3. Plate Motions and Boundaries


Expedition Menu

1. Introduction

2. Plate Motion

3. Plate Motions & Boundaries

4. Example 2

5. Review

6. Rates

7. Full Rates

8. South Atlantic

9. Life Cycle of Lithosphere

10. Discussion

Contact Don Reed
Dept. of Geology
San José State University
ęCopyright 1999
Last Updated on June 21, 1999

boundaries.JPG (15332 bytes)

There are three types of plate boundaries

  • divergent = plates move apart and oceanic lithosphere is created by seafloor spreading

  • convergent = plates converge together and oceanic lithosphere is recycled (consumed) by subduction

  • transform = plates slide by each other, moving parallel to the plate boundary but in opposite directions on either side, and lithosphere is conserved, neither formed or consumed

  • Plate motion is always parallel to transform faults,  it is the only plate boundary that uniquely constrains the direction of plate motion.


plates.gif (15739 bytes)


Cut out the triangle on the page in your handout.

Be careful...try to keep the remaining sheet of paper in one piece. 

First examine the arrow on the triangular-shaped plate A showing the direction of relative plate motion with respect to plate B (plate B is the piece of paper surrounding plate A -- the one with a hole in it).

Put the triangular piece of paper of Plate A -- back into the hole (exactly into hole) -- once it is in its proper place,  move plate A in the direction of the arrow.

Using the plate motion, write the name of the type of plate boundary along each boundary that surrounds plate A

The animation at the left shows, the same thing as your cutout,  the "relative plate motion" of plates A and B, meaning the motion of one plate, plate A, relative to another plate, so at least two plates are involved!!!

In this problem, plate B is considered stationary and A is moving, but it could be just the opposite, plate B could be thought as moving and plate A fixed -- all depends on your point of view!


    Here is examine another example