Endogenous processes - geological processes associated with energy arising in the bowels of the Earth. Endogenous processes include tectonic movements of the earth's crust, magmatism, metamorphism, seismic and tectonic processes. The main sources of energy for endogenous processes are heat and the redistribution of material in the interior of the Earth according to density (gravitational differentiation). These are processes of internal dynamics: they occur as a result of the influence of energy sources internal to the Earth. The deep heat of the Earth, according to most scientists, is predominantly of radioactive origin. A certain amount of heat is also released during gravitational differentiation. The continuous generation of heat in the bowels of the Earth leads to the formation of its flow to the surface (heat flow). At some depths in the bowels of the Earth, with a favorable combination of material composition, temperature and pressure, centers and layers of partial melting can arise. Such a layer in the upper mantle is the asthenosphere - the main source of magma formation; convection currents can arise in it, which are the presumed cause of vertical and horizontal movements in the lithosphere. Convection also occurs on the scale of the entire mantle, possibly separately in the lower and upper layers, in one way or another leading to large horizontal movements of lithospheric plates. The cooling of the latter leads to vertical subsidence (plate tectonics). In the zones of volcanic belts of island arcs and continental margins, the main sources of magma in the mantle are associated with ultra-deep inclined faults (Wadati-Zavaritsky-Benioff seismofocal zones) extending beneath them from the ocean (to a depth of approximately 700 km). Under the influence of heat flow or directly the heat brought by rising deep magma, so-called crustal magma centers appear in the earth's crust itself; reaching the near-surface parts of the crust, magma penetrates them in the form of intrusions (plutons) of various shapes or pours out onto the surface, forming volcanoes. Gravitational differentiation led to the stratification of the Earth into geospheres of different densities. On the surface of the Earth, it also manifests itself in the form of tectonic movements, which, in turn, lead to tectonic deformations of the rocks of the earth’s crust and upper mantle; the accumulation and subsequent release of tectonic stresses along active faults lead to earthquakes. Both types of deep processes are closely related: radioactive heat, reducing the viscosity of the material, promotes its differentiation, and the latter accelerates the transfer of heat to the surface. It is assumed that the combination of these processes leads to uneven temporal transport of heat and light matter to the surface, which, in turn, can explain the presence of tectonomagmatic cycles in the history of the earth’s crust. Spatial irregularities of the same deep processes are used to explain the division of the earth's crust into more or less geologically active areas, for example, geosynclines and platforms. The formation of the Earth's topography and the formation of many important minerals are associated with endogenous processes.

Exogenous- geological processes caused by energy sources external to the Earth (mainly solar radiation) in combination with gravity. Electrochemical processes occur on the surface and in the near-surface zone of the earth’s crust in the form of its mechanical and physicochemical interaction with the hydrosphere and atmosphere. These include: Weathering, geological activity of wind (aeolian processes, Deflation), flowing surface and groundwater (Erosion, Denudation), lakes and swamps, waters of seas and oceans (Abrasia), glaciers (Exaration). The main forms of manifestation of environmental damage on the Earth's surface are: destruction of rocks and chemical transformation of the minerals composing them (physical, chemical, and organic weathering); removal and transfer of loosened and soluble products of rock destruction by water, wind and glaciers; deposition (accumulation) of these products in the form of sediments on land or at the bottom of water basins and their gradual transformation into sedimentary rocks (Sedimentogenesis, Diagenesis, Catagenesis). Energy, in combination with endogenous processes, participates in the formation of the Earth's topography and in the formation of sedimentary rock strata and associated mineral deposits. For example, under conditions of specific weathering and sedimentation processes, ores of aluminum (bauxite), iron, nickel, etc. are formed; as a result of selective deposition of minerals by water flows, placers of gold and diamonds are formed; under conditions favorable to the accumulation of organic matter and sedimentary rock strata enriched with it, combustible minerals arise.

9- General information about minerals

Mineral(from Late Latin "minera" - ore) - a natural solid with a certain chemical composition, physical properties and crystalline structure, formed as a result of natural physical and chemical processes and is an integral part of the Earth's Crust, rocks, ores, meteorites and other planets of the Solar systems. The science of mineralogy is the study of minerals.

The term "mineral" means a solid natural inorganic crystalline substance. But sometimes it is considered in an unjustifiably expanded context, classifying some organic, amorphous and other natural products as minerals, in particular some rocks, which in a strict sense cannot be classified as minerals.

· Some natural substances that are liquids under normal conditions are also considered minerals (for example, native mercury, which comes to a crystalline state at a lower temperature). Water, on the contrary, is not classified as a mineral, considering it as a liquid state (melt) of the mineral ice.

· Some organic substances - oil, asphalt, bitumen - are often mistakenly classified as minerals.

· Some minerals are in an amorphous state and do not have a crystalline structure. This applies mainly to the so-called. metamict minerals that have the external form of crystals, but are in an amorphous, glass-like state due to the destruction of their original crystal lattice under the influence of hard radioactive radiation from the radioactive elements included in their composition (U, Th, etc.). There are clearly crystalline minerals, amorphous - metacolloids (for example, opal, lechatelierite, etc.) and metamict minerals, which have the external form of crystals, but are in an amorphous, glass-like state.

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Origin and early history of the earth

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Exogenous processes
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Questions

1.Endogenous and exogenous processes

.Earthquake

.Physical properties of minerals

.Epeirogenic movements

.Bibliography

1. EXOGENOUS AND ENDOGENOUS PROCESSES

Exogenous processes - geological processes occurring on the surface of the Earth and in the uppermost parts of the earth's crust (weathering, erosion, glacial activity, etc.); are caused mainly by the energy of solar radiation, gravity and the vital activity of organisms.

Erosion (from Latin erosio - erosion) is the destruction of rocks and soils by surface water flows and wind, including the separation and removal of fragments of material and accompanied by their deposition.

Often, especially in foreign literature, erosion is understood as any destructive activity of geological forces, such as sea surf, glaciers, gravity; in this case, erosion is synonymous with denudation. For them, however, there are also special terms: abrasion (wave erosion), exaration (glacial erosion), gravitational processes, solifluction, etc. The same term (deflation) is used in parallel with the concept of wind erosion, but the latter is much more common.

Based on the speed of development, erosion is divided into normal and accelerated. Normal always occurs in the presence of any pronounced runoff, occurs more slowly than soil formation and does not lead to noticeable changes in level and shape earth's surface. Accelerated is faster than soil formation, leads to soil degradation and is accompanied by a noticeable change in topography. For reasons, natural and anthropogenic erosion are distinguished. It should be noted that anthropogenic erosion is not always accelerated, and vice versa.

The work of glaciers is the relief-forming activity of mountain and cover glaciers, consisting in the capture of rock particles by a moving glacier, their transfer and deposition when the ice melts.

Endogenous processes Endogenous processes are geological processes associated with energy arising in the depths of the solid Earth. Endogenous processes include tectonic processes, magmatism, metamorphism, and seismic activity.

Tectonic processes - the formation of faults and folds.

Magmatism is a term that combines effusive (volcanism) and intrusive (plutonism) processes in the development of folded and platform areas. Magmatism is understood as the totality of all geological processes, the driving force of which is magma and its derivatives.

Magmatism is a manifestation of the Earth's deep activity; it is closely related to its development, thermal history and tectonic evolution.

Magmatism is distinguished:

geosynclinal

platform

oceanic

magmatism of activation areas

By depth of manifestation:

abyssal

hypabyssal

surface

According to the composition of magma:

ultrabasic

basic

alkaline

In the modern geological era, magmatism is especially developed within the Pacific geosynclinal belt, mid-ocean ridges, reef zones of Africa and the Mediterranean, etc. The formation of a large number of diverse mineral deposits is associated with magmatism.

Seismic activity is a quantitative measure of the seismic regime, determined by the average number of earthquake sources in a certain range of energy magnitudes that occur in the territory under consideration during a certain observation time.

2. EARTHQUAKES

geological earth's crust epeirogenic

The effect of the internal forces of the Earth is most clearly revealed in the phenomenon of earthquakes, which are understood as shaking of the earth's crust caused by displacements of rocks in the bowels of the Earth.

Earthquake- a fairly common phenomenon. It is observed on many parts of continents, as well as on the bottom of oceans and seas (in the latter case they speak of a “seaquake”). Number of earthquakes per globe reaches several hundred thousand per year, i.e., on average, one or two earthquakes occur per minute. The strength of an earthquake varies: most of them are detected only by highly sensitive instruments - seismographs, others are felt directly by a person. The number of the latter reaches two to three thousand per year, and they are distributed very unevenly - in some areas such strong earthquakes very common, while in others they are extremely rare or even practically absent.

Earthquakes can be divided into endogenousassociated with processes occurring deep within the Earth, and exogenous, depending on processes occurring near the Earth's surface.

To natural earthquakesThese include volcanic earthquakes caused by volcanic eruptions and tectonic earthquakes caused by the movement of matter in the deep interior of the Earth.

To exogenous earthquakesinclude earthquakes occurring as a result of underground collapses associated with karst and some other phenomena, gas explosions, etc. Exogenous earthquakes can also be caused by processes occurring on the surface of the Earth itself: rock falls, meteorite impacts, falling water from high altitude and other phenomena, as well as factors associated with human activity (artificial explosions, machine operation, etc.).

