Structure of Tectonic Plates

Tectonic plates are made up of the earth’s crust and the outermost part of its mantle. There are two different kinds of plates: the oceanic plate and the continental plate. The oceanic plate is denser while the continental plate is lighter. Plates are typically about 100 kilometers thick. The plates as a whole make up the earth’s lithosphere. The layer of mantle rock under the plates is the asthenosphere. The mantle can reach temperatures between 1300°C and 2000°C.

The edges of the plates are called plate boundaries and are zones of movements and instability. Many tectonic processes such as folding, faulting, earthquakes and volcanic activity occur at these plate boundaries.

Scientists believe that the plates move because of slow convection currents in the mantle. Magma, which is liquid mantle material, expands and rises when intensely heated. The rising magma spreads out beneath the plates and the cools and sinks. This continuous heating and cooling of the magma forms a convection current in the mantle. The rising and spreading convection currents pull the plates apart while the cooling drags the plates together, making the plates move.

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