The thickness of the earth's crust. Earth's crust

Introduction

Compared to size the globe, the earth's crust is 1/200 of its radius. But this "film" is the most complex in structure and still the most mysterious formation on our planet. The main feature of the crust is that it serves as a boundary layer between the earth and the outer space that surrounds us. In this transitional zone between the two elements of the universe - space and the substance of the planet - the most complex physicochemical processes were constantly taking place, and, what is remarkable, traces of these processes are largely preserved.

The main objectives of the work are:

Consider the main types crust and its components;

Define tectonic structures the earth's crust;

Consider the mineral composition of the earth's crust and rocks.

> Structure and thickness of the earth's crust

The first ideas about the existence of the earth's crust were expressed by the English physicist W. Hilbert in 1600. They proposed to divide the bowels of the earth into two unequal parts: the crust or shell and the solid core.

The development of these ideas is contained in the works of L. Descartes, G. Leibniz, J. Buffon, M. V. Lomonosov and many other, foreign and domestic scientists. In the beginning, the study of the earth's crust was focused on the study of the earth's crust of the continents. Therefore, the first crustal models reflected the structural features of the continental type crust.

The term "crust" was introduced in geographical science Austrian geologist E. Suess in 1881 (8) In addition to this term, this layer has another name - sial, composed of the first letters of the most common elements here - silicon (silicium, 26%) and aluminum (aluminum, 7.45%) ...

In the first half of the 20th century, the study of the structure of the subsoil began to be carried out using seismology and seismics. Analyzing the nature of seismic waves from the earthquake in Croatia in 1909, seismologist A. Mohorovicic, as already mentioned, identified a clearly traced seismic boundary at a depth of about 50 km, which he defined as the base of the earth's crust (the surface of Mohorovicic, Moho, or M).

In 1925, V. Konrad fixed above the Mohorovichich boundary one more interface inside the crust, which also received his name - the Konrad surface, or surface K - the boundary between the "granite" and "basalt" layers is the Konrad division.

Scientists have proposed to call the upper crustal layer about 12 km thick "granite layer", and the lower 25 km thick - "basalt". The first two-layer model of the structure of the earth's crust appeared. Further studies made it possible to measure the thickness of the crust in different regions of the continents. It was found that in low-lying areas it is 35? 45 km, and in the mountains it increases to 50? 60 km (the maximum crustal thickness - 75 km is recorded in the Pamirs). Such thickening of the earth's crust was called by B. Gutenberg "the roots of the mountains".

It was also found that the granite layer has a seismic wave velocity of 5? 6 km / s, typical for granites, and the lower one is 6? 7 km / s, typical for basalts. The earth's crust, consisting of granite and basalt layers, was called consolidated crust, on which another, upper, sedimentary layer is located. Its power varied within 0 5-6 km (the maximum thickness of the sedimentary layer reaches 20-25 km).

A new step in the study of the structure of the earth's crust of the continents was made as a result of the introduction of powerful explosive sources of seismic waves.

In 1954 G.A. Gamburtsev developed a method of deep seismic sounding (DSS), which made it possible to "illuminate" the bowels of the Earth to a depth of 100 km.

Seismic studies began to be carried out according to special profiles, which made it possible for scientists to obtain continuous information about the structure of the earth's crust. Seismic exploration was carried out in the coastal zones of the seas and oceans, and in the early 60s, global studies of the bottom of the World Ocean began with this method. The idea of the existence of two fundamentally different types of crust: continental and oceanic was scientifically substantiated.

The DSS materials allowed Soviet geophysicists (Yu.N. Godin, NI Pavlinkova, NK Bulin, etc.) to refute the idea of the existence of the ubiquitous Konrad surface. This was also confirmed by the drilling of the Kola superdeep well, which did not penetrate the base of the granite layer at the depth indicated by geophysicists.

The idea of the existence of several interfaces such as the Conrad surface began to develop, the positions of which were determined not so much by a change in the composition of crystalline rocks, but by a different degree of their metamorphism. It was thought that metamorphic rocks play a significant role in the composition of the granite and basalt layers of the earth's crust (Yu.N. Godin, I.A.Rezanov, V.V. Belousov, etc.).

The increase in the speed of seismic waves was explained by an increase in the basicity of rocks and a high degree of their metamorphism. Thus, the composition of the "granite" layer should include not only granitoids, but also metamorphic rocks (such as gneisses, micaceous schists, etc.), arising from primary sedimentary deposits. The layer began to be called granite-metamorphic, or granite-gneiss. It was understood as a set of igneous and sedimentary-metamorphic rocks, the composition and phase state of which determine the physical parameters close to those of unaltered granites or granitoids, i.e. density of the order of 2.58? 2.64 g / cm and reservoir velocity 5.5? 6.3 km / s.

The composition of the "basalt" layer was assumed to contain rocks of the deep (granulite) stage of metamorphism. They began to call it granulite-basic, granulite-eclogite, and understand it as a set of igneous and metamorphosed rocks of average, basic or similar composition, having physical parameters: density 2.8? 3.1 g / cm, reservoir velocity 6.6? 7.4 km / s. Judging by the experimental data, debris (xenoliths) of deep rocks from the pipes of the explosion, this layer can be composed of granulites, gabbroids, basic gneisses and eclogite-like rocks.

The terms "granite" and "basalt" layer remained in circulation, but they were taken in quotation marks, thereby emphasizing the conventionality of their composition and name.

The modern stage in the development of ideas about the structure of the earth's crust of continents began in the 80s of the last century and is characterized by the creation of a three-layer model of the consolidated crust. Studies of a number of domestic (N.I. Pavlenkova, I.P. Kosminskaya) and foreign (S. Mueller) scientists have proved that in the structure of the earth's crust of continents, in addition to the sedimentary layer, it is necessary to distinguish at least three, not two, layers : top, middle and bottom (fig. 1).

