What facts prove the movement of lithospheric plates. Collection of tasks to prepare for the exam
For a long time in geology, the prevailing judgment about the constancy of the position of oceans and continents. It was believed that they were formed in antiquity and since then have maintained their position on the planet. Geologists were convinced that the lithosphere, that is, the earth's crust, moves only vertically, thereby changing the height of the continents and the level of the ocean.
IN late XIX centuries, some scientists began to assume that the modern continents in the past were a single continent. At that time, this theory had no proof and it was difficult for people to imagine the drift of huge tracts of land on the surface of the Earth.
At the beginning of the 20th century, the theory of the drift of lithospheric plates became very popular. The essence of the idea is that the entire solid shell of the Earth is divided into blocks. They constantly move a few centimeters a year. These areas are called lithospheric plates. There are three types of plate drift: shear, convergence, and divergence.
The author of this idea was the German geophysicist Alfred Wagener. The idea of a possible movement of continents came to him when he noticed the similarity of the shores of America and Africa. Research in the field of paleontology also indicated the presence in the deep past of the possibility of overland movement between Brazil and Africa. Wagener and his supporters began to search for evidence of the theory of lithospheric plates.
The first proof of the theory was the identity of the coastlines of the continents. The similarity between Africa and South America is more pronounced, the outlines are less noticeable. Indian Ocean... Wagener suggested that in ancient times there was a single huge continent - Pangea.
The theory of plate drift is also confirmed by the unity of flora and fauna. Ancient land and freshwater animals were unable to travel great distances. Flora could not settle on the continents if they were located at the same great distance as at present.
Another proof of continental drift on the Earth's surface was the discovery of traces of a very large glaciation that occurred about three hundred million years ago. Glacier traces are found in South America, South Africa, India. Given the current position of the continents, it is difficult to imagine that such remote areas were frozen almost simultaneously. Moreover, they are now in equatorial latitudes.
Along with the followers of the theory, there were also its opponents. The beginning of doubts in the logic of the idea of the movement of lithospheric plates was laid by geophysicists. Wagener and his supporters have never been able to explain what forces are moving the continents along the Earth's surface. Geophysicists have rejected the assumption that lithospheric plates move under the influence of inertia caused by the rotation of the planet. This power is not enough to overcome the magma resistance.
The theory was unexpectedly confirmed in the field of paleomagnetic research. Since the fifties of the XX century, an active study of the ocean floor began. Scientists have determined that molten mantle material rises through cracks in the mid-ocean ridge. Over time, this process increases the area of the ocean. The leaked substance is magnetized during solidification, maintaining this state for millions of years. Studying the polarity of these parts of the ocean, scientists realized that during the entire existence of the planet, its poles changed their position. Considering the remanent magnetization of the continents, scientists noticed that a single direction of the ancient poles can be achieved only if all modern continents are combined into a single whole.
Discovery of primary magnetization rocks contributed to the revival and final confirmation of the theory of drift of lithospheric plates.
Dear Readers! If you choose the Unified State Exam as the final or entrance exam in biology, then you need to know and understand the requirements for passing this exam, the nature of the questions and tasks encountered in the examination papers. To help applicants, the EKSMO publishing house will publish the book “Biology. Collection of tasks for preparing for the exam ”. This book is a training manual, which is why the material included in it exceeds the school level of requirements. However, for those high school students who decide to enter higher educational establishments to faculties where biology is taken, this approach will be useful.
In our newspaper, we publish only the tasks of Part C for each section. They have been completely updated both in terms of content and structure of presentation. Since this guide is focused on exams 2009/2010 school year, then we decided to give options for the tasks of part C in a much larger volume than it was done in previous years.
You are offered approximate options for questions and tasks of different difficulty levels with a different number of elements for the correct answer. This is done to ensure that you have enough big choice possible correct answers to a specific question. In addition, the questions and tasks of Part C are structured as follows: one question and elements of the correct answer to it are given, and then options for this question are offered for independent reflection. The answers to these options should be obtained by you yourself, applying both the knowledge gained during the study of the material and the knowledge gained when reading the answers to the main question. All questions should be answered in writing.
A significant part of the tasks in Part C are tasks in pictures. Similar to them have already been in the examination papers in 2008. In this manual, their set is somewhat expanded.
We hope that this study guide will help high school students not only prepare for exams, but also provide an opportunity for those wishing to learn the basics of biology in the remaining two years of study in grades 10-11.
General Biology (Part C)
The tasks of this part are divided into sections: cytology, genetics, evolutionary theory, ecology. Each section offers tasks for all levels of the exam... Such a construction of the general biological part of the manual will allow you to more fully and systematically prepare for the exam, because Part C includes, in summary form, virtually all of the material in Parts A and B.