Genetically, earthquakes can be classified as follows: Natural

Endogenous: a) tectonic, b) volcanic. Exogenous: a) karst landslides, b) atmospheric c) from waves, waterfalls, etc. Artificial

a) from explosions, b) from artillery fire, c) from artificial rock collapse, d) from transport, etc.

In the geology course, only earthquakes associated with endogenous processes are considered.

When strong earthquakes occur in densely populated areas, they cause enormous harm to humans. In terms of disasters caused to humans, earthquakes cannot be compared with any other natural phenomenon. For example, in Japan, during the earthquake of September 1, 1923, which lasted only a few seconds, 128,266 houses were completely destroyed and 126,233 were partially destroyed, about 800 ships were lost, and 142,807 people were killed or missing. More than 100 thousand people were injured.

It is extremely difficult to describe the phenomenon of an earthquake, since the whole process lasts only a few seconds or minutes, and a person does not have time to perceive all the variety of changes taking place in nature during this time. Attention is usually focused only on the colossal destruction that occurs as a result of an earthquake.

This is how M. Gorky describes the earthquake that occurred in Italy in 1908, of which he was an eyewitness: “The earth hummed dully, groaned, hunched under our feet and worried, forming deep cracks - as if in the depths some huge worm, dormant for centuries, had woken up and was tossing and turning. ...Shuddering and staggering, the buildings tilted, cracks snaked along their white walls, like lightning, and the walls crumbled, falling asleep on the narrow streets and the people among them... The underground rumble, the rumble of stones, the squeal of wood drowned out the cries for help, the cries of madness. The earth is agitated like the sea, throwing palaces, shacks, temples, barracks, prisons, schools from its chest, destroying hundreds and thousands of women, children, rich and poor with each shudder. "

As a result of this earthquake, the city of Messina and a number of other settlements were destroyed.

The general sequence of all phenomena during an earthquake was studied by I.V. Mushketov during the largest Central Asian earthquake, the Alma-Ata earthquake of 1887.

On May 27, 1887, in the evening, as eyewitnesses wrote, there were no signs of an earthquake, but domestic animals behaved restlessly, did not take food, broke from their leash, etc. On the morning of May 28, at 4:35 a.m., an underground rumble was heard and quite strong push. The shaking lasted no more than a second. A few minutes later the hum resumed; it resembled the dull ringing of numerous powerful bells or the roar of passing heavy artillery. The roar was followed by strong crushing blows: plaster fell in houses, glass flew out, stoves collapsed, walls and ceilings fell: the streets were filled with gray dust. The most severely damaged were the massive stone buildings. The northern and southern walls of houses located along the meridian fell out, while the western and eastern walls were preserved. At first it seemed that the city no longer existed, that all the buildings were destroyed without exception. The shocks and tremors, although less severe, continued throughout the day. Many damaged but previously standing houses fell from these weaker tremors.

Landslides and cracks formed in the mountains, through which streams of underground water came to the surface in some places. The clayey soil on the mountain slopes, already heavily wetted by rain, began to creep, cluttering the river beds. Collected by the streams, this entire mass of earth, rubble, and boulders, in the form of thick mudflows, rushed to the foot of the mountains. One of these streams stretched for 10 km and was 0.5 km wide.

The destruction in the city of Almaty itself was enormous: out of 1,800 houses, only a few houses survived, but the number of human casualties was relatively small (332 people).

Numerous observations showed that the southern walls of houses collapsed first (a fraction of a second earlier), and then the northern ones, and that the bells in the Church of the Intercession (in the northern part of the city) struck a few seconds after the destruction that occurred in the southern part of the city. All this indicated that the center of the earthquake was south of the city.

Most of the cracks in the houses were also inclined to the south, or more precisely to the southeast (170°) at an angle of 40-60°. Analyzing the direction of the cracks, I.V. Mushketov came to the conclusion that the source of the earthquake waves was located at a depth of 10-12 km, 15 km south of Alma-Ata.

The deep center or focus of an earthquake is called the hypocenter. INIn plan it is outlined as a round or oval area.

Area located on the surface The earth above the hypocenter is calledepicenter . It is characterized by maximum destruction, with many objects moving vertically (bouncing), and cracks in houses are located very steeply, almost vertically.

The area of ​​the epicenter of the Alma-Ata earthquake was determined to be 288 km ² (36 *8 km), and the area where the earthquake was most powerful covered an area of ​​6000 km ². Such an area was called pleistoseist (“pleisto” - largest and “seistos” - shaken).

The Alma-Ata earthquake continued for more than one day: after the tremors of May 28, 1887, tremors of lesser strength occurred for more than two years. at intervals of first several hours, and then days. In just two years there were over 600 strikes, increasingly weakening.

In the history of the Earth, earthquakes have been described since big amount tremors. For example, in 1870, tremors began in the province of Phocis in Greece, which continued for three years. In the first three days, the tremors followed every 3 minutes; during the first five months, about 500 thousand tremors occurred, of which 300 were destructive and followed each other with an average interval of 25 seconds. Over three years, over 750 thousand strikes occurred.

Thus, an earthquake does not occur as a result of a one-time event occurring at depth, but as a result of some long-term process of movement of matter in the inner parts of the globe.

Usually the initial large shock is followed by a chain of smaller shocks, and this entire period can be called the earthquake period. All shocks of one period come from a common hypocenter, which can sometimes shift during development, and therefore the epicenter also shifts.

This is clearly visible in a number of examples of Caucasian earthquakes, as well as the earthquake in the Ashgabat region, which occurred on October 6, 1948. The main shock followed at 1 hour 12 minutes without preliminary shocks and lasted 8-10 seconds. During this time, enormous destruction occurred in the city and surrounding villages. One-story houses made of raw bricks crumbled, and the roofs were covered with piles of bricks, household utensils, etc. Individual walls of more solidly built houses fell out, and pipes and stoves collapsed. It is interesting to note that round buildings (elevator, mosque, cathedral, etc.) withstood the shock better than ordinary quadrangular buildings.

The epicenter of the earthquake was located 25 km away. southeast of Ashgabat, in the area of ​​the Karagaudan state farm. The epicentral region turned out to be elongated in a northwestern direction. The hypocenter was located at a depth of 15-20 km. The length of the pleistoseist region reached 80 km and its width 10 km. The period of the Ashgabat earthquake was long and consisted of many (more than 1000) tremors, the epicenters of which were located northwest of the main one within a narrow strip located in the foothills of Kopet-Dag

The hypocenters of all these aftershocks were at the same shallow depth (about 20-30 km) as the hypocenter of the main shock.

Earthquake hypocenters can be located not only under the surface of continents, but also under the bottom of seas and oceans. During seaquakes, the destruction of coastal cities is also very significant and is accompanied by human casualties.

The strongest earthquake occurred in 1775 in Portugal. The pleistoseist region of this earthquake covered a huge area; the epicenter was located under the bottom of the Bay of Biscay near the capital of Portugal, Lisbon, which was hit the hardest.

The first shock occurred on the afternoon of November 1 and was accompanied by a terrible roar. According to eyewitnesses, the ground rose up and then fell a full cubit. Houses fell with a terrible crash. The huge monastery on the mountain swayed so violently from side to side that it threatened to collapse every minute. The tremors continued for 8 minutes. A few hours later the earthquake resumed.

The Marble embankment collapsed and went under water. People and ships standing near the shore were drawn into the resulting water funnel. After the earthquake, the depth of the bay at the embankment site reached 200 m.

The sea retreated at the beginning of the earthquake, but then a huge wave 26 m high hit the shore and flooded the coast to a width of 15 km. There were three such waves, following one after another. What survived the earthquake was washed away and carried out to sea. More than 300 ships were destroyed or damaged in Lisbon harbor alone.

The waves of the Lisbon earthquake passed through the entire Atlantic Ocean: near Cadiz their height reached 20 m, on the African coast, off the coast of Tangier and Morocco - 6 m, on the islands of Funchal and Madera - up to 5 m. The waves crossed the Atlantic Ocean and were felt off the coast America on the islands of Martinique, Barbados, Antigua, etc. The Lisbon earthquake killed over 60 thousand people.

Such waves quite often arise during seaquakes; they are called tsutsnas. The speed of propagation of these waves ranges from 20 to 300 m/sec depending on: the depth of the ocean; wave height reaches 30 m.

The appearance of tsunamis and low tide waves is explained as follows. In the epicentral region, due to the deformation of the bottom, a pressure wave is formed that propagates upward. The sea in this place only swells strongly, short-term currents are formed on the surface, diverging in all directions, or “boils” with water being thrown up to a height of up to 0.3 m. All this is accompanied by a hum. The pressure wave is then transformed at the surface into tsunami waves, spreading out in different directions. Low tides before a tsunami are explained by the fact that water first rushes into an underwater hole, from which it is then pushed into the epicentral region.

When the epicenters occur in densely populated areas, earthquakes cause enormous disasters. The earthquakes in Japan were especially destructive, where over 1,500 years, 233 major earthquakes with a number of tremors exceeding 2 million were recorded.

