Plate Plate TectonicsTectonics

Restless Restless planetplanet

The Structure of the Earth The Structure of the Earth &&

What is the theory of plate tectonics?

The Theory of Plate Tectonics states that the continents have moved and are still moving…about as fast as your fingernails grow.

In 1912, Alfred Wegener introduced a hypothesis of continental drift, but he did not fully understand what caused the plates to move.

As scientists amassed more data, Wegener’s

hypotheses was amended to become the Plate Tectonic Theory.

A theory is an explanation of a scientific process that has been successfully tested.

What is the theory of plate What is the theory of plate tectonics good for?tectonics good for?

The motion of Earth's plates help scientists to understand why earthquakes, volcanoes, and mountain building occur.

Scientists believe these plates have been moving for millions of years.

Their research indicates that 250 millions years ago, the Earth's continents were all grouped together into one super-continent called Pangaea.

PangaeaPangaea About 200 million years ago, Pangaea covered approximately 30% of Earth’s surface.

A large ocean, Panthalassa, covered the rest of the planet.

Some clues leading scientists to accept the idea of Pangaea were:

• Fossil clues• Rock Clues • Climate Clues

• Fossil clues: Fossils of the reptile Mesosaurus have been found in South America and Africa. Since the reptile couldn’t swim that distance, Wegener hypothesized that this reptile lived on both continents when they were joined.

Additionally, plant fossils and matching rock layers have been found on both continents.

• Rock Clues: Similar rocks were found in United States, Western Europe, and Greenland.

• Climate Clues: Glacial deposits found in South America, Africa, India and Australia provide additional evidence that continents were connected.

Structure of the EarthStructure of the Earth

The Earth is The Earth is made up of 3 made up of 3 main layers:main layers:• CrustCrust• MantleMantle• CoreCore

Inner core

Outer core

Mantle

Crust

The CrustThe Crust This is where we live!This is where we live!

The Earth’s crust is The Earth’s crust is made of:made of:

1. Continental Crust

- thick- buoyant / kind of floats

-(less dense than oceanic crust) - mostly old

2. Oceanic Crust

-thin- dense

-(sinks under continental crust)- young

Let’s model the Earth’s Let’s model the Earth’s layerslayers

What are the What are the layers of the layers of the Earth?Earth?

How are the How are the peach layers peach layers similar to Earth’s similar to Earth’s layers?layers?

What are the What are the limitations of limitations of this model?this model?

The Earth’s layersThe Earth’s layers

The crust, mantle and core are labels The crust, mantle and core are labels for describing the three different for describing the three different kindskinds of materials the Earth is made of materials the Earth is made of.of.

The lithosphere, asthenosphere, The lithosphere, asthenosphere, mesosphere, outer core & inner core mesosphere, outer core & inner core distinguish between the 5 distinguish between the 5 physicalphysical layers of the Earth.layers of the Earth.

Lick All My Orange Ice Cream

Question:

Describe the difference between the crust-mantle- core AND LAMOIC

How do we know what the How do we know what the Earth is made of?Earth is made of?

Geophysical surveys: Mostly seismic wave Geophysical surveys: Mostly seismic wave experiments, experiments, fieldwork, boreholes, minesfieldwork, boreholes, mines

What is Plate Tectonics?What is Plate Tectonics?

If you look at a map of the world, you may notice that some 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.of the continents could fit together like pieces of a puzzle.

QuestionQuestion

Describe plate tectonics in your own Describe plate tectonics in your own wordswords

Why are there tectonic plate interactions?

Earth is a warm planet sailing through cold space. Most of the mantle of our planet is hot enough to flow.

The surface of Earth, however, is chilled as it loses heat into space. As a result, the rocks of Earth’s surface are hard and brittle.

The cold outer layer of our planet, which holds together as a rigid shell, is not made of one solid piece.

Instead, this shell is broken into separate pieces, or tectonic plates (lithosphere), that slide on top of the mobile interior (asthenosphere).

The tectonic plates are driven by the flowing part of the mantle, it sets them in motion.

The movement of the plates causes a complex puzzle of plate collisions around the globe.

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

which are moved in various directions. which are moved in various directions. (Plate examples: Eurasian, African, Indo-(Plate examples: Eurasian, African, Indo-

Austrailian, Pacific, North American and South Austrailian, Pacific, North American and South American platesAmerican plates

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

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

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

What are tectonic plates made What are tectonic plates made of?of?

Plates are Plates are made of rigid made of rigid lithospherelithosphere..

The lithosphere is made up of the crust and the upper part of the mantle.

What lies beneath the tectonic What lies beneath the tectonic plates?plates?

