Theory of Plate Tectonics. Concept & Explanation.

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 A] What are Plates in geographical term?



  • Plates are hard and rigid segments of lithosphere including the rigid upper part of mantle and oceanic-continental crust that floats on the underlying asthenosphere.
  • The lithospheric plates move over the plastic asthenosphere under the influence of thermal convective currents.
  • Thermal convection currents are nothing but radio energy which is created by radio-active decaying of rocks inside the core.
  • The movement of crustal plates cause pressure and tensions upon the rock, leading to deformation of land surface.
  • Further, these plate movements cause seismicity, volcanicity, occurrence of various landforms, formation of mountains, etc. 


B] What is Plate Tectonics Theory?


  • Plate tectonics theory is majorly based on two scientific concepts- Continental Drift and Sea-floor Spreading.
  • Plate tectonics theory is a comprehensive scientific theory describing large-scale motion of tectonic plates of Earth's lithosphere over the Asthenosphere.
  • The theory has been built on the concept of continental drift, an idea developed during early decades of the 20th century.
  • This theory is categorized within three types of Plate Boundaries:
1. Divergent Plate Boundaries:
  • These plate margins are formed due to divergence of the lithospheric plates, representing zone of divergence where there is continuous upliftment of molten lava and thus, new oceanic crust is formed.
  • These type of plate margins are characterized by mid-oceanic ridges where two oceanic plates split apart to form new oceanic crust and also moves in opposite directions.
  • As these plate margins lead to formation of new crust, they are known as Constructive Plate Margins.
  • Divergent movement of plates results in volcanic activity of fissure flow of basaltic magma, creation of new oceanic crust, formation of submarine mountain ridges, occurrence of shallow focus earthquakes and drifting of oceanic plates.
  • The Mid-Atlantic Ridge is a well-known example of a divergent plate boundary, and the Great Rift Valley in Africa is an example of a continental rift zone.


2. Convergent Plate Boundaries:
  • They are also known as "Destructive Plate Margins", because two plates move towards each other to converge along a line, leading to edge of one plate overriding the other plate.
  • The denser plate is subducted inside the lighter plate and as it reaches molten part of mantle, it is completely consumed and destroyed.
  • Convergence and subduction of heavier plate under lighter plate margins results in occurrence of explosive volcanic eruptions, formation of folded mountains, island arcs and oceanic trenches.
  • The Himalayan mountain ranges is the best example of continental convergent plate boundaries.


3. Transform Plate Boundaries:



  • Transform plate boundaries are also called "Shear Plate Margins", where two plates pass or slide past each other along transform faults.
  • These are also known as Conservative plates because the crust is neither created nor destroyed.
  • This transformation occurs by displacing massive amounts of rocks for a long distance or creating valleys and ridges along the boundary.
  • The San Andreas Fault, a boundary between North American Plate and the Pacific Plate, created a major earthquake in 1906 when it moved nearly 300 miles.