The movement of these crustal plates (due to convection currents in the mantle) causes the formation of various landforms and is the principal cause of all earth movements.Lithospheric plates ( tectonic plates) vary from minor plates to major plates, continental plates (Arabian plate) to oceanic plates (Pacific plate), sometimes a combination of both continental and oceanic plates (Indo-Australian plate).
The oceanic plates contain mainly the Simatic crust and are relatively thinner, while the continental plates contain Sialic material and are relatively thicker.
The lithosphere includes the crust and top mantle with its thickness range varying between 5-100 km in oceanic parts and about 200 km in the continental areas.Plates move horizontally over the asthenosphere as rigid units.The movement of these plates is attributed to the convention currents being generated in the upper mantle.the lithosphere is believed to have been broken into fragments that are floating on a ductile layer called asthenosphere (upper part of the mantle).Lithosphere – The crust and part of the upper mantle = lithosphere (100 km thick, and less dense than the material below it so it “floats”)Īsthenosphere – The plastic layer below the lithosphere = asthenosphere (The plates of the lithosphere float on the asthenosphere) The theory rejects the ideas of SIAL, SIMA based classification.The earth’s interiors according to mechanical rigidity can be classified into –.The relative movement of the plates typically ranges from zero to 100 mm annually. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries.Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform.The Earth’s lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates. The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken up into tectonic plates.It is an improvement over the Wegener’s continental drift theory and has been considered as the most sophisticated and comprehensive theory about the drift of continents and the expansion of sea floors.This theory is based on the 2 principle hypothesis – Arthur Holmes convection current hypothesis, and the concept of seafloor spreading’ advocated by Hess.The development towards the theory began in the 1960s with extensive seafloor mapping.The comprehensive theory which tries to explain most of the dynamism of earth crust and features of the endogenetic forces.
The geo scientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s. The theoretical model builds on the concept of continental drift developed during the first few decades of the 20th century. Plate tectonics is a scientific theory describing the large-scale motion of 7 large plates and the movements of a larger number of smaller plates of the Earth‘s lithosphere, over the last hundreds of millions of years. The term plate tectonics was first used by Tuzo Wilson, of the University of Toronto but the Plate Tectonics theory was first published by W.J Morgan of the Princeton University in 1962.