Is mantle convection caused by plate movement?
No, the convection currents cause plate movement, not the other way around. If there weren’t convection currents, then there would be no plate movement and no core activity, and the Earth would die; like the moon. P.S.D. is wrong about the light crust part; the light crust is what are continents are made out of, and it’s granitic (and is lighter than the magma, so it cannot be subducted). Oceanic crust is basaltic, and is heavier than or the same weight as the magma, and so is pushed down into the magma by either a continental crust or another oceanic plate.
