Plate TectonicsPlate Tectonics

What is Plate Tectonics?What 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

The CrustThe Crust

• Outermost layer• 5 – 100 km thick• Made of Oxygen, Silicon, Aluminum

The MantleThe Mantle

• Layer of Earth between the crust and the core

• Contains most of the Earth’s mass

• Has more magnesium and less aluminum and silicon than the crust

• Is denser than the crust

The CoreThe Core

• Below the mantle and to the center of the Earth

• Believed to be mostly Iron, smaller amounts of Nickel, almost no Oxygen, Silicon, Aluminum, or Magnesium

Earth’s LayersEarth’s LayersThe Earth's rocky outer crust solidified billions of years ago, soon after the Earth formed.

This crust is not a solid shell; it is broken up into huge, thick plates that drift atop the soft, underlying mantle.

Tectonic platesTectonic plates

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”

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

• Ocean plates - plates below the oceans

• Continental plates - plates below the continents

How Plates MoveHow Plates Move

http://pubs.usgs.gov/gip/dynamic/unanswered.html

Plates move because there is slow movement of hot, softened mantle that lies below the rigid plates

Plate BoundariesPlate Boundaries

Divergent BoundariesDivergent Boundaries

• Boundary between two plates that are moving apart or rifting

• RIFTING causes SEAFLOOR

SPREADING

Divergent BoundariesDivergent BoundariesTwo tectonic plates separateseparate (move

apart)Most happen on the sea floor

Sea-floor Sea-floor Spreading!Spreading!

Features of Divergent Features of Divergent BoundariesBoundaries

• Mid-ocean ridges

• rift valleys

• fissure volcanoes

Sea floor spreadingSea floor spreading

• Large continents begin to crack and split apart

• The gaps fill with water

• Small seas become oceans

• The mid ocean ridge continues to produce new crust

Sea Floor SpreadingSea Floor Spreading

Sea Floor SpreadingSea Floor Spreading

• Mid Ocean Ridges – underwater mountain chains that run through the Earth’s Basins

• Magma rises to the surface and solidifies and new crust forms

• Older Crust is pushed

farther away from the ridge

Divergent Boundary – Divergent Boundary – Arabian and African PlatesArabian and African Plates

Plates move away from each other

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

Convergent BoundariesConvergent BoundariesTwo tectonic plates collidecollide

Continental-Oceanic Collisions

Oceanic-Oceanic Collisions

Continental-Continental Collisions

Convergent BoundariesConvergent Boundaries• Continental-Oceanic Collisions:

– Continental plate collides with oceanic plate

– The denser oceanic plate sinks (subducts) beneath the less-dense continental crust

Convergent BoundariesConvergent BoundariesContinental-Oceanic Collisions:

Subduction may cause a chain of volcanoes to form along the plate boundary

Convergent BoundariesConvergent Boundaries• Oceanic-Oceanic Collisions:

– Oceanic plate collides with oceanic plate

– The denser of the 2 oceanic plates sinks (subducts)

Convergent Boundary – Indian and Eurasian Convergent Boundary – Indian and Eurasian PlatesPlates

Andes Mountains, Andes Mountains, South AmericaSouth America

Type 2Type 2

• Ocean plate colliding with another ocean 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 along faults

Transform BoundariesTransform BoundariesTwo tectonic plates slide past slide past

one anotherone another

Building tension

Releases tension in a sudden, often violent, jerk called an

EARTHQUAKE!!

Transform BoundariesTransform Boundaries• The San Andreas fault is an

example of a transform boundary

◦The Pacific plate (west of fault) is moving northwest

◦The North American plate (east of fault) is moving southeast

Pacific Plate

San Andreas Fault, CASan Andreas Fault, CA

A fault is a break in a rock across which there is observable movement.

When the break occurred an earthquake was generated, whether or not anyone was there to detect it.

Sometimes faults die at depth and do not break the surface. Sometimes they do such as for the Armenia 1988 earthquake.

Normal Fault

Normal Fault

Reverse Fault

Reverse Fault

Strike-Slip Fault

Strike-Slip Fault

Strike-Slip Fault

Strike Slip Fault

Causes of Plate Causes of Plate TectonicsTectonics

Convection CurrentsConvection Currents

• Hot magma in the Earth moves toward the surface, cools, get denser, and then sinks again with the pull of gravity

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

Continents CollideContinents Collide

• Eventually when plates move together the continental crust collides

• The heat and pressure make metamorphic rock

• It also pushes and folds the rocks into high mountains

• The Himalayas rise to 8848m and are still growing today

So the Earth must be growing?So the Earth must be growing?

• Dense heavy oceanic crust can be subducted below less denser continental crust.

• The friction melts rock• This magma rises

through the crust to form new volcanoes

• This is happening in South America (The Andes)