Top layer, 8? 15 km, is marked by an increase in the speed of seismic waves with depth, block structure, the presence of relatively numerous cracks and faults. Layer outsole with speeds of 6.1? 6.5 km / s is defined as the boundary of K. According to a number of scientists, the upper layer of the consolidated crust corresponds to the granite-metamorphic layer in the two-layer crustal model.

The second (middle) layer to a depth of 20? 25 km (sometimes up to 30 km) is characterized by a slight decrease in the velocity of elastic waves (about 6.4 km / s), the absence of velocity gradients. Its base is distinguished as the boundary of K. It is believed that the second layer is composed of rocks of the type of basalts, therefore it can be identified with the "basalt" layer of the crust.

Fig. 1 High-speed columns for the main structural elements of the continents (according to N.I. Pavlenkova). 1 - sedimentary layer; 2-4 - layers of the consolidated crust (2 - upper, 3 - middle, 4 - lower); 5 and 6 - mantle.

The third (lower) layer, traced to the base of the crust, is high-speed (6.8 × 7.7 km / s). It is characterized by a thin layering and an increase with depth of the velocity gradient. It is represented by ultrabasic rocks, so it cannot be classified as a "basalt" layer of the crust. There are suggestions that the lower crustal layer is a product of the transformation of the material of the upper mantle, a kind of weathering zone of the mantle (N.I. Pavlenkova). In the classical model of the structure of the crust, the middle and lower layers make up the granulite-basic layer.

The structure and thickness of the earth's crust varies somewhat within different regions of the continents. Thus, the following structural features are characteristic of the earth's crust, deep platform depressions and foredeeps: high thickness of the sedimentary layer (up to half the thickness of the entire crust); thinner and more high-speed, than in other parts of the platforms, consolidated crust; the elevated position of the surface of M. The upper ("granite") layer of the consolidated crust often wedges out or sharply becomes thinner, and the thickness of the middle layer is also significantly reduced.

1.Types of the earth's crust.
2. Hypotheses of tectonic development of the Earth and the earth's crust.
3. Hypothesis of the movement of the plates of the lithosphere.

1.Types of the earth's crust.

There are 2 main types of the earth's crust: continental and oceanic and 2 transitional types - subcontinental and suboceanic.

Continental the type of the earth's crust has a thickness of 35 to 75 km, in the shelf area - 20 - 25 km, and on the continental slope it wedges out. There are 3 layers of continental crust:

1st - upper, composed of sedimentary rocks with a thickness of 0 to 10 km. on platforms and 15 - 20 km. in the tectonic troughs of mountain structures.

2nd - medium " granite - gneiss"Or" granite " - 50% granites and 40% gneisses and other metamorphosed rocks. Its average thickness is 15 - 20 km ... (in mountain structures up to 20 - 25 km.).

3rd - lower, "basalt" or " granite - basalt» , compositionally close to basalt. Thickness from 15 - 20 to 35 km. The border between"Granite" and "basalt" layers - Conrad's section.

According to modern data oceanic the type of the earth's crust also has a three-layer structure with a thickness of 5 to 9 (12) km., more often 6 -7 km.

1st layer - upper, sedimentary, consists of loose sediments. Its thickness is from several hundred meters to 1 km.

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

3rd layer - lower, not exposed by drilling. It is composed of basic igneous rocks of the gabro type with subordinate ultrabasic rocks (serpentinites, pyroxenites).

Subcontinental type of earth surface in structure, it is similar to the continental, but does not have a clearly defined Conrad section. This type of crust is usually associated with island arcs - the Kuril, Aleutian and continental margins.

1st layer - upper, sedimentary - volcanic, thickness - 0.5 - 5 km. (on average 2 - 3 km.).

2nd layer - island arc,"Granite" , thickness 5 - 10 km.

3rd layer - "basalt" , at depths of 8 - 15 km., with a thickness of 14 - 18 to 20 - 40 km.

Suboceanic the type of the earth's crust is confined to the basin parts of the marginal and inland seas (Okhotsk, Japanese, Mediterranean, Black, etc.). In structure, it is close to the oceanic, but differs in an increased thickness of the sedimentary layer.

The 1st upper - 4 - 10 km and more, is located directly on the third oceanic layer with a thickness of 5 - 10 km.

The total thickness of the earth's crust is 10 - 20 km., In some places up to 25 - 30 km. by increasing the sedimentary layer.

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

2. Hypotheses of tectonic development of the Earth and the earth's crust.

Continental drift hypothesis.

The most complete hypothesis of continental drift was developed in 1912 by the famous German geophysicist A. Wegener.

According to A. Wegener's ideas, the entire surface of the Earth was originally covered with a continuous thin granite layer. In the Paleozoic era, all the granite material was collected in one block. A single foremother was formed - Pangea (Greek."Pan" - universal, "ge" - Earth). He towered above the level of the boundless aboutkeana. The reason for this could be the influence of tidal and centrifugal forces. Tidal forces are associated with the attraction of the Sun and Moon; they operate on the earth's surface from east to west. Centrifugal forces are caused by the rotation of the Earth and are directed from the poles to the equator. In the middle of the Mesozoic era, Pangea began to split into separate blocks - continents. Under the influence of the same forces, they began to sail away from each other in a latitudinal direction. For example, America broke away from Europe and Africa and moved westward. In between, the Atlantic Ocean emerged. South America and Africa experienced a clockwise turn in their movement. As a result of the movement of Antarctica to the south, Australia to the southeast, and Hindustan to the northeast, a Indian Ocean... Thus, in the Wegener's hypothesis, the Atlantic and Indian oceans are considered as secondary, and the Pacific Ocean as the remnant of the primary ocean. Its area was gradually decreasing as a result of advancing on it from all sides of the continents.

