Together with part of the upper mantle, it consists of several very large blocks, which are called lithospheric plates. Their thickness is different - from 60 to 100 km. Most plates include both continental and oceanic crust. There are 13 main plates, of which 7 are the largest: American, African, Indo-, Amur.
The plates lie on the plastic layer of the upper mantle (asthenosphere) and slowly move relative to each other at a speed of 1-6 cm per year. This fact was established by comparing photographs taken with artificial satellites Earth. They suggest that the configuration in the future may be completely different from the current one, since it is known that the American lithospheric plate is moving towards the Pacific, and the Eurasian one is approaching the African, Indo-Australian, and also the Pacific. The American and African lithospheric plates are slowly moving apart.
The forces that cause the separation of lithospheric plates arise when the mantle substance moves. Powerful ascending flows of this substance push apart the plates, break the earth's crust, forming deep faults in it. Due to underwater outpourings of lavas, strata are formed along the faults. Freezing, they seem to heal wounds - cracks. However, the stretch increases again, and breaks occur again. So, gradually increasing lithospheric plates diverge in different directions.
There are fault zones on land, but most of them are in ocean ridges on where the earth's crust is thinner. The largest fault on land is located in the east. It stretched for 4000 km. The width of this fault is 80-120 km. Its outskirts are dotted with extinct and active ones.
Collision is observed along other plate boundaries. It happens in different ways. If the plates, one of which has an oceanic crust and the other a continental one, approach each other, then the lithospheric plate, covered by the sea, sinks under the continental one. In this case, arcs () or mountain ranges () arise. If two plates with a continental crust collide, then the edges of these plates are crushed into folds of rocks, and mountainous regions are formed. So they arose, for example, on the border of the Eurasian and Indo-Australian plates. The presence of mountainous areas in internal parts the lithospheric plate suggests that once there was a boundary between two plates, firmly soldered to each other and turned into a single, larger lithospheric plate. Thus, we can draw a general conclusion: the boundaries of lithospheric plates are mobile areas to which volcanoes are confined , zones, mountainous areas, mid-ocean ridges, deep-sea depressions and trenches. It is at the boundary of lithospheric plates that are formed, the origin of which is associated with magmatism.
What do we know about the lithosphere?
Tectonic plates are large stable areas of the Earth's crust that are constituent parts lithosphere. If we turn to tectonics, the science that studies lithospheric platforms, we find out that large areas earth's crust from all sides are limited by specific zones: volcanic, tectonic and seismic activity. It is at the junctions of neighboring plates that phenomena occur, which, as a rule, have catastrophic consequences. These include both volcanic eruptions and strong earthquakes on the scale of seismic activity. In the process of studying the planet, platform tectonics played a very important role. Its significance can be compared to the discovery of DNA or the heliocentric concept in astronomy.
If we recall the geometry, then we can imagine that one point can be the point of contact of the boundaries of three or more plates. The study of the tectonic structure of the earth's crust shows that the most dangerous and rapidly collapsing are the junctions of four or more platforms. This formation the most unstable.
The lithosphere is divided into two types of plates, different in their characteristics: continental and oceanic. It is worth highlighting the Pacific platform, composed of oceanic crust. Most of the others consist of the so-called block, when the continental plate is soldered into the oceanic one.
The location of the platforms shows that about 90% of the surface of our planet consists of 13 large, stable areas of the earth's crust. The remaining 10% fall on small formations.
Scientists have compiled a map of the largest tectonic plates:
- Australian;
- Arabian subcontinent;
- Antarctic;
- African;
- Hindustan;
- Eurasian;
- Nazca plate;
- Cooker Coconut;
- Pacific;
- North and South American platforms;
- Scotia plate;
- Philippine plate.
From theory, we know that the solid shell of the earth (lithosphere) consists not only of the plates that form the relief of the surface of the planet, but also of the deep part - the mantle. Continental platforms have a thickness of 35 km (in the flat areas) to 70 km (in the zone of mountain ranges). Scientists have proven that the plate in the Himalayas has the greatest thickness. Here the thickness of the platform reaches 90 km. The thinnest lithosphere is found in the ocean zone. Its thickness does not exceed 10 km, and in some areas this figure is 5 km. Based on the information about the depth at which the epicenter of the earthquake is located and what is the speed of propagation of seismic waves, calculations are made of the thickness of the sections of the earth's crust.