Below the Below the lithosphere lithosphere (which makes (which makes up the up the tectonic tectonic plates) is the plates) is the asthenospherasthenosphere.e.

Plate MovementPlate Movement ““Plates” of lithosphere are moved Plates” of lithosphere are moved

around by the underlying hot mantle around by the underlying hot mantle convection currentsconvection currents

Convection CurrentsConvection Currents Hot magmaHot magma in the Earth in the Earth

moves toward the surface, moves toward the surface, cools, then sinks again.cools, then sinks again.

Creates Creates convectionconvection currentscurrents beneath the plates beneath the plates that that cause the plates cause the plates to move to move..

There are three types of plate-plate interactions

based upon relative motion:

Convergent boundary - where plates collide

Divergent boundary - where plates separate

Transform boundary - where plates slide past one another

What happens at a convergent boundary?

What forms around that boundary?

Plates converge, which means two plates move toward each other. Usually an oceanic plate converges with a continental plate.

Since oceanic plates are more dense than continental plates, ocean plates are subducted or go down into the mantle in an area called the subduction zone.

Convergent boundaries make Convergent boundaries make subduction zonessubduction zones

A convergent boundary can also create a deep-sea trench.

At the subduction zone, the temperature of the rocks rises and causes them to melt, which forms magma that is forced upwards to create volcanoes.

There are three There are three stylesstyles of of convergent plate boundariesconvergent plate boundaries• Continent-continent collisionContinent-continent collision• Continent-oceanic crust collisionContinent-oceanic crust collision• Ocean-ocean collisionOcean-ocean collision

Convergent BoundariesFYI

Forms Forms mountainsmountains,, e.g. European Alps, e.g. European Alps, HimalayasHimalayas

Continent-Continent Collision

Himalayas

Convergent boundaries making Convergent boundaries making mountainsmountains

There is little or no subduction to produce the high temperature required for melting the rocks.

When two continental plates collide (same densities) and push up the crust, they form mountain ranges such as the Himalayas. This is an example of uplift.

No volcanoes form.

Called SUBDUCTIONCalled SUBDUCTION

Continent-Oceanic Crust Collision

Oceanic lithosphere Oceanic lithosphere subducts underneath the subducts underneath the continental lithospherecontinental lithosphere

Oceanic lithosphere Oceanic lithosphere heats and dehydrates as heats and dehydrates as it subsides it subsides

The melt rises forming The melt rises forming volcanismvolcanism

E.g. The AndesE.g. The Andes

Subduction

When two oceanic plates collide, one runs When two oceanic plates collide, one runs over the other which causes it to sink into over the other which causes it to sink into the mantle forming a the mantle forming a subduction zonesubduction zone. .

The subducting plate is bent downward to The subducting plate is bent downward to form a very deep depression in the ocean form a very deep depression in the ocean floor called a floor called a trenchtrench. .

The worlds deepest parts of the ocean are The worlds deepest parts of the ocean are found along trenches. found along trenches. • Ex. The Mariana Trench is 11 km deep!Ex. The Mariana Trench is 11 km deep!

Ocean-Ocean Plate Collision

Divergent boundary

Plates separate, which means two plates move away from each other.

Usually an oceanic plate diverges from another oceanic plate.

Seafloor spreading occurs at divergent oceanic plate boundaries and leads to the creation of new ocean floor.

What happens at a divergent boundary?

What forms along that boundary?

As two tectonic plates slowly separate, molten material rises from within the mantle to fill the opening. As the ocean floor slowly separates, new rocks form at the mid-ocean ridge that is forming.

The Mid-Atlantic Ridge is getting wider at a rate of 2.5 cm every year.

Mid-Mid-ocean ocean ridgesridges

Mid-ocean ridges are Mid-ocean ridges are underwater mountain underwater mountain chains.chains.

Although named “mid-Although named “mid-ocean”, there are not ocean”, there are not necessarily at the center of necessarily at the center of the ocean.the ocean.

Spreading ridgesSpreading ridges• As plates move apart new material is As plates move apart new material is

erupted to fill the gaperupted to fill the gap

Divergent Boundaries

Sea floor Sea floor spreadingspreading

When the sea floor moves, magma moves upward and flows from cracks at the mid ocean ridge.

The magma cools and forms a new sea floor.

This sea floor spreading idea is supported by the following

observations:1. When scientists tested rocks at the mid-

ocean ridge and on both sides of the ridge, they found that the youngest rocks were closer to the ridge and older rocks were farther away from the ridge.

2. Earth has a magnetic field that from time to time reverses magnetic north and south poles. Volcanic rock provides a record of the magnetic poles at the time the rock cooled, thus past reversals are recorded in rocks forming along mid-ocean ridges.