Great disasters are caused by earthquakes in China. During the disaster on December 16, 1920, over 200 thousand people died in the Kansu region, and the main cause of death was the collapse of dwellings dug in the loess. Earthquakes of exceptional magnitude occurred in America. An earthquake in the Riobamba region in 1797 killed 40 thousand people and destroyed 80% of buildings. In 1812, the city of Caracas (Venezuela) was completely destroyed within 15 seconds. The city of Concepcion in Chile was repeatedly almost completely destroyed, the city of San Francisco was severely damaged in 1906. In Europe, the greatest destruction was observed after the earthquake in Sicily, where in 1693 50 villages were destroyed and over 60 thousand people died.

On the territory of the USSR, the most destructive earthquakes were in the south of Central Asia, in the Crimea (1927) and in the Caucasus. The city of Shemakha in Transcaucasia suffered especially often from earthquakes. It was destroyed in 1669, 1679, 1828, 1856, 1859, 1872, 1902. Until 1859, the city of Shemakha was the provincial center of Eastern Transcaucasia, but due to the earthquake the capital had to be moved to Baku. In Fig. 173 shows the location of the epicenters of the Shemakha earthquakes. Just as in Turkmenistan, they are located along a certain line extended in the northwest direction.

When earthquakes occur significant changes on the surface of the Earth, expressed in the formation of cracks, dips, folds, the raising of individual areas on land, the formation of islands at sea, etc. These disturbances, called seismic, often contribute to the formation of powerful landslides, screes, landslides, mudflows and mudflows in mountains, the emergence of new sources, the cessation of old ones, the formation of mud hills, gas emissions, etc. Disturbances formed after earthquakes are called post-seismic.

Phenomena. associated with earthquakes both on the surface of the Earth and in its interior are called seismic phenomena. The science that studies seismic phenomena is called seismology.

3. PHYSICAL PROPERTIES OF MINERALS

Although the main characteristics of minerals (chemical composition and internal crystal structure) are established on the basis of chemical analyzes and X-ray diffraction, they are indirectly reflected in properties that are easily observed or measured. To diagnose most minerals, it is enough to determine their luster, color, cleavage, hardness, and density.

Shine(metallic, semi-metallic and non-metallic - diamond, glass, greasy, waxy, silky, pearlescent, etc.) is determined by the amount of light reflected from the surface of the mineral and depends on its refractive index. Based on transparency, minerals are divided into transparent, translucent, translucent in thin fragments, and opaque. Quantitative determination of light refraction and light reflection is possible only under a microscope. Some opaque minerals reflect light strongly and have a metallic luster. This is common in ore minerals such as galena (lead mineral), chalcopyrite and bornite (copper minerals), argentite and acanthite (silver minerals). Most minerals absorb or transmit a significant portion of the light falling on them and have a non-metallic luster. Some minerals have a luster that transitions from metallic to non-metallic, which is called semi-metallic.

Minerals with a non-metallic luster are usually light-colored, some of them are transparent. Quartz, gypsum and light mica are often transparent. Other minerals (for example, milky white quartz) that transmit light, but through which objects cannot be clearly distinguished, are called translucent. Minerals containing metals differ from others in light transmission. If light passes through a mineral, at least in the thinnest edges of the grains, then it is, as a rule, non-metallic; if the light does not pass through, then it is ore. There are, however, exceptions: for example, light-colored sphalerite (zinc mineral) or cinnabar (mercury mineral) are often transparent or translucent.

Minerals differ in the qualitative characteristics of their non-metallic luster. The clay has a dull, earthy sheen. Quartz on the edges of crystals or on fracture surfaces is glassy, ​​talc, which is divided into thin leaves along the cleavage planes, is mother-of-pearl. Bright, sparkling, like a diamond, shine is called diamond.

When light falls on a mineral with a non-metallic luster, it is partially reflected from the surface of the mineral and partially refracted at this boundary. Each substance is characterized by a certain refractive index. Because it can be measured with high precision, it is a very useful mineral diagnostic feature.

The nature of the luster depends on the refractive index, and both of them depend on the chemical composition and crystal structure of the mineral. In general, transparent minerals containing heavy metal atoms are characterized by high luster and a high refractive index. This group includes such common minerals as anglesite (lead sulfate), cassiterite (tin oxide) and titanite or sphene (calcium titanium silicate). Minerals composed of relatively light elements can also have high luster and a high refractive index if their atoms are tightly packed and held together by strong chemical bonds. A striking example is diamond, which consists of only one light element, carbon. To a lesser extent, this is also true for the mineral corundum (Al 2O 3), transparent colored varieties of which - ruby ​​and sapphires - are precious stones. Although corundum is composed of light atoms of aluminum and oxygen, they are so tightly bound together that the mineral has a fairly strong luster and a relatively high refractive index.

Some glosses (oily, waxy, matte, silky, etc.) depend on the state of the surface of the mineral or on the structure of the mineral aggregate; a resinous luster is characteristic of many amorphous substances (including minerals containing the radioactive elements uranium or thorium).

Color- a simple and convenient diagnostic sign. Examples include brass yellow pyrite (FeS 2), lead-gray galena (PbS) and silver-white arsenopyrite (FeAsS 2). In other ore minerals with a metallic or semi-metallic luster, the characteristic color may be masked by the play of light in a thin surface film (tarnish). This is common to most copper minerals, especially bornite, which is called "peacock ore" because of its iridescent blue-green tarnish that quickly develops when freshly fractured. However, other copper minerals are painted in familiar colors: malachite - green, azurite - blue.

Some non-metallic minerals are unmistakably recognizable by the color determined by the main chemical element (yellow - sulfur and black - dark gray - graphite, etc.). Many non-metallic minerals consist of elements that do not provide them with a specific color, but they have colored varieties, the color of which is due to the presence of impurities of chemical elements in small quantities that are not comparable with the intensity of the color they cause. Such elements are called chromophores; their ions are characterized by selective absorption of light. For example, a deep purple amethyst owes its color to an insignificant admixture of iron in quartz, and a thick green color emerald is associated with the small chromium content of beryl. Colors in normally colorless minerals can result from defects in the crystal structure (caused by unoccupied atomic positions in the lattice or the incorporation of foreign ions), which can cause selective absorption of certain wavelengths in the spectrum white light. Then the minerals are painted in additional colors. Rubies, sapphires and alexandrites owe their color to precisely these light effects.

Colorless minerals can be colored by mechanical inclusions. Thus, thin scattered dissemination of hematite gives quartz a red color, chlorite - green. Milky quartz is clouded with gas-liquid inclusions. Although mineral color is one of the most easily determined properties in mineral diagnostics, it must be used with caution as it depends on many factors.

Despite the variability in the color of many minerals, the color of the mineral powder is very constant, and therefore is an important diagnostic feature. Typically, the color of a mineral powder is determined by the line (the so-called “line color”) that the mineral leaves when it is passed over an unglazed porcelain plate (biscuit). For example, the mineral fluorite comes in different colors, but its streak is always white.

Cleavage- very perfect, perfect, average (clear), imperfect (unclear) and very imperfect - is expressed in the ability of minerals to split in certain directions. A fracture (smooth, stepped, uneven, splintered, conchoidal, etc.) characterizes the surface of the split of a mineral that did not occur along cleavage. For example, quartz and tourmaline, whose fracture surface resembles a glass chip, have a conchoidal fracture. In other minerals, the fracture may be described as rough, jagged, or splintered. For many minerals, the characteristic is not fracture, but cleavage. This means that they cleave along smooth planes directly related to their crystal structure. The bonding forces between the planes of the crystal lattice can vary depending on the crystallographic direction. If they are much larger in some directions than in others, then the mineral will split across the weakest bond. Since cleavage is always parallel to the atomic planes, it can be designated by indicating crystallographic directions. For example, halite (NaCl) has cube cleavage, i.e. three mutually perpendicular directions of possible split. Cleavage is also characterized by the ease of manifestation and the quality of the resulting cleavage surface. Mica has very perfect cleavage in one direction, i.e. easily splits into very thin leaves with a smooth shiny surface. Topaz has perfect cleavage in one direction. Minerals can have two, three, four or six cleavage directions along which they are equally easy to split, or several cleavage directions of varying degrees. Some minerals have no cleavage at all. Since cleavage, as a manifestation of the internal structure of minerals, is their constant property, it serves as an important diagnostic feature.

Hardness- the resistance that the mineral provides when scratched. Hardness depends on the crystal structure: the more tightly the atoms in the structure of a mineral are connected to each other, the more difficult it is to scratch. Talc and graphite are soft plate-like minerals, built from layers of atoms bonded together by very weak forces. They are greasy to the touch: when rubbed against the skin of the hand, individual thin layers slip off. The hardest mineral is diamond, in which the carbon atoms are so tightly bonded that it can only be scratched by another diamond. At the beginning of the 19th century. Austrian mineralogist F. Moos arranged 10 minerals in increasing order of their hardness. Since then, they have been used as standards for the relative hardness of minerals, the so-called. Mohs scale (Table 1)

Table 1. MOH HARDNESS SCALE

MineralRelative hardnessTalc 1 Gypsum 2 Calcite 3 Fluorite 4 Apatite 5 Orthoclase 6 Quartz 7 Topaz 8 Corundum 9 Diamond 10

To determine the hardness of a mineral, it is necessary to identify the hardest mineral that it can scratch. The hardness of the mineral being examined will be greater than the hardness of the mineral it scratched, but less than the hardness of the next mineral on the Mohs scale. Bonding forces can vary depending on the crystallographic direction, and since hardness is a rough estimate of these forces, it can vary in different directions. This difference is usually small, with the exception of kyanite, which has a hardness of 5 in the direction parallel to the length of the crystal and 7 in the transverse direction.

