First of all, it is necessary to understand the very concept of "tectonic structure". Tectonic structures mean areas of the earth's crust that are different in structure, composition and formation conditions, the main determining factor in the development of which is tectonic movements along with magmatism and metamorphism.

The main tectonic structure, of course, can be called the earth's crust itself with its structural and compositional features. As mentioned above, the earth's crust is heterogeneous on the globe, it is divided into 4 types, two of which are main - continental and oceanic. Accordingly, the next in rank tectonic structures will be continents and oceans, the characteristic difference between which lies in the structural features of the crust that composes them. The structures that make up the continents and oceans will be of lower rank. The most important of them are platforms, mobile geosynclinal belts, and border areas of ancient platforms and folded belts.

The earth's crust (and lithosphere) reveals regions that are seismic (tectonically active) and aseismic (calm). The inner regions of the continents and the ocean floor - continental and oceanic platforms - are calm. Narrow seismic zones are located between the platforms, which are marked by volcanism, earthquakes, and tectonic movements. These zones correspond to mid-ocean ridges and junctions of island arcs or marginal mountain ranges and deep-sea trenches at the periphery of the ocean.

The following structural elements are distinguished in the oceans:

Mid-ocean ridges are mobile belts with axial rifts of the graben type;

Oceanic platforms are calm areas of abyssal basins with complicating uplifts.

On the continents, the main building blocks are:

Geosynclinal belts

Mountain structures (orogens), which, like mid-ocean ridges, can show tectonic activity;

The platforms are generally tectonically calm vast territories with a thick cover of sedimentary rocks.

A characteristic feature of the structure of narrow graben-like

continental troughs (rifts) is a relatively low speed of propagation of elastic vibrations in the upper mantle: 7.6? 7.8 km / s. This is attributed to the partial melting of the mantle material under the rifts, which in turn indicates an upwelling of hot masses from the upper mantle to the crust base (asthenospheric upwelling). Attention is drawn to the thinning of the earth's crust in rift zones up to 30 35 km, and the decrease in thickness occurs mainly due to the "granite" layer. So, according to VB Sollogub and AV Chekunov, the thickness of the crust of the Ukrainian shield reaches 60 km, the share of the "granite" layer is 25? 30 km. The nearby Dnieper-Donets graben-shaped trough, which is identified with a rift, has an earth's crust no more than 35 km thick, of which 10? 15 km is the "granite" layer. Such a crustal structure exists despite the fact that the Ukrainian Shield experienced prolonged uplift and intense erosion, and the Dnieper-Donets rift - stable subsidence, starting from the Riphean.

Geosynclinal belts are linearly elongated areas of the earth's crust with tectonic processes actively manifested within them. As a rule, the first stages of the birth of the belt are accompanied by subsidence of the crust and the accumulation of sedimentary rocks. The final, proper orogenic stage is the uplift of the crust, accompanied by volcanism and magmatism. Within the geosynclinal belts, anticlinoria, synclinoria, median massifs, intermontane depressions filled with detrital material coming from the molasse mountains are distinguished. Molasses are rich in minerals, including caustobilites. Geosynclinal belts frame and separate ancient platforms. The largest belts are: Pacific, Ural-Okhotsk, Mediterranean, North Atlantic, Arctic. Currently, activity has been preserved in the Pacific and Mediterranean belts.

Mountain-fold areas of continents (orogens) are characterized by

by "swelling" of the crustal thickness. Within their limits, on the one hand, an uplift of the relief is observed, on the other, a deepening of the surface M, i.e. the existence of the roots of the mountains. Subsequently, it was proved that this concept is valid for the mountain-folding areas as a whole, but inside them both roots and anti-roots are observed.

