A tectonic plate (also called a lithospheric plate) is a massive, irregularly-shaped slab of solid rock, generally composed of both continental and oceanic lithosphere.
Plates move horizontally over the asthenosphere as rigid units. 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.
A plate may be referred to as the continental plate or oceanic plate depending on which of the two occupy a larger portion of the plate.
Pacific plate is largely an oceanic plate whereas the Eurasian plate may be called a continental plate. There are three types of plate boundaries:
1. Divergent Boundaries: The sites where the plates move away from each other are called spreading sites. The best-known example of divergent boundaries is the Mid-Atlantic Ridge.
2. Convergent Boundaries: Where the crust is destroyed as one plate dived under another. (Nepal quack). The location where sinking of a plate occurs is called a subduction zone.
3. Transform Boundaries: Where the crust is neither produced nor destroyed as the plates slide horizontally past each other. Also, the rotation of the earth has its effect on the separated blocks of the plate portions.
