Detail of Plate tectonic theory

Plate tectonic theory

Plate tectonic theory

·      It was a great scientific achievement of the decade of 1960s; it is based on the two major scientific concepts

o   The concept of continental drift

o   The concept of sea – floor spreading

·      Lithosphere is internally made of rigid plates (first used by Canadian geophysicist J.T. Wilson in 1965), six major plates and 20 minor plates have been identified so far.

·      Six major plates are Eurasian plate, Indian – Australian plate, American plate, Pacific plate, African plate and Antarctic plate.

·      W.J.Morgan and Le Pichon elaborated the various aspects of plate tectonics in 1968

·      Now the continental drift and the displacement are considered a reality on the basis of plate tectonics.

·      Tectonic plate boundaries are most important because all tectonic activities occur along the plate margins.




Plate margins are generally divided into three groups

Constructive plate margins

·      These are also called divergent plate margins or accreting plate margins.

·      It represents zone of divergence where there is continuous upwelling of molten material (lava) and thus new oceanic crust is continuously formed.

Destructive plate margins

·      These are also called as consuming plate margins or convergent plate margins.

·      Two plates move towards each other or two plates converge along a line and leading edge of one plate overrides the other plate.

·      The overridden plate is subducted or thrust into the mantle and thus part of the crust (plate) is lost in the mantle.

Conservative plate margins

·      These are also called as shear plate margins

·      Two plates pass or slide past one another along a transform faults and thus crust is neither created nor destroyed.


 Fig- Different types of plate margins

Conclusion

·      H. Hess postulated the concept of plate tectonics in 1960, in support of continental drift.

·      The continents and ocean move with the movement of these plates.

·      The present shape and arrangement of continent and ocean basins could be attained because of continuous movement of different plates.

·       Plate tectonic theory is based on the evidences of sea floor spreading and palaeomagnetism .

Sea – floor spreading

·      Propounded by the Harry Hess of the Princeton University in the year 1960.

·      He propounded that mid – oceanic ridges were situated on the rising thermal convection currents, coming up from the mantle.

·      The oceanic crust move in opposite directions from mid – oceanic ridges.

·      This molten lava cool down and solidify to form new crust along the trailing ends of divergent plates (oceanic crust).

·      Thus there is continuous creation of new crust along the mid – oceanic ridges and the expanding crusts (plates) are destroyed along the oceanic trenches.

·      These facts prove that continents and ocean basins are in constant motion.