Tectonics is a branch of geology that studies the structure of the earth's crust and the movement of lithospheric plates. But it is so multifaceted that it plays a significant role in many other Earth sciences. Tectonics is used in architecture, geochemistry, seismology, in the study of volcanoes and in many other areas.
Science tectonics
Tectonics is a relatively young science; it studies the motion of lithospheric plates. For the first time, the idea of plate movement was voiced in the theory of continental drift by Alfred Wegener in the 1920s. But it got its development only in the 60s of the XX century, after conducting studies of the relief on the continents and the bottom of the ocean. The material obtained made it possible to take a fresh look at previously existing theories. The theory of lithospheric plates appeared as a result of the development of ideas from the theory of continental drift, the theory of geosynclines, and the contraction hypothesis.
Tectonics is a science that studies the strength and nature of the forces that form mountain ranges, crush rocks into folds, and stretch the earth's crust. It underlies all geological processes taking place on the planet.
Contraction hypothesis
The contraction hypothesis was put forward by the geologist Elie de Beaumont in 1829 at a meeting of the French Academy of Sciences. It explains the processes of mountain building and folding of the earth's crust under the influence of a decrease in the volume of the Earth due to cooling. The hypothesis was based on the ideas of Kant and Laplace about the primary fiery-liquid state of the Earth and its further cooling. Therefore, the processes of mountain building and folding were explained as processes of compression of the earth's crust. Subsequently, cooling, the Earth decreased its volume and crumpled into folds.
Contractional tectonics, the definition of which confirmed the new doctrine of geosynclines, explained the uneven structure of the earth's crust, became a solid theoretical basis for the further development of science.
Theory of Geosynclines
It existed at the turn of the late XIX and early XX centuries. She explains tectonic processes by the cyclic oscillatory movements of the earth's crust.
The attention of geologists was drawn to the fact that the rocks can lie both horizontally and deployed. Horizontally occurring rocks were assigned to platforms, and dislocated rocks - to folded areas.
According to the theory of geosynclines, at the initial stage, due to active tectonic processes, there is a deflection, lowering of the earth's crust. This process is accompanied by sediment drift and the formation of a thick sedimentary stratum. In the future, the process of mountain building and the appearance of folding. The geosynclinal regime is estimated to be platform, which is characterized by insignificant tectonic movements with the formation of a small thickness of sedimentary rocks. The final stage is the continent formation stage.
For almost 100 years, geosynclinal tectonics dominated. The geology of that time lacked factual material; subsequently, the accumulated data led to the creation of a new theory.
Theory of lithospheric plates
Tectonics is one of the directions in geology, which formed the basis of the modern theory of the movement of lithospheric plates.
According to the theory of lithospheric plates, part of the earth's crust is lithospheric plates, which are in continuous motion. Their movement occurs relative to each other. In the zones of extension of the earth's crust (mid-ocean ridges and continental rifts), a new oceanic crust forms (spreading zone). In the submerged zones of the blocks of the earth's crust, the old crust is absorbed, as well as the oceanic submersion under the continental (subduction zone). The theory also explains the causes of earthquakes, mountain building processes and volcanic activity.
Global plate tectonics includes such a key concept as the geodynamic setting. It is characterized by a combination of geological processes, within one territory, in a certain period of geological time. The same geodynamic situation is characterized by the same geological processes.
Globe structure
Tectonics is a branch of geology that studies the structure of planet Earth. The earth, in a rough approximation, has the shape of a flattened ellipsoid and consists of several shells (layers).
The following layers are distinguished in the structure of the globe :
- Earth's crust.
- Mantle.
- Core.
The Earth’s crust is the outer hard layer of the Earth, it is separated from the mantle by a border called the surface of Mohorovich.
The mantle, in turn, is divided into upper and lower. The boundary separating the layers of the mantle is the layer of Golitsin. The earth's crust and the upper part of the mantle, up to the asthenosphere, are the lithosphere of the Earth.
The core is the center of the globe, separated from the mantle by the border of Guttenberg. It is divided into a liquid outer and solid inner core, between them there is a transition zone.
The structure of the earth's crust
The structure of the earth's crust is directly related to the science of tectonics. Geology studies not only the processes occurring in the bowels of the Earth, but also its structure.
The Earth’s crust is the upper part of the lithosphere, is the outer hard shell of the Earth, it is composed of rocks of different physicochemical composition. According to physico-chemical parameters, there is a division into three layers:
- Basaltic.
- Granite gneiss.
- Sedimentary.
