what are tactonic plates?

Plate tectonics (from the Late Latin tectonicus, from the Greek: τεκτονικός "pertaining to building")^[1] is a scientific theory that describes the large scale motions of Earth's lithosphere. The theory builds on the concepts of continental drift, developed during the first decades of the 20th century, and accepted by the majority of the geoscientific community when the concepts of seafloor spreading were developed in the late 1950s and early 1960s.

The lithosphere is broken up into tectonic plates. In the case of the Earth, there are currently seven or eight major (depending on how they are defined) and many minor plates. The lithospheric plates ride on the asthenosphere. These plates move in relation to one another at one of three types of plate boundaries: convergent, or collisional boundaries; divergent boundaries, also called spreading centers; and conservative transform boundaries. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries. The lateral relative movement of the plates typically varies from 0–100 mm annually.^[2]

The tectonic plates are composed of two types of lithosphere: thicker continental and thin oceanic. The upper part is called the crust, again of two types (continental and oceanic). This means that a plate can be of one type, or of both types. One of the main points the theory proposes is that the amount of surface of the (continental and oceanic) plates that disappears in the mantle along the convergent boundaries by subduction is more or less in equilibrium with the new (oceanic) crust that is formed along the divergent margins by seafloor spreading. This is also referred to as the conveyor belt principle. In this way, the total surface of the globe remains the same. This is in contrast with earlier theories advocated before the Plate Tectonics paradigm, as it is sometimes called, became the main scientific model, theories that proposed gradual shrinking (contraction) or gradual expansion of the globe, and that still exist in science as alternative models.^[3]

Tectonic plates are able to move because the Earth's lithosphere has a higher strength and lower density than the underlying asthenosphere. Lateral density variations in the mantle result in

. Their movement is thought to be driven by a combination of the motion of seafloor away from the spreading ridge (due to variations in topography and density of the crust that result in

) and

, downward

, at the

zones. A different explanation lies in different forces generated by the rotation of the globe and tidal forces of the

and the

.

wikipedia ravi???

u r right best source of information isn't it 

yup...