A feature of orogens is also the presence in the lower crust -

the upper mantle of areas of decrease in the velocities of elastic vibrations (less than 8 km / s). In terms of their parameters, these areas are similar to the bodies of the heated mantle in the axial parts of the rifts. Normal mantle velocities in orogens are observed at depths of 50 60 km or more. Another feature of the structure of the orogen crust is an increase in the thickness of the upper layer at a rate of 5.8? 6.3 km / s. It is composed of a metamorphic complex that has undergone an inversion. In some cases, layers of reduced velocities are found in its composition. So, in the Alps, two layers of reduced velocities were revealed, occurring at depths of 10 20 km and 25? 50 km. The velocities of longitudinal waves within their limits are equal, respectively: 5.5? 5.8 km / s and 6 km / s.

Such low velocities (especially near the upper layer) suggest the existence of a liquid phase in the solid crust of the Alps. Thus, the complex of geophysical data indicates

widespread thickening of the crust under continental mountain-folding structures, the existence of lateral heterogeneity within them, the presence of orogens in the crust - special bodies with seismic wave velocities intermediate between the crust and mantle.

The platform is a large geological structure with tectonic stability and stability. By age, they are divided into ancient (Archean and Proterozoic origin) and young, laid down in the Phanerozoic. Ancient platforms are divided into two groups: northern (Lavrasian) and southern (Gondwana). The northern group includes: North American, Russian (or East European), Siberian, Chinese-Korean. The southern group includes the African-Arabian, South American, Australian, Hindustan, Antarctic platforms. Ancient platforms occupy large areas of land (about 40%). Young people make up a much smaller area of the continents (5%); they are located either between the ancients (West Siberian), or along their periphery (East Australian, Central European).

Both ancient and young platforms have a two-layer structure: a crystalline basement composed of deeply metamorphosed rocks (gneisses, crystalline schists) with a large number of granite structures, and a sedimentary cover composed of oceanic and terrigenous sediments, as well as organo-volcanogenic rocks. The part of the ancient platforms that is covered with a cover is called a slab. These areas are generally characterized by a general tendency towards subsidence and sagging of the foundation. Areas of platforms not covered by a sediment cover are called shields and are characterized by an uplift direction. Smaller platform ledges, often covered by the sea, are called massifs. Young platforms differ from the ancients not only in age. Their basement is less metamorphosed, it contains fewer granite intrusions, so it would be more accurate to call it folded. Due to their age, the basement and cover are not sufficiently differentiated in young platforms; therefore, it is rather difficult to define a clear boundary between them, in contrast to ancient platforms. In addition, young platforms are completely covered with a sedimentary cover, shields in their structure are extremely rare, therefore they are usually called simply plates. It was noted that plates are more common on the platforms of the northern row, while shields are more common on the platforms of the southern row.

Within the plates are distinguished: syneclises, anteclises, aulacogens. Syneclises are large gentle basement depressions, anteclises, in turn, are large and gentle basement uplifts. In the areas of syneclises, the thickness of the sedimentary cover is increased, while the tops of the anteclises can protrude to the surface in the form of massifs. Aulacogenes are linear troughs hundreds of kilometers long and tens of kilometers wide, limited by faults. On the slopes of the anteclises and syneclises, tectonic structures of a lower rank are located: placanticline (folds with a very small slope), flexure and domes.

In the border areas, marginal seams, marginal troughs, marginal volcanic belts are distinguished. Edge seams are fault lines along which shields and folded belts are connected. Foredeeps are confined to the boundaries of mobile belts and platforms. Marginal volcanic belts are located along the outskirts of platforms in places where volcanism occurs. They are composed mainly of granite-gneiss and volcanic rocks.

In addition to them, additional tectonic structures have recently been identified: through belts that separate folded bedding of rocks, rift belts similar to aulacogens, but having a greater extent and not containing rocks crumpled into folds in their composition, deep faults.