For less precise definition hardness, you can use the following, simpler, practical scale.

2 -2.5 Thumbnail 3 Silver coin 3.5 Bronze coin 5.5-6 Penknife blade 5.5-6 Window glass 6.5-7 File

In mineralogical practice, the measurement of absolute hardness values ​​(the so-called microhardness) using a sclerometer device, which is expressed in kg/mm, is also used. 2.

Density.The mass of atoms of chemical elements varies from hydrogen (the lightest) to uranium (the heaviest). All other things being equal, the mass of a substance consisting of heavy atoms is greater than that of a substance consisting of light atoms. For example, two carbonates - aragonite and cerussite - have a similar internal structure, but aragonite contains light calcium atoms, and cerussite contains heavy lead atoms. As a result, the mass of cerussite exceeds the mass of aragonite of the same volume. The mass per unit volume of a mineral also depends on the atomic packing density. Calcite, like aragonite, is calcium carbonate, but in calcite the atoms are less densely packed, so it has less mass per unit volume than aragonite. The relative mass, or density, depends on the chemical composition and internal structure. Density is the ratio of the mass of a substance to the mass of the same volume of water at 4 ° C. So, if the mass of a mineral is 4 g, and the mass of the same volume of water is 1 g, then the density of the mineral is 4. In mineralogy, it is customary to express density in g/ cm 3.

Density is an important diagnostic feature of minerals and is not difficult to measure. First, the sample is weighed in air and then in water. Since a sample immersed in water is subject to an upward buoyant force, its weight there is less than in air. The weight loss is equal to the weight of water displaced. Thus, density is determined by the ratio of the mass of a sample in air to its weight loss in water.

Pyro-electricity.Some minerals, such as tourmaline, calamine, etc., become electrified when heated or cooled. This phenomenon can be observed by pollinating a cooling mineral with a mixture of sulfur and red lead powders. In this case, sulfur covers positively charged areas of the mineral surface, and minium covers areas with a negative charge.

Magneticity -This is the property of some minerals to act on a magnetic needle or be attracted by a magnet. To determine magnetism, use a magnetic needle placed on a sharp tripod, or a magnetic shoe or bar. It is also very convenient to use a magnetic needle or knife.

When testing for magnetism, three cases are possible:

a) when a mineral in its natural form (“by itself”) acts on a magnetic needle,

b) when the mineral becomes magnetic only after calcination in the reducing flame of a blowpipe

c) when the mineral does not exhibit magnetism either before or after calcination in a reducing flame. To calcinate with a reducing flame, you need to take small pieces of 2-3 mm in size.

Glow.Many minerals that do not glow on their own begin to glow under certain special conditions.

There are phosphorescence, luminescence, thermoluminescence and triboluminescence of minerals. Phosphorescence is the ability of a mineral to glow after exposure to one or another ray (willite). Luminescence is the ability to glow at the moment of irradiation (scheelite when irradiated with ultraviolet and cathode rays, calcite, etc.). Thermoluminescence - glow when heated (fluorite, apatite).

Triboluminescence - glow at the moment of scratching with a needle or splitting (mica, corundum).

Radioactivity.Many minerals containing elements such as niobium, tantalum, zirconium, rare earths, uranium, and thorium often have quite significant radioactivity, easily detectable even by household radiometers, which can serve as an important diagnostic sign.

To test for radioactivity, the background value is first measured and recorded, then the mineral is brought, possibly closer to the detector of the device. An increase in readings of more than 10-15% can serve as an indicator of the radioactivity of the mineral.

Electrical conductivity.A number of minerals have significant electrical conductivity, which allows them to be clearly distinguished from similar minerals. Can be checked with a regular household tester.

4. EPEIROGENIC MOVEMENTS OF THE EARTH'S CRUST

Epeirogenic movements- slow secular uplift and subsidence of the earth's crust, not causing change primary occurrence of layers. These vertical movements are oscillatory in nature and reversible, i.e. the rise may be replaced by a fall. These movements include:

Modern ones, which are recorded in human memory and can be measured instrumentally by repeated leveling. The speed of modern oscillatory movements on average does not exceed 1-2 cm/year, and in mountainous areas it can reach 20 cm/year.

Neotectonic movements are movements during the Neogene-Quaternary time (25 million years). Fundamentally, they are no different from modern ones. Neotectonic movements are recorded in modern relief and the main method of studying them is geomorphological. The speed of their movement is an order of magnitude lower, in mountainous areas - 1 cm/year; on the plains - 1 mm/year.

Ancient slow vertical movements are recorded in sections of sedimentary rocks. The speed of ancient oscillatory movements, according to scientists, is less than 0.001 mm/year.

Orogenic movementsoccur in two directions - horizontal and vertical. The first leads to the collapse of rocks and the formation of folds and thrusts, i.e. to the reduction of the earth's surface. Vertical movements lead to the raising of the area where folding occurs and often the appearance of mountain structures. Orogenic movements occur much faster than oscillatory movements.

They are accompanied by active effusive and intrusive magmatism, as well as metamorphism. In recent decades, these movements have been explained by the collision of large lithospheric plates, which move horizontally along the asthenospheric layer of the upper mantle.

TYPES OF TECTONIC FAULTS

Types of tectonic disturbances

a - folded (plicate) forms;

In most cases, their formation is associated with compaction or compression of the Earth's substance. Fold faults are morphologically divided into two main types: convex and concave. In the case of a horizontal cut, layers that are older in age are located in the core of the convex fold, and younger layers are located on the wings. Concave bends, on the other hand, have younger deposits in their cores. In folds, the convex wings are usually inclined to the sides from the axial surface.

b - discontinuous (disjunctive) forms

Discontinuous tectonic disturbances are those changes in which the continuity (integrity) of rocks is disrupted.

Faults are divided into two groups: faults without displacement of the rocks separated by them relative to each other and faults with displacement. The first ones are called tectonic cracks, or diaclases, the second ones are called paraclases.

BIBLIOGRAPHY

1. Belousov V.V. Essays on the history of geology. At the origins of Earth science (geology until the end of the 18th century). - M., - 1993.

Vernadsky V.I. Selected works on the history of science. - M.: Science, - 1981.

Povarennykh A.S., Onoprienko V.I. Mineralogy: past, present, future. - Kyiv: Naukova Dumka, - 1985.

Modern ideas of theoretical geology. - L.: Nedra, - 1984.

Khain V.E. The main problems of modern geology (geology on the threshold of the 21st century). - M.: Scientific world, 2003..

Khain V.E., Ryabukhin A.G. History and methodology of geological sciences. - M.: MSU, - 1996.

Hallem A. Great geological disputes. M.: Mir, 1985.

Geological processes are processes that change the composition, structure, relief and deep structure of the earth's crust. Geological processes, with a few exceptions, are characterized by scale and long duration (up to hundreds of millions of years); in comparison with them, the existence of humanity is a very short episode in the life of the Earth. In this regard, the vast majority of geological processes are not directly observable. They can be judged only by the results of their impact on certain geological objects - rocks, geological structures, types of relief of continents and ocean floors. Of great importance are observations of modern geological processes, which, according to the principle of actualism, can be used as models that allow us to understand the processes and events of the past, taking into account their variability. Currently, a geologist can observe different stages of the same geological processes, which greatly facilitates their study.

All geological processes occurring in the interior of the Earth and on its surface are divided into endogenous And exogenous. Endogenous geological processes occur due to the internal energy of the Earth. According to modern concepts (Sorokhtin, Ushakov, 1991), the main planetary source of this energy is the gravitational differentiation of terrestrial matter. (Components with increased specific gravity, under the influence of gravitational forces, tend to the center of the Earth, while lighter ones concentrate at the surface). As a result of this process, a dense iron-nickel core was released in the center of the planet, and convective currents arose in the mantle. A secondary source of energy is the energy of radioactive decay of matter. It accounts for only 12% of the energy used for the tectonic development of the Earth, and the share of gravitational differentiation is 82%. Some authors believe that the main source of energy for endogenous processes is the interaction of the Earth’s outer core, which is in a molten state, with inner core and a mantle. Endogenous processes include tectonic, magmatic, pneumatolithic-hydrothermal and metamorphic.

Tectonic processes are those under the influence of which tectonic structures of the earth’s crust are formed - mountain-fold belts, troughs, depressions, deep faults, etc. Vertical and horizontal movements of the earth's crust also belong to tectonic processes.

Magmatic processes (magmatism) are the totality of all geological processes associated with the activity of magma and its derivatives. Magma- a fiery liquid molten mass that forms in the earth's crust or upper mantle and turns into igneous rocks when solidified. By origin, magmatism is divided into intrusive and effusive. The term “intrusive magmatism” combines the processes of formation and crystallization of magma at depth with the formation of intrusive bodies. Effusive magmatism (volcanism) is a set of processes and phenomena associated with the movement of magma from the depths to the surface with the formation of volcanic structures.