The process of formation of lithospheric plates
The lithosphere is composed primarily of crystalline substances, formed as a result of cooling of magma at the exit to the surface. The description of the structure of the platforms speaks of their heterogeneity. The process of formation of the earth's crust took place over a long period, and continues to this day. Through microcracks in the rock, molten liquid magma came to the surface, creating new bizarre forms. Its properties changed depending on the change in temperature, and new substances were formed. For this reason, minerals that are at different depths differ in their characteristics.
The surface of the earth's crust depends on the influence of the hydrosphere and atmosphere. There is constant weathering. Under the influence of this process, the forms change, and the minerals are crushed, changing their characteristics with the same chemical composition. As a result of weathering, the surface became looser, cracks and microdepressions appeared. In these places deposits appeared, which we know as soil.
Map of tectonic plates
At first glance it seems that the lithosphere is stable. Its upper part is such, but the lower part, which is distinguished by viscosity and fluidity, is mobile. The lithosphere is divided into a certain number of parts, the so-called tectonic plates. Scientists cannot say how many parts the earth's crust consists of, since in addition to large platforms, there are also smaller formations. The names of the largest plates were given above. The process of formation of the earth's crust is ongoing. We do not notice this, since these actions occur very slowly, but by comparing the results of observations for different periods, we can see how many centimeters a year the boundaries of formations are shifting. For this reason, the tectonic map of the world is constantly updated.
Tectonic Plate Cocos
The Cocos platform is a typical representative of the oceanic parts of the earth's crust. It is located in Pacific region. In the west, its boundary runs along the ridge of the East Pacific Rise, and in the east its boundary can be defined by a conventional line along the coast of North America from California to the Isthmus of Panama. This plate is subducting under the neighboring Caribbean plate. This zone is characterized by high seismic activity.
Mexico suffers the most from earthquakes in this region. Among all the countries of America, it is on its territory that the most extinct and active volcanoes are located. The country has suffered a large number of earthquakes with a magnitude greater than 8 points. The region is quite densely populated, therefore, in addition to destruction, seismic activity also leads to a large number of victims. Unlike Cocos, located in another part of the planet, the Australian and West Siberian platforms are stable.
Movement of tectonic plates
For a long time, scientists have been trying to find out why one region of the planet has mountainous terrain, while another is flat, and why earthquakes and volcanic eruptions occur. Various hypotheses were built mainly on the knowledge that was available. Only after the 50s of the twentieth century was it possible to study the earth's crust in more detail. Mountains formed at the sites of plate faults were studied, chemical composition these plates, and also created maps of regions with tectonic activity.
In the study of tectonics, a special place was occupied by the hypothesis of the displacement of lithospheric plates. Back in the early twentieth century, the German geophysicist A. Wegener put forward a bold theory about why they move. He carefully studied the outlines of the western coast of Africa and the eastern coast of South America. The starting point in his research was precisely the similarity of the outlines of these continents. He suggested that, perhaps, these continents used to be a single whole, and then a break occurred and the shift of parts of the Earth's crust began.
His research touched upon the processes of volcanism, the stretching of the surface of the ocean floor, the viscous-liquid structure the globe. It was the works of A. Wegener that formed the basis of the research conducted in the 60s of the last century. They became the foundation for the emergence of the theory of "lithospheric plate tectonics".
This hypothesis described the model of the Earth as follows: tectonic platforms with a rigid structure and different masses were placed on the plastic substance of the asthenosphere. They were in a very unstable state and were constantly moving. For a simpler understanding, we can draw an analogy with icebergs that are constantly drifting in ocean waters. Similarly, tectonic structures, being on a plastic substance, are constantly moving. During displacements, the plates constantly collided, came one on top of the other, joints and zones of separation of the plates arose. This process was due to the difference in mass. Areas of increased tectonic activity were formed at the collision sites, mountains arose, earthquakes and volcanic eruptions occurred.