That. there is a wide variety of tectonic structures, due to their scale, divided into different ranks: from planetary (earth's crust) to local (shields, massifs). In addition to the scale, tectonic structures also differ in shape (uplifted, bent) and in the complex of tectonic processes prevailing in them (uplift, subsidence, volcanism).

earth crust rock

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

Scientific research allows you 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 differ both in composition and in 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 media, 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 Mohorovici 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 red-hot mantle of the Earth. The M boundary lies at the level where the seismic wave velocity increases from 7.4 to 8.0 km / s.

The chemical composition of the Earth

Studying the shells of our planet, scientists have drawn interesting and even startling conclusions. Features of the structure 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, sodium. Combining with each other in various combinations, they form homogeneous physical bodies - minerals. They can enter into the composition of rocks in different concentrations. The structure of the earth's crust is very heterogeneous. So, rocks in generalized form are aggregates of more or less constant chemical composition. These are independent geological bodies. They are understood as a clearly delineated area of the earth's crust, which has the same origin and age within its boundaries.

Rocks by groups

1. Magmatic. The name speaks for itself. They arise from cooled magma flowing from the vents of ancient volcanoes. The structure of these rocks directly depends on the rate of solidification of the lava. The larger it is, the smaller the crystals of the substance. Granite, for example, 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. Considering the structure of the earth's crust, we see that it consists of magmatic minerals by 60%.

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

Detrital. 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 animal or plant remains. These are oil shale, gas, oil, coal, limestone, phosphorites, chalk.

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

Minerals and rocks, which mankind 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 naturally and after being processed.

Types of useful minerals. Their classification

Based on physical condition and aggregation, minerals can be categorized:

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

Characteristics of certain types of minerals

In terms of composition and application, they are distinguished:

Combustible (coal, oil, gas).
Ore. They include radioactive (radium, uranium) and noble metals (silver, gold, platinum). There are ferrous ores (iron, manganese, chromium) and non-ferrous metals (copper, tin, zinc, aluminum).
Non-metallic minerals play an essential role in such a concept as the structure of the earth's crust. Their geography is extensive. 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 across our planet directly depends on external factors and geological patterns.

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

Ore minerals most often correspond to the basement, ledges, and folded regions of platform plates. In such places, they can create huge belts in length.

Core

The earth's shell is known to be 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 have not been obtained, but presumably it consists of nickel and iron.

The outer core is molten and even more powerful than the inner core. The latter is under tremendous pressure. The substances of which it is composed are in a permanent solid state.

Mantle

The Earth's geosphere surrounds the core and makes up about 83 percent of the entire shell 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 it that magma is formed) and into 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 are part of the lithosphere, you need to give some concepts.

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

The 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. This means "stone shell". Its capacity 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 break its boundaries and penetrate the lithosphere. She is the source of volcanism. Here are molten foci of magma, which penetrates the earth's crust and pours out onto the surface. By studying these processes, scientists have been 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 tough, thin and very fragile layer. It is composed of a combination of substances, in which more than 90 chemical elements have been found to date. They are not uniformly distributed. Seven constituents account for 98 percent of the mass of the earth's crust. 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 distinguished.
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 composed of one or more minerals.

The 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 sections can be dated to the Late Jurassic.
Its thickness practically does not change with 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 voluminous areas, it ranges from 5 to 10 kilometers. This type of the 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 uniform. It has several layers.

Sedimentary. It is mainly formed by rocks. Clays and shales prevail here, and carbonate, volcanic and sandy rocks are also widespread. Mineral resources such as gas, oil and coal can be found in sedimentary layers. All of them are of organic origin.
Granite layer. It consists of igneous and metamorphic rocks, which 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.
The basalt layer is formed by rocks close to the mineral of the same name. It is denser than granite.

Depth and change in temperature of the earth's crust

The surface layer is warmed up by the sun's heat. This is a 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 area 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 provides for its presence, and its temperature is determined by the internal heat of the Earth and increases with depth.

The rise in temperature occurs due to the decay of radioactive substances that are part of the rocks. These are primarily radium and uranium.