The hypothesis of the expansion of the Earth.

Proponents of this hypothesis suggest that the volume of the globe was originally much smaller than it is now. The radius of the Earth was 3500 - 4000 km., And its surface was half the size of modern. Oceans did not exist yet. The continental crust covered the entire globe with a continuous shell. According to some researchers, the expansion of the Earth began at the end of the Paleozoic era. Others believe it happened in the Cretaceous. From that moment on, the radius of the Earth began to increase annually by approximately 0.6 mm. As a result of expansion, the originally single continental crust cracked. Separate continents were formed, they moved further and further away from each other as the Earth continued to expand. In the intervals between the continents, the subcrustal layer was exposed. The mantle material rising from below penetrated here, forming a new oceanic type crust.

Ripple hypothesis.

At the beginning of the twentieth century. the idea was expressed that the epochs of the Earth's expansion were replaced by the epochs of its contraction.

According to them, epochs of compression correspond to mountain-building phases, epochs of expansion correspond to periods of dormancy and subsidence of the basins. Stretching of the earth's crust is concentrated mainly in rift zones. It is compensated by compression of the crust in the area of deep-sea trenches and mountain-folded systems. Compression and stretching effects are distributed unevenly on the surface of the Earth. As a result of multiple alternating compression and extension, crustal blocks drift from extension zones to compression zones. So, for example, the Syrian - Arabian plate moves from the grabens of the Red Sea and the Gulf of Aden towards the folded ranges of the Taurus, Zagros and the Caucasus.

3. Hypothesis of the movement of the plates of the lithosphere.

Features of the movement of lithospheric plates were described in the late 60s by W. Jason Morgan, Xavier Le Pinnon, and others. According to their views, the Earth's surface is divided into 9 main ones (1. Pacific; 2. North American; 3. Euro-Asian; 4. Coconut; 5. Nazca; 6. South American; 7. African; 8. Indo - Australian; 9. Antarctic) and several small rigid lithospheric plates. They include not only continents, but also adjacent parts of the ocean floor. The main boundaries of the lithosphere plates are rifts of mid-oceanic ridges, deep-sea trenches and folded mountains on the outskirts of the continents.

From the line of mid-oceanic ridges, due to the formation of the oceanic crust here, the lithospheric plates are moving apart (in different directions). The buildup of oceanic crust along the axes of the rift valleys is compensated by its destruction at the opposite edge of the plate - in the zone of the deep-sea trench. It is assumed that here the oceanic lithosphere plate moving from the middle ridge bends and plunges into the asthenosphere at an angle of 45° under the advancing plate of the continental lithosphere. This submersion occurs to a depth of 700 km..

A number of scientists believe that such views are poorly reasoned.

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Plan:

Introduction 2

1. General information about the structure of the Earth and the composition of the earth's crust 3

2. Types of rocks that make up the earth's crust 4

2.1. Sedimentary rocks 4

2.2. Igneous rocks 5

2.3. Metamorphic rocks 6

3. The structure of the earth's crust 6

4. Geological processes occurring in the earth's crust 9

4.1. Exogenous processes 10

4.2. Endogenous processes 10

Conclusion 12

List of used literature 13

Introduction

All knowledge about the structure and history of the development of the earth's crust constitutes a subject called geology. The earth's crust is the upper (stone) shell of the Earth, also called the lithosphere (in Greek, "cast" - stone).

Geology as a science is subdivided into a number of independent departments that study certain questions of the structure, development and history of the earth's crust. These include: general geology, structural geology, geological mapping, tectonics, mineralogy, crystallography, geomorphology, paleontology, petrography, lithology, and mineral geology, including the geology of oil and gas.

The main provisions of general and structural geology are the foundation for understanding the issues of oil and gas geology. In turn, the main theoretical provisions on the origin of oil and gas, the migration of hydrocarbons and the formation of their accumulations underlie the search for oil and gas. In the geology of oil and gas, the regularities of the distribution of various types of hydrocarbon accumulations in the earth's crust are also considered, which serve as the basis for predicting the oil and gas content of the regions and regions under study and are used in prospecting and exploration for oil and gas.

This work will consider issues related to the earth's crust: its composition, structure, processes occurring in it.

1. General information about the structure of the Earth and the composition of the earth's crust

In general, the planet Earth has the shape of a geoid, or an ellipsoid flattened at the poles and equator, and consists of three shells.

In the center is core(radius 3400 km), around which is located mantle in the depth interval from 50 to 2900 km. The inner part of the core is assumed to be solid, iron - nickel composition. The mantle is in a molten state, in the upper part of which magma chambers are located.

At a depth of 120 - 250 km under the continents and 60 - 400 km under the oceans lies a layer of the mantle called asthenosphere... Here the substance is in a state close to melting, its viscosity is greatly reduced. All lithospheric plates seem to float in a semi-liquid asthenosphere, like ice floes in water.

Above the mantle is Earth's crust, the power of which changes dramatically on the continents and in the oceans. The base of the crust (the surface of Mohorovichich) is located at a depth of 40 km on average under the continents, and at a depth of 11 - 12 km under the oceans. Therefore, the average thickness of the crust under the oceans (minus the water column) is about 7 km.

The earth's crust is composed mountain porosdy, i.e., communities of minerals (polymineral aggregates) that have arisen in the earth's crust as a result of geological processes. Minerals- natural chemical compounds or native elements with certain chemical and physical properties and arising in the earth as a result of chemical and physical processes. Minerals are divided into several classes, each of which combines tens and hundreds of minerals. For example, sulfur compounds of metals form the sulfide class (200 minerals), sulfuric acid salts form 260 minerals of the sulfate class. There are classes of minerals: carbonates, phosphates, silicates, the latter of which are most widespread in the earth's crust and form more than 800 minerals.

