tectonic plates

• The Earth’s tectonic plates are constantly moving. However, this movement is slow, and rates vary from less than 2.5cm /yr to over 15cm/yr. Tectonic plates move as the asthenosphere, which is ductile, is weak enough to accommodate the movement of the solid and brittle plates above it.
• Three theories have been put forward for the movement of tectonic plates on top of the asthenosphere. None have been completely proven. The theories are:

  • convection currents
  • ridge push
  • slab pull
• The initial explanation for the movement of tectonic plates was convection currents in the mantle. The theory suggests these convection currents are created by heat from within the Earth – much of which is generated by radioactive decay in the core.
• Another explanation for plate movement is ridge push. Newly-formed plates at oceanic ridges (constructive plate margins) are warm, and so have a higher elevation at the oceanic ridge than the colder, more dense plate material further away; gravity causes the higher plate at the ridge to push away, causing the plates to move away from each other.
• The most recently proposed and most likely explanation for tectonic movements is slab pull. At destructive plate margins, the denser oceanic plate sinks into the mantle under the influence of gravity, which pulls the rest of the plate along with it into the mantle.

  Recent research has shown that the major driving force for most plate movement is slab pull because the plates with more of their edges being subducted are the faster-moving ones. However, ridge push has also been presented in recent research to be a force that drives the movement of plates.