Plate Tectonics

Areas of InterestAreas of Interest

Plate TectonicsPlate TectonicsPlate BoundariesPlate Boundaries

Causes of Plate TectonicsCauses of Plate TectonicsEvidencesEvidences

Earth Tectonic PlatesEarth Tectonic Plates

Plate TectonicsPlate Tectonics

Plate tectonicsPlate tectonics (from (from GreekGreek tektōntektōn "builder") is a "builder") is a theorytheory of of geologygeology that has that has been developed to explain the observed been developed to explain the observed evidence for large scale motions of the evidence for large scale motions of the EarthEarth's 's lithospherelithosphere

The outermost part of the Earth's The outermost part of the Earth's interior is made up of two layers: above interior is made up of two layers: above is the is the lithospherelithosphere, comprising the , comprising the crustcrust and the rigid uppermost part of the and the rigid uppermost part of the mantlemantle. Below the lithosphere lies the . Below the lithosphere lies the asthenosphereasthenosphere

The lithosphere is broken up into what The lithosphere is broken up into what are called are called tectonic platestectonic plates

The lateral movement of the plates is The lateral movement of the plates is typically at speeds of 0.66 to 8.50 typically at speeds of 0.66 to 8.50 centimeters per yearcentimeters per year

This movement is caused by This movement is caused by convection current in the mantleconvection current in the mantle

Mid-Atlantic Ridge moves as fast as fingernails grow

Continental Drift TheoryContinental Drift Theory

Super-Continent PANGAEA

Sea-Floor Spreading

Atlantic 65 m.y. ago

Present Day Atlantic

Continental Drift + Sea Floor Continental Drift + Sea Floor Spreading = Plate TectonicsSpreading = Plate Tectonics

These plates move in relation to These plates move in relation to one another at one of three types one another at one of three types of plate boundaries: of plate boundaries: convergentconvergent or or collision boundaries, collision boundaries, divergentdivergent or or spreading boundaries, and spreading boundaries, and transformtransform boundaries. boundaries. EarthquakesEarthquakes, , volcanic activityvolcanic activity, , mountainmountain-building, -building, and and oceanic trenchoceanic trench formation occur formation occur along plate boundariesalong plate boundaries

Types of plate boundaries

Three types of plate boundaries exist, characterized by the way the plates move relative to each other. They are associated with different types of surface phenomena. The different types of plate boundaries are:

1. Transform Plate Boundaries2. Divergent Plate Boundaries3. Convergent Plate Boundaries

The Earth’s PlatesThe Earth’s Plates

Plate Boundaries and Plate Boundaries and EarthquakesEarthquakes

Transverse bounaries occur where the plates slide laterally past one another The San Andreas Fault in California is one example. Other examples of transform faults include the Alpine Fault in New Zealand and the North Anatolian Fault in Turkey.Volcanoes are rare but earthquakes are common.

1. Transform boundaries

San Andreas Fault, CASan Andreas Fault, CA

2. Divergent Boundaries2. Divergent Boundaries

Boundary between two plates Boundary between two plates that are moving apart or riftingthat are moving apart or rifting

RIFTING causes SEAFLOOR RIFTING causes SEAFLOOR

SPREADINGSPREADING

Features of Divergent Features of Divergent BoundariesBoundaries

Mid-ocean ridgesMid-ocean ridges rift valleysrift valleys fissure volcanoesfissure volcanoes

Bridge across the Álfagjá rift on the Reykjanes peninsula in southwest Iceland, the boundary of the Eurasian and North American continental tectonic plates.

3. Convergent Boundaries3. Convergent Boundaries

Boundaries between two Boundaries between two plates that are collidingplates that are colliding

There are 3 types…There are 3 types…

Type 1Type 1Ocean plate colliding with a Ocean plate colliding with a

less dense continental plateless dense continental plateSubduction Zone: where the Subduction Zone: where the

less dense plate slides under less dense plate slides under the more dense platethe more dense plate

VOLCANOES occur at VOLCANOES occur at subduction zones subduction zones

Type 2Type 2

Ocean plate colliding with Ocean plate colliding with another ocean plateanother ocean plate

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

Type 3Type 3

A continental plate colliding A continental plate colliding with another continental platewith another continental plate

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

faulted mountains form.faulted mountains form.

Convection CurrentsConvection Currents

Hot magma in the Earth Hot magma in the Earth moves toward the surface, moves toward the surface, cools, then sinks again.cools, then sinks again.

Creates convection currents Creates convection currents beneath the plates that cause beneath the plates that cause the plates to move.the plates to move.

What Drives the plates?What Drives the plates?

The Plate Tectonics ModelThe Plate Tectonics Model

The Plate Tectonics ModelThe Plate Tectonics Model

Evidence for Continental DriftEvidence for Continental Drift

I.I. Early EvidenceEarly EvidenceA.A. Puzzle-like fit of the continentsPuzzle-like fit of the continentsB.B. Fossil cluesFossil clues

A.A. MesosaurusMesosaurusB.B. GlossopterisGlossopterisC.C. PlantsPlants

C.C. Climate cluesClimate cluesA.A. GlaciersGlaciersB.B. Glacial depositsGlacial deposits

D.D. Rock cluesRock clues

A. Puzzle-like fit of the Continents

• The edges of some continents look as if they would fit together like a puzzle.

South America

Africa

Coast Line Fit:

Fit of Fit of Continents Continents Across the Across the

AtlanticAtlantic

B. Fossil Clues: MesosaurusB. Fossil Clues: Mesosaurus

A freshwater swimming reptile A freshwater swimming reptile Fossils found in South America and Africa.Fossils found in South America and Africa. Wegener thought that this reptile lived on both Wegener thought that this reptile lived on both

continents when the continents were connected.continents when the continents were connected.