Geometric gradient - the amount of 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 affect 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.

Crustal and lithosphere structures

When considering the deformations of rocks, which are a consequence (result) of the movements of the earth's crust and lithosphere, it is clear that the Earth is in continuous development. Ancient movements and other geological processes associated with them formed a certain structure of the earth's crust, i.e. geological structures or tectonics of the earth's crust. Modern and partly recent movements continue to change ancient structures, create modern structures, which are often superimposed on the "old" structures.

The term tectonics from Latin means "construction". The term "tectonics" is understood, on the one hand, "the structure of any part of the earth's crust, determined by the totality of tectonic disturbances and the history of their development," and on the other hand, "the doctrine of the structure of the earth's crust, geological structures and the laws of their location and development ... In the latter case, a synonym for the term geotectonics. "

V.P. Gavrilov gives the most optimal concept: "Geological structures are areas of the earth's crust or the lithosphere, which differ from neighboring areas by certain combinations of composition (name and genesis), age, conditions (forms) of occurrence and geophysical parameters of the rocks composing them." Based on this definition, a geological structure can be called a rock layer, a fault, and larger structures of the earth's crust, consisting of a system of elementary structures, ie. it is possible to distinguish geological structures of different levels or ranks: global, regional, local and local. In practice, surveyors performing geological mapping identify local and local structures.

The largest and most global structures of the earth's crust are continents or areas with a continental type of the earth's crust and ocean depressions, or areas with an oceanic type of the earth's crust, as well as areas of their junction, which are often characterized by active modern movements that change and complicate ancient structures (Fig. 38, 39). The builders are developing, first of all, sections of the continents. All continents are based on ancient ( pre-Riphean ) platforms that are surrounded or crossed by mining - folded belts and areas.

Platforms are called large blocks of the earth's crust with a two-tiered (storey) structure. The lower structural level, composed of dislocated complexes of sedimentary, igneous and metamorphic rocks, is called a folded (crystalline) basement (basement, basement), which was formed by the most ancient dislocation movements.

The upper floor is composed of almost horizontally deposited sedimentary rocks of considerable thickness - a sedimentary (platform) cover. It was formed due to younger vertical movements - subsidence and uplift of individual blocks of the basement, which were repeatedly flooded by the sea, due to which they turned out to be covered with alternating layers of sedimentary marine and continental deposits.

For a long time during the formation of the cover, the blocks of the earth's crust within the platforms were characterized by weak seismicity and the absence or rare manifestation of volcanism; therefore, by the nature of the tectonic regime, they belong to relatively stable, rigid and inactive structures of the continental crust. Due to the powerful almost horizontal cover, the platforms are characterized by leveled landforms and slow modern vertical movements. Ancient and young platforms are distinguished depending on the age of the folded basement.

Ancient platforms ( cratons) have a Precambrian, according to some authors even pre-Riphean, basement, covered by sedimentary rocks (deposits) of the Upper Proterozoic (Riphean), Paleozoic, Mesozoic and Cenozoic systems.

For more than 1 billion years, the blocks of ancient platforms were stable and relatively inactive, with a predominance of vertical movements. Ancient platforms (East European, Siberian, Sino-Korean, South China, Tarim, Hindustan, Australian, African, North and South American, East Brazilian and Antarctic) underlie all continents (Fig. 40). The main structures of the ancient platforms are shields and slabs. Shields are positive (relatively elevated), as a rule, isometric in plan, sections of platforms in which the pre-Riphean basement emerges to the surface, and the sedimentary cover is practically absent or has negligible thickness. In the basement, there are Early Archean (White Sea) blocks of granite-gneiss domes, Late Archean-Early Proterozoic (Karelian) folded zones of greenstone belts from metamorphosed greenstone-altered volcanics of basic composition and sedimentary rocks, incl. ferruginous quartzites.

