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Plate tectonic theory notes

Plate tectonic theory 
There are certain theories which explain the origin of numerous relief features of earth like folding and faulting, vulcanicity, earthquakes, mountain building etc. Plate tectonic theory notes, is the most acceptable theory that explains all these features in a justified manner.

The plate tectonic theory notes, is the outcome of various theories that was put forwarded by different scientists and geographers. In other words, this theory is the result of the efforts of different scientists. The plate tectonic theory came into existence from 1960s. It explains the formation of mountains due to the movement of different plates of the earth.

Plate tectonic theory notes

 plate tectonic theory

The concept of plate tectonic theory is the extended version of sea floor spreading. This hypothesis is based of the sea floor spreading as forwarded by Harry Hess and further confirmed by Vine and Mathews by their interpretation of linear magnetic anomalies. In 1965, Tuzo Wilson first used the term 'plate' in his definition of transform falls. 

But in 1967, W.Z Morgan of Princestone University first outlined the hypothesis of plate tectonic theory. D.P Mackanjee of Cambridge and Parker of America were drawn to the conclusions similar to that of Wilson. Through their published research findings Tuzo Wilson, Mackanjee and Parker laid the foundation of this theory, although proposed by Morgan.

This theory, states that the lithosphere of the earth in respect to size is divided into 6 major plates and 8 minor plates. These plates are constantly moving due to thermal convective currents, which are originated deep within the earth. All the tectonic, seismic and volcanic events take place along the boundaries of the the plates.

The plate margin is the edge part of a particular plate and a plate boundary is the surface trace zone of the plates in motion. 

On the basis of movement, creation and destruction of geomaterials, plate boundaries are divided into 

(i) Constructive plate boundary-They represent the divergence zone where there is continuous upwelling of lavaz due to which oceanic crust is formed. They are also called divergent or attriting plate boundary.

(ii) Destructive plate boundary - These plate moves towards each other or converge along a line leading of one plate to subduct into the mantle. They are also called convusing or conversing plate boundary. 

(iii) Conservative plate boundary
- These plates pass or slide one another along transformed fault resulting to neither creation nor destruction of crust. They are also called sial plate boundary.

Assumptions of the plate tectonic theory 
(i) The area of the earth surface is fixed and during the last 600 million years, the radius of the earth doesn't appear to increase by more than a rate of 5%. The amount of crust created consumed is equal to the amount of crust created.

(ii) There is spreading of the sea floor and new oceanic crust is continuously created at active mid oceanic ridges and are destroyed in the trenches.

(iii) The new crust that gets formed becomes a part of a plate, which includes both oceanic and continental crust. The process by which one plate gets consumed and disappears under another plate, is called subduction.

Mechanism of plate creation and movement 
(i) In 1948 Beno Gutenberg of California, stated that there is a low velocity zone in the upper part of the mantle about 80 km below the earth's surface. Here the velocity of the earthquake waves slows down.

(ii) As the velocity of the seismic waves slows decelerates with the acceleration of temperature, the temperature of the low velocity zone accelerates rapidly.

(iii) This layer is extremely hot and the mantle is almost in the molten state. The rocks are weak and have less strength.

(iv) There is a region where 100 to 150 km thick layer gets decoupled from the deeper mantle. This hot and weak layer situated 100 km below the lithosphere is known as Esthonsphere.

(v) Due to thermal instability in the mantle, heat is conducted upwards through the movement of molten material. The process of convection flow in the interior may be due to the movement of the plate.

(vi) According to some, the plates slides from the ridges to the trenches under the influence of the gravity. While according to others, the sinking crust beneath the trench system constantly pulls the crust in that direction and is being compensated by the upwelling of magma in the ridges.

Although there are several mechanisms for the movement of plates but the process of the convective currents is the most possible mechanism for the plate tectonic theory, and further for the formation of the mountains. The plate tectonic theory notes has almost solved certain problems and confusions regarding the origin of the oceans, continents and mountain building.

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