C1 group assignments (advanced level)
All tasks of group C must be given written answers with explanations.
Questions about cytology
The answer to this question should be short but precise. Central to this question are the words - "levels of organization" and "scientific basis". The level of organization is the way and form of existence of living systems. For example, the cellular level of organization includes cells. Therefore, it is necessary to find out what is common, which made it possible to highlight the levels of the organization. Such a general is the systematic organization of living bodies and their gradual complication (hierarchy).
Elements of the correct answer
The scientific grounds for dividing living systems into levels are the following provisions.
1. Living systems become more complex as they develop: cell - tissue - organism - population - species, etc.
2. Each more highly organized living system includes previous systems. Tissues are made of cells, organs are made of tissues, an organism is made of organs, etc.
Answer the following questions yourself
What properties do all levels of life organization have in common?
What is common and different between cellular and population levels life?
Prove that on cellular level all the properties of living systems are manifested.
Elements of the correct answer
1. The model can be applied to influences that are inapplicable to living bodies.
2. Modeling allows you to change any characteristics of the object.
Answer yourself
How would you explain I.P. Pavlova "Observation collects what nature offers him, but experience takes from nature what he wants"?
Give two examples of the use of the experimental method in cytology.
What research methods can be used to separate different cellular structures?
Elements of the correct answer
1. The polarity of a water molecule determines its ability to dissolve other hydrophilic substances.
2. The ability of water molecules to form and break hydrogen bonds between them provides water with heat capacity and thermal conductivity, the transition from one state of aggregation to others.
3. The small size of the molecules ensures their ability to penetrate between the molecules of other substances.
Answer yourself
What happens to a cell if the concentration of salts in it is higher than outside the cell?
Why don't cells shrink and burst from swelling in saline?
Elements of the correct answer
1. Scientists have found that a protein molecule has primary, secondary, tertiary and quaternary structures.
2. Scientists have found that a protein molecule consists of many different amino acids linked by peptide bonds.
3. Scientists have established the sequence of amino acid residues in the ribonuclease molecule, i.e. its primary structure.
Answer yourself
What are the chemical bonds involved in the formation of a protein molecule?
What factors can lead to protein denaturation?
What are the features of the structure and functions of enzymes?
In what processes are the protective functions of proteins manifested?
Elements of the correct answer
1. These organic compounds perform a building (structural) function.
2. These organic compounds perform an energetic function.
Answer yourself
Why is food rich in cellulose prescribed to normalize bowel function?
What is the structural function of carbohydrates?
Elements of the correct answer
1. DNA is built on the principle of a double helix in accordance with the rule of complementarity.
2. DNA consists of repeating elements - 4 types of nucleotides. Different nucleotide sequences encode different information.
3. The DNA molecule is capable of self-reproduction, and, consequently, of copying information and transmitting it.
Answer yourself
What facts prove the individuality of the DNA of an individual?
What does the concept of "versatility genetic code"; what facts support this universality?
What is scientific merit D. Watson and F. Crick?
Elements of the correct answer
1. Differences in the names of DNA and RNA are explained by the composition of their nucleotides: deoxyribose carbohydrate in DNA nucleotides, and ribose in RNA.
2. Differences in the names of RNA species (informational, transport, ribosomal) are associated with the functions they perform.
Answer yourself
What two conditions must be constant so that the bonds between two complementary DNA strands do not break down spontaneously?
How do DNA and RNA differ in structure?
What other compounds are nucleotides in, and what do you know about them?
Elements of the correct answer
1. Cellular theory has established the structural and functional unit of the living.
2. Cellular theory has established the unit of reproduction and development of living things.
3. The cellular theory has confirmed the generality of the structure and origin of living systems.
Answer yourself
Why, despite the obvious differences in the structure and functions of cells of different tissues, they speak of unity cellular structure alive?
What are the main discoveries in biology that made it possible to formulate the cellular theory?
Elements of the correct answer
1. Substances enter the cell by diffusion.
2. Substances penetrate into the cell due to active transport.
3. Substances enter the cell by pinocytosis and phagocytosis.
Answer yourself
What is the difference between active transport of substances through cell membrane from passive?
What substances are removed from the cell and how?
Elements of the correct answer
1. In prokaryotes, the cell lacks a nucleus, mitochondria, Golgi apparatus and endoplasmic reticulum.
2. Prokaryotes do not have true sexual reproduction.
Answer yourself
Why are mature erythrocytes or platelets not classified as prokaryotic cells, despite the absence of nuclei in them?