Fossil Clues: GlossopterisFossil Clues: Glossopteris

Fossil FernFossil Fern Found in Africa, Found in Africa,

Australia, India, Australia, India, South America and South America and Antarctica.Antarctica.

Wegener believed Wegener believed that all these areas that all these areas were connected.were connected.

Ancient Fossils: Plants and Dinosaurs

Climate Clues: Glacial DepositsClimate Clues: Glacial Deposits

Glacial deposits and grooved bedrock Glacial deposits and grooved bedrock found in southern areas of South found in southern areas of South America, Africa, India, and Australia. America, Africa, India, and Australia.

Indicates that these continents were Indicates that these continents were once covered with glaciers.once covered with glaciers.

Wegener believed that these Wegener believed that these continents were covered with ice near continents were covered with ice near Earth’s South Pole at one time.Earth’s South Pole at one time.

C. Climatic Clue :Ancient GlaciationsC. Climatic Clue :Ancient Glaciations

Present GlaciationsPresent Glaciations

Rock CluesRock Clues Similar rock structures Similar rock structures areare found on found on

different continents.different continents. Mountains found in the eastern U.S. Mountains found in the eastern U.S.

are similar to those found in Greenland are similar to those found in Greenland and western Europe.and western Europe.

The clues found in rocks, support the The clues found in rocks, support the idea that continents were connected idea that continents were connected when these rock structures formed.when these rock structures formed.

Rocks Clues :Ancient MountainsRocks Clues :Ancient Mountains

Present MountainsPresent Mountains

Major Plates

The main plates are:• African Plate covering Africa - Continental plate • Antarctic Plate covering Antarctica - Continental plate • Australian Plate covering Australia (fused with

Indian Plate between 50 and 55 million years ago) - Continental plate

• Eurasian Plate covering Asia and Europe - Continental plate

• North American Plate covering North America and north-east Siberia - Continental plate

• South American Plate covering South America - Continental plate

• Pacific Plate covering the Pacific Ocean - Oceanic plate

The minor Plates are:• Caribbean Plate• Arabian Plate• Cocos Plate• Juan de Fuca Plate • Nazca Plate • Philippine Plate • Scotia Plate

Minor Plates

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 for What direction do plates go for

each?each? Which boundary has a subduction Which boundary has a subduction

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

What is the Lithosphere?What is the Lithosphere?

The crust and part of the upper The crust and part of the upper mantle = lithospheremantle = lithosphere100 km thick 100 km thick Less dense than the material Less dense than the material

below it so it “floats”below it so it “floats”

What is the Asthenoshere?What is the Asthenoshere?

The plastic layer below the The plastic layer below the lithosphere = asthenospherelithosphere = asthenosphere

The plates of the lithosphere The plates of the lithosphere float on the asthenospherefloat on the asthenosphere

Causes of Plate Causes of Plate TectonicsTectonics

2 Types of Plates2 Types of Plates

Ocean plates - plates below Ocean plates - plates below the oceansthe oceans

Continental plates - plates Continental plates - plates below the continentsbelow the continents

Andes Mountains, Andes Mountains, South AmericaSouth America

How Plates MoveHow Plates Move

Aleutian Islands, AlaskaAleutian Islands, Alaska

Benioff’s Interpretation UpdatedBenioff’s Interpretation Updated

Where Does Ocean Where Does Ocean Crust Go? Crust Go? Hugo Benioff, 1954Hugo Benioff, 1954

Where the Plates MeetWhere the Plates Meet

Hot Spots: HawaiiHot Spots: Hawaii

Brief History of Plate TectonicsBrief History of Plate Tectonics

Idea of Continental Drift began to form in Idea of Continental Drift began to form in 1830’s when the shapes of the continents 1830’s when the shapes of the continents across the Atlantic were knownacross the Atlantic were known

Alfred Wegener was the first one to Alfred Wegener was the first one to systematically expound the ideasystematically expound the idea

Lack of reliable data prevented the Lack of reliable data prevented the acceptance of the such model until its acceptance of the such model until its revival in early 1960’srevival in early 1960’s

Rates of Plate MotionsRates of Plate Motions

The relative plate motion rates vary from The relative plate motion rates vary from about 2 cm to over 10 cm/yrabout 2 cm to over 10 cm/yr

Average rate: about 5 cm/yr or as fast as Average rate: about 5 cm/yr or as fast as your finger nail growthyour finger nail growth

San Andreas – average rateSan Andreas – average rate Pacific Plate near Japan – 10 cm/yrPacific Plate near Japan – 10 cm/yr

Scientists Reject Wegener’s Theory Scientists Reject Wegener’s Theory

Wegener provided more than evidence for Wegener provided more than evidence for his theory. his theory.

He attempted to explain how drift took He attempted to explain how drift took place.place.

Unfortunately, Wegener could not provide Unfortunately, Wegener could not provide a satisfactory explanation for the force that a satisfactory explanation for the force that pushes or pulls the continents.pushes or pulls the continents.

Therefore, scientists rejected his theory.Therefore, scientists rejected his theory.

Climate CluesClimate Clues

Fossils of warm weather plants Fossils of warm weather plants were found on islands in the were found on islands in the Arctic Ocean. Arctic Ocean.

Wegener believed that these Wegener believed that these islands drifted from tropical islands drifted from tropical regions.regions.