2. Types of rocks that make up the earth's crust

So, rocks are natural aggregates of minerals of more or less constant mineralogical and chemical composition, forming independent geological bodies that make up the earth's crust. The shape, size and mutual arrangement of mineral grains determine the structure and texture of rocks.

According to the conditions of education (genesis) distinguish between: sedimentary,igneous and metamorphic rocks.

2.1. Sedimentary rocks

Genesis sedimentary rocks- either the result of destruction and redeposition of pre-existing rocks, or precipitation from aqueous solutions (various salts), or - the result of the vital activity of organisms and plants. A characteristic feature of sedimentary rocks is their layering, reflecting the changing conditions of deposition of geological sediments. They make up about 10% of the mass of the earth's crust and cover 75% of the Earth's surface. St. 3/4 of minerals (coal, oil, gas, salt, ores of iron, manganese, aluminum, placers of gold, platinum, diamonds, phosphorites, building materials). Depending on the source material, sedimentary rocks are subdivided into detrital (terrygene), chemogenic, organogenic (biogenic) and mixed.

Clastic rocks are formed due to the accumulation of debris of collapsed rocks, i.e. these are rocks composed of fragments of older rocks and minerals. According to the size of the fragments, coarse-detrital (lumps, gravel, gravel, pebbles), sandy (sandstones), silty (silts, siltstones) and clay rocks are distinguished. The most widespread in the earth's crust are such clastic rocks as sands, sandstones, siltstones, and clays.

Chemogenic rocks are chemical compounds that are formed as a result of precipitation from aqueous solutions. These include: limestones, dolomites, rock salts, gypsum, anhydrite, iron and manganese ores, phosphorites, etc.

Organogenic rocks accumulate as a result of the withering away and burial of animals and plants, i.e. organogenic rocks (from organ and Greek genes - giving birth, born) (biogenic rocks) - sedimentary rocks consisting of the remains of animals and plant organisms or products of their vital activity (limestone-shell rock, chalk, fossil coals, oil shale, etc.) ...

Breeds mixed genesis, as a rule, are formed due to a different combination of all the factors considered above. Among these rocks are sandy and clayey limestones, marls (strongly calcareous clays), etc.

2.2. Igneous rocks

Genesis igneous rocks- the result of solidification of magma at depth or on the surface. Magma, being molten and saturated with gaseous components, pours out from the upper part of the mantle.

The composition of magma mainly includes the following elements: oxygen, silicon, aluminum, iron, calcium, magnesium, sodium, potassium, hydrogen. In small amounts, magma contains: carbon, titanium, phosphorus, chlorine and other elements.

Magma, penetrating into the earth's crust, can solidify at different depths or pour out onto the surface. In the first case, intrusive rocks, in the second - effusive... In the process of cooling hot magma in the layers of the earth's crust, minerals of various structures (crystalline, amorphous, etc.) are formed. These minerals form rocks. For example, at great depths, when magma solidifies, granites are formed, at a relatively shallow depth - quartz porphyries, etc.

Effusive rocks are formed during the rapid solidification of magma on the surface of the Earth or on the seabed. An example is tuff, volcanic glass.

Intrusive rocks- igneous rocks formed as a result of the solidification of magma in the thickness of the earth's crust.

Igneous rocks by the content of SiO 2 (quartz and other compounds) are divided into: acidic (SiO 2 more than 65%), medium - 65-52%, basic (52-40%) and ultrabasic (less than 40% SiO 2). According to the content of quartz in the rocks, the color of the rocks changes. Acidic ones are usually light in color, basic and ultrabasic ones are dark to black. Felsic rocks include: granites, quartz porphyries; to the middle: syenite, diorite, nepheline syenite; to the main ones: gabbro, diabase, basalt; to ultrabasic: pyroxenes, peridotites and dunites.

2.3. Metamorphic rocks

Metamorphic rocks formed as a result of exposure high temperatures and pressures on rocks of a different primary genesis (sedimentary or igneous), that is, due to chemical transformations under the influence of metamorphism. Metamorphic rocks include: gneisses, crystalline schists, marble. For example, marble is formed due to the metamorphism of the primary sedimentary rock - limestone.

3. The structure of the earth's crust

The earth's crust is conventionally subdivided into three layers: sedimentary, granite and basalt. The structure of the earth's crust is shown in Fig. 1.

1 - water, 2 - sedimentary layer, 3 - granite layer, 4 - basalt layer, 5 - deep faults, igneous rocks, 6 - mantle, M - Mohorovichich (Moho) surface, K - Konrad surface, OD - island arc, CX - mid-ocean ridge

Rice. 1. Scheme of the structure of the earth's crust (according to M.V. Muratov)

Each of the layers is heterogeneous in composition, however, the name of the layer corresponds to the predominant type of rocks, characterized by the corresponding velocities of seismic waves.

The top layer is represented by sedimentary rocks, where the velocity of propagation of longitudinal seismic waves is less than 4.5 km / s. For the middle granite layer, wave velocities of the order of 5.5-6.5 km / s are characteristic, which experimentally corresponds to granites.

The sedimentary layer is thin in the oceans, but has a significant thickness on the continents (in the Caspian region, for example, according to geophysical data, it is assumed 20-22 km).

Granite layer absent in the oceans, where the sedimentary layer directly overlies basalt... Basalt layer - the lower layer of the earth's crust located between the surface of Konrad and the surface of Mohorovichi. It is characterized by the speed of propagation of longitudinal waves from 6.5 to 7.0 km / s.

