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4.8: Tectonic Plate Motions

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What is tectonics?

Dividing the lithosphere into plates is one thing. Having the plates move around on the planet is another! A conveyor belt is a good analogy for how a plate moves. How the plates move and where they move is the "tectonics" half of plate tectonics.

Plate Motions

Scientists have determined the direction that each plate is moving ( Figure below ). Plates move around the Earth’s surface at a rate of a few centimeters a year. This is about the same rate that fingernails grow.

Earth's plates are shown in different colors. Arrows show the direction the plate is moving.

How Plates Move

Convection within the Earth’s mantle causes the plates to move. Mantle material is heated above the core. The hot mantle rises up towards the surface ( Figure below ). As the mantle rises it cools. At the surface the material moves horizontally away from a mid-ocean ridge crest. The material continues to cool. It sinks back down into the mantle at a deep sea trench. The material sinks back down to the core. It moves horizontally again, completing a convection cell.

Plates move for two reasons. Upwelling mantle at the mid-ocean ridge pushes plates outward. Cold lithosphere sinking into the mantle at a subduction zone pulls the rest of the plate down with it.

Seafloor spreading takes place as plates move apart from each other at a mid-ocean ridge. Mantle convection drives seafloor spreading.

Summary

  • Plates move by seafloor spreading
  • Seafloor spreading is driven by mantle convection.
  • Plates move as if on a conveyor belt.

Practice

Use this resource to answer the questions that follow.

Tectonic Plate Movement at http://www.youtube.com/watch?v=prfgw8uKXA8 (3:18)

  1. What would the Earth look like without the biosphere and atmosphere?
  2. What are plates?
  3. How fast are the plates moving?
  4. What happens at the ridges?
  5. What are subduction zones?
  6. What heats Earth's interior?

Review

  1. Describe how convection takes place in the mantle.
  2. How does mantle convection cause seafloor spreading?
  3. How does seafloor spreading move plates?

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Description

Difficulty Level:

Basic

Grades:

6 , 7

Date Created:

Jan 04, 2013

Last Modified:

Aug 24, 2014

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