Question

What is the driving force for the movement of the lithospheric plates?

Answer 1

According to plate tectonic theory, the movement of plates is by thermal energy from earth core. The energy drives convective current which moves the plates.

Answer 2

In addition to the convective current, another factor that drives the movement of plates is the difference in density of plates and their underlying layers. Plates will sink down if they are denser and lift up if they are lighter.