A large area of foundations is covered by a sedimentary cover and is called a slab. . The slabs, in comparison with the shields, represent the lowered sections of the platform. Depending on the depth of the basement and, accordingly, the thickness of the sedimentary cover, anteclises and syneclises, pericratonic troughs and aulacogenes, and other smaller structural elements are distinguished.

Anteclises - areas of slabs, within which the depth of the foundation does not exceed 1 ... 2 km, and in some areas the foundation can go out onto the earth's surface. The thin sedimentary cover has an anticlinal surface bend (Voronezh anteclise).

Syneclises are large, gently sloping isometric or slightly elongated structures within plates, bounded by adjacent shields, anteclises, etc. The depth of the basement and, accordingly, the thickness of sedimentary rocks is more than 3 ... 5 km. The wings have a synclinal curvature of the surfaces (Moscow, Tunguska). The slopes of anteclises and syneclises are usually composed of ramparts (gentle uplifts) and flexures (bends of folds reflecting deep faults - Zhigulevskaya flexure).

The greatest depth of occurrence (up to 10 ... 12 km) of the basement is observed in aulacogenes . Aulacogenes are relatively long (up to several hundred kilometers) and narrow troughs, bounded by faults and filled with thick strata of not only sedimentary, but volcanic rocks (basalts), which makes them similar in structure to rift-type structures. Many aulacogens were reborn into syneclises. Among the smaller structures on the slabs, there are deflections and depressions, arches and ramparts, and salt domes.

Young platforms have a young Archean-Proterozoic-Paleozoic or even Paleozoic-Mesozoic age of the basement rocks and, accordingly, even younger age of the cover rocks - Meso-Cenozoic. The most striking example of a young platform is the West Siberian plate, the sedimentary cover of which is rich in oil and gas deposits. In contrast to the ancient ones, young platforms do not have shields, but are surrounded by mountain-fold belts and areas.

Folded belts fill the gaps between ancient platforms or separate them from the ocean troughs. Within their limits, rocks of various origins are intensively crushed into folds, penetrated by a large number of faults and intrusive bodies, which indicates their formation under conditions of compression and pushing of lithospheric plates. The largest fold belts include the Ural-Mongolian (Okhotsk), North Atlantic, Arctic, Pacific (often subdivided into East and West Pacific) and Mediterranean. They all originated at the end of the Proterozoic. The first three belts completed their development by the end of the Paleozoic, i.e. they have existed as folded belts for more than 250 ... 260 million years. During this time, within their limits, not dislocation horizontal, but vertical, relatively slow motions prevail. The last two belts, the Pacific and Mediterranean, continue their development, expressed in the manifestation of earthquakes and volcanism.

In the fold belts, fold areas are distinguished, which were formed in the place of sharply differentiated and mobile areas of the geological past, i.e. where there were probably both spreading and subduction processes or other tectonic movements characteristic of modern areas. Folded regions are distinguished from each other by the time of formation of their constituent structures and by the age of rocks, which are crumpled into folds, penetrated by faults and intrusions. On survey maps of the structure of the earth's crust, the following areas are usually distinguished: Baikal folding, formed in the Late Proterozoic; Caledonian - in the early Paleozoic; Hercynian or Variscian - on the border of the Carboniferous and Permian; Cimmerian or Laramian - in the Late Jurassic and Cretaceous; alpine - at the end of the Paleogene, Cenozoic - in the middle of the Miocene. Separate sections of mobile belts, in which the formation of the main folded structures continues (seismofocal zones of deep-focus earthquakes), are considered by many scientists as modern geosynclinal regions. . Thus, the concepts of geosyncline and vergent boundaries, especially the Wadati-Zavaritsky-Benioff zone, are used for the same structures (areas) of the earth's crust. Only the concept of geosynclinal is used, as a rule, for ancient folded regions and belts by supporters of the geosynclinal theory (fixism), according to which vertical movements played a leading role in the formation of folded regions. The second concept is used by supporters of the theory of the movement of lithospheric plates (mobilism) for convergent boundaries, on which horizontal movements prevail under compression, leading to the formation of faults, folds and, as a consequence, the uplift of the earth's crust, i.e. modern developing areas of folding.