Why are viruses not classified as independent organisms?
Why are eukaryotic organisms more diverse in their structure and level of complexity?
Elements of the correct answer
1. By the chromosome set of an animal, you can determine its type.
2. By the chromosome set of an animal, you can determine its sex.
3. The presence or absence of hereditary diseases can be determined by the chromosome set of an animal.
Answer yourself
Do chromosomes exist in every cell of a multicellular organism? Prove the answer with examples.
How and when can you see chromosomes in a cell?
Elements of the correct answer
The structural elements of the Golgi complex are:
1) tubules;
2) cavities;
3) bubbles.
Answer yourself
What is the structure of chloroplast?
What is the structure of mitochondria?
What must be contained in mitochondria in order for them to synthesize proteins?
Show that both mitochondria and chloroplasts can multiply.
Elements of the correct answer
Differences should be noted in:
1) the nature of metabolism;
2) terms of life;
3) reproduction.
Answer yourself
How will the transplantation of a nucleus from another organism affect a single-celled organism?
Elements of the correct answer
1. The presence of a double membrane with characteristic nuclear pores, due to which the connection between the nucleus and the cytoplasm is ensured.
2. The presence of nucleoli, in which RNA is synthesized and ribosomes are formed.
3. The presence of chromosomes, which are the hereditary apparatus of the cell and ensure the division of the nucleus.
Answer yourself
Which cells do not contain nuclei?
Why do non-nuclear cells of prokaryotes multiply, but non-nuclear cells of eukaryotes do not?
Elements of the correct answer
1. Most cells are similar in basic structural elements, vital properties and the process of division.
2. Cells differ from each other by the presence of organelles, specialization in the functions performed, and the intensity of metabolism.
Answer yourself
Give examples of the correspondence between the structure of a cell and its function.
Give examples of cells with different levels of metabolic rate.
Elements of the correct answer
1. As a result of synthesis, more complex substances are formed than those that have entered into a reaction; the reaction proceeds with the absorption of energy.
2. When decaying, simpler substances are formed than those that have entered into a reaction; the reaction proceeds with the release of energy.
Answer yourself
What are the functions of enzymes in metabolic reactions?
Why are more than 1000 enzymes involved in biochemical reactions?
17. What types of energy is light energy converted into during photosynthesis and where does this conversion take place? |
Elements of the correct answer
1. Light energy is converted into chemical and thermal energy.
2. All transformations occur in the thylakoids of gran chloroplasts and in their matrix (in plants); in other photosynthetic pigments (bacteria).
Answer yourself
What happens in the light phase of photosynthesis?
What happens during the dark phase of photosynthesis?
Why is it experimentally difficult to detect the process of plant respiration in the daytime?
Elements of the correct answer
1. The code "triplet" means that each of the amino acids is encoded by three nucleotides.
2. The code is "unambiguous" - each triplet (codon) encodes only one amino acid.
3. The code "degenerate" means that each amino acid can be encoded by more than one codon.
Answer yourself
Why do we need “punctuation marks” between genes and why are they not inside genes?
What does the concept of "universality of the DNA code" mean?
What is the biological meaning of transcription?
Elements of the correct answer
1. Examples of organisms in which there is an alternation of generations are mosses, ferns, jellyfish and others.
2. In plants, there is a change of gametophyte and sporophyte. In jellyfish, the stages of the polyp and jellyfish alternate.
Answer yourself
What are the main differences between mitosis and meiosis?
What is the difference between the concepts of "cell cycle" and "mitosis"?
Elements of the correct answer
1. Isolated cells of an organism living in an artificial environment are called cell culture (or cell culture).
2. Cell cultures are used to obtain antibodies, medicinal substances, as well as to diagnose diseases.
Elements of the correct answer
1. Interphase is necessary for storing substances and energy in preparation for mitosis.
2. In the interphase, the hereditary material doubles, which subsequently ensures its uniform distribution among the daughter cells.
Answer yourself
Are the gametes produced by the body the same or different in their genetic makeup? Please provide evidence.
Which organisms have an evolutionary advantage - haploid or diploid? Please provide evidence.
C2 level quests
Elements of the correct answer
Errors were made in sentences 2, 3, 5.
In Proposition 2, notice one of the non-macronutrient elements.
In Proposition 3, one of the listed elements is erroneously referred to as trace elements.
Proposition 5 erroneously indicates an element that performs the named function.