On continents and oceans, the earth's crust varies in composition and thickness. The continental crust under mountain structures reaches 70 km, on the plains - 25-35 km. In this case, the upper layer (sedimentary) is usually 10-15 km, with the exception of the Caspian Sea region, etc. Below there is a granite layer up to 40 km thick, and in the base of the crust - a basalt layer also up to 40 km.

The border between the crust and the mantle is called Mohorovicic surface... In it, the speed of propagation of seismic waves increases abruptly. In general terms, the shape of the surface of Mohorovichich is a mirror image of the relief of the outer surface of the lithosphere: it is higher under the oceans, and lower under the continental plains.

Conrad surface(named after the Austrian geophysicist V. Konrad, 1876-1962) - the interface between the "granite" and "basalt" layers of the continental crust. The velocity of longitudinal seismic waves when passing through the Konrad surface increases abruptly from about 6 to 6.5 km / s. In some places, the Konrad surface is absent and seismic wave velocities increase gradually with depth. Sometimes, on the contrary, there are several surfaces of an abrupt increase in velocities.

The oceanic crust is thinner than the continental crust and has a two-layer structure (sedimentary and basalt layers). The sedimentary layer is usually loose, several hundred meters thick, and the basaltic layer is from 4 to 10 km thick.

The so-called transitionbark type... In such areas, the continental crust becomes oceanic and is characterized by average values of the layer thicknesses. At the same time, under the marginal sea, as a rule, there is no granite layer, but under the island arc it can be traced.

Island arc- underwater mountain range, the tops of which rise above the water in the form of an arched archipelago. Island arcs are part of the transition zone from the mainland to the ocean; characterized by seismic activity and vertical movements of the earth's crust.

Mid ocean ridges- the largest landforms of the ocean floor, forming a single system of mountain structures with a length of over 60 thousand km, with relative heights of 2-3 thousand m and a width of 250-450 km (in some areas up to 1000 km). They represent uplifts of the earth's crust, with highly dissected ridges and slopes; in the Pacific and Arctic oceans, mid-ocean ridges are located in the marginal parts of the oceans, in the Atlantic - in the middle.

4. Geological processes occurring in the earth's crust

During the entire geological history, various geological processes have taken place and are taking place on the earth's surface and inside the earth's crust, which affect the formation of mineral deposits.

Sedimentary strata and such minerals as coal, oil, gas, oil shale, phosphorites and others are the result of the activity of living organisms, water, wind, sunlight and everything else associated with them.

For oil to form, for example, it is necessary, first of all, to accumulate a huge amount of fossil remains in sedimentary strata submerging to a considerable depth, where, under the influence of high temperatures and pressures, this biomass is converted into oil or natural gas.

All geological processes are subdivided into exogenous (surface) and endogenous (internal).

4.1. Exogenous processes

Exogenous processes- This is the destruction of rocks on the surface of the Earth, the transfer of their debris and accumulation in the seas, lakes, rivers. To a greater extent, elevated areas of the terrain (mountains, hills) are subject to destruction, and the accumulation of debris of destroyed rocks occurs, on the contrary, in low areas (depressions, reservoirs).

Exogenous processes occur under the influence of atmospheric phenomena (the action of precipitation, wind, melting of glaciers, the life of animals and plants, the movement of rivers and other water flows, etc.).

Surface processes associated with the destruction of rocks are also called weathering or denudation. Under the influence of weathering, a kind of leveling of the relief occurs, as a result of which exogenous processes are weakened, and in a number of places (on the plains) they practically die out.

4.2. Endogenous processes

Also play an important role in oil formation endogenous processes, which include various movements of parts of the earth's crust (horizontal and vertical tectonic movements), earthquakes, volcanic eruptions and outpouring of magma (liquid fiery lava) to the Earth's surface, to the bottom of seas and oceans, as well as deep faults in the earth's crust, tectonic disturbances, folding, etc. etc. Ie endogenous processes include processes taking place inside the Earth.

During geological history, the earth's crust has been subjected to both vertical oscillatory movements and horizontal displacements of lithospheric plates. The indicated global changes in the stony shell of the Earth undoubtedly influenced the formation processes of oil and gas accumulations.

Due to vertical movements, large depressions and troughs were formed, where thick sediments accumulated.

The latter, in turn, could produce hydrocarbons (oil and gas). In other areas, on the contrary, large uplifts arose, which are also of interest in oil and gas terms, since they could accumulate hydrocarbons.

With horizontal displacements of lithospheric plates, some continents merged and others split, which also affected the formation and accumulation of oil and gas. At the same time, in some areas of the earth's crust, favorable conditions arose for the accumulation of significant concentrations of hydrocarbons.

Endogenous processes also include metamorphism, i.e. recrystallization of rocks under the influence of high temperatures and pressures. Metamorphism is classified into three types.

Regional metamorphism- This is a change in the composition of rocks that submerge to great depths and are exposed to high temperature and pressure.

Another kind - dynamometamorphism arises from the action of tectonic lateral pressure on rocks, which undergo crushing, splitting into tiles and acquire a shale appearance.

In the process of introducing magma into rocks, there is also contact metamorphism as a result of which, near the contact zone of magmatic melts with host rocks, partial remelting and recrystallization of the latter occurs.

Conclusion

Forecasting oil and gas content, prospecting and exploration for oil and gas are based on knowledge of the geology of oil and gas, which, in turn, rests on a solid foundation - general and structural geology.

Questions of general geology include the study of the geological age of the layers of the earth's crust, the composition of rocks that make up the crust, the geological history of the Earth and geological processes occurring in the interior and on the surface of the planet.

