explain how contintal plates are moved around on the earth's surface?

Answer 1

Besides the plastic or semi-liquid nature of the asthenosphere, there are two other mechanisms that help drive plate tectonics. These are called slab-push, and slab-pull.

At the mid-ocean ridges there are believed to be upwellings of hot magma from within the asthenosphere. This magma flows upward forming a series of mid-ocean mountain ranges and faults. As these ridges grow in mass they begin to slide downward and away from the ridges, pushing oceanic crust outward and away from the ridges. This is known as slab-push.

Slab pull works on the opposite side of the oceanic plates, where oceanic crust is being subducted, or forced under, continental plates. These subducting plates extend very deep into the earth, and because they are colder than the asthenosphere, they do not immediately become part of the asthenosphere. The weight of these sinking plates actually pulls the oceanic crust behind it downward and towards the subduction zone.

The combination of these forces create a conveyer-belt like effect on oceanic plates. Since the process rarely works perfectly, there are variations that cause continents to be moved as well. Differences in the rate of motion among ocean basins creates inequality. The result is that at present the Atlantic Ocean is widening, while the Mediterranean is closing. Australia is moving towards south east Asia and California (at least one part of it) is moving towards Alaska.

USGS illustration:
http://pubs.usgs.gov/gip/dynamic/Vigil.html

For some plate tectonics animations see:
http://www.scotese.com/moreinfo.htm

Answer 2

All lithospheric plates, regardless of oceanic or continental crust, rest atop the asthenosphere. This partially molten layer of rock acts as a "lubricant" for the plates to move along. Motion itself is driven by convection in the mantle.