There is also a division in the structure of the earth's crust. Four main types of the earth's crust are distinguished:
- Continental.
- Oceanic
- Subcontinental.
- Suboceanic.
The continental crust is represented by all three layers, its thickness varies from 35 to 75 km. The upper sedimentary layer is widely developed, but, as a rule, has a small thickness. The next layer, granite gneiss, has maximum power. The third layer, basalt, is composed of metamorphic rocks.
The oceanic crust is represented by two layers - sedimentary and basalt, its thickness is 5-20 km.
Subcontinental crust, like continental, consists of three layers. The difference is that the thickness of the granite-gneiss layer in the subcontinental crust is much less. This type of crust is found on the border of the continent with the ocean, in the field of active volcanism.
The suboceanic crust is close to oceanic. The difference is that the thickness of the sedimentary layer can reach 25 km. This type of crust is confined to the deep troughs of the earth's crust (inland seas).
Lithosphere plate
Lithospheric plates are large blocks of the earth's crust, which are part of the lithosphere. Plates are able to move relative to each other along the upper part of the mantle - the asthenosphere. The plates are separated from each other by deep-sea trenches, mid-ocean ridges and mountain systems. A characteristic feature of lithospheric plates is that they are able to maintain rigidity, shape and structure for a long time.
Earth tectonics suggests that lithospheric plates are in constant motion. Over time, they change their outline - they can split or grow together. To date, 14 large lithospheric plates have been identified.
Plate tectonics
The process that forms the appearance of the Earth is directly related to the tectonics of lithospheric plates. World tectonics implies that the movement is not continents, but lithospheric plates. Facing each other, they form mountain ranges or deep oceanic depressions. Earthquakes and volcanic eruptions are a consequence of the movement of lithospheric plates. Active geological activity is confined mainly to the edges of these formations.
The movement of lithospheric plates was detected by satellites, but the nature and mechanism of this process remains a mystery.
Ocean tectonics
In the oceans, the processes of destruction and accumulation of sediments are slow in nature, so tectonic movements are well reflected in the relief. The bottom relief has a complex structure. Tectonic structures formed as a result of vertical movements of the earth's crust and structures obtained due to horizontal movements are distinguished.
The structures of the ocean floor include such relief forms as abyssal plains, ocean basins and mid-ocean ridges. In the basin zone, as a rule, a calm tectonic situation is observed; in the zone of mid-ocean ridges, tectonic activity of the earth's crust is noted.
Ocean tectonics also includes structures such as deep-sea trenches, oceanic mountains, and guillots.
Reasons moving plates
The driving geological force is the tectonics of the world. The main reason for the movement of plates is mantle convection, which is created by heat-gravity currents in the mantle. This is due to the temperature difference at the surface and in the center of the earth. Inside the rock they heat up, they expand and decrease in density. Light fractions begin to float, and cold and heavy masses fall in their place. The process of heat transfer occurs continuously.
On the movement of the plates are still glad factors. For example, the asthenosphere in the zones of upward flows is elevated, and in the zones of immersion - omitted. Thus, an inclined plane is formed and the process of “gravitational” sliding of the lithosphere plate occurs. Subduction zones also influence, where the cold and heavy oceanic crust stretches under the hot continental.
The thickness of the asthenosphere under the continents is much less, and the viscosity is greater than under the oceans. Under the ancient parts of the continents, the asthenosphere is practically absent, so in these places they do not move and remain in place. And since the lithosphere plate includes both the continental and oceanic parts, the presence of the ancient continental part will impede the movement of the plate. The movement of purely oceanic plates is faster than mixed, and especially continental.
There are a lot of mechanisms that drive the plates, conditionally they can be divided into two groups:
- Mechanisms that set in motion under the action of the mantle current.
- Mechanisms associated with the application of forces to the edges of plates.
The combination of processes of the driving forces reflects the geodynamic process as a whole, which covers all layers of the Earth.
Architecture and Tectonics
Tectonics is not only a purely geological science associated with processes occurring in the bowels of the Earth. It is also used in everyday life. In particular, tectonics is used in the architecture and construction of any building, whether it be buildings, bridges or underground structures. Here, the laws of mechanics are the basis. In this case, tectonics is understood as the degree of strength and stability of the structure in a given specific area.
The theory of lithospheric plates does not explain the relationship of plate movements with deep processes. We need a theory that would explain not only the structure and movement of lithospheric plates, but also the processes occurring inside the Earth. The development of such a theory is associated with the union of specialists such as geologists, geophysicists, geographers, physicists, mathematicians, chemists, and many others.