A special group is allocated hydrothermal processes. These are the processes of formation of minerals as a result of their deposition in cracks or pores of rocks from hydrothermal solutions. Hydrotherms – liquid hot aqueous solutions circulating in the earth's crust and participating in the processes of movement and deposition of minerals. Hydrotherms are often more or less enriched in gases; if the gas content is high, then such solutions are called pneumatolytic-hydrothermal. Currently, many researchers believe that hydrotherms are formed by mixing underground waters of deep circulation and juvenile waters formed by the condensation of magma water vapor. Hydrotherms move through cracks and voids in rocks towards low pressure - towards the earth's surface. Being weak solutions of acids or alkalis, hydrotherms are characterized by high chemical activity. As a result of the interaction of hydrothermal fluids with host rocks, minerals of hydrothermal origin are formed.

Metamorphism – a complex of endogenous processes that cause changes in the structure, mineral and chemical composition of rocks under conditions of high pressure and temperature; In this case, rock melting does not occur. The main factors of metamorphism are temperature, pressure (hydrostatic and unilateral) and fluids. Metamorphic changes consist of the disintegration of the original minerals, molecular rearrangement and the formation of new minerals that are more stable under given environmental conditions. All types of rocks undergo metamorphism; The resulting rocks are called metamorphic.

Exogenous processes – geological processes occurring due to external energy sources, mainly the Sun. They occur on the surface of the Earth and in the uppermost parts of the lithosphere (in the zone of influence of factors hypergenesis or weathering). Exogenous processes include: 1) mechanical crushing of rocks into their constituent mineral grains, mainly under the influence of daily air temperature changes and due to frost weathering. This process is called physical weathering; 2) chemical interaction of mineral grains with water, oxygen, carbon dioxide and organic compounds, leading to the formation of new minerals – chemical weathering; 3) the process of movement of weathering products (the so-called transfer) under the influence of gravity, through moving water, glaciers and wind in the area of ​​sedimentation (ocean basins, seas, rivers, lakes, relief depressions); 4) accumulation sediment layers and their transformation due to compaction and dehydration into sedimentary rocks. During these processes, deposits of sedimentary minerals are formed.

The variety of forms of interaction between exogenous and endogenous processes determines the variety of structures of the earth's crust and the topography of its surface. Endogenous and exogenous processes are inextricably linked with each other. At their core, these processes are antagonistic, but at the same time inseparable, and this entire complex of processes can be conditionally called geological form of movement of matter. She's also in Lately includes human activities.

Over the last century, there has been an increase in the role of technogenic (anthropogenic) factors in the overall complex of geological processes. Technogenesis– a set of geomorphological processes caused by human production activities. Based on their focus, human activity is divided into agricultural, exploitation of mineral deposits, construction of various structures, defense and others. The result of technogenesis is technogenic relief. The boundaries of the technosphere are constantly expanding. Thus, the depths of oil and gas drilling on land and offshore are increasing. Filling reservoirs in mountainous seismically dangerous areas causes artificial earthquakes in some cases. Mining is accompanied by the release of huge volumes of “waste” rocks onto the daytime surface, resulting in the creation of a “lunar” landscape (for example, in the area of ​​Prokopyevsk, Kiselevsk, Leninsk-Kuznetsky and other cities of Kuzbass). Dumps from mines and other industries, garbage dumps create new forms of technogenic relief, taking over an increasing part of agricultural land. Reclamation of these lands is carried out very slowly.

Thus, human economic activity has now become an integral part of all modern geological processes.

Geological processes are divided into endogenous and exogenous.

Endogenous processes are geological processes associated with energy arising in the bowels of the Earth. These include tectonic movements of the earth's crust, magmatism, rock metamorphism and seismic activity. The main sources of energy for endogenous processes are heat and gravitational instability - the redistribution of material in the interior of the Earth according to density (gravitational differentiation).

Endogenous processes include:

• - tectonic - movement of the earth’s crust, varied in direction and intensity, causing its deformation (crushing into folds) or ruptures of layers;
• - seismic - associated with earthquakes;
• - magmatic - associated with magmatic activity;
• - volcanic - associated with volcanic activity;
• - metamorphic - the process of transforming rocks under the influence of pressure and temperature without the introduction or removal of chemical components;
• - skarns - metasomatic mineral and rock formation as a result of the impact on various rocks (mainly limestones and dolomites) of high-temperature solutions containing Fe, M?, Ca, 81, Al and other substances in varying quantities with a wide participation of volatile components (water , carbon dioxide, C1, B, C, etc.), and in a wide range of temperatures and pressures with the general evolution of solutions as the temperature decreases from alkaline to acidic;
• - greisen - metasomatic change of granite rocks under the influence of gases released from cooling magma with the transformation of feldspars into light mica;
• - hydrothermal - deposits of metal ores (Au, Cu, Pb, Sn, XV, etc.) and non-metallic minerals (talc, asbestos, etc.), the formation of which is associated with the deposition or redeposition of ore matter from hot deep aqueous solutions, often associated with magma chambers cooling in the earth's crust.

Tectonic movements- mechanical movements of the earth's crust, caused by forces acting in it and mainly in the Earth's mantle, and leading to deformation of the rocks that make up the crust. Tectonic movements are usually associated with changes in the chemical composition, phase state (mineral composition) and internal structure of rocks undergoing deformation. Tectonic movements simultaneously cover very large areas.

Geodetic measurements show that almost the entire surface of the Earth is continuously in motion, but the speed of tectonic movements is small, varying from hundredths to a few tens of millimeters per year, and only the accumulation of these movements over a very long (tens to hundreds of millions of years) geological time leads to large total movements of individual sections of the earth's crust.

The American geologist G. Gilbert proposed (1890), and the German geologist H. Stille developed (1919) a classification of tectonic movements dividing them into epeirogenic, expressed in long-term uplifts and subsidences of large areas of the earth’s surface, and orogic, manifesting episodically (orogenic phases) in certain zones by the formation of folds and discontinuities and leading to the formation of mountain structures. This classification is still used today, but its main drawback is the unification into the concept of orogenesis of two fundamentally different processes - folding and rupture formation, on the one hand, and mountain building, on the other. Other classifications have been proposed. One of them (domestic geologists A.P. Karpinsky, M.M. Tetyaev, etc.) provided for the identification oscillatory folding And rupture-forming tectonic movements, the other (German geologist E. Harman and Dutch scientist R.W. van Bemmelen) - undation (wave) And undulation (folded) tectonic movements. It became clear that tectonic movements are very diverse both in the form of manifestation and in the depth of origin, as well as, obviously, in the mechanism and reasons for their occurrence.

According to another principle, tectonic movements were divided by M.V. Lomonosov into slow (centuries-old) And fast. Fast movements are associated with earthquakes and, as a rule, are distinguished by high speeds, several orders of magnitude higher than the speed of slow movements. Displacements of the earth's surface during earthquakes amount to several meters, sometimes more than 10 m. However, such displacements occur sporadically.

The division of tectonic movements into vertical (radial) And horizontal (tangential), although it is largely conditional in nature, since these movements are interconnected and transform into one another. Therefore, it is more correct to talk about tectonic movements with a predominant vertical or horizontal component. The prevailing vertical movements cause the rise and fall of the earth's surface, including the formation of mountain structures. They are the main reason for the accumulation of thick layers of sedimentary rocks in the oceans and seas, and partly on land. Horizontal movements are most clearly manifested in the formation of large displacements of individual blocks of the earth's crust relative to others with an amplitude of hundreds and even thousands of kilometers, in their thrusts with an amplitude of hundreds of kilometers, as well as in the formation of oceanic depressions thousands of kilometers wide as a result of the sliding of blocks of continental crust.

Tectonic movements are distinguished by a certain periodicity or unevenness, which is expressed in changes in sign and (or) speed over time. Relatively short-period vertical movements with frequent changes of sign (reversible) are called oscillatory. Horizontal movements usually retain their direction for a long time and are irreversible. Oscillatory tectonic movements are probably the cause transgressions And regressions sea, formation of sea and river terraces.

Based on the time of manifestation, the latest tectonic movements are distinguished, which are directly reflected in the modern topography of the Earth and therefore are recognized not only by geological, but also geomorphological methods, and modern tectonic movements, which are also studied by geodetic methods (re-leveling, etc.). They form the subject of research in modern tectonics.

Tectonic movements of the distant geological past are established by the distribution of transgressions and regressions of the ocean, by the total thickness (thickness) of accumulated sediments, by the distribution of their facies and sources of clastic material carried down in depressions. In this way, the vertical component of the movement of the upper layers of the earth's crust or the surface of the consolidated foundation located under the sedimentary cover is determined. The level of the World Ocean is used as a reference, which is considered almost constant, with possible deviations of up to 50-100 m during melting or formation of glaciers, as well as more significant ones - up to several hundred meters as a result of changes in the capacity of oceanic depressions during their expansion and the formation of mid-ocean basins. ridges

Large horizontal movements, which are not recognized by all scientists, are established both from geological data, by graphically straightening folds and restoring thrust rock strata in their original position, and on the basis of studying the residual magnetization of rocks and paleoclimate changes. It is believed that with a sufficient amount of paleomagnetic and geological data, it is possible to restore the former location of continents and oceans and determine the speed and direction of movements that occurred in subsequent times, for example, from the end of the Paleozoic era.

