Plate Tectonic Boundaries

The Core (The center)

The center part of the earth

made of nickel and iron. Its

temperature is 4,000 to 9,000

degrees F. The outer core is

fluid and the inner core is solid.

The Mantle (The middle)

The mantle extends from 50

miles to a depth of 1,750

miles beneath the Earth's

surface. The upper part is

solid and the lower part is

fluid.

The Crust (The surface)

The thin rigid outermost layer of

the Earth is the crust. The

thinnest crust (oceanic) is 3

miles and the thickest

(continental) is 50 miles.

Tectonic Plates

The Earth's crust and rigid upper mantle are

broken into eight enormous slabs called tectonic

plates. There are also seven small tectonic

plates.

The Nature of the

Tectonic Plates

The tectonic plates consist

of the crust and a rigid

portion of the upper

mantle, together called the

lithosphere. A plate is

about 60 miles thick.

Tectonic Plates Float

Similar to the way wood blocks

float on water because they are

less dense, the plates float on

the much denser mantle.

Plate Mobility

Tectonic plates are in constant motion. On

average, plates move 2 or 3 inches each year.

Global positioning satellites (GPS) allow

the precise motion of the continents to be

measured.

What Causes

plates to move?

1.Mantle

Convection

2.Ridge Push

3.Slab Pull

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hment.action?quick=12p&att=2775

Mantle Convection

• Convection currents in the mantle force

tectonic plates apart along divergent ridges.

http://education.sdsc.edu/optipute

r/flash/convection.htm

Ridge Push

• The plates are pushed apart at divergent

margins along ocean ridges.

Slab Pull

When the ocean floor descends back into

mantle, the slab of oceanic crust pulls the

entire slab down.

Rift Push Slab Pull

The edges of tectonic plates are where earthquakes and volcanoes

occur.

Three types of plate boundaries •Divergent (spread apart)

•Convergent (come together)

•Transform (slide past each other)

Transform Convergent

Divergent

Let’s talk about divergent

plate boundaries

Major Divergent Boundaries

New Technology after

World War II

At the end of World War II,

technologies were developed

to study the ocean floor.

Echo Sounding

Creates profiles of the sea

bottom using sound waves.

Sea Floor Spreading

The Mid-Atlantic Ridge

Echo-sounding shows that

there is a mountain range

(7000 feet high) running

down the middle of the

Atlantic Ocean floor.

Sea Floor Spreading

The Great

Rift Valley

The Mid-

Atlantic

Ridge has a v-

shaped valley

running down

its crest. This

valley is

called a rift

valley

because here

the crust of

the Earth is

being torn

apart.

Sea Floor Spreading

These v-shaped

valleys are the

location of

recent volcanic

activity.

Sea Floor Spreading

The World's Mid-Ocean Ridges

The mid –ocean ridge system wraps

around the entire planet.

Sea Floor Spreading

Glomar

Challenger In the

Late 1960's a floating

drill rig named

Glomar Challenger

took samples (called

cores) of the ocean

bottom.

Sea Floor Spreading

A core library.

The JOIDES Resolution This is a

drilling ship of the ocean drilling

program. It has recovered more than 104

miles of core samples in the Atlantic,

Pacific, Indian, and Arctic oceans.

Sea Floor Spreading

Alvin Alvin is a manned deep-ocean research

sumersible operated by the Woods Hole

Oceanographic Institute. The three-person

vessel allows for two scientists and one pilot to

dive for up to nine hours at 15,000feet.

Sea Floor Spreading

Click to see a 4 minute

video/audio clip about Alvin.

Sea Floor Spreading

In 1962, a Princeton

University scientist,

Harry Hess, proposed the

hypothesis of sea floor

spreading.

An Ocean Floor

of Volcanic Lava

Samples show that

beneath a blanket of

overlying mud, the

ocean floors are

made up of

hardened lava.

Pillow Lavas

On the ocean

floor lava

squeezes out to

form pillow

shapes.

Sea Floor Spreading

Pillow Lava

Lava that forms

under water has a

pillow shape. The

mid- ocean ridges

are composed of

this type of lava.

