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15. Plate Boundaries
Try Again!

Expedition Menu

1. Introduction

2. Theory

3. Formation

4. Evidence

5. Earth's Interior

6. Magnetic Field

7. Heat Engine

8. Mid-ocean Ridge

9. On the Ridge

10. Seafloor Spreading

11. Magnetic History

12. Magnetic Patterns

13. The Plates

14. More on Plates

15. Boundaries

16. Divergent

17. Convergent

18. Transform

Divergent plate boundaries (above)

Where plates diverge or move apart by seafloor spreading.  These are sites where lithosphere is created! 
Plate motion is away from divergent plate boundaries.

Convergent plate boundary

If plates diverge along one type of plate boundary, then they must converge or move together along another type of plate boundary, which we call a convergent plate boundary.  Oceanic lithosphere sinks back into the mantle by a process called subduction.  So the lithosphere is created at divergent plate boundaries and is recycled back into the interior of the Earth along convergent plate boundaries through subduction.
Plate motion is towards convergent plate boundaries.

Transform plate boundary

The third, and final, type of plate boundary is the transform plate boundary where one plate slides horizontally by another plate and the lithosphere is conserved (not created or recycled).  

Plate motion is parallel to transform plate boundaries!

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You should now be able to name each type of plate boundary in the diagram above. 

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

The diagram above shows the three types of plate boundaries  -- they are:

a) transfer, horizontal and upward
b) subsiding, rapping and tapping
c) transform, divergent and convergent