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Tectonic Plates

Tectonic plates (also called lithospheric plate) is a massive, irregularly-shaped slab of solid rock, generally composed of both continental and oceanic lithosphere....

Tectonic plates (also called lithospheric plate) is a massive, irregularly-shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.

The concept of Tectonic Plates was first introduced in 1967.

Continental Drift Theory
  • Continental Drift: The movement of continents across the ocean bed is known as continental drift. This drifting takes millions of years to complete this process.
  • Continental drift theory was given by Alfred Wegener in 1915. This theory has explained the origin of continents and ocean basins.
  • Though it was a Dutch cartographer, Abraham Ortelius, who was the first to work on the concept of symmetrical coasts on the Atlantic Ocean’s sides.
  • According to Wegener, all the continents formed a single continental mass which is called “Pangaea” which means all earth. This supercontinent was surrounded by a mega ocean called “Panthalassa ” meaning all water.
  • Subsequently, Laurasia and Gondwanaland continued to break into various smaller continents that exist today. Thus, Wegener proposed that continents are floating and constantly drifting on the earth’s surface. His hypothesis, later on, became the basis of present-day plate tectonic theory.
Forces Responsible for Continental Drift
  1. Gravitational forces
  2. Pole-fleeing force, and
  3. Buoyancy force
Evidence Supporting Continental Drift Theory
  1. The Matching of Continents (Jig-Saw-Fit)
  2. Rocks of Same Age Across the Oceans
  3. Distribution of Fossils
Seafloor Spreading Theory
  • Sea floor spreading theory was given by Harry Hess.
  • The theory states that in the middle of ocean, the oceanic plates are moving away from each other in the middle of the oceans.
  • At the oceanic continental plate boundary, the oceanic plate gets subduct under the continental plate.
Forces that cause Seafloor spreading 
Convectional current theory :
  • It was  was proposed by Arthur Holmes addresses the forces which cause the sea floor spreading.
  • According to Holmes the heat which is generats from the radioactive decay of substances deep inside the Earth (the mantle) creates magma which consists of molten rocks, volatiles, dissolved gases among other material.
  • Further this magma, heat and gases seek a path to escape which leads to the formation of convection currents in the mantle.
  • According to the theory of Seafloor spreading, convectional cells are the force behind drifting of continents thus these conventional cells are explained by convectional current theory of Holmes
  • These ocean plates get subducts under the continental plates (since ocean plates are denser than continental plates), when these two types of plates converge.
How many tectonic plates are there?
There are 13 plates on the earth, 7 are in large size and 6 are in small size. Large plates are:
  • Eurasian Plate
  • Indian Austral Plate
  • African Plate
  • North American Plate
  • South American Plate
  • Antarctic Plate
  • Pacific Plate
Tectonic plate movement
  • The convergence or destructive boundary
  • Divergences or constructive boundary
  • Transverse boundary or no creation and destructive

The convergence boundary: 

When plates move towards each other, the heavy plate submerges under the lighter plate. The following are the types of convergence boundaries

  • Continent-Continent Convergence (C-C)
  • Ocean-Continent Convergence (O-C)
  • Ocean-Ocean Convergence (O-O)

Continent – Continent convergence(C-C):  The convergence of the Indian plate and the Eurasian plate is an example of C-C convergence. In this type of interaction, heavier continents’ plates will be submerge. Since the continent plates are high in thickness hence volcanic activities can be rarely seen, however, at the boundary line earthquake, fold mountains, and landslides phenomenons are common.

Continent-Ocean convergence(C-O):  The conversion of the pacific ocean plate and the American plate is an example of the C-O boundary. Generally, ocean plates are heavier than continental plates, and the submergence of ocean plates happens in this case. At the boundary line, trench, volcanic mountain, and fold mountain, earthquakes, and landslides are common phenomena.

Ocean-ocean convergence (O-O):   In this case, two ocean plates converge and one of the heavy ocean plates submerges under the other. Volcanic activities and earthquakes are the common phenomena of this convergence. The ring of fire in the Pacific Ocean is an example of the O-O convergence.

The Divergence boundary:

When plates move away from each other than a divergence boundary is created.

The following are the types of divergence boundaries:

  • Continent-Continent divergence (C-C)
  • Ocean-Continent divergence (O-C)
  • Ocean-Ocean divergence (O-O)

Continent-Continent divergence (C-C) : The African rift valley is an example of a C-C divergence. In this type of movement, in the first phase crack happens in the boundaries line. Second phase, the valley is created and in the later phase, the ocean is created.

Continent-Ocean divergence(C-O):  Expansion of the ocean can happen in this case.

Ocean -ocean divergence(O-O): The Atlantic mid-ocean ridge is an example of the O-O divergence.

The transverse boundaries:

The transverse boundary is created when the plate slides each other without submergence and the creation of any plates. The alpine fault in New Zealand is an example of a transverse boundary.

Tectonic Plates,Tectonic Plates

Read More : Volcanism

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