Iceland has a divergent Iceland has a divergent plate boundary running plate boundary running through its middlethrough its middle

Iceland: An example of continental rifting

Where plates slide past each otherWhere plates slide past each other

Transform Boundaries

Above: View of the San Andreas transform fault

What happens at the transform boundary? What forms along that

boundary? Plates slide past each other, and faults or breaks

in the Earth’s crust can form there from stress. Stress- the amount of force put on a rock When one plate suddenly slips past another

plate and releases the stress, earthquakes occur. The San Andreas fault is part of a transform

boundary where the Pacific plate slides against the North American plate.

……what’s the connection?what’s the connection?

Volcanoes and Plate Tectonics…

Volcanos are mostly focused at plate boundaries

Pacific Ring of Fire

Hotspot volcano chain- Hawaiian Islands

Pacific Ring of Fire Most of the active

volcanoes and earthquakes are located at the plate boundaries.

The Pacific Ring of Fire is an area of almost constant earthquake and volcanic activity.

It circles the Pacific Ocean basin.

- Subduction - Rifting - Hotspots- Subduction - Rifting - Hotspots

Volcanoes are formed by:

Hot mantle plumes breaching the Hot mantle plumes breaching the surface in the middle of a tectonic surface in the middle of a tectonic plateplate

What are Hotspot Volcanoes?

Photo: Tom Pfeiffer / www.volcanodiscovery.com

The Hawaiian island chain are examples of hotspot volcanoes.

The tectonic plate moves over a fixed hotspot forming a chain of volcanoes.

The volcanoes get younger from one end to the other.

……what’s the connection?what’s the connection?

Earthquakes and Plate Tectonics…

As with volcanoes, earthquakes are As with volcanoes, earthquakes are not not randomly distributed over the globerandomly distributed over the globe

At the boundaries between plates, At the boundaries between plates, friction causes plates to stick together. friction causes plates to stick together. When built up energy causes them to When built up energy causes them to “unstick”, earthquakes occur.“unstick”, earthquakes occur.

Figure showing the distribution of earthquakes around the globe

Where do earthquakes Where do earthquakes form? form?

Figure showing the tectonic setting of earthquakes

Plate Tectonics SummaryPlate Tectonics Summary The Earth is made up of 3 main layers (core, The Earth is made up of 3 main layers (core,

mantle, crust) & 5 physical layers (LAMOIC)mantle, crust) & 5 physical layers (LAMOIC) On the surface of the Earth are tectonic On the surface of the Earth are tectonic

plates that slowly move around the globeplates that slowly move around the globe Plates are made of crust and upper mantle Plates are made of crust and upper mantle

(lithosphere) and move on the asthenosphere(lithosphere) and move on the asthenosphere There are 2 types of plates: oceanic and There are 2 types of plates: oceanic and

continentalcontinental There are 3 types of plate boundaries: There are 3 types of plate boundaries:

convergent, divergent & transformconvergent, divergent & transform Volcanoes and Earthquakes are closely linked Volcanoes and Earthquakes are closely linked

to the borders of the tectonic platesto the borders of the tectonic plates

ConvergentConvergent TransformTransformDivergentDivergent

C-C form mountains C-C form mountains using upliftusing uplift

Ex. Alps, HimalayasEx. Alps, Himalayas

O-O form O-O form subduction zones subduction zones

trenchestrenchesEx. Mariana TrenchEx. Mariana Trench

C-O form volcanoes C-O form volcanoes from subduction from subduction zones Ex. Andes zones Ex. Andes

Mts.Mts.

O-O form mid-ocean O-O form mid-ocean ridges (underwater ridges (underwater

mountain chains) with mountain chains) with sea floor spreadingsea floor spreading

C-C breaks continental C-C breaks continental crust apart and exposes crust apart and exposes

magma on Earth’s magma on Earth’s surfacesurface

Ex. IcelandEx. Iceland

All will create fault lines All will create fault lines that build up pressure to that build up pressure to

release earthquakesrelease earthquakesEx. San Andes fault CAEx. San Andes fault CA

Age of Oceanic Crust

Courtesy of www.ngdc.noaa.gov

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

tectonics?tectonics? What is the lithosphere?What is the lithosphere? What is the asthenosphere?What is the asthenosphere? What is the connection between What is the connection between

the two?the two? What are the two types of plates?What are the two types of plates?

Questions...Questions... What are the three types of What are the three types of

boundaries?boundaries? What direction do plates go What direction do plates go

for each?for each? Which boundary has a Which boundary has a

subduction zone…what subduction zone…what occurs at a subduction zone?occurs at a subduction zone?

Questions...Questions...

What causes plates to move?What causes plates to move? How is a convection current How is a convection current

formed?formed?