1. Plate Tectonics Chapter - 8
The lithosphere is broken into rigid plates that move in relationship to one another on the asthenosphere
(see page in textbook)

2. Objectives:
Identify the evidence that A. Wegener used to support Continental Drift
Explain how the theory of Plate Tectonics helps predict the locations of earthquakes and volcanoes
AZ Science Standard: Demonstrate the relationships among earthquakes, volcanoes, mountain ranges, mid-ocean ridges, deep sea trenches, and tectonic plates

3. 8.1 What is Plate Tectonics?
The theory that describes the formation, movements, and interactions of these plates.
The lithosphere is broken into rigid plates that move in relationship to one another on the asthenosphere.
8.1 What is Plate Tectonics?

4. 8.1 What is Plate Tectonics?
The lithosphere is our crust that sits on top of the asthenosphere.
8.1 What is Plate Tectonics?

5. 8.1 What is Plate Tectonics?
Plate Tectonics Theory
Early evidence included shapes of the continents (South America and Africa)
Similar fossil record
Similar locations of rivers flowing into the ocean
Similar plants growing
Similar coastal rock formation.
Initially, there was little acceptance of Wegner’s theory because he couldn’t explain why they moved.
8.1 What is Plate Tectonics?

6. The theory of plate tectonics helps explain the locations of earthquakes and volcanoes.

7. 8.1 What is Plate Tectonics?
The theory of plate tectonics helps explain the locations of earthquakes and volcanoes.
Therefore, characteristic features associated with plate boundaries:
Earthquake activity
Volcanic activity
High heat flow
8.1 What is Plate Tectonics?

8. 8.1 What is Plate Tectonics?
DEFINE:
Plate Tectonics - a theory that describes the formation, movement, and interactions of the plates on the lithosphere.
Continental Drift – movement of continents.
Mid-Ocean Ridge - a long chain of volcanic mountains on the ocean floor.
8.1 What is Plate Tectonics?

9. 8.1 What is Plate Tectonics?
What observations support the continental drift hypothesis?
Earthquakes and volcanoes occur in concentrated belts that correspond to present tectonic plate boundaries.
8.1 What is Plate Tectonics?

10. 8.1 What is Plate Tectonics?
What evidence in support of plate tectonics is provided by studies of the ocean floor?
Magnetic reversals in rocks on either side of the Mid-Atlantic Ridge; High heat flow along ridges; Youngest crust is close to ridge axis.
8.1 What is Plate Tectonics?

11. Magnetic Reversals

12. Objectives:
Discuss verbally the differences among the three types of plate boundaries
Contrast the three different types of convergent boundaries

13. 8.2 Types of Plate Boundaries
Minerals in igneous rocks can show the direction of Earth’s polarity field at the time the rocks were formed.
8.2 Types of Plate Boundaries

14. 8.2 Types of Plate Boundaries
Transform Boundary
8.2 Types of Plate Boundaries

15. 8.2 Types of Plate Boundaries
Convergent Boundary
8.2 Types of Plate Boundaries

16. 8.2 Types of Plate Boundaries
Divergent Boundary
8.2 Types of Plate Boundaries

17. 8.2 Types of Plate Boundaries
Mid Atlantic Ridge
Hydrothermal vents
New rocks are forming
Earthquakes occur here
8.2 Types of Plate Boundaries

18. 8.2 Types of Plate Boundaries
Types of Plate Boundaries summary
Boundary
Process involved
Features
Current Example
Divergent
Sea-floor spreading
Mid-ocean ridges
Rift valleys
Earthquake activity
Volcanic activity
Mid-Atlantic Ridge
East pacific Rise
Convergent
Ocean-ocean
Deep sea trenches
Volcanic island arcs
Island of Indonesia
Mariana Islands
Ocean-Continent subduction
Deep sea trench bordering continent
Volcanoes along coast-line
Western coast of South America
Transform
Plates sliding past each other
San Andreas Fault
North Anatolian Fault (Turkey)
Fracture zones along mid-ocean ridges
8.2 Types of Plate Boundaries

19. 8.2 Types of Plate Boundaries
New oceanic crust is formed at a divergent boundary when:
Step 1 - Molten rock forces its way upward into the rifts that form when two lithospheric plates separate.
Step 2 - As the molten rock cools, new oceanic crust forms.
Step 3 - The older oceanic crust moves away from the mid-ocean ridge.
8.2 Types of Plate Boundaries

20. 8.2 Types of Plate Boundaries
Two different types of subduction boundaries are:
Oceanic-oceanic plate convergence – two features are a deep-sea trench and a volcanic island arc on the overriding plate. (Marianna trench)
Oceanic-continental plate convergence – a deep-sea trench and an inland mountain chain and volcanoes characterize this type of subduction boundary. (the Andes)
8.2 Types of Plate Boundaries

21. 8.2 Types of Plate Boundaries
Describe what happens at a collision boundary, identify a collision boundary:
Two Continental plates collide, forming a single, larger continent and pushing up the crust to form a mountain range.
Ex: Himalayan and Appalachian Mountains
8.2 Types of Plate Boundaries

22. 8.2 Types of Plate Boundaries
When two oceanic plates converge, the denser plate is subducted.
A chain of volcanoes commonly forms when an oceanic plate subducts under a continental plate.
Fracture zones that offset portions of mid- ocean ridges are examples of divergent boundaries.
8.2 Types of Plate Boundaries

23. 8.2 Types of Plate Boundaries
Describe the movement of plates at a transform boundary, give example.
Plates slide past each other at a transform boundary.
Ex: San Andreas fault; and the fracture zones along mid-ocean ridges.
8.2 Types of Plate Boundaries

24. Objectives:
Discuss mantle convection as a possible cause of plate movements
Compare and contrast ridge push and slab pull

25. 8.3 Causes of Plate Movements
Three hypotheses for plate movement:
Mantle convection - convection currents within the mantle are pushing the plates.
Ridge push - hot mantle at ridge is lighter and lifts up at the ridge, as it spreads, it cools, and denser material slides off ridge.
Slab pull – sub-ducted material “pulls” the plate with it as it slides downward under other plate.
8.3 Causes of Plate Movements

26. Explain how Earth’s landmasses have changed positions over the past 200 million years
Discuss the roles of plate tectonics, igneous activity, and deposition in the formation of continental landmasses

27. 8.4 Plate Movements and Continetal Growth
The breakup of Pangaea is a process that is continuing today.
8.4 Plate Movements and Continetal Growth

28. 8.4 Plate Movements and Continetal Growth
North American Craton
An expanse of ancient rock at the core of the North American Continent formed 2.5 billion yrs ago.
8.4 Plate Movements and Continetal Growth

29. 8.4 Plate Movements and Continetal Growth
Sources of Growth Material
Deep sea sediments most likely contribute to continent growth by being scraped off in a subduction zone and left at the surface.
Igneous rock from plutons and volcano ash, lava, and rock material.
Terranes are large blocks of lithospheric plates that have been moved over thousands of kilometers and attached to the edge of a continent – three characteristics:
Each terrane block is bound by major faults
Rocks and fossils found in the terrane do not match those of neighboring terranes
Magnetic record found in the terrane does not match that of neighboring terranes.
8.4 Plate Movements and Continetal Growth

30. 8.4 Plate Movements and Continental Growth
Density plays a big part in plate tectonics
Basic density info:
Density is mass per unit volume
Usually as grams per cubic centimeter
g/cc
An object that weighs 12 grams and takes up 6 cubic centimeters has a density of (12grams/6cc)=2g/cc
8.4 Plate Movements and Continental Growth