The displacement rate was no more than 18 cm per year. Faults formed, into which magma entered from the deep layers of the lithosphere. For this reason, the rocks that make up the oceanic platforms are of different ages. But scientists have put forward an even more incredible theory. According to some representatives of the scientific world, magma came to the surface and gradually cooled, creating a new bottom structure, while the "excess" of the earth's crust, under the influence of plate drift, sank into the earth's interior and again turned into liquid magma. Be that as it may, the movements of the continents occur in our time, and for this reason new maps are being created to further study the process of drifting tectonic structures.
Unlike other continents, which are large fragments of the fragmented foremothers of Gondwana and Laurasia, Eurasia was formed as a result of the union of ancient lithospheric blocks. Approaching under the influence of internal processes, at different geological times, these blocks were connected by "seams" of folded belts, gradually "composing" the mainland in its modern configuration and size (see figures).
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And you know that... |
The modern continent of Eurasia is located in the junction zone of five large lithospheric plates. Four of them are continental, one is oceanic. Most of Eurasia belongs to the continental Eurasian plate. The southern peninsulas of Asia belong to two different continental plates: the Arabian (Arabian Peninsula) and the Indo-Australian (Indostan Peninsula). The northeastern margin of Eurasia is part of the fourth continental plate - the North American. And the eastern part of the mainland with adjacent islands is the zone of interaction between Eurasia and the oceanic Pacific plate. Folded belts are being formed in the junction zones of lithospheric plates. On the southern edge of the Eurasian plate - the Alpine-Himalayan belt: it contains the southern outskirts of Europe, the Crimean Peninsula and Asia Minor, the Caucasus, the Armenian and Iranian highlands, the Himalayas. On the eastern edge of the mainland - the Pacific belt, in which the Kamchatka Peninsula, the Sakhalin Islands, the Kuril Islands, the Japanese, and the Malay Archipelago are located.
IN composition of the Eurasian continent, includes five ancient platforms; all of them are "fragments" of the ancient foremother Pangea. Three platforms - East European, Siberian and Chinese - after the split of Pangea made up the ancient northern continent of Laurasia. Two - Arabian and Indian - were part of the ancient southern continent of Gondwana. The platforms are "connected" to each other by folded belts that formed at different geological times.
All ancient platforms of Eurasia have a two-tiered structure: the rocks of the sedimentary cover lie on the crystalline basement. The foundations are composed of igneous and metamorphic rocks, the sedimentary cover is composed of marine and continental sedimentary rocks. Each platform has plates and shields.
Each of the platforms has its own characteristics. The Chinese platform is fragmented into several disparate blocks, the largest of which are Chinese-Korean And South Chinese. The Siberian and Indian platforms are penetrated to the base by ancient powerful cracks and volcanic intrusions (intrusions). The basement of the East European Platform is dissected by troughs and deep depressions. The Arabian platform is split and stretched into pieces by a modern fault - a rift (see pictures on the right). The sedimentary covers of the platforms differ in thickness and in the rocks that make them up. The platforms of Eurasia are characterized by different intensity of modern tectonic movements.
Fold belts in Eurasia formed at different geological times. During ancient folding, the Atlantic and Ural-Mongolian belts were formed. Subsequently, different areas of these belts developed differently: some experienced subsidence, others experienced uplift. Those that sank were flooded by the seas, and a thick layer of marine sediments gradually accumulated on the folded base. These areas have acquired a two-tiered structure. This - young platforms , the largest of which are West European and Scythian (in Europe), West Siberian and Turan (in Asia). The areas that experienced uplifts were folded mountain systems(Tien Shan, Altai, Sayans). During the entire time of their existence, their folds (mountain ranges) were exposed to external forces. Therefore, at present they are severely destroyed, and ancient crystalline rocks are exposed on the surface.
Alpine-Himalayan and Pacific folded belts arose at a later geological time and has not yet been finally formed. They are young. The surface of the mountains, which represent these belts, has not yet had time to collapse. Therefore, it is composed of young sedimentary rocks of marine origin, hiding at a considerable depth the crystalline cores of the folds. These belts are characterized by high seismicity - volcanism is manifested here, earthquakes are concentrated. In such areas, volcanic rocks overlap sedimentary rocks or are embedded in their thickness.
Now let's move on to minerals.