2. Find errors in the text provided. Indicate the numbers of sentences in which mistakes were made, explain them. 1. Proteins are irregular biopolymers, the monomers of which are nucleotides. 2. Residues of monomers are interconnected by peptide bonds. 3. The sequence of monomers supported by these bonds forms the primary structure of the protein molecule. 4. The next structure is secondary, supported by weak hydrophobic chemical bonds... 5. The tertiary structure of a protein is a twisted molecule in the form of a globule (ball). 6. This structure is supported by hydrogen bonds. |
Elements of the correct answer
Errors were made in sentences 1, 4, 6.
In Proposition 1, the monomers of the protein molecule are incorrectly indicated.
In Proposition 4, the chemical bonds that support the secondary structure of the protein are incorrectly indicated.
Proposition 6 incorrectly indicates the chemical bonds that support the tertiary structure of the protein.
According to modern lithospheric plate theory the entire lithosphere is divided by narrow and active zones - deep faults - into separate blocks that move in the plastic layer of the upper mantle relative to each other at a rate of 2-3 cm per year. These blocks are called lithospheric plates.
The peculiarity of lithospheric plates is their rigidity and ability, in the absence of external influences, to keep their shape and structure unchanged for a long time.
Lithospheric plates are mobile. Their movement along the surface of the asthenosphere occurs under the influence of convective currents in the mantle. Individual lithospheric plates can diverge, approach or slide relative to each other. In the first case, tension zones with cracks appear between the plates along the boundaries of the plates, in the second - zones of compression, accompanied by the thrust of one plate onto another (thrust - obduction; thrust - subduction), in the third - shear zones - faults along which the neighboring plates slide. ...
At the points of convergence of the continental plates, they collide, and mountain belts are formed. This is how the Himalayan mountain system arose, for example, on the border of the Eurasian and Indo-Australian plates (Fig. 1).
Fig. 1. Collision of continental lithospheric plates
With the interaction of the continental and oceanic plates, the plate with the oceanic crust is pushed under the plate with the continental crust (Fig. 2).
Fig. 2. Collision of continental and oceanic lithospheric plates
As a result of the collision of continental and oceanic lithospheric plates, deep-sea trenches and island arcs are formed.
The divergence of lithospheric plates and the formation as a result of this crust oceanic type is shown in Fig. 3.
The axial zones of the mid-oceanic ridges are characterized by rifts(from the English. rift - crevice, crack, break) - large linear tectonic structure of the earth's crust hundreds, thousands, tens, and sometimes hundreds of kilometers wide, formed mainly by horizontal stretching of the crust (Fig. 4). Very large rifts are called rift belts, zones or systems.
Since the lithospheric plate is a single plate, each of its faults is a source of seismic activity and volcanism. These sources are concentrated within relatively narrow zones, along which mutual movements and friction of adjacent plates occur. These zones were named seismic belts. Reefs, mid-ocean ridges and deep-sea trenches are mobile areas of the Earth and are located at the boundaries of lithospheric plates. This indicates that the process of the formation of the earth's crust in these zones is currently taking place very intensively.
Fig. 3. Divergence of lithospheric plates in the zone among the nno-oceanic ridge
Fig. 4. Rift formation diagram
Most of the fractures of lithospheric plates are at the bottom of the oceans, where the earth's crust is thinner, but they are also found on land. The largest fault on land is located in the east of Africa. It stretches for 4000 km. The width of this fault is 80-120 km.
At present, seven of the largest slabs can be distinguished (Fig. 5). Of these, the largest in area is the Pacific Ocean, which consists entirely of the oceanic lithosphere. As a rule, the Nazca plate is also referred to as large, which is several times smaller in size than each of the seven largest. At the same time, scientists suggest that in fact the Nazca plate is much larger than we see it on the map (see Fig. 5), since a significant part of it went under the neighboring plates. This plate also consists only of the oceanic lithosphere.
Fig. 5. Lithospheric plates of the Earth
An example of a plate that includes both continental and oceanic lithosphere is, for example, the Indo-Australian lithospheric plate. The Arabian Plate consists almost entirely of the continental lithosphere.
The theory of lithospheric plates is important. First of all, it can explain why in some places of the Earth there are mountains, and in others - plains. With the help of the theory of lithospheric plates, it is possible to explain and predict catastrophic phenomena occurring at plate boundaries.
Fig. 6. The outlines of the continents do seem to be compatible
Continental drift theory
The theory of lithospheric plates originates from the theory of continental drift. Back in the 19th century. many geographers have noted that when looking at the map, one can notice that the shores of Africa and South America, when approached, seem to be compatible (Fig. 6).