Structural geology studies the structure, movement and development of the earth's crust, the forms of bedding of rocks, the reasons for their occurrence and development.

It is necessary to know the conditions of bedding of rocks in order to correctly approach the identification of mineral deposits, including the discovery of deposits and locations of oil and gas. It is known that most of the accumulations of oil and gas are located in anticlines, which are traps for hydrocarbons. Therefore, the search for structural oil and gas traps is carried out on the basis of studying the structural features of the earth's crust in the studied territories.

List of used literature:

Mstislavskaya L.P., Pavlinich M.F., Filippov V.P., "Fundamentals of oil and gas production", publishing house "Oil and Gas", Moscow, 2003

Mikhailov A.E., "Structural Geology and Geological Mapping", Moscow, "Nedra", 1984

Maltseva A.K., Bakirov E.A., Ermolkin V.I., "Geology of oil and gas and oil and gas provinces", Moscow, "Oil and gas", 1998

Geological Dictionary, Moscow, "Nedra", 1973

www. ence. ru

There are two main types of the earth's crust: oceanic and continental. The transitional type of the earth's crust is also distinguished.

Oceanic crust. The thickness of the oceanic crust in the modern geological era ranges from 5 to 10 km. It consists of the following three layers:

1) the upper thin layer of marine sediments (thickness no more than 1 km);

2) middle basalt layer (thickness from 1.0 to 2.5 km);

3) the lower layer of gabbro (about 5 km thick).

Continental (continental) crust. The continental crust is more complex and thicker than the oceanic crust. Its capacity is on average 35-45 km, and in mountainous countries it increases to 70 km. It also consists of three layers, but differs significantly from the ocean:

1) the lower layer, composed of basalts (thickness about 20 km);

2) the middle layer occupies the main thickness continental crust and is conventionally called granite. It is composed mainly of granites and gneisses. This layer does not extend under the oceans;

3) the upper layer is sedimentary. Its average thickness is about 3 km. In some areas, the thickness of precipitation reaches 10 km (for example, in the Caspian lowland). In some areas of the Earth, the sedimentary layer is absent altogether and a granite layer emerges on the surface. Such areas are called shields (for example, Ukrainian Shield, Baltic Shield).

On the continents, as a result of the weathering of rocks, a geological formation is formed, which is called weathering crust.

The granite layer is separated from the basalt layer Conrad surface , at which the speed of seismic waves increases from 6.4 to 7.6 km / sec.

The border between the earth's crust and the mantle (both on the continents and on the oceans) runs along Mohorovicic surface (Moho line). The speed of seismic waves on it abruptly increases to 8 km / h.

In addition to the two main types - oceanic and continental - there are also areas of the mixed (transitional) type.

On continental shoals or shelves, the crust has a thickness of about 25 km and is generally similar to the continental crust. However, a layer of basalt can fall out in it. V East Asia in the area of island arcs ( Kurile Islands, Aleutian Islands, Japanese islands and others), the earth's crust is of a transitional type. Finally, the crust of the mid-oceanic ridges is very complex and so far little studied. There is no Moho boundary here, and the mantle material rises along faults into the crust and even to its surface.

The concept of "earth's crust" should be distinguished from the concept of "lithosphere". The concept of "lithosphere" is broader than the "crust". Into the lithosphere modern science includes not only the earth's crust, but also the uppermost mantle to the asthenosphere, that is, to a depth of about 100 km.

The concept of isostasy ... The study of the distribution of gravity showed that all parts of the earth's crust are continents, mountainous countries, plains are balanced on the upper mantle. This balanced position of them is called isostasy (from Latin isoc - even, stasis - position). Isostatic equilibrium is achieved due to the fact that the thickness of the earth's crust is inversely proportional to its density. The heavy oceanic crust is thinner than the lighter continental crust.

Isostasy - in fact, it is not even equilibrium, but a striving for equilibrium, continuously disturbed and restored again. So, for example, the Baltic shield after melting continental ice Pleistocene glaciation rises by about 1 meter per century. Finland's area is constantly increasing due to the seabed. The territory of the Netherlands, on the contrary, is decreasing. The zero line of equilibrium is currently passing somewhat south of 60 0 N latitude. Modern St. Petersburg is about 1.5 m higher than St. Petersburg during the time of Peter the Great. As the data of modern scientific research show, even the severity of large cities is sufficient for the isostatic fluctuation of the territory below them. Consequently, the earth's crust in the zones of large cities is very mobile. In general, the relief of the earth's crust is a mirror image of the Moho surface, the bottom of the earth's crust: high level its upper boundary. So, under the Pamir, the depth of the Moho surface is 65 km, and in the Caspian lowland - about 30 km.

Thermal properties of the earth's crust ... Daily fluctuations in soil temperature spread to a depth of 1.0 - 1.5 m, and annual fluctuations in temperate latitudes in countries with continental climate to a depth of 20-30 m. At the depth where the influence of annual temperature fluctuations ceases due to heating of the earth's surface by the Sun, there is a layer of constant soil temperature. It is called isothermal layer ... Below the isothermal layer deep into the Earth, the temperature rises, and this is already caused by the internal heat of the earth's interior. Internal heat is not involved in the formation of climates, but it serves as the energy basis for all tectonic processes.

The number of degrees by which the temperature increases for every 100 m depth is called geothermal gradient ... The distance in meters, when lowering by which the temperature increases by 1 0 С is called geothermal stage ... The magnitude of the geothermal step depends on the relief, the thermal conductivity of rocks, the proximity of volcanic foci, the circulation of groundwater, etc. On average, the geothermal step is 33 m. on platforms), it can reach 100 m.

TOPIC 5. MATTERS AND OCEANS

Continents and parts of the world

Two qualitatively different types of the earth's crust - continental and oceanic - correspond to two main levels of planetary relief - the surface of the continents and the ocean bed.

