sea trenches. There are more than 800 active volcanoes on Earth, spewing a lot of lava, gases and water vapor onto the surface of the planet.

Knowledge of the structure and history of the development of the lithosphere is important for the search for mineral deposits, for making forecasts of natural disasters that are associated with the processes occurring in the lithosphere. It is assumed, for example, that it is at the boundaries of plates that ore minerals are formed, the origin of which is associated with the intrusion of igneous rocks into the earth's crust.

1. What is the structure of the lithosphere? What phenomena occur at the boundaries of its plates?
2. How are seismic belts located on Earth? Tell us about earthquakes and volcanic eruptions known to you from radio and television messages. newspapers. Explain the reasons for these phenomena.
3. How should one work with a map of the structure of the earth's crust?
4. Is it true that the distribution of the continental crust coincides with the land area? 5. Where do you think new oceans could form on Earth in the far future? New continents?