The speed of horizontal movements is determined by supporters of mobilism by the width of the newly formed oceans (Atlantic, Indian), by paleomagnetic data indicating changes in latitude and orientation in relation to the meridians, and by the width of stripes of magnetic anomalies of different signs formed during the expansion of the ocean floor, which are compared with the duration of epochs different polarities of the Earth's magnetic field. These estimates, as well as the speed of modern horizontal movements measured by geodetic methods in rifts (East Africa), folded areas (Japan, Tajikistan) and strike-slip faults (California), are 0.1-10 cm/g. Over millions of years, the speed of horizontal movements changes slightly, the direction remains almost constant.

Vertical movements, on the contrary, have a variable, oscillatory character. Repeated leveling shows that the rate of subsidence or uplift on the plains usually does not exceed 0.5 cm/year, while the rise in mountainous areas (for example, in the Caucasus) reaches 2 cm/year. At the same time, the average speeds of vertical tectonic movements, determined for large time intervals (for example, over tens of millions of years), do not exceed 0.1 cm/year in mobile belts and 0.01 cm/year on platforms. This difference in velocities measured over short and long periods of time indicates that in geological structures only the integral result of secular vertical movements is recorded, which accumulates by summing up fluctuations of the opposite sign.

The similarity of tectonic movements repeating on the same tectonic structures allows us to speak about the inherited nature of vertical tectonic movements. Tectonic movements usually do not include movements of rocks in the near-surface zone (tens of meters from the surface), caused by disturbances in their gravitational equilibrium under the influence of exogenous (external) geological processes, as well as periodic rises and falls of the earth's surface caused by solid tides of the Earth due to the attraction of the Moon and Sun. It is controversial to classify as tectonic movements processes associated with the restoration of isostatic equilibrium, for example, uplifts during the reduction of large ice sheets such as the Antarctic or Greenland. Movements of the earth's crust caused by volcanic activity are local in nature. The causes of tectonic movements have not yet been reliably established; Various assumptions have been made in this regard.

According to a number of scientists, deep tectonic movements are caused by a system of large convection currents covering the upper and middle layers of the Earth's mantle. Such currents are apparently associated with the stretching of the earth's crust in the oceans and compression in folded areas, above those zones where the approach and subsidence of counter currents occurs. Other scientists (V.V. Belousov) deny the existence of closed convection currents in the mantle, but admit the rise of lighter products of its differentiation heated in the lower mantle, causing upward vertical movements of the crust. The cooling of these masses causes it to sink. In this case, horizontal movements are not given significant importance, and they are considered derivatives of vertical ones. When clarifying the nature of movements and deformations of the earth's crust, some researchers assign a certain role to stresses arising in connection with changes in the speed of rotation of the Earth, others consider them too insignificant.

The deep heat of the Earth is predominantly of radioactive origin. The continuous generation of heat in the bowels of the Earth leads to the formation of a heat flow directed to the surface. At some depths, with a favorable combination of material composition, temperature and pressure, pockets and layers of partial melting can appear. Such a layer in the upper mantle is the asthenosphere - the main source of magma formation; Convection currents may arise in it, which are the presumed cause of vertical and horizontal movements of the lithosphere. In the zones of volcanic belts of island arcs and continental margins, the main sources of magma are associated with ultra-deep inclined faults (Zavaritskogo-Benioff zones), extending underneath them from the ocean (to a depth of approximately 700 km). Under the influence of heat flow or directly the heat brought by rising deep magma, so-called crustal magma chambers arise in the earth's crust itself; reaching the near-surface parts of the crust, magma penetrates into them in the form of intrusions of various shapes or pours out onto the surface, forming volcanoes.

Gravitational differentiation led to the stratification of the Earth into geospheres of different densities. On the surface of the Earth, it also manifests itself in the form of tectonic movements, which, in turn, lead to tectonic deformations of the rocks of the earth’s crust and upper mantle. The accumulation and subsequent release of tectonic stress along active faults leads to earthquakes.

Both types of deep processes are closely related: radioactive heat, reducing the viscosity of the material, promotes its differentiation, and the latter accelerates the transfer of heat to the surface. It is assumed that the combination of these processes leads to uneven temporal transport of heat and light matter to the surface, which, in turn, can be explained by the presence of tectonomagmatic cycles in the history of the earth’s crust.

Tectonic cycles(stages) - large (more than 100 million years) periods of the geological history of the Earth, characterized by a certain sequence of tectonic and general geological events. They are most clearly manifested in the mobile regions of the Earth, where the cycle begins with subsidence of the earth's crust with the formation of deep sea basins, the accumulation of thick layers of sediments, underwater volcanism, and the formation of basic and ultrabasic intrusive igneous rocks. Island arcs arise, andesitic volcanism appears, the sea basin is divided into smaller ones, and fold-thrust deformations begin. Next, the formation of folded and fold-cover mountain structures occurs, bordered and separated by advanced (edge, foothill) and intermountain troughs, which are filled with products of mountain destruction - mopasses. This process is accompanied by regional metamorphism, granite formation, and liparite-basalt ground volcanic eruptions.

A similar sequence of events is observed on the platforms: a change in continental conditions due to sea transgression, and then again regression and the establishment of a continental regime with the formation of weathering crusts, with a corresponding change in the type of sediments - first continental, then lagoonal, often salt-bearing or coal-bearing, then marine clastic, in the middle of the cycle they are predominantly carbonate or siliceous, at the end they are again marine, lagoonal (salt) and continental (sometimes glacial).

Intense fold-thrust deformations and mountain building in some mobile zones often correspond to the formation of new subsidence zones in their rear and the formation of rift systems - aulacogens on platforms.

The average duration of tectonic cycles in the Phanerozoic is 150-180 million years (in the Precambrian, tectonic cycles were apparently longer). Along with such cycles, larger ones are sometimes distinguished - megacycles (megastages) - lasting hundreds of millions of years. In Europe, partly in North America and Asia, the following cycles were established in the Late Precambrian and Phanerozoic: Grenville (Middle Riphean); Baikal (late Riphean-Vendian); Caledonian (Cambrian-Devonian); Hercynian (Devonian-Permian); Cimmerian or Mesozoic (Triassic-Jurassic); Alpine (Cretaceous-Cenozoic).

The original schematic idea of ​​tectonic cycles as strictly synchronous on the scale of the entire planet, repeating everywhere and distinguished by the same set of phenomena, is still rightly disputed. In fact, the end of one cycle and the beginning of another often turn out to be synchronous (in different, often adjacent regions). In each individual mobile system, usually one or two cycles are most fully expressed, immediately preceding its transformation into a folded mountain system, and the earlier ones are distinguished by the incompleteness of the set of phenomena characteristic of them, which sometimes merge with each other. On the scale of the entire history of the Earth, tectonic cyclicity appears only as a complication of its general directional development. Individual cycles form stages of megacycles, and they, in turn, form major stages in the history of the Earth as a whole. The reasons for the cyclicity have not yet been established. Suggestions have been made about the periodic accumulation of heat and an increase in heat flow emanating from the deep interior of the Earth, about cycles of ascent or circulation (convection) of differentiation products of mantle matter, etc.

Spatial irregularities of the same deep-seated processes are used to explain the division of the earth's crust into more or less geologically active regions, for example, mountain-folded areas and platforms.

The formation of the Earth's topography and the formation of many important minerals are associated with endogenous processes.

Exogenous processes are geological processes caused by energy sources external to the Earth (mainly solar radiation) in combination with gravity. Exogenous processes occur on the surface and in the near-surface zone of the earth’s crust in the form of its mechanical and physicochemical interaction with the hydrosphere and atmosphere. These include sedimentation and the formation of deposits of sedimentary minerals, weathering, geological activity of wind (aeolian processes, deflation), flowing surface and groundwater (erosion, denudation), lakes and swamps, waters of seas and oceans (abrasion), glaciers (exaration) .

Exogenous processes include different types weathering in the form destruction:

• - deflationary - blowing, grinding and grinding of rocks with mineral particles carried by the wind;
• - mudflows - the formation and movement of mud or mud-stone flows;
• - erosion - erosion of soils and rocks by water flows;

or different processes savings precipitation:

• - alluvial - river deposits in the form of sand, pebbles, conglomerates;
• - deluvial - movement of rock weathering products down the slope under the influence of gravity, rain and melt water;
• - colluvial - displacement of slope debris under the influence of gravity;
• - landslides - separation of land masses and rocks and their movement along the slope under the influence of gravity;
• - sediment-forming - deposition of precipitation from water, air (in calm areas) or on slopes under the influence of gravity;
• - proluvial - the movement of rock destruction products by temporary flows and their deposition at the foot of the mountains, often in the form of alluvial cones;
• - ore-forming - accumulation of ore matter under the influence of various reasons: native gold - as a result of precipitation from water flows, aluminum oxides - precipitation from aqueous solutions, etc.;
• - eluvial - products of rock destruction remain at the site of their formation.

