Theory of Plate TectonicsTheory of Plate Tectonics

Plate TectonicsPlate TectonicsPlate BoundariesPlate Boundaries

Causes of Plate TectonicsCauses of Plate Tectonics

Plate TectonicsPlate Tectonics

What is Plate TectonicsWhat is Plate Tectonics

• The Earth’s crust and upper mantle are broken into sections called plates.

• Plates move around on top of the mantle like rafts.

What is the Lithosphere?What is the Lithosphere?

• The crust and part of the upper mantle = lithosphere

–100 km thick –Less dense than the material

below it so it “floats”

What is the What is the AsthenoshereAsthenoshere??

• The plastic layer below the lithosphere = asthenosphere

• The plates of the lithosphere float on the asthenosphere.

2 Types of Plates2 Types of Plates

• Oceanic plates - plates below the oceans.–Contain mostly basalt.

• Continental plates - plates below the continents.–Contain mostly rhyolite.

Plate BoundariesPlate Boundaries

Divergent BoundariesDivergent Boundaries

• Boundary between two plates that are moving apart or rifting.

• RIFTING causes SEAFLOOR

SPREADING.

Features of Divergent Features of Divergent BoundariesBoundaries

• Mid-ocean ridges• Rift valleys• Fissure volcanoes

Convergent BoundariesConvergent Boundaries

• Boundaries between two plates that are colliding.

• There are 3 types…

Type 1Type 1• Oceanic plate colliding with a less

dense continental plate.

• Subduction Zone: where the more dense plate slides under the less dense plate.

• VOLCANOES occur at subduction zones.

Ring of Fire Animations

Andes Mountains, Andes Mountains, South AmericaSouth America

Type 2Type 2• Oceanic plate colliding with

another oceanic plate.

• The more dense plate slides under the less dense plate creating a subduction zone called a TRENCH.

Aleutian Islands, AlaskaAleutian Islands, Alaska

Type 3Type 3

• A continental plate colliding with another continental plate.

• Have Collision Zones:–a place where folded and thrust

faulted mountains form.

Transform Fault BoundariesTransform Fault Boundaries

• Boundary between two plates that are sliding past each other.

• EARTHQUAKES occur along these faults.

San Andreas Fault, CASan Andreas Fault, CA

Causes of Plate Causes of Plate TectonicsTectonics

Convection CurrentsConvection Currents• Hot magma in the Earth moves

toward the surface, cools, then sinks again.

• Creates convection currents beneath the plates that cause the plates to move.