Sea Floor Spreading & Plate Tectonic

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 Sea Floor Spreading

  • Hess (1961) to propose his hypothesis, known as the “sea floor spreading”.
  • Constant eruptions at the crest of oceanic ridges cause the rupture of the oceanic crust and the new lava wedges into it, pushing the oceanic crust on either side. The ocean floor, thus spreads.
Plate Tectonic
  • 1967, McKenzie and Parker and also Morgan.
  • A tectonic plate (also called lithospheric plate) is a massive, irregularly-shaped slab of solid rock, generally composed of both continental and oceanic lithospheres
  • A plate may be referred to as the continental plate (Eurasian plate) or oceanic plate (Pacific plate)
Seven major and some minor plates
  1. Antarctica and the surrounding oceanic plate
  2. North American (with western Atlantic floor separated from the South American plate along the Caribbean islands) plate
  3. South American (with western Atlantic floor separated from the North American plate along the Caribbean islands) plate
  4. Pacific plate
  5. India-Australia-New Zealand plate
  6. Africa with the eastern Atlantic floor plate
  7. Eurasia and the adjacent oceanic plate.
Some important minor plates are listed below:
  1. Cocos plate: Between Central America and Pacific plate.
  2. Nazca plate: Between South America and Pacific plate.
  3. Arabian plate: Mostly the Saudi Arabian landmass.
  4. Philippine plate: Between the Asiatic and Pacific plate.
  5. Caroline plate: Between the Philippine and Indian plate (North of New Guinea).
  6. Fuji plate: North-east of Australia.
Types of plate boundaries/ Plate Margin
Divergent Boundaries
  • Where new crust is generated as the plates pull away from each other. The sites where the plates move away from each other are called spreading sites.
  • Mid-Atlantic Ridge
Convergent Boundaries
  • Where the crust is destroyed as one plate dived under another. The location where sinking of a plate occurs is called a subduction zone.
    • Between an oceanic and continental plate
    • Between two oceanic plates
    • Between two continental plates
  • Ex: Eurasian and indo Australian plate – form Himalayas.
Transform Boundaries
  • Crust is neither produced nor destroyed.
  • Transform faults are the planes of separation generally perpendicular to the mid oceanic ridges.
Rates of Plate Movement
  • Artic Ridge – less than 2.5cm/yr.
  • East Pacific Rise near Easter Island, in the South Pacific about 3,400 km west of Chile – More than 15cm/yr.
  • Drift – Atlantic – 5cm/yr & Greenland – 2cm/yr.

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