Weathering- the process of destruction and change of rocks in the conditions of the earth's surface as a result of mechanical and chemical effects of the atmosphere, ground and surface waters and organisms. According to the nature of the environment in which weathering occurs, it can be atmospheric And underwater Based on the type of weathering effects on rocks, there are: physical weathering, leading only to the mechanical disintegration of the rock into fragments; chemical weathering, in which the chemical composition of the rock changes with the formation of minerals that are more resistant to the conditions of the earth’s surface; organic (biological) weathering, which comes down to mechanical fragmentation or chemical change of rock as a result of the vital activity of organisms. A unique type of weathering is soil formation, in which biological factors play a particularly active role. Weathering of rocks occurs under the influence of water (precipitation and groundwater), carbon dioxide and oxygen, water vapor, atmospheric and ground air, seasonal and daily temperature fluctuations, the vital activity of macro- and microorganisms and their decomposition products. In addition to the listed agents, the speed and degree of weathering, the thickness of the resulting weathering products and their composition are also influenced by the relief and geological structure of the area, the composition and structure of the source rocks. The overwhelming number of physical and chemical weathering processes (oxidation, sorption, hydration, coagulation) occur with the release of energy. Typically, the types of weathering act simultaneously, but depending on the climate, one or another of them predominates.

Physical weathering occurs mainly in dry and hot climates and is associated with sharp fluctuations in the temperature of rocks when heated sun rays(insolation) and subsequent night cooling; a rapid change in the volume of the surface parts of rocks leads to their cracking. In areas with frequent temperature fluctuations around 0 °C, mechanical destruction of rocks occurs under the influence of frost weathering; When water that has penetrated into cracks freezes, its volume increases and the rock ruptures.

Chemical and organic types of weathering are characteristic mainly of layers with a humid climate. The main factors of chemical weathering are air and especially water containing salts, acids and alkalis. Aqueous solutions, circulating in the rock mass, in addition to simple dissolution, are also capable of producing complex chemical changes.

Physical and chemical weathering processes occur in close connection with the development and vital activity of animals and plants and the action of their decay products after death. The most favorable conditions for the formation and preservation of weathering products (minerals) are tropical or subtropical climate conditions and insignificant erosional dissection of the relief. At the same time, the thickness of rocks that have undergone weathering is characterized (from top to bottom) by geochemical zoning, expressed by a complex of minerals characteristic of each zone. The latter are formed as a result of successive processes: rock decay under the influence of physical weathering, leaching of bases, hydration, hydrolysis and oxidation. These processes often proceed until the complete decomposition of primary minerals, up to the formation of free oxides and hydroxides.

Depending on the degree of acidity - alkalinity of the environment, as well as the participation of biogenic factors, minerals of different chemical compositions are formed: from those that are stable in an alkaline environment (in the lower horizons) to those that are stable in an acidic or neutral environment (in the upper horizons). The diversity of weathering products, represented by various minerals, is determined by the composition of the minerals of primary rocks. For example, on ultramafic rocks (serpentinites), the upper zone is represented by rocks in the cracks of which carbonates (magnesite, dolomite) are formed. This is followed by horizons of carbonatization (calcite, dolomite, aragonite), hydrolysis, which is associated with the formation of nontronite and accumulation of nickel (NiO up to 2.5%), silicification (quartz, opal, chalcedony). The zone of final hydrolysis and oxidation is composed of hydrogoethite (ocher), goethite, magnetite, manganese oxides and hydroxides (nickel- and cobalt-containing). Large deposits of nickel, cobalt, magnesite and naturally alloyed iron ores are associated with weathering processes.

In cases where weathering products do not remain at the site of their formation, but are carried away from the surface of weathering rocks by water or wind, peculiar forms of relief often arise, depending both on the nature of weathering and on the properties of the rocks in which the process appears to manifest itself. emphasizes the features of their structure (Fig. 15).

Rice. 15.

Russia (TSB).

Igneous rocks (granites, diabases, etc.) are characterized by massive rounded weathering forms; for layered sedimentary and metamorphic - stepped (cornices, niches, etc.). The heterogeneity of rocks and the unequal resistance of their different sections against weathering leads to the formation of outliers in the form of isolated mountains, pillars (Fig. 16), towers, etc.

In a humid climate, on inclined surfaces of homogeneous rocks that are relatively easily soluble in water, for example, limestone, flowing water corrodes irregular shape depressions separated by sharp projections and ridges, resulting in an uneven surface known as carr.

Rice. 16.

the Yenisei River near Krasnoyarsk (TSB).

During the degeneration of residual weathering products, many soluble compounds are formed, which are carried by groundwater into water basins and become part of dissolved salts or precipitate. Weathering processes lead to the formation of various sedimentary rocks and many minerals: kaolins, ocher, refractory clays, sands, ores of iron, aluminum, manganese, nickel, cobalt, placers of gold, platinum, etc., oxidation zones of pyrite deposits with their minerals and etc.

Deflation(from Late Lat. With1 e/1 aio- blowing, blowing away) - fluttering, destruction of rocks and soils under the influence of wind, accompanied by the transfer and grinding of torn particles. Deflation is especially strong in deserts, in those parts from which the prevailing winds blow (for example, in the southern part of the Karakum Desert). The combination of deflation and physical weathering processes leads to the formation of whittled rocks of bizarre shapes in the form of towers, columns, obelisks, etc.

Soil erosion- soil destruction by water and wind, movement of destruction products and their redeposition.

Education aeolian landforms occurs under the influence of wind mainly in areas with an arid climate (deserts, semi-deserts); It is also found along the shores of seas, lakes and rivers with scanty vegetation cover that is unable to protect loose and weathered substrate rocks from the action of the wind. Most common accumulative And accumulative-deflationary forms, formed as a result of the movement and deposition of sand particles by the wind, as well as developed (deflationary) aeolian landforms resulting from blowing (deflation) loose products of weathering, destruction of rocks under the influence of dynamic impacts of the wind itself and especially under the impact of impacts of small particles carried by the wind in a wind-sand flow.

The shape and size of accumulative and accumulative-deflationary formations depend on the wind regime (strength, frequency, direction, structure of the wind flow) prevailing in the area and operating in the past, on the saturation of sand particles in the wind-sand flow, the degree of connectivity of the loose substrate with vegetation, on moisture and other factors, as well as the nature of the underlying terrain. The greatest influence on the appearance of aeolian landforms in sandy deserts is exerted by the regime active winds, acting similarly to a water flow with turbulent movement of the medium near a solid surface. For medium- and fine-grained dry sand (with a grain diameter of 0.5-0.25 mm), the minimum active wind speed is 4 m/s. Accumulative and deflationary-accumulative forms, as a rule, move in accordance with the seasonally dominant wind direction: progressively under the annual influence of active winds of the same or similar directions; oscillatory and oscillatory-translational, if the directions of these winds change significantly during the year (to the opposite, perpendicular, etc.). The movement of bare sandy accumulative forms occurs especially intensively (at a speed of up to several tens of meters per year).

Accumulative and deflationary-accumulative aeolian relief forms of deserts are characterized by the simultaneous presence of overlapping forms of several categories of magnitude: 1st category - wind ripples, height from fractions of a millimeter to 0.5 m, distance between ridges from several millimeters to 2.5 m; 2nd category - thyroid accumulations with a height of at least 40 cm; 3rd category - dunes up to 2-3 m high, connecting into a ridge longitudinal to the winds or into a dune chain transverse to the winds; 4th category - dune relief up to 10-30 m high; 5th and 6th categories - large forms (up to 500 m in height), formed mainly by rising air currents. In the deserts of the temperate zone, where vegetation plays an important role, restraining the work of the wind, relief formation proceeds more slowly and the largest forms do not exceed 60-70 m, the most characteristic here are bite braids, spit mounds and bite mounds with a height of several decimeters to 10-10. 20 m.

Since the prevailing wind regime (trade wind, monsoon-breeze, cyclonic, etc.) and the consolidation of the loose substrate are primarily determined by zonal-geographical factors, accumulative and accumulative-deflationary aeolian relief forms are generally distributed zonally. According to the classification proposed by geographer B.A. Fedorovich, bare, easily mobile sandy forms are characteristic mainly of tropical extra-arid deserts (Sahara, deserts of the Arabian Peninsula, Iran, Afghanistan, Taklamakan); semi-overgrown, weakly mobile - mainly for extratropical deserts (deserts of Central Asia and Kazakhstan, Dzungaria, Mongolia, Australia); overgrown, mostly stationary dune forms - for non-desert areas (mainly ancient glacial regions of Europe, Western Siberia, North America). A detailed classification of accumulative and deflationary-accumulative aeolian landforms depending on the wind regime is given in the description of dunes and dunes.

Among the produced microforms (up to several tens of centimeters in diameter), the most common are lattice or honeycomb rocks, composed mainly of terrigenous rocks; among the forms average size(meters and tens of meters) - yardangs, hollows, boilers And blowing niches, oddly shaped rocks(mushroom-shaped, ring-shaped etc.), clusters of which often form entire aeolian “cities”; large worked out forms (several kilometers across) include blowing basins And saline-deflation depressions, formed under the combined influence of intense processes of physicochemical (salt) weathering and deflation (including huge areas of up to hundreds of kilometers; for example, the Karagiye depression in Western Kazakhstan). A comprehensive study of aeolian landforms, their morphology, origin, and dynamics is important in the economic development of deserts.

