Tectonic Plates

1. The Theory of Plate
Tectonics
Chapter 7 Section 3

2. The Theory of Plate Tectonics
 The Earth’s lithosphere (crust and upper
mantle) is divided into tectonic plates.
 These plates move on top of the
asthenosphere.
 We know that these plates move in
different ways.

3. Tectonic Plates

4. Tectonic Plate Boundaries
 A boundary is a place where tectonic
plates touch.
 There are 3 types of tectonic plate
boundaries:
 Convergent- move toward each other
 Divergent- move away from each other
 Transform- move past each other

5. The numbers on the map represent the rate at which plates are moving in
centimeters.

6. Plate Movement

7. Convergent Boundary
• When two plates collide, or move toward
each other, the boundary is called
convergent
• There are 3 types of convergent
boundaries, depending on what type of
crust comes together.
• Continental-continental-mountains form
• Continental-oceanic- subduction zone-
volcanoes
• Oceanic-oceanic- subduction zone-
volcanoes

8. What forms at a Convergent
Boundary?
1. Continental meets continental
2. MOUNTAIN RANGES form

9.  Dense oceanic crust sinks below the
continental crust and sinks into the
asthenosphere.
 This is a subduction zone.
 A VOLCANO forms
What forms at a Convergent
Boundary?

10. What forms at a Convergent
Boundary?
►One oceanic plate sinks below another
oceanic plate.
►Another subduction zone
►A VOLCANO

11. What forms at a Divergent
Boundary
 Two tectonic plates move away from each other.
 On the sea floor at the mid-ocean ridge this is called
sea floor spreading.
 As the plates move apart, magma rises to fill the gaps.
 The magma is cooled and forms new ocean floor.
The volcanic country of Iceland,
which straddles the Mid-Atlantic
Ridge, offers scientists a natural
laboratory for studying on land the
processes also occurring along the
submerged parts of a spreading
ridge. Iceland is splitting along the
spreading center between the North
American and Eurasian Plates, as
North America moves westward
relative to Eurasia.

12. Mid Ocean Ridge-
Atlantic Ocean

13. Divergent Boundary
On-land exposure of the
Mid-Atlantic Ridge in Iceland.
Sea Floor Spreading

14. What forms at a Transform
Boundary?
Two tectonic plates
move past one
another.
Their edges are jagged
and irregular.
As they grind together
and jerk, they slide
past each other
creating earthquakes.

15. Transform
Boundary

16. Possible Causes of Plate
Movement
• Convection Currents: hot rock deep in
the Earth rises, cooler rock sinks. This
movement of magma causes plates to
move
• Ridge push
• Slab pull
• http://my.hrw.com/sh/hz5/0030289211/student/ch07/sec03/qc01/hz507_03_q01fs.htm

17. Tracking Tectonic Plate Movement
• Plates move very slowly, centimeters to inches a
year.
• GPS, Global Positioning System, measures the
rate of movement.
• Radio signals beam continuously from satellites
to the Earth.
• By recording the time it takes for the Ground
station to move a given distance, scientists can
measure the speed at which plates move.
• Plate Boundary Animation
• http://www.classzone.com/books/earth_science
/terc/content/visualizations/es0804/es0804pag
e01.cfm?chapter_no=visualization
• http://wwnorton.com/college/geo/earth4/anim
ations.aspx