The emergence of the hypothesis of the movement of continents is associated with the name of a German scientist Alfred Wegener(1880-1930) (Fig. 7), who most fully developed this idea.
Wegener wrote: “In 1910, the idea of moving continents came to my mind for the first time ... when I was struck by the similarity of the outlines of the coast on both sides Atlantic Ocean". He suggested that in the early Paleozoic there were two large continents on Earth - Laurasia and Gondwana.
Laurasia was the northern continent, which included the territories of modern Europe, Asia without India and North America. Southern mainland- Gondwana united modern territories South America, Africa, Antarctica, Australia and Hindustan.
Between Gondwana and Laurasia was the first seafood - Tethys, like a huge bay. The rest of the Earth was occupied by the Panthalassa Ocean.
About 200 million years ago, Gondwana and Laurasia were united into a single continent - Pangea (Pan - universal, Ge - earth) (Fig. 8).
Fig. 8. The existence of a single continent of Pangea (white - land, points - shallow sea)
Approximately 180 million years ago, the continent of Pangea again began to separate into its component parts, which were mixed on the surface of our planet. The division took place as follows: first, Laurasia and Gondwana reappeared, then Laurasia was divided, and then Gondwana also split. Oceans were formed due to the split and divergence of parts of Pangea. The Atlantic and Indian oceans can be considered young; old - Quiet. The Arctic Ocean has become isolated with an increase in land mass in the Northern Hemisphere.
Fig. 9. Location and directions of continental drift in the Cretaceous period 180 million years ago
A. Wegener found many confirmations of the existence of a single continent of the Earth. The existence in Africa and South America of the remains of ancient animals - Listosaurs seemed to him especially convincing. They were reptiles, similar to small hippos, that lived only in freshwater bodies of water. So, to swim huge distances on the salty sea water they couldn't. He found similar evidence in the plant kingdom.
Interest in the hypothesis of the movement of continents in the 30s of the XX century. slightly decreased, but in the 60s it revived again, when, as a result of studies of the relief and geology of the ocean floor, data were obtained indicating the processes of expansion (spreading) of the oceanic crust and "diving" of some parts of the crust under others (subduction).
Plate tectonics (plate tectonics) is a modern geodynamic concept based on the provision of large-scale horizontal displacements relative to integral fragments of the lithosphere (lithospheric plates). Thus, plate tectonics considers the movements and interactions of lithospheric plates.
For the first time, the hypothesis of the horizontal movement of crustal blocks was made by Alfred Wegener in the 1920s within the framework of the continental drift hypothesis, but this hypothesis did not receive support at that time. It was only in the 1960s that studies of the ocean floor provided conclusive evidence of horizontal plate movements and the processes of expansion of the oceans due to the formation (spreading) of the oceanic crust. The revival of ideas about the predominant role of horizontal movements took place within the framework of the "mobilistic" direction, the development of which led to the development of the modern theory of plate tectonics. The main principles of plate tectonics were formulated in 1967-68 by a group of American geophysicists - W.J. Morgan, C. Le Pichon, J. Oliver, J. Isaacs, L. Sykes in the development of the earlier (1961-62) ideas of American scientists G. Hess and R. Digz on the expansion (spreading) of the ocean floor
Basics of plate tectonics
The fundamentals of plate tectonics can be summarized in several fundamental
1. The upper rocky part of the planet is divided into two shells, significantly different in rheological properties: the rigid and fragile lithosphere and the underlying plastic and mobile asthenosphere.
2. The lithosphere is divided into plates, constantly moving along the surface of the plastic asthenosphere. The lithosphere is divided into 8 large plates, dozens of medium plates, and many small ones. Between the large and medium slabs, there are belts composed of mosaics of small crustal slabs.
Plate boundaries are areas of seismic, tectonic, and magmatic activity; the inner regions of the plates are weakly seismic and are characterized by a weak manifestation of endogenous processes.
More than 90% of the Earth's surface falls on 8 large lithospheric plates:
Australian plate,
Antarctic plate,
African plate,
Eurasian plate,
Hindustan plate,
Pacific plate,
North American Plate,
South American Plate.
Middle plates: Arabian (subcontinent), Caribbean, Philippine, Nazca and Cocos and Juan de Fuca, etc.
Some lithospheric plates are composed exclusively of oceanic crust (for example, the Pacific Plate), others include fragments of both oceanic and continental crust.
3. There are three types of relative displacements of plates: divergence (divergence), convergence (convergence) and shear displacements..
Accordingly, three types of main plate boundaries are distinguished.
Divergent boundaries- boundaries along which the slabs move apart.