Abrasion(from lat. I'm sorry- scraping, shaving) - destruction by waves and surf of the shores of seas, lakes and large reservoirs. The intensity of abrasion depends on the degree of wave action of the reservoir. The most important condition, which predetermines the abrasion development of the coast, is the relatively steep angle of the initial slope (more than 1 °) of the coastal part of the sea or lake bottom. Abrasion creates an abrasion terrace, or bench, and an abrasion ledge, or cliff, on the banks (Fig. 17). The sand, gravel, and pebbles formed as a result of the destruction of rocks can be involved in the processes of sediment movement and serve as material for coastal accumulative forms. Part of the material is carried by waves and currents to the foot of the abrasive underwater slope and forms a leaning accumulative terrace here. As the abrasion terrace expands, abrasion gradually fades (as the strip of shallow water expands, to overcome which wave energy is consumed) and, with the arrival of sediment, can be replaced by accumulation. On the slopes of artificial reservoirs, the slopes of which in the past were formed by factors other than abrasion, the rate of abrasion is especially high - up to ten meters per year.

Rice. 17.

K - cliff; AT - abrasion terrace (bench); PAT - underwater accumulative terrace; WC - water level. The dotted line indicates the pre-abrasive relief (BER).

Exaration(from Late Lat. ehagayo- gouging) - glacial gouging, destruction by a glacier of the rocks that make up its bed, and removal of destruction products (rejects, boulders, pebbles, sand, clay, etc.) by a moving glacier. As a result of exaration, troughs, lake basins, “ram’s foreheads”, “curly rocks”, glacial scars, and shading appear. Along with the destruction of rocks, they are smoothed, polished and polished.

Main forms of manifestation exogenous processes on the surface of the Earth:

• - destruction of rocks and chemical transformation of their constituent minerals (physical, chemical, organic weathering);
• - removal and transfer of loosened and soluble products of rock destruction by water, wind and glaciers;
• - deposition (accumulation) of these products in the form of sediments on land or at the bottom of water basins and their gradual transformation into sedimentary rocks as a result of successive processes of sedimentogenesis, diagenesis and catagenesis.

Exogenous processes in combination with endogenous ones are involved in the formation of the Earth's topography, in the formation of sedimentary rock strata and associated mineral deposits. For example, under conditions of specific weathering and sedimentation processes, ores of aluminum (bauxite), iron, nickel, etc. are formed; as a result of selective deposition of minerals by water flows, placers of gold and diamonds are formed; under conditions favorable to the accumulation of organic matter and sedimentary rocks enriched with it, combustible minerals arise.

Throughout the existence of the Earth, its surface has continuously changed. This process continues today. It proceeds extremely slowly and imperceptibly for a person and even many generations. However, it is these transformations that ultimately radically change the appearance of the Earth. Such processes are divided into exogenous (external) and endogenous (internal).

Classification

Exogenous processes are the result of the interaction of the planet’s shell with the hydrosphere, atmosphere and biosphere. They are studied in order to accurately determine the dynamics of the geological evolution of the Earth. Without exogenous processes, the patterns of development of the planet would not have developed. They are studied by the science of dynamic geology (or geomorphology).

Experts have adopted a universal classification of exogenous processes, divided into three groups. The first is weathering, which is a change in properties under the influence of not only wind, but also carbon dioxide, oxygen, the vital activity of organisms and water. The next type of exogenous processes is denudation. This is the destruction of rocks (and not a change in properties as in the case of weathering), their fragmentation by flowing waters and winds. The last type is accumulation. This is the formation of new ones due to sediments accumulated in depressions of the earth's relief as a result of weathering and denudation. Using the example of accumulation, we can note the clear interconnection of all exogenous processes.

Mechanical weathering

Physical weathering is also called mechanical weathering. As a result of such exogenous processes, rocks turn into blocks, sand and debris, and also disintegrate into fragments. The most important factor in physical weathering is insolation. Due to heating by the sun's rays and subsequent cooling, periodic changes in the volume of the rock occur. It causes cracking and disruption of bonds between minerals. The results of exogenous processes are obvious - the rock splits into pieces. The greater the temperature amplitude, the faster this happens.

The rate of crack formation depends on the properties of the rock, its foliation, layering, and cleavage of minerals. Mechanical failure can take several forms. From a material with a massive structure, pieces break off that look like scales, which is why this process is also called scaling. And granite breaks up into blocks with the shape of a parallelepiped.

Chemical destruction

Among other things, the dissolution of rocks is facilitated by the chemical action of water and air. Oxygen and carbon dioxide are the most active agents that are dangerous to the integrity of surfaces. Water carries salt solutions, and therefore its role in the process of chemical weathering is especially great. Such destruction can be expressed in a variety of forms: carbonation, oxidation and dissolution. In addition, chemical weathering leads to the formation of new minerals.

For thousands of years, water flows down surfaces every day and seeps through pores formed in decaying rocks. Liquid takes out a large number of elements, thereby leading to the decomposition of minerals. Therefore, we can say that there are no absolutely insoluble substances in nature. The only question is how long they retain their structure despite exogenous processes.

Oxidation

Oxidation mainly affects minerals, which include sulfur, iron, manganese, cobalt, nickel and some other elements. This chemical process is especially active in an environment saturated with air, oxygen and water. For example, in contact with moisture, metal oxides that are part of rocks become oxides, sulfides become sulfates, etc. All these processes directly affect the topography of the Earth.

As a result of oxidation, sediments of brown iron ore (orzands) accumulate in the lower layers of the soil. There are other examples of its influence on the terrain. Thus, weathered rocks containing iron are covered with brown crusts of limonite.

Organic weathering

Organisms also participate in the destruction of rocks. For example, lichens (the simplest plants) can settle on almost any surface. They support life by extracting nutrients using secreted organic acids. After the simplest plants, woody vegetation settles on rocks. In this case, the cracks become home to roots.

Characteristics of exogenous processes cannot do without mentioning worms, ants and termites. They make long and numerous underground passages and thereby contribute to the penetration of atmospheric air, which contains destructive carbon dioxide and moisture, into the soil.

Ice influence

Ice is an important geological factor. It plays a significant role in the formation of the earth's topography. In mountainous areas, ice moving along river valleys changes the shape of drains and smoothes surfaces. Geologists called this destruction exaration (gouging out). Moving ice performs another function. It transports clastic material that has broken off from rocks. Weathering products fall off the slopes of valleys and settle on the surface of the ice. Such eroded geological material is called a moraine.

No less important is ground ice, which forms in the soil and fills ground pores in permafrost and permafrost areas. Climate is also a contributing factor here. The lower the average temperature, the greater the depth of freezing. Where the ice melts in the summer, pressure waters rush to the surface of the earth. They destroy the relief and change its shape. Similar processes are repeated cyclically from year to year, for example, in the north of Russia.

Sea factor

The sea occupies about 70% of the surface of our planet and, without a doubt, has always been an important geological exogenous factor. Ocean water moves under the influence of wind, tidal currents and tidal currents. This process is associated with significant destruction of the earth's crust. The waves, which splash even with the weakest sea waves off the coast, constantly undermine the surrounding rocks. During a storm, the surf force can be several tons per square meter.

The process of demolition and physical destruction of coastal rocks by sea water is called abrasion. It flows unevenly. An eroded bay, cape or isolated rocks may appear on the shore. In addition, the breaking waves create cliffs and ledges. The nature of destruction depends on the structure and composition of coastal rocks.

At the bottom of the oceans and seas, continuous processes of denudation occur. Intense currents contribute to this. During storms and other disasters, powerful deep waves are formed, which on their way encounter underwater slopes. When a collision occurs, the sludge liquefies and destroys the rock.

Wind work

The wind makes a difference like nothing else. It destroys rocks, transports small fragmentary material and deposits it in an even layer. At a speed of 3 meters per second, the wind moves leaves, at 10 meters it shakes thick branches, raises dust and sand, at 40 meters it uproots trees and demolishes houses. Dust devils and tornadoes do especially destructive work.

The process of wind blowing away rock particles is called deflation. In semi-deserts and deserts, it forms significant depressions on the surface composed of salt marshes. The wind acts more intensely if the ground is not protected by vegetation. Therefore, it deforms mountain basins especially strongly.

Interaction

The interaction of exogenous and endogenous geological processes plays a huge role in the formation. Nature is designed in such a way that some give rise to others. For example, external exogenous processes eventually lead to the appearance of cracks in the earth's crust. Through these holes, magma enters from the bowels of the planet. It spreads in the form of covers and forms new rocks.

Magmatism is not the only example of how the interaction of exogenous and endogenous processes works. Glaciers help level the terrain. This is an external exogenous process. As a result, a peneplain (a plain with small hills) is formed. Then, as a result of endogenous processes (tectonic movement of plates), this surface rises. Thus, internal and may contradict each other. The relationship between endogenous and exogenous processes is complex and multifaceted. Today it is studied in detail within the framework of geomorphology.