1. Plate Tectonics – Section 17.3
Earth Science
Plate Tectonics – Section 17.3

2. Objectives
Describe how Earth’s tectonic plates result in many geologic features.
Compare and contrast the three types of plate boundaries and the features associated with each.
Generalize the processes associated with subduction zones.

3. Key Concept
Volcanoes, mountains, and deep-sea trenches form at the boundaries between the plates.

4. Vocabulary tectonic plate divergent boundary rift valley
convergent boundary
Subduction
transform boundary
mid-ocean ridge

5. The Theory of Plate Tectonics
Tectonic plates are huge pieces of crust and rigid upper mantle that fit together at their edges to cover Earth’s surface.

6. The Theory of Plate Tectonics
Plate tectonics is the theory that describes how tectonic plates move and shape Earth’s surface.
They move in different directions and at different rates relative to one another.
They interact with one another at their boundaries.

7. Divergent Boundaries
Regions where two tectonic plates are moving apart are called divergent boundaries.
Most divergent boundaries are found along the seafloor in rift valleys.
The formation of new ocean crust at most divergent boundaries accounts for;
high heat flow
Volcanism
earthquakes
associated with these boundaries.

8. Divergent Boundaries
Some divergent boundaries form on continents. When continental crust begins to separate, the stretched crust forms a long, narrow depression called a rift valley.

9. Convergent Boundaries
At convergent boundaries, two tectonic plates are moving toward each other.
When two plates collide, the denser plate eventually descends below the other, less-dense plate in a process called subduction.

10. Subduction
Subduction Zone

11. Convergent Boundaries
There are three types of convergent boundaries, classified according to the type of crust involved. The differences in density of the crustal material affect how they converge.
Oceanic-oceanic convergent boundary
Oceanic-continental convergent boundary
Continental-Continental convergent boundary

12. Oceanic-Oceanic Convergent Boundary
In the oceanic-oceanic convergent boundary, a subduction zone is formed when one oceanic plate, which is denser as a result of cooling, descends below another oceanic plate.
The process of subduction creates an ocean trench.

13. Oceanic-Oceanic Convergent Boundary
In an oceanic-oceanic convergent boundary,
water carried into Earth by the subducting plate
lowers the melting temperature of the plate,
causing it to melt at shallower depths.
The molten material is less dense so it rises back to the surface,
where it often erupts and forms an arc of volcanic islands that parallel the trench.

14. Oceanic-Continental Convergent Boundary
When an oceanic plate converges with a continental plate, the denser oceanic plate is subducted. Oceanic- continental convergence produces
a trench
volcanic arc
The result is a mountain range with many volcanoes.

15. Continental-Continental Convergent Boundary
Continental- continental boundaries form when two continental plates collide, long after an oceanic plate has converged with a continental plate. This forms a vast mountain range, such as the Himalayas.

16. Transform Boundaries
A region where two plates slide horizontally past each other is a transform boundary.

17. Transform Boundaries
Transform boundaries are characterized by long faults, sometimes hundreds of kilometers in length, and by shallow earthquakes.
Most transform boundaries offset sections of ocean ridges. Sometimes transform boundaries occur on continents.
One of the best know examples of a transform boundary is the San Andreas Fault.

18. Summary – Convergent Boundaries
Boundary Type
Characteristic Features
Examples
Continental-continental Convergent Boundary
Folded Mountains
Himalayas (including Mt. Everest)
Oceanic-oceanic Convergent Boundary
Subduction Zone
Forms Ocean Trench
Forms Arc of Volcanic Islands
Aleutian Trench and Aleutian Islands (N. Pacific)
Marinas Trench and Marinas Islands (W. Pacific)
Oceanic-continental Convergent Boundary
Subduction Zone (Oceanic Plate Subducted)
Forms Arc of Volcanic Mountains on Continent
Peru-Chile Trench and Andes Mountains

19. Summary – Transform Boundaries
Boundary Type
Characteristic Features
Examples
Transform Boundary
Plates slide horizontally past each other
Long Faults
Crust Deformed or Fractured Here
Most Found in Ocean Ridges
Can be found on Continental Crust
Movement causes Earthquakes
San Andreas Fault
Gibbs Fracture Zone (in Mid-Atlantic Ridge)

20. Summary – Divergent Boundaries
Boundary Type
Characteristic Features
Examples
Divergent Boundary
Most Found on Seafloor in Rift Valleys
Here is Where Seafloor Spreading Starts
High Heat Flow
Volcanism
Earthquakes
Rift Valleys on Continental Crust can Lead to a New Ocean Basin.
Mid-Atlantic Ridge
Rift Valley in Eastern Africa