The processes of horizontal stretching of the lithosphere are called rifting... These boundaries are confined to continental rifts and mid-ocean ridges in oceanic basins.
The term "rift" (from the English rift - rupture, crack, gap) is applied to large linear structures of deep origin, formed during the stretching of the earth's crust. In terms of structure, they are graben-like structures.
Rifts can be laid both on the continental and on the oceanic crust, forming a single global system oriented relative to the geoid axis. In this case, the evolution of continental rifts can lead to a rupture of the continuity of the continental crust and the transformation of this rift into an oceanic rift (if the expansion of the rift stops before the stage of rupture of the continental crust, it is filled with sediments, turning into an aulacogen).
The process of sliding plates in zones of oceanic rifts (mid-oceanic ridges) is accompanied by the formation of a new oceanic crust due to magmatic basaltic melt coming from the asthenosphere. This process of formation of a new oceanic crust due to the influx of mantle matter is called spreading(from the English spread - to spread, unfold).
The structure of the mid-ocean ridge
In the course of spreading, each extension pulse is accompanied by the inflow of a new portion of mantle melts, which, while solidifying, build up the edges of plates diverging from the MOR axis.
It is in these zones that the formation of a young oceanic crust takes place.
Convergent boundaries- boundaries along which the collision of plates occurs. There can be three main variants of interaction in a collision: "oceanic - oceanic", "oceanic - continental" and "continental - continental" lithosphere. Depending on the nature of the colliding plates, several different processes can take place.
Subduction- the process of shifting the oceanic plate under the continental or other oceanic. Subduction zones are confined to the axial parts of deep-sea trenches, conjugated with island arcs (which are elements of active margins). Subduction boundaries account for about 80% of the length of all convergent boundaries.
When the continental and oceanic plates collide, a natural phenomenon is the underdling of the oceanic (heavier) plate under the edge of the continental; when two oceanic ones collide, the older (that is, the cooler and denser) of them sinks.
Subduction zones have a characteristic structure: their typical elements are a deep-sea trench - a volcanic island arc - a back-arc basin. A deep-sea trench is formed in the bend and underthrust zone of the subducting plate. As it sinks, this plate begins to lose water (which is abundant in the composition of sediments and minerals), the latter, as is known, significantly reduces the melting point of rocks, which leads to the formation of melting centers that feed the volcanoes of the island arcs. In the rear of a volcanic arc, some stretching usually occurs, which determines the formation of a back-arc basin. In the zone of the back-arc basin, stretching can be so significant that it leads to rupture of the plate crust and opening of the basin with oceanic crust (the so-called back-arc spreading process).
The subsidence of the subducting plate into the mantle is traced by earthquake foci arising at the contact of the plates and inside the subducting plate (colder and therefore more fragile than the surrounding mantle rocks). This seismic focal zone was named Benioff-Zavaritsky zone.
In the subduction zones, the process of the formation of a new continental crust begins.
A much rarer process of interaction between the continental and oceanic plates is the process obduction- thrusting of a part of the oceanic lithosphere onto the edge of the continental plate. It should be emphasized that in the course of this process, the separation of the oceanic plate occurs, and only its upper part - the crust and several kilometers of the upper mantle - is advancing.
In the collision of continental plates, the crust of which is lighter than the material of the mantle, and as a result, is not able to submerge in it, the process takes place collisions... In the course of the collision, the edges of the colliding continental plates are crushed, crumpled, systems of large thrusts are formed, which leads to the growth of mountain structures with a complex fold-thrust structure. A classic example This process is served by the collision of the Hindustan plate with the Eurasian one, accompanied by the growth of the grandiose mountain systems of the Himalayas and Tibet.
Collision process model
The collision process replaces the subduction process, completing the closure of the oceanic basin. At the same time, at the beginning of the collision process, when the edges of the continents have already approached, the collision is combined with the process of subduction (the subsidence of the oceanic crust continues under the edge of the continent).
Large-scale regional metamorphism and intrusive granitoid magmatism are typical for collisional processes. These processes lead to the creation of a new continental crust (with its typical granite-gneiss layer).
Transform boundaries- boundaries along which shear displacements of plates occur.
The boundaries of the Earth's lithospheric plates
1 – divergent boundaries ( but - mid-ocean ridges, b - continental rifts); 2 – transform boundaries; 3 – convergent boundaries ( but - island arc, b - active continental margins, in - collisional); 4 – direction and speed (cm / year) of plate movement.
4. The volume of the oceanic crust absorbed in the subduction zones is equal to the volume of the crust arising in the spreading zones. This position emphasizes the opinion about the constancy of the volume of the Earth. But this opinion is not the only and definitively proven. It is possible that the volume of the plans changes pulsatingly, or there is a decrease in its decrease due to cooling.
