Lithospheric Plates

Definition

• A plate is a broad segment of the lithosphere that floats on the underlying asthenosphere and moves independently of the other plates.

Major and Minor Lithospheric Plates

• Major Lithospheric Plates
  • Antarctica and the surrounding oceanic plate
  • North American plate
  • South American plate
  • Pacific plate
  • India-Australia-New Zealand plate
  • Africa with the eastern Atlantic floor plate
  • Eurasia and the adjacent oceanic plate
• Minor Lithospheric Plates
  • Cocos plate: Between Central America and Pacific plate
  • Nazca plate: Between South America and Pacific plate
  • Arabian plate: Mostly the Saudi Arabian landmass
  • Philippine plate: Between the Asiatic and Pacific plate
  • Caroline plate: Between the Philippine and Indian plate (North of New Guinea)
  • Fuji plate: North-east of Australia
  • Turkish plate
  • Aegean plate (Mediterranean region)
  • Caribbean plate
  • Juan de Fuca plate (between Pacific and North American plates)
  • Iranian plate.

Type of Plate Boundaries

• Divergent Boundaries
  • A divergent boundary occurs when two tectonic plates move away from each other.

• • Associated Features
    • Earthquake: Divergence of plates causes isostatic imbalance triggering earthquake waves.
    • Volcanism: Gaps created due to divergence of plates led to emergence of molten magma from the mantle to the surface. For example – Mount Gahinga volcanoes in the East African Rift between the African and Arabian plates.
    • Creation of Rift Valleys: Divergent boundaries can also develop within a continent resulting in a continental rift valley such as The East African Rift, and the Baikal Rift Valley.

• Convergent Boundaries
  • When two plates come together, it is known as a convergent boundary.
  • Common outcomes of convergence are volcanism, earthquakes, formation of trenches, fold mountains etc.
  • Three types of convergent boundaries are
    • Oceanic–continental Convergence
      • Oceanic crust may collide with a continent. The oceanic plate is denser, so it undergoes subduction. 
      • This means that the oceanic plate sinks beneath the continent and melts in the hot asthenosphere leading to the emergence of volcanic islands.
      • It also leads to the formation of fold mountains .
      • For example – Pacific Ring of Fire, and Andes mountains.

• • • Ocean–Ocean Convergence
      • In collisions between two oceanic plates, the cooler, denser oceanic lithosphere sinks beneath the warmer, less dense oceanic lithosphere. 
      • As the slab sinks deeper into the mantle, it releases water from dehydration of hydrous minerals in the oceanic crust.
      • Leads to the formation of oceanic trenches, shallow and deep-focus earthquakes and volcanic activity.
      • For example – Aleutian Islands and the Mariana Islands.
    • Continent-Continent Convergence
      • Continent-Continent (C-C) convergence is formed between two continental plates.
      • When the plates converge, oceanic sediments are squeezed and upthrust between the plates and these squeezed sediments appear as fold mountains along the plate margins.
      • For example – Himalayan mountains

• Transform Boundaries
  • A transform boundary is formed as tectonic plates slide horizontally past each other but parts of these plates get stuck at the places where they touch.
  • These boundaries are conservative because plate interaction occurs without creating or destroying crust.
  • For example – San Andreas Fault in California