Structural-tectonic principle of separation of continents. The fundamentally qualitative difference between the continental and oceanic crust, as well as some significant differences in the structure of the upper mantle under the continents and oceans, oblige to distinguish continents not apparently by their surroundings by oceans, but according to the structural-tectonic principle.

The structural-tectonic principle states that, firstly, the continent includes a continental shelf (shelf) and a continental slope; secondly, at the base of each continent there is a core or an ancient platform; third, each continental lump is isostatically balanced in the upper mantle.

From the point of view of the structural-tectonic principle, a continent is called an isostatically balanced mass of the continental crust, which has a structural core in the form of an ancient platform, to which younger folded structures adjoin.

In total, there are six continents on Earth: Eurasia, Africa, North America, South America, Antarctica and Australia. Each continent has one platform, and only at the basis of Eurasia there are six of them: Eastern European, Siberian, Chinese, Tarim (Western China, Taklamakan desert), Arabian and Hindustan. The Arabian and Hindustan platforms are parts of ancient Gondwana that joined Eurasia. Thus, Eurasia is a heterogeneous anomalous continent.

The boundaries between the continents are quite obvious. The border between North America and South America runs along the Panama Canal. The border between Eurasia and Africa is drawn along the Suez Canal. The Bering Strait separates Eurasia from North America.

Two rows of continents ... V modern geography the following two rows of continents stand out:

1. Equatorial continents (Africa, Australia and South America).

2. Northern row of continents (Eurasia and North America).

Outside of these ranks is Antarctica - the southernmost and coldest continent.

The modern arrangement of the continents reflects the long history of the development of the continental lithosphere.

The southern continents (Africa, South America, Australia and Antarctica) are parts ("fragments") of the single Paleozoic mega-continent of Gondwana. The northern continents at that time were united into another mega-continent - Laurasia. Between Laurasia and Gondwana in the Paleozoic and Mesozoic, there was a system of vast sea basins, called the Tethys Ocean. Ocean Tethys stretched from North Africa, across southern Europe, Caucasus, Western Asia, the Himalayas to Indochina and Indonesia. In the Neogene (about 20 million years ago), an alpine fold belt arose on the site of this geosyncline.

According to its large size, the supercontinent of Gondwana. According to the law of isostasy, it had a thick (up to 50 km) crust, which was deeply immersed in the mantle. Under them in the asthenosphere convection currents were especially intense pains, the softened substance of the mantle moved actively. This led first to the formation of a bulge in the middle of the continent, and then to its splitting into separate blocks, which, under the action of the same convection currents, began to move horizontally. As proved mathematically (L. Euler), the movement of the contour on the surface of the sphere is always accompanied by its rotation. Consequently, parts of Gondwana not only moved, but also deployed in geographic space.

The first split of Gondwana occurred on the border of the Triassic and Jurassic (about 190-195 million years ago); split off Afro-America. Then, on the Jurassic-Cretaceous border (about 135-140 million years ago), South America separated from Africa. On the border of the Mesozoic and Cenozoic (about 65-70 million years ago), the Hindustan block collided with Asia and Antarctica moved away from Australia. In the present geological era, the lithosphere, according to the neomobilists, is divided into six plate blocks that continue to move.

The collapse of Gondwana aptly explains the shape of the continents, their geological similarity, as well as the history of vegetation and fauna. southern continents.

The history of the split in Laurasia has not been studied as thoroughly as in Gondwana.

The concept of parts of the world ... In addition to the geologically determined division of land into continents, there is also the division of the earth's surface into separate parts of the world that has developed in the process of cultural and historical development of mankind. There are six parts of the world in total: Europe, Asia, Africa, America, Australia with Oceania, Antarctica. On one continent of Eurasia there are two parts of the world (Europe and Asia), and two continents of the western hemisphere (North America and South America) form one part of the world - America.

The border between Europe and Asia is rather arbitrary and is drawn along the watershed line of the Ural ridge, the Ural River, the northern part of the Caspian Sea and the Kuma-Manych depression. In the Urals and the Caucasus, there are deep fault lines separating Europe from Asia.

Area of continents and oceans. Land area is calculated within the current coastline. The surface area of the globe is approximately 510.2 million km 2. About 361, 06 million km 2 is occupied by the World Ocean, which is approximately 70.8% of the total surface of the Earth. The land accounts for about 149, 02 million km 2, which is about 29, 2% of the surface of our planet.

Square modern continents characterized by the following values:

Eurasia - 53, 45 km 2, including Asia - 43, 45 million km 2, Europe - 10, 0 million km 2;

Africa - 30, 30 million km 2;

North America - 24, 25 million km 2;

South America - 18, 28 million km 2;

Antarctica - 13, 97 million km 2;

Australia - 7, 70 million km 2;

Australia with Oceania - 8, 89 km 2.

Modern oceans have area:

Pacific Ocean - 179, 68 million km 2;

Atlantic Ocean - 93, 36 million km 2;

Indian Ocean - 74, 92 million km 2;

Arctic Ocean - 13, 10 million km 2.

Between the northern and southern continents, in accordance with their different origins and development, there is a significant difference in the area and nature of the surface. The main geographical differences between the northern and southern continents boil down to the following:

1.It is incomparable in size with other continents of Eurasia, which concentrates more than 30% of the planet's land mass.

2.U northern continents significant in terms of shelf area. Especially significant is the shelf in the Arctic Ocean and Atlantic oceans, as well as in Yellow, Chinese and Bering Seas The Pacific... The southern continents, with the exception of Australia's submarine continuation in the Arafura Sea, are almost devoid of a shelf.