Geosyncline is the name of the most active mobile areas of the earth's crust. They are located between the platforms and represent, as it were, their movable joints. Geosynclines are characterized by tectonic movements of various sizes, earthquakes, volcanism, and folding. In the zone of geosynclines, there is an intensive accumulation of thick strata of sedimentary rocks. About 72% of the total mass of sedimentary rocks are confined to them, and only 28% on the platforms. The development of the geosyncline ends with the formation of folding, i.e. areas with intense crushing of rocks into folds, active ruptured dislocations and, as a consequence, ascending vertical tectonic movements. This process is called orogeny (mountain building) and leads to the dissection of the relief. This is how mountain ranges and intermountain depressions - mountainous countries - arise.

Anticlinoria, synclinoria, foredeeps and other smaller structures are distinguished within the mountain-folded areas. A distinctive feature of the structure of anticlinoria is that in their cores (axial parts) lie the most ancient or intrusive (deep) igneous rocks, which are replaced by "younger" rocks to the periphery of the structures. The axial parts of the synclinoria are composed of "younger" rocks. For example, in the cores of the anticlinoria of the Ural mountain-folded Hercynian (Paleozoic) region, Archean-Proterozoic metamorphic rocks or intrusive rocks are exposed. In particular, the cores of the East Ural anticlinorium are composed of granitoids, therefore it is sometimes called the anticlinorium of granite intrusions. In the synclinoria of this area, as a rule, Devonian-Carboniferous sedimentary-volcanogenic rocks are metamorphosed to varying degrees; in the edge deflection - thick strata of the "youngest" Paleozoic - Permian, rocks. At the end of the Paleozoic (about 250 ... 260 million years ago), when the Ural mountain-fold area was formed, high ridges existed in the place of anticlinoria, and in the place of synclinoria and foredeep there were depressions-troughs. In the mountains, where rocks are exposed on the earth's surface, exogenous processes are activated: weathering, denudation and erosion. River streams cut and cut the ascending region into ridges and valleys. A new geological stage begins - the platform stage.

Thus, the structural elements of the earth's crust - geological structures, of different levels (ranks) have a certain development and structural features, expressed in a combination of various rocks, conditions (forms) of their occurrence, age, and also affect the shape of the earth's surface - relief. In this regard, civil engineers, when preparing various design materials and during the construction, operation of structures, especially roads, pipelines and other highways, must take into account the peculiarities of the movement and structure of the earth's crust and lithosphere.

Tectonic movements of the earth's crust

The fact that the surface of the Earth is never at rest was already known to the ancient Greeks and the inhabitants of the Scandinavian Peninsula. They guessed that the Earth was going up and down. The proof of this was the ancient coastal settlements, which found themselves in a few centuries far from the sea. The reason for this is tectonic movements that are located in the depths of the Earth.

Definition 1

Tectonic movements- these are mechanical movements within the earth's crust, as a result of which it changes its structure.

The types of tectonic movements were first identified in $ 1758. M.V. Lomonosov... In his work " About the layers of the earth"($ 1763) he defines them.

Remark 1

As a result of tectonic movements, the deformation of the earth's surface occurs - its shape changes, the occurrence of rocks is disturbed, mountain building processes occur, earthquakes, volcanism, and deep ore formation occur. The nature and intensity of destruction of the Earth's surface, sedimentation, the distribution of land and sea also depend on these movements.

The distribution of ocean transgressions and regressions, the total thickness of sedimentary deposits and the distribution of their facies, and clastic material carried away in the depression are indicators of the tectonic movements of the geological past. They have a certain periodicity, expressed in changes in sign and (or) speed over time.