5. The main cause of plate movement is mantle convection. caused by mantle heat-gravity currents.
The source of energy for these currents is the temperature difference between the central regions of the Earth and the temperature of its near-surface parts. In this case, the main part of endogenous heat is released at the boundary of the core and mantle during the process of deep differentiation, which determines the decay of the primary chondrite material, during which the metal part rushes to the center, increasing the core of the planet, and the silicate part is concentrated in the mantle, where it further undergoes differentiation.
The rocks heated in the central zones of the Earth expand, their density decreases, and they rise, giving way to sinking colder and therefore heavier masses that have already given off part of the heat in the near-surface zones. This process of heat transfer goes on continuously, resulting in the formation of ordered closed convective cells. In this case, in the upper part of the cell, the flow of matter occurs almost in the horizontal plane, and it is this part of the flow that determines the horizontal movement of the matter of the asthenosphere and the plates located on it. In general, the ascending branches of the convective cells are located under the zones of divergent boundaries (MOR and continental rifts), and the descending branches - under the zones of convergent boundaries.
Thus, the main reason for the movement of lithospheric plates is "dragging" by convective currents.
In addition, a number of other factors act on the plates. In particular, the surface of the asthenosphere turns out to be somewhat raised above the zones of ascending branches and more lowered in the zones of immersion, which determines the gravitational "sliding" of the lithospheric plate located on an inclined plastic surface. Additionally, there are processes of pulling the heavy cold oceanic lithosphere in the subduction zones into the hot, and as a consequence, less dense asthenosphere, as well as hydraulic wedging by basalts in the MOR zones.
Figure - Forces acting on lithospheric plates.
The main driving forces of plate tectonics are applied to the bottom of the intraplate parts of the lithosphere - the forces of mantle drag FDO under the oceans and FDC under the continents, the magnitude of which depends primarily on the asthenospheric current velocity, and the latter is determined by the viscosity and thickness of the asthenospheric layer. Since under the continents the thickness of the asthenosphere is much less, and the viscosity is much higher than under the oceans, the magnitude of the force FDC almost an order of magnitude inferior to FDO... Under the continents, especially their ancient parts (continental shields), the asthenosphere almost wedges out, so the continents seem to be “stranded”. Since most lithospheric plates modern earth include both oceanic and continental parts, it should be expected that the presence of a continent in the plate should generally “slow down” the movement of the entire plate. This is how it actually happens (the fastest moving are the almost purely oceanic plates of the Pacific, Coconut and Nazca; the slowest are the Eurasian, North American, South American, Antarctic and African, a significant part of which is occupied by continents). Finally, at convergent plate boundaries, where the heavy and cold edges of lithospheric plates (slabs) sink into the mantle, their negative buoyancy creates a force FNB(the index in the designation of strength - from English negative buoyance). The action of the latter leads to the fact that the subducting part of the plate sinks in the asthenosphere and pulls the entire plate along with it, thereby increasing the speed of its movement. Obviously the strength FNB acts sporadically and only in certain geodynamic settings, for example, in cases of the above-described slab collapse through the 670 km section.
Thus, the mechanisms that set the lithospheric plates in motion can be conditionally attributed to the following two groups: 1) associated with the forces of mantle "dragging" ( mantle drag mechanism), applied to any points of the base of the slabs, in Fig. 2.5.5 - forces FDO and FDC; 2) associated with the forces applied to the edges of the plates ( edge-force mechanism), in the figure - forces FRP and FNB... The role of this or that driving mechanism, as well as those or other forces, is assessed individually for each lithospheric plate.
The combination of these processes reflects the general geodynamic process, covering areas from the surface to the deepest zones of the Earth.
Mantle convection and geodynamic processes
Currently, two-cell mantle convection with closed cells (according to the model of through-mantle convection) or separate convection in the upper and lower mantle with accumulation of slabs under subduction zones (according to the two-tiered model) is developing in the Earth's mantle. The probable poles of the uplift of mantle material are located in northeastern Africa (approximately under the junction zone of the African, Somali, and Arabian plates) and in the area of Easter Island (under the median ridge The Pacific- East Pacific Rise).
The equator of the subsidence of mantle material runs along an approximately continuous chain of convergent plate boundaries along the periphery of the Pacific and eastern Indian Oceans.
