Theory of Plate TectonicsTheory of Plate Tectonics:

• Lithosphere is broken up into many plates that move

• Interactions when the plates touch, explain most of the Earth’s land and ocean features

• Earthquakes can occur at all plate boundaries

Plate BoundariesTransfor

m

Divergent

Convergent

What happens at a divergent boundary?• Motion: Plates moving apart

• Features/Processes: o Sea floor spreadingo Mid-ocean ridgeo Volcanic activity

Ex: Mid-Atlantic Ridge

Ex: The Great Rift Valley • Divergent

boundary on a continent

• New ocean forming

DivergBound_PC

What happens at a transform boundary?

• Motion: Plates slide past each other

• Features/Processes: Many earthquakes

Ex: San Andreas Fault

What happens at a convergent boundary?• Motion: Plates

are pushed together

• Features depend on which types of plates are converging (details below)

Convergent(oceanic crust vs. continental

crust)• Oceanic subducts under continental because…o The oceanic crust has a greater density

• Trench is created off the coast• Volcanic Mountains created on land due to rising

magma

magma

Ex: The Andes Mountains

Convergent(oceanic crust vs. oceanic

crust)• The OLDER oceanic plate will sink beneath the newero The older plate is denser b/c it has more time to

compact • Trench is created in between the plates• A volcanic island arc is created due to rising magma

mag

ma

Examples: Island Arcs of1. Aleutian Islands, Alaska 2. Japan

3. The Philippines

Convergent(continental vs. continental)• Both plates collide and deform

o neither subducts because both plates have similar, low densities

• The crust thickens as mountains are pushed upwardo metamorphism of rocks takes place from

pressure

Ex: The Himalayas

ConvergMargV2

MotionAtPlate_PC

Explain this diagram:

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