Tectonic movements in speed can be fast and slow (secular), flowing constantly. Earthquakes, for example, are classified as fast tectonic movements. There is a short-term but significant impact on tectonic structures. Slow motions are insignificant in strength, but in time they are stretched over many millions of years.

The types of tectonic movements are considered according to the signs:

Direction of movement;
The intensity of the impact;
The depth and scale of their manifestation;
Time of manifestation.

Tectonic movements of the earth's crust can be vertical and horizontal.

Tectonic structures of the earth's crust

Definition 2

Tectonic structures- These are huge areas of the earth's crust, limited by deep faults, differing in structure, composition and formation conditions.

The most important tectonic structures are platforms and geosynclinal belts.

Definition 3

Platforms Are stable and stable areas of the earth's crust.

By age, the platforms can be ancient and young, called plates. The ancients occupy about $ 40 \% $ of land, and the area of young platforms is much smaller. The structure of both platforms is two-layer - the crystalline basement and the sedimentary cover.

Specialists within the slabs distinguish between:

Syneclises are large gentle basement depressions;
Anteclises are large and gentle basement uplifts;
Aulacogenes are linear troughs limited by faults.

Definition 4

Geosynclinal belts- are elongated areas of the earth's crust with actively manifested tectonic processes.

Within these belts, there are:

Anticlinorium is a complex complex of folds of the earth's crust;
Synclinorium is a complex form of folded dislocations of the layers of the earth's crust.

In addition to geosynclinal belts and platforms, there are other tectonic structures - through belts, rift belts, deep faults.

Types of tectonic movements

Modern geology distinguishes two main types of tectonic movements - epeirogenic (oscillatory) and orogenic (folded).

Epeirogenic or slow secular uplifts and subsidence of the earth's crust do not change the primary bedding of the strata. They are oscillatory and reversible. This means that raising can be replaced by lowering.

The result of these movements is:

Changing the boundaries of land and sea;
Accumulation of sediments in the sea and destruction of the adjacent part of the land.

Distinguish among them the following movements:

Modern at a rate of $ 1-2 $ cm per year;
Neotectonic at a rate from $ 1 $ cm per year to $ 1 $ mm per year;
Ancient slow vertical movement at a rate of $ 0.001 mm per year.

Orogenic movements occur in two directions - horizontal and vertical. When moving horizontally, rocks are crushed into folds. With vertical movement, the folding area rises, and mountain structures arise.

Remark 2

Horizontal movements are the main, because there is a displacement of large areas of the earth's crust relative to each other. Convection heat fluxes in the asthenosphere and upper mantle are considered factors these movements, and the duration and constancy in time - their features... As a result of horizontal movements, first order structures- continents, oceans, planetary faults. To formations second order include platforms and geosynclines.

Tectonic disturbances

Lava flows and sedimentary rocks initially occur in horizontal layers, but such layers are rare. On the walls of quarries and high cliffs, it can be seen that the layers are most often inclined or fragmented - these are tectonic disturbances... They are folded and bursting. Anticlinal and synclinal folds are distinguished.

Definition 5

Anticlines- these are layers of rocks, convex upward. Synclines- these are layers of rocks with a bulge facing down.

In addition to folded faults, there are tectonic ruptures that form when large fractures split the rock into blocks. These blocks move relative to each other along the cracks and form fractured structures. These violations occur during intense squeezing or stretching of rocks. In the process of stretching rocks, reverse faults or thrusts occur, and at the place of rupture, the earth's crust shrinks. Fractures can form certain structures, or they can occur singly. Examples of such violations are horsts and grabens.

Definition 6

Horst Is a raised block of rocks between two faults. Graben Is a submerged block of rocks between two faults.

Cracks can appear in the continuous layers of the earth's crust even without moving blocks, which is the result of any stresses during the movement of the crust. In rocks where cracks appear, weakened zones appear that are amenable to weathering.