3. Most of the southern continents fall on ancient platforms. V North America and Eurasia, ancient platforms occupy a smaller part of the total area, and most of it falls on the territory formed by the Paleozoic and Mesozoic mountain building. In Africa, 96% of its territory falls on platform areas and only 4% on mountains of Paleozoic and Mesozoic age. In Asia, only 27% falls on ancient platforms and 77% on mountains of various ages.

4. The coastline of the southern continents, formed mostly by split cracks, is relatively straight; peninsulas and mainland islands few. The northern continents are characterized by an exceptionally winding coastline, an abundance of islands, peninsulas, often far reaching into the ocean. Of the total area, islands and peninsulas account for about 39% in Europe, North America - 25%, Asia - 24%, Africa - 2.1%, South America- 1.1% and Australia (excluding Oceania) - 1.1%.

There are 2 main types of the earth's crust: continental and oceanic and 2 transitional types - subcontinental and suboceanic (see Fig.).

1- sedimentary rocks;

2- volcanic rocks;

3- granite layer;

4- basalt layer;

5- border of Mohorovichich;

6- upper mantle.

The continental type of the earth's crust has a thickness of 35 to 75 km, in the shelf area - 20 - 25 km, and wedges out on the continental slope. There are 3 layers of continental crust:

1st - upper, composed of sedimentary rocks with a thickness of 0 to 10 km. on platforms and 15 - 20 km. in the tectonic troughs of mountain structures.

2nd - medium "granite - gneiss" or "granite" - 50% granite and 40% gneisses and other metamorphosed rocks. Its average thickness is 15 - 20 km. (in mountain structures up to 20 - 25 km.).

3rd - lower, "basalt" or "granite - basalt", compositionally close to basalt. Thickness from 15 - 20 to 35 km. The boundary between the "granite" and "basalt" layers is Konrad's section.

According to modern data, the oceanic type of the earth's crust also has a three-layer structure with a thickness of 5 to 9 (12) km., More often 6–7 km.

1st layer - upper, sedimentary, consists of loose sediments. Its thickness is from several hundred meters to 1 km.

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

3rd layer - lower, not exposed by drilling. It is composed of basic igneous rocks of the gabro type with subordinate ultrabasic rocks (serpentinites, pyroxenites).

The subcontinental type of the earth's surface is similar in structure to the continental one, but does not have a clearly pronounced Konrad division. This type of crust is usually associated with island arcs - the Kuril, Aleutian and continental margins.

1st layer - upper, sedimentary - volcanic, thickness - 0.5 - 5 km. (on average 2 - 3 km.).

2nd layer - island arc, "granite", thickness 5 - 10 km.

3rd layer - "basalt", at depths of 8 - 15 km., Thickness from 14 - 18 to 20 - 40 km.

The suboceanic type of the earth's crust is confined to the basin parts of the marginal and inland seas (Okhotsk, Japanese, Mediterranean, Black, etc.). In structure, it is close to the oceanic, but differs in an increased thickness of the sedimentary layer.

The 1st upper - 4 - 10 km and more, is located directly on the third oceanic layer with a thickness of 5 - 10 km.

The total thickness of the earth's crust is 10 - 20 km., In some places up to 25 - 30 km. by increasing the sedimentary layer.

The structure of the earth's crust

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

Some areas of the continents are formed on the surface by the most ancient rocks of the Archean (AR) and Proterozoic (PT) ages. They are very metamorphosed: clays turned into metamorphic shales, sandstones - into crystalline quartzites, limestones - into marbles. There are many granites among them. The areas on the surface of which these most ancient rocks emerge are called crystalline massifs or shields (Baltic, Canadian, African, Brazilian, etc.).

Other areas on the continents are occupied by rocks of predominantly younger age - Paleozoic, Mesozoic, Cenozoic (Pz, Mz, Kz) age. These are mainly sedimentary rocks, although among them there are also rocks of igneous origin, poured out to the surface in the form of volcanic lava or intruded and solidified at a certain depth. There are two categories of land areas: 1) platforms - plains: beds of sedimentary rocks lie calmly, almost horizontally, in them there are rare and small folds. There are very few igneous, especially intrusive, rocks in such rocks; 2) folded zones (geosynclines) - mountains: sedimentary rocks are strongly crushed into folds, penetrated by deep cracks; igneous rocks that have intruded or poured onto the surface are common. Differences between platforms or folded zones lie in the age of the rocks lying quietly or crumpled into folds. Therefore, platforms are ancient and young. Saying that platforms could have formed in different time, we thus indicate the different ages of the folded zones.

Maps depicting the location of platforms and folded zones of different ages and some other features of the structure of the earth's crust are called tectonic. They complement geological maps, representing the most objective geological documents that illuminate the structure of the earth's crust.

Types of the earth's crust

The thickness of the earth's crust is not the same under the continents and oceans. It is larger under mountains and plains, thinner under oceanic islands and oceans. Therefore, there are two main types of the earth's crust - continental (continental) and oceanic.

The average thickness of the continental crust is 42 km. But in the mountains it increases to 50-60 and even up to 70 km. Then they talk about the "roots of the mountains." The average thickness of the oceanic crust is about 11 km.

Thus, the continents represent, as it were, unnecessary accumulations of the masses. But these masses would have to create a stronger attraction, and in the oceans, where the lighter water is the attracting body, the force of gravity would have to weaken. But in reality, there are no such differences. The force of gravity is approximately the same everywhere on the continents and oceans. Hence the conclusion is obtained: the continental and oceanic masses are balanced. They obey the law of isostasy (equilibrium), which reads as follows: the additional masses on the surface of the continents correspond to a lack of masses at depth, and vice versa, to a lack of masses on the surface of the oceans must correspond to some heavy masses at depth.