The current regime of mantle convection, which began about 200 million years ago with the disintegration of Pangea and gave rise to modern oceans, will in the future be replaced by a single-cell regime (according to the model of mantle convection) or (according to alternative model) convection will become through the mantle due to the collapse of slabs through the 670 km section. This may lead to a collision of continents and the formation of a new supercontinent, the fifth in the history of the Earth.
6. Displacements of plates obey the laws of spherical geometry and can be described on the basis of Euler's theorem. Euler's rotation theorem states that any rotation three-dimensional space has an axis. Thus, rotation can be described by three parameters: the coordinates of the rotation axis (for example, its latitude and longitude) and the rotation angle. Based on this position, the position of the continents in past geological eras can be reconstructed. Analysis of the movements of the continents led to the conclusion that every 400-600 million years they unite into a single supercontinent, which undergoes further disintegration. As a result of the split of such a supercontinent Pangea, which occurred 200-150 million years ago, modern continents were formed.
Some evidence of the reality of the mechanism of plate tectonics
Aging of the oceanic crust age with distance from the spreading axes(see figure). An increase in the thickness and stratigraphic completeness of the sedimentary layer is noted in the same direction.
Figure - Map of the age of the rocks of the oceanic floor of the North Atlantic (after W. Pitman and M. Talvani, 1972). In different colors areas of the ocean floor of different age intervals are identified; the numbers indicate the age in millions of years.
Geophysical data.
Figure - Tomographic profile through the Hellenic Trench, Crete and the Aegean Sea. Gray circles are earthquake hypocenters. Blue color shows a plate of a plunging cold mantle, red - a hot mantle (according to V. Spekman, 1989)
Remains of the huge Faralon plate, which disappeared in the subduction zone under the North and South America, recorded as slabs of the "cold" mantle (section across North America, along S-waves). By Grand, Van der Hilst, Widiyantoro, 1997, GSA Today, v. 7, No. 4, 1-7
Linear magnetic anomalies in the oceans were discovered in the 1950s during the geophysical study of the Pacific Ocean. This discovery allowed Hess and Diez in 1968 to formulate the theory of ocean floor spreading, which grew into the theory of plate tectonics. They have become one of the strongest proofs of the theory's correctness.
Figure - Formation of strip magnetic anomalies during spreading.
The reason for the origin of strip magnetic anomalies is the process of the birth of the oceanic crust in the spreading zones of mid-ocean ridges, the erupted basalts, when they cool below the Curie point in the Earth's magnetic field, acquire remanent magnetization. The direction of the magnetization is the same as the direction magnetic field Earth, however, due to periodic reversals of the Earth's magnetic field, the erupted basalts form bands with different directions of magnetization: direct (coincides with modern direction magnetic field) and reverse.
Figure - Diagram of the formation of the strip structure of the magnetoactive layer and magnetic anomalies of the ocean (Vine - Matthews model).
There are two types of lithosphere. The oceanic lithosphere has an oceanic crust about 6 km thick. It is mostly covered by the sea. The continental lithosphere is covered by the continental crust 35 to 70 km thick. For the most part, this crust protrudes above, forming land.
Slabs
Rocks and minerals
Moving plates
The plates of the earth's crust are constantly moving in different directions, albeit very slowly. average speed their movement is 5 cm per year. Your nails grow at about the same rate. Since all the plates are tightly adjacent to each other, the movement of any of them acts on the surrounding plates, forcing them to gradually move. Plates can move in different ways, which can be seen at their borders, but the reasons for the movement of the plates are still unknown to scientists. Apparently, this process may have no beginning or end. Nevertheless, some theories argue that one type of plate movement can be, so to speak, "primary", and from it all other plates are already set in motion.
One type of plate movement is the "diving" of one plate under another. Some scholars believe that it is this type of movement that causes all other movements of the plates. At some boundaries, molten rock, breaking through to the surface between two plates, solidifies along their edges, pushing these plates apart. This process can also cause all other plates to move. It is also believed that, in addition to the primary shock, plate movement is stimulated by gigantic heat fluxes circulating in the mantle (see article ““).
Drifting continents
Scientists believe that since the formation of the primary earth's crust, plate movement has changed the position, shape and size of continents and oceans. This process was named tectonics slabs... Various evidences are given for this theory. For example, the outlines of continents such as South America and Africa look like they once formed a single whole. There was also an undeniable similarity in the structure and age of the rocks that make up the ancient mountain ranges on both continents.
1. According to scientists, the land masses that now form South America and Africa were connected to each other more than 200 million years ago.
2. Apparently, the floor of the Atlantic Ocean gradually expanded as new rock formed at the plate boundaries.
3. Now South America and Africa are moving away from each other at a speed of about 3.5 cm per year due to plate movement.
