What is Plate Tectonics?

Directions:

•Read each slide then

fill in the blank with

the RED underlined

word.

Plate tectonics

• The theory that explains

why and how continents

move and is the study of

the formation of features

in Earth’s crust.

• If you look at a map of the world, you may notice that some of the

continents could fit together like pieces of a puzzle.

Plate Tectonics• The Earth’s crust is divided into 12 major

plates which are moved in various directions.

• This plate motion causes them to collide, pull apart, or scrape against each other.

• Each type of interaction causes a characteristic set of Earth structures or “tectonic” features.

• The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.

World Plates

What are tectonic plates made of?

• Plates are made

of rigid

lithosphere

.The lithosphere is

made up of the

crust and the upper

part of the mantle.

What lies beneath the tectonic plates?

• Below the

lithosphere (which

makes up the

tectonic plates) is the

asthenosphere.

Moving pieces of the lithosphere • “Plates” of lithosphere are moved around by

the underlying hot mantle convection

currents (cells)

What drives lithospheric plates?Convection currents cells in Earth’s lower

mantle drive the lithospheric plates on the

surface.

Here again we see the effect of heat on

materials. The rocks of the lower mantle are not

brittle like the rocks of the lithosphere. They are

hot enough so that they flow very slowly. The

core heats the rock material of the lower mantle.

As it is heated, it expands and becomes less

dense.

What drives lithospheric plates?• Over time, the far edge cools and becomes

denser. Eventually, it may sink below another

lithospheric plate and enter the lower mantle.

This sinking process is called subduction. As

the now-cool subducting plate enters the

lower mantle, it cools the nearby lower mantle

material in turn. Cooling makes the nearby

material denser and it sinks deeper into the

lower mantle. This sinking completes the lower

mantle convection current cell.

Copy

Practical Exercise 1

Supercontinents!

What happens at tectonic plate

boundaries?

How plates move relative to

each other• Earth’s surface is covered with

lithospheric plates. Unlike our single

imaginary plate, the boundaries of real

plates touch each other. Plates move

apart at divergent boundaries, collide at

convergent boundaries, and slide by

each other at transform fault boundaries.

• Imagine a single plate, moving in one direction

on Earth’s surface. One edge of the plate—the

trailing edge—moves away from things. This

edge is called a divergent boundary. The

opposite edge—called the leading edge—

bumps into anything in the way. This edge is

called a convergent boundary. The sides of

our imaginary plate do not collide with or move

away from another plate. These sides slide by

other plates. An edge of a lithospheric plate that

slides by another plate is called a transform

fault boundary.

How movement at the

boundaries of lithospheric plates

affects Earth’s surface.

At convergent boundaries,

tectonic plates collide with each

other. The events that occur at

these boundaries are linked to

the types of plates (oceanic or

continental) that are interacting.

A.Oceanic-Oceanic- Subduction creates a trench• Creates island arc (volcanic island), Deep Ocean Trenches,,

Undersea Volcanism. ex. Mariana Trench, Japan, Aleutian Islands (Alaska), Phillipines, Sumatra (2004 Tsunami)

B.Oceanic-continental- When the two collide the plates converge, one is denser the denser subduct under the other oceanic plate creating volcanic islands, Deep Ocean Trenches, Stratovolcanoes and Volcanic Mts. on Land. ex. Cascade Mountains in the Pacific Northwest US and the Andes Mountains in South America.

C.Continental-continental- Continental crust cannot subductdue to its low density. Therefore, when two continental pieces of crust converge, they fold and uplift creating faulted mountains, Folded Mountains on Land. ex. Himalayan Mts., the Alps in Europe, the Appalachian Mts. (ancient orogonies or mountain building events) in the Eastern United States. Compression, Reverse faulting, Strong earthquakes.

• There are three styles of convergent plate

boundaries

– Continent-continent collision

– Continent-oceanic crust collision

– Ocean-ocean collision

Convergent Boundaries

• Forms mountains, e.g. European Alps, Himalayas

Continent-Continent Collision

Himalayas

• Called SUBDUCTION

Continent-Oceanic Crust Collision

• Oceanic lithosphere subducts underneath the continental lithosphere

• Oceanic lithosphere heats and dehydrates as it subsides

• The melt rises forming volcanism

• E.g. The Andes

Subduction

• When two oceanic plates collide, one runs over the

other which causes it to sink into the mantle forming

a subduction zone.

• The subducting plate is bent downward to form a very

deep depression in the ocean floor called a trench.

• The worlds deepest parts of the ocean are found

along trenches.

– E.g. The Mariana Trench is 11 km deep!

Ocean-Ocean Plate Collision

Aleutian Islands, Alaska

Helpful Hints…

• Convergent = “Connecting” boundaries

• May work like a trash compactor smashing

rock.

– Rock goes crunches up to make folded

mountains.

– Rock goes down “under” @ subduction zone.

Please return to the Blog

You will finish your notes on

this page!

Slip, Slide, and Collide.

Use the following link :

http://www.learner.org/interactives/dyna

micearth/slip.html

• Divergent

• Convergent

• Transform

Three types of plate boundary

…what’s the connection?

Earthquakes and Plate

Tectonics…

Plate Tectonics Summary

• The Earth is made up of 3 main layers (core, mantle, crust)

• On the surface of the Earth are tectonic plates that slowly move around the globe

• Plates are made of crust and upper mantle (lithosphere)

• There are 2 types of plate

• There are 3 types of plate boundaries

• Volcanoes and Earthquakes are closely linked to the margins of the tectonic plates

“

”

Motion of the Earth’s Plates

Convection

currents

within the

earth's

mantle

PUSH our

tectonic

plates.

Please return to the Blog

You will finish your notes on

this page!

Slip, Slide, and Collide.

Use the following link :

http://www.learner.org/interactives/dyna

micearth/slip.html