Sea Floor Spreading

Pillow lava at

Avila Point,

California

Sea Floor Spreading Black Smokers

Black smokers are chimneys

built by mineral-rich

superheated water. They are

found on the deep ocean

ridges.

Using fossils to Date

Ocean Floor Rock

Scientists can

determine the age of

the lava floor by

dating fossil

skeletons of

microscopic sea

organisms that are

found in the mud

above.

Sea Floor Spreading

Potassium-Argon Dating Lava contains a small amount of

radioactive potassium. Over time potassium -40 changes into

argon gas. By measuring the proportion of K-40 to argon the

age of the lava can be determined.

Sea Floor Spreading

Age of the Atlantic

Ocean Floor

Samples show that

newly hardened lava

forms along the Mid–

Atlantic Rift which gets

progressively older as

you approach the coasts.

The oldest sea floor is

200 million years old and

located near the

continent’s edge.

Sea Floor Spreading

The Age of the World’s Basaltic Lava Ocean Floor

Sea Floor Spreading

Worldwide Sea

Floor

All the world’s

ocean floors show

the same pattern:

The ocean floors

are made of a type

of hardened lava

called basalt.

New ocean crust

forms along a

central crack,

called a rift.

The ocean floors

are younger than

200 million years.

Sea Floor Spreading

Destruction of

Sea Floor

According to Hess,

old sea floor is

recycled back into

the Earth along deep

ocean trenches. This

process, where

ocean crust is

destroyed is called

subduction.

Let’s talk about convergent

plate boundaries

Tectonic Plates can

converge in three ways:

1. Oceanic Plate to

Oceanic Plate

2. Oceanic Plate to

Continental Plate

3. Continental Plate to

Continental Plate

Convergent Plate Boundaries Tectonic plates are

destroyed at most convergent boundaries where one

plate slides beneath the other in a process called plate

subduction.

Marianas

Subduction Zone A subduction zone occurs when an ocean plate is

forced down into the mantle beneath a second plate.

Deep Trench As the ocean plate

descends beneath the overriding

plate , it bends , producing a deep

ocean trench.

The

Destruction of

Sea Floor

When an

oceanic plate

collides with a

continent or

another

ocean plate, it

undergoes

subduction

which creates

an ocean

trench.

The Deepest Ocean Depth

The deepest place in the

ocean is in the Mariana

Trench, south of Japan. The

bottom of the trench is nearly

7 miles below the surface.

Challenger Deep

The deepest part of the

trench (35,800 feet) is

called the Challenger Deep.

Ocean Plate – Ocean Plate Convergence: Volcanic Island Arc When two ocean plates collide, one

descends beneath the other. Less dense magma rises

creating volcanoes on the ocean floor. These volcanoes

create an arc-shaped chain of volcanic islands.

The Aleutian Trench

The Aleutian islands

of Alaska are a

Volcanic Island Arc

created by the

subduction of the

Pacific plate beneath

the North American

Plate.

Ocean Plate - Continental Plate Convergence

When an ocean plate collides with a continental plate, the

denser ocean plate descends. Volcanoes form on the edge of

the continent. These volcanoes are called Continental Volcanic

Arcs.

The Andes A Continental

Volcanic Arc The Andes of

South America are a

continental volcanic arc

produced by the subduction of

the Nazca oceanic plate

beneath South America.

Cascade Range

Volcanoes

Continental Plate-Continental Plate Convergence

When two continents collide, neither one will subduct

into the mantle. One plate overrides the other and

mountains form. The collision of India with Eurasia is

an example of continent to continent collision. The

Himalaya mountains are the result.

The Himalayas The Himalayas extend along the India

– China border and contain most of the world's tallest

mountains.

Mount Everest At

29,028 feet, Mount

Everest is the

world's tallest

mountain.

Continent to Continent

The Himalayas The Himalayas are 1600 miles long and contain 9 of the

14 tallest mountains in the world. Everest and Makalu are the prominent

peaks in the photo below.