Cracks can be:

Shrinkage and compaction cracks - dewatering of rocks;
Cooling cracks typical of igneous lavas;
Cracks parallel to the contacts of the intrusion.

They indicate that on our planet many hundreds of millions of years ago, both rigid and inactive blocks - platforms and shields, and mobile mountain belts, which are often called geosynclinal, were formed. These include both huge, framing seas and whole ones. In the XX century. these scientific ideas were supplemented with new data, among which, first of all, the discovery of mid-ocean ridges and oceanic basins should be called.

The most stable areas of the earth's crust are platforms. Their area is many thousands and even millions of square kilometers. Once they were mobile, but over time they turned into rigid arrays. Platforms usually have two floors. The lower floor is built from ancient crystalline rocks, the upper one from younger ones. The rocks on the lower floor are called the foundation of the platform. The protrusions of such a foundation can be observed in, on, in and. Due to their massiveness and rigidity, these protrusions are called shit. These are the most ancient sites: the age of many reaches 3-4 billion years. During this time, irreversible changes, recrystallization, compaction and other metamorphoses have occurred in the rocks.

The upper floors of the platforms are formed by huge strata of sedimentary rocks that have accumulated over hundreds of millions of years. In these strata, gentle folds, ruptures, swells and domes are observed. Traces of especially large uplifts and subsidences are anteclises and syneclises. in its shape it resembles a giant hill with an area of 60 - 100 thousand km2. The height of such a hill is small - about 300 - 500 m.

The outskirts of the anteclise descend in steps to those around them (from the Greek syn - together and enklisis - inclination). On the outskirts of syneclises and anteclises, there are often separate shafts and domes - small tectonic forms. For the platforms, first of all, rhythmic oscillations are characteristic, which led to a sequential change of ups and downs. In the process of these movements, deflections, small folds, tectonic cracks arose.

The structure of the sedimentary cover on the platforms is complicated by tectonic structures, the appearance of which is not easy to explain. For example, under the northern part of the seabed and under the Caspian lowland, there is a huge basin, closed on all sides, with a depth of more than 22 km. This basin is 2,000 km across. It is filled with clays, limestones, rock salt and other rocks. The upper 5 - 8 km of precipitation is attributed to the Paleozoic age. According to geophysical data, in the center of this depression there is no granite-gneiss layer and the sedimentary stratum lies directly on the granulite-basalt layer. Such a structure is more typical for depressions with an oceanic type of the earth's crust, therefore the Caspian depression is considered a relic of the most ancient Precambrian oceans.

Orogenic belts are the exact opposite of the platforms - mountain belts that arose on the site of the former geosynclines. They, like the platforms, belong to long-term tectonic structures, but the speed of movement of the earth's crust in them turned out to be much higher, and the forces of compression and extension created large mountain ranges and depressions on the surface of the Earth. Tectonic stresses in orogenic belts alternately increased, then sharply decreased, and therefore it is possible to trace the growth phases of mountain structures, and the phases of their destruction.

Lateral compression of crustal blocks in the past often led to the division of blocks into tectonic plates, each of which was 5-10 km thick. Tectonic plates were warped and often pushed one on top of the other. As a result, the ancient rocks were thrust over the younger rocks. Large thrust faults, measured in tens of kilometers, are referred to by scientists as overhangs. There are especially many of them in, and, but nappes are also found on platforms, where the displacement of the plates of the earth's crust led to the formation of folds and ramparts, for example, in the Zhiguli mountains.

The bottom of the seas and oceans has long remained a poorly explored area of the Earth. Only in the first half of the XX century. mid-ocean ridges were discovered, which were subsequently discovered in all the oceans of the planet. They had a different structure and age. The results of deep-sea drilling also contributed to the study of the structure of the mid-ocean ridges. The axial zones of mid-oceanic ridges, together with rift depressions, are displaced by hundreds and thousands of kilometers. These displacements most often occur along large faults (the so-called transform faults), which were formed in different geological epochs.