Theory of Plate TectonicsTheory of Plate Tectonics

Plate TectonicsPlate Tectonics

Plate BoundariesPlate Boundaries

Causes of Plate TectonicsCauses of Plate Tectonics

Plate TectonicsPlate Tectonics

Questions...Questions...• What is the theory of plate

tectonics?

• What is the lithosphere?

• What is the asthenosphere?

• What are the two types of plates?

What is the Theory of Plate What is the Theory of Plate Tectonics?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 What is the LithosphereLithosphere??

• The crust and part of the upper mantle = lithosphere–100 km thick

–Less dense than the material below it so it “floats” on molten rock.

What is the What is the AsthenoshereAsthenoshere??

• The plastic like layer below the lithosphere = asthenosphere

• The plates of the lithosphere float on the asthenosphere

2 Types of Plates2 Types of Plates

• Ocean plates - plates below the oceans (Basalt)

• Continental plates - plates below the continents (Granite)

Plate BoundariesPlate Boundaries

Questions...Questions...

• What are the three types of boundaries?

• What direction do plates go for each?

• Which boundary has a subduction zone…what occurs at a subduction zone?

(1) Divergent Boundaries(1) Divergent Boundaries

• Boundary between two plates that are moving apart

• RIFTING causes SEAFLOOR

SPREADING - Samples collected by the Glomar Challenger showed that the youngest rocks on the ocean floor are found in the center of mid ocean ridges.

Features of Divergent Features of Divergent BoundariesBoundaries

• Mid-ocean ridges

• rift valleys

• fissure (narrow opening) volcanoes

(2) Convergent Boundaries(2) Convergent Boundaries

• Boundaries between two plates that are colliding

• There are 3 types…

Type 1Type 1• Ocean plate collides with a

less dense continental plate• Subduction Zone: where the

more dense plate slides under the less dense plate

• VOLCANOES occur at subduction zones

Andes Mountains, Andes Mountains, South AmericaSouth America

Type 2Type 2

• Ocean plate collides with another ocean plate

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

Aleutian Islands, AlaskaAleutian Islands, Alaska

Type 3Type 3

• A continental plate collides with another continental plate

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

faulted MOUNTAINS form.

(3) Transform Fault Boundaries(3) Transform Fault Boundaries

• Boundary between two plates that are sliding past each other

• EARTHQUAKES along faults–Earthquakes produce seismic

waves that travel through Earth.

San Andreas Fault, CASan Andreas Fault, CA

Causes of Plate Causes of Plate TectonicsTectonics

Questions...Questions...

• What causes plates to move?

• How is a convection current formed?

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.

Continental DriftContinental Drift

• The hypothesis of Continental drift was that all the continents once were joined as a single super continent and have since drifted apart. To support his hypothesis,

Alfred Wegener provided evidence from fossils to support the theory of continental drift.