The Theory of Plate Tectonics

Concepts:• What is the theory of plate tectonics?

• What are the three types of plate boundaries?

Terms:• J. Tuzo Wilson• Plate• Scientific theory• Plate tectonics• Fault• Divergent boundary• Rift valley• Convergent boundary• Transform boundary

J. Tuzo Wilson and Plates• A Canadian scientist, J. Tuzo Wilson, observed that there are cracks in the continent similar to those on the ocean floor.

• In 1965, Wilson proposed a new way of looking at these cracks.

• According to Wilson, the lithosphere is broken into separate sections called plates.

Lithospheric Plates

The Theory of Plate Tectonics

•The theory of plate tectonics explain the formation, movement, and subduction of Earth’s plates.

How do the plates move?• The theory of plate tectonics states that pieces of Earth’s

lithosphere are driven by convection currents in the mantle.

• As the plates move, they collide, pull apart, or grind past each other producing spectacular changes in Earth’s surface. • Volcanoes, mountain ranges, and deep ocean trenches

• The plates move very slow about 1-24 centimeters a year.• About as fast as your fingernails grow. • They have been moving for tens of millions of years.

As we review each plate boundary, complete a tree map and include the following:

• Focus Questions:1. Plate Boundary2. Which direction are the plates moving at

these boundaries in relationship to each other?

3. What action occur at each location/type of plate boundary?

4. What forms because of these actions?1. Examples

Tree Map

Plate Boundary

Plate Movement

Definition

Action Action

Examples Examples

Location Location

Arrows

Types of plate boundaries

• Divergent plate boundary 1. Ocean: Mid Oceanic Ridge2. Land: Continental Rift zone

• Convergent plate boundary1. Oceanic-oceanic convergence – Subduction

Trench2. Continental-continental convergence – No

Subduction - Mountains3. Oceanic - continental convergence – Subduction

Trench

• Transform plate boundary• Earthquakes• Crust is neither created nor destroyed.

Divergent plate boundaries

A place where two plates move apart, or diverge

Ocean

Mid-Ocean Ridge E.g. Mid-Atlantic ridge is a result of sea floor spreading

new basaltic magma rises to the surface along the ridge forming new oceanic crust.

http://epod.usra.edu/blog/2010/08/mid-atlantic-ridge-in-iceland.html

Thingvellir Rift Valley

Slicing through the center of Iceland is the Mid-Atlantic Ridge. This is the boundary between theNorth American and Eurasian tectonic plates

Thingvellir National Park, in southwestern Iceland, is one of the few spots in the world where an underwater ridge rises above the water surface.Iceland is one of the most geologically active places on Earth with more than 15 volcanoes that have erupted in the last century.

Land• Rift valleys may increase in size till water fills them to form a Sea

• The Red Sea and the Gulf of Aden were once rift valleys.

These rift valleys often have volcanoes lining them.

Mt. Kilimanjaro

Great African Rift Valley

The formation of the Atlantic Ocean

Divergent Plate Boundaries

In the Ocean• Ridge• Action: oceanic plates move apart• Sea floor spreading

• Mid-Ocean Ridge • Example: Mid Atlantic

Ridge• Longest mountain Range

On Land• Rift • Action: Continental crust pull apart • Examples: Iceland, Great Rift Valley in East Africa

• Oceans and Seas form• Example: Atlantic Ocean and Red Sea

• Volcanoes• Example: Mt. Kilimanjaro

Tree Map

Divergent Plate Boundary

Plate Movement Ocean: Ridge Land: Rift

Action: Sea-floor spreading

Example: Mid Atlantic Ridge

Oceans and Seas form: Examples: Atlantic Ocean and the Red Sea

A place where to plates move apart, or diverge

Action: Continental crust pull apart

Examples: Iceland, Great Rift Valley in East Africa

Oceans and Seas formExample: Atlantic Ocean and Red Sea

VolcanoesExample: Mt. Kilimanjaro

Convergent Plate Boundaries

1. Ocean crust to ocean crust collision

2. Ocean crust to continental crust collision

3. Continental crust to continental crust collision

The place where two plates come together, or converge.

Three types of convergent plate boundaries:

Tree Map• Name of plate boundary• Draw arrows to indicate direction the plates

move in relationship to each other.• Create a Tree map of the 3 types of

convergent boundaries, the events that occur there, and an example of each occurrence. i.e. action, formations, examples

• Compare the items in your map, which convergent boundary type does NOT result in volcanoes? Why?

Mt. Hood

Trench

Island arc

Aleutian Islands

Oceanic - continental

convergence

E.g. Andes mountains

The forces of plate tectonics are responsible for the formation of the Andes. The Nazca plate and a part of the Antarctic plate have been subducting beneath the South American plate, which is a process that continues today and causes earthquakes andvolcanic eruptions in the regionhttp://www.windows2universe.org/geography/andes.html

Quick Review

The sub-continent of India has collided with the Eurasian continent to form the Himalayas

• Types Convergent plate boundaries

Oceanic-oceanic convergenceIslands

Japan, Aleutian IslandsVolcanoes- Mt PinatuboTrenches Earthquakes

Oceanic - continental convergenceVolcanoes - Andes, CascadesTrenches Earthquakes

Continental-continental convergenceNo volcanoesMountain building - Himalayas

Convergent Boundaries

• 3 types of convergent boundaries• Ocean to ocean crust

• Crust melting forms volcanic island arc, ex Aleutian Islands• Volcanoes – Philippines- Mt Pinatubo• Subduction forms trench

• Ocean to continental crust• Crust melting forms volcanic mountain ranges, ex Andes, cascade

range, Mt Rainer, Mt Baker• Subduction zones forms, trenches, • Ocean crust denser than continental crust.

• Ocean crust slides/subducts under the continental crust• Continental to continental crust

• No melting of crust = no volcanoes• No subduction• Folding of crust = Non-volcanic mountains are formed -Example

Mt Everest

Tree Map

Convergent Plate Boundaries

Ocean to ocean crust Ocean to continental crust Continental to continental crust

Crust melting forms volcanic island arc, ex Aleutian Islands

Volcanoes – Philippines- Mt Pinatubo

Subduction forms trenches

Crust melting forms volcanic mountain ranges, ex Andes, cascade range, Mt Rainer, Mt Baker

Subduction zones forms trenches Ocean crust denser than continental crust.

Ocean crust slides/subducts under the continental crust

No melting of crust = no volcanoes

No subduction

Folding of crust = Non-volcanic mountains are formed

-Example Mt Everest

Transform Boundary

A place where two plates slip past each other, moving in opposite directions

Pacific plate

North American plate

San Andres Fault

Earthquake in action• http://www.classzone.com/books/earth_science/terc/conte

nt/visualizations/es1005/es1005page01.cfm?chapter_no=visualization

Transform plate boundary

• Action: Earthquakes• Forms: fault• Example: San Andres fault• No crustal melting = No volcanoes

Transform Boundary• Draw arrows to indicate direction the

plates move in relationship to each other.

• Name a location of a transform boundary.

• Name the event that occurs at transform boundaries.

• Could a volcano erupt in Los Angeles? Why or why?

Transform Boundary

Direction

Is a place where two plates slip past each other

Forms

Faults

Earthquakes

Example: San Andres fault

No crustal melting = No volcanoes

Crust is neither created nor destroyed