Plate Tectonics

Overview:

• The Lithosphere and the Crust

• Basic Concepts of Plate Tectonics

• Plate Movements and Boundaries

Inside the Earth:

The Lithosphere:

The Basic Concepts:

- the earth is covered by several large lithospheric plates

These plates move slowly (about a few cm./yr)

• Due to convection cells in the asthenosphere

Convection movement driven by heat from the core:

Mantle convection produces lateral forces at the boundary between the

mantle and the crust

Theory of Plate Tectonics:

Plate Movement and Boundaries

• Divergent Boundarieso Plates move aparto Volcanic activityo Earthquakes shallowo Two types of boundaries

OceanicContinental

Oceanic divergent boundary

• Sea-floor spreading of ocean platesMid-Atlantic Ridge

Page 43, Worrall

Continental Divergent Boundary

• Continental Rifting,

eventually oceanic

crust is formedModern example ; East African Rift

Convergent Boundaries

• Plates move towards each other• Volcanic activity common• Deep, medium and shallow earthquakes• Three types;

Ocean to oceanOcean to continentContinent to continent

Ocean to Ocean- convergence

• Subduction - process which one plate slides under the other (subducts)

• Volcanic arc islands are formed

Ocean to Continent Convergence

• Ocean lithophere subductssubducts under continent

•Most tectonic activity occurs at or near these boundaries

Continent to Continent - Convergence

• Subduction does not occur

• Mountain building occurs without volcanic activity

• Collision of India with Eurasia

• Height is still increasing

Transform Boundaries

• Plates slide past each other

• Little or no volcanic activity

• Shallow but strong earthquakes

• Example: San Andreas Fault

West Coast: unstable -subduction zone and transform fault zone

A

Divergent

B

Convergent

C

Transform

•plates are moving apart

•new crust is created

•Magma is coming to the surface

•plates are coming together

•crust is returning to the mantle

•plates are slipping past each other

•crust is not created or destroyed

A

Divergent

B

Convergent

C

TransformContinental crust

rift valley

Oceanic crust mid-ocean ridge

2 continental plates mountain range

Plates move against each other

Stress builds up

Stress is released

earthquake

2 oceanic plates oroceanic + continental subduction

The Big Picture