Describe the Principle of Plate Tectonics.

Basic Concepts of Plate Tectonics

The following three main assumptions are behind the concept of plate tectonics-

(i) The ocean floor expands and new oceanic crust is constantly formed on the active ocean ridges and its destruction occurs in the craters.

(ii) The surface area of ​​the earth is constant and the radius of the earth has not increased by more than 56 in the last 600 million years. From this, it can be said that the construction and destruction of the new earth’s surface are almost equal.

(iii) After the formation of a new crust, it gets incorporated into a larger plate which is generally formed by both continental and oceanic crust. Although there are some plates in which only the oceanic crust is found. The induction of one plate into another plate is called reversion. The deformation in the plates occurs at the edges instead of inside.


The different plates on the Earth are moving with respect to each other, as well as the spheres are connected on the surface of the Earth. This means that the motion of all plates is to some extent expedient, and a change in the direction or velocity of one plate is not possible without a concomitant change in the other plate.

Adjacent plate boundaries at mid-oceanic ridges are of the same type, but adjacent plate boundaries at the boundary of two plates may also differ. There is no geometric restriction on the form or shape of the plate. It can have any form and any combination of boundaries at its limit. But the shape of the boundaries of the plates and their relative velocity should be such that there cannot be any change in the surface area of ​​the earth. If the area of ​​two plates increases, then the area of ​​the other plates should decrease, otherwise, the surface area of ​​the Earth cannot remain constant.

Therefore, theoretically, some plates may collapse and transfer mid-oceanic ridges and deep-sea craters with respect to each other. Due to physical reasons, the destruction of the plate, which includes the continental crust, is never possible. Therefore, when the continental part of a plate comes near the crater or sink, there is a change in the Bhima motion or the relative motion between the two plate ends. It is possible to form a plate by joining two plates. When two continents come near each other from either side of a sink, there is the formation of folded mountain ranges. This is how the Himalayas Mountains were formed.

Plate tectonics and the formation of continental crust and mountains

When two continental plates collide, the plate of higher density gets zoned downwards, due to which mountains are formed there. Due to the collision of the Eurasian and Indian plates, Tethys has folded and changed into the Himalayan Mountains. The Alps Mountains originated from the collision of the European plates with the African.

When the continental oceanic plates collide with each other, the oceanic plates of higher density are pushed down. This is how the Raki and Andes mountains originated. Most of the world’s volcanoes and earthquakes are found on plate boundaries. The origin of deep earthquakes in the middle of the oceans is sea trenches. The displacement of continents can also be proved by plate tectonics. The Pacific Ocean is continuously shrinking. It is an eroding ocean. This type of continuous encroachment of the American Plate continues. 

Deep lines at the bottom of the oceans and fault lines discovered in the North Atlantic Ocean are considered to be particularly important evidence from this point of view. According to Harry Hess, the core or mantle inside the Earth is heated by radioactive materials, which gives rise to convection currents. 

These convective currents, while flowing upwards, shed their lava from the upper layer of the mantle upwards from the weakness zone. The surface is formed at mid-oceanic ridges by this hot material (lava). Reaching above, this lava gradually condenses and solidifies to form the lithosphere. These layers of flowing lava solidify and are called plates. The present continents and oceans have been formed due to the movement of plates.

Explanation of Seismic and Volcanic Actions by Plate Tectonics – Plate tectonics helps in understanding the distribution of earthquakes and volcanoes on Earth. Most of the earthquakes and volcanoes of the world are found in narrow, semi-discontinuous, and fixed belts. 

These belts are mainly concentrated in plate boundaries. In fact, in the demarcation of plates, the strips of seismic action have been used. Seismicity Ocean ridges, trench arc systems, and division zones, all these shapes are indicative of plate boundaries. All plates descend into the mantle. 

Diagonally inclined earthquake generation zones are found near all the poles of the Pacific Ocean, they are called Benioff Zones. These were first detected by the seismologist Hugo Benny-Off, generally, the seismicity of the Benny-Off area is related to the downward movement of the surface.

Benio from the collision of two plates So much heat is generated in the F region that the rocks of the oceanic plate and the lower part of the continental plate melt and the molten material moves upwards. 

It has to pass through the thick continental crust to rise to the top. Most of it gets deposited in the form of impermeable rocks under the surface which is called batholiths. Volcanoes originate from the molten material that appears on the surface in the form of lava.

There is a difference between the volcanoes of the destructive plate boundary and the constructive plate boundary. Volcanoes of the destructive plate boundary are continental and the volcanoes of the constructive plate boundary are oceanic. It is clear from the distribution of volcanoes in the world that active volcanoes are found along the mid-oceanic ridge.

 Most of the volcanoes are associated with constructive edges in the plate. In these, volcanic lava is formed from such vessels which have less potash and which are formed due to characteristic melting in the mantle. 

The amount of silica is high in basalt lava of volcanic shore volcanoes related to the Pacific and Alpine mountain ranges. Andesite rocks are found in almost all volcanoes. Their characteristics are between that of basalt and granite. Its color is light brown and 60% silica is found in it.

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