Earthquakes and Plate TectonicsEarthquakes and Plate Tectonics

Global Problems in GeologyGlobal Problems in Geology

Distribution of Continents

Mid-ocean Ridges

Trenches

Orogenic BeltsOrogenic Belts

• Deformation

• Metamorphism

• Volcanism

• Earthquakes

Development of Continental Development of Continental

DriftDrift

• Lots of people had noticed that the

coastlines of Africa and South America are

similar

• Frank Taylor (1910) • Frank Taylor (1910)

• Alfred Wegener (1912) Die Entstehung

Der Kontinente Und Ozeane

JigsawJigsaw--Puzzle Fit of Puzzle Fit of

ContinentsContinents

• Continental Fit

Fit of Fit of

Continents Continents

Across the Across the

AtlanticAtlanticAtlanticAtlantic

Atlantic 65 m.y. agoAtlantic 65 m.y. ago

Present Day AtlanticPresent Day Atlantic

Wegener’s Wegener’s

TheoryTheory

Theory of Plate TectonicsTheory of Plate Tectonics

Plate TectonicsPlate Tectonics

Plate BoundariesPlate BoundariesPlate BoundariesPlate Boundaries

Causes of Plate TectonicsCauses of Plate Tectonics

What is Plate TectonicsWhat is Plate Tectonics

• The Earth’s crust and upper

mantle are broken into

sections called platessections called plates

• Plates move around on top of

the mantle like rafts

The LithosphereThe Lithosphere

The crust and the upper layer of the

mantle together make up a zone of rigid,

brittle rock called the Lithosphere.

The Asthenosphere

The asthenosphere is the semi-rigid part of the middle mantle that flows like hot asphalt under a heavy heavy weight.

Plate TectonicsPlate 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.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.

The The LithosphericLithospheric PlatesPlates

The crust of the Earth is broken into many pieces

called plates. The plates "float" on the soft, semi-rigid asthenosphere.

What is the What is the LithosphereLithosphere??

• The crust and part of the upper

mantle = lithosphere

–100 km thick –100 km thick

–Less dense than the material

below it so it “floats”

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

• Plates are

made of rigid

lithosphere.lithosphere.

The lithosphere is made

up of the crust and the

upper part of the mantle.

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

• Below the

lithosphere lithosphere

(which makes

up the tectonic

plates) is the

asthenosphere.

What is the What is the AsthenoshereAsthenoshere??

• The plastic layer below the

lithosphere = asthenosphere

• The plates of the lithosphere• 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 • Continental plates - plates

below the continents

Plate BoundariesPlate Boundaries

• Divergent

Three types of plate boundary

• Convergent

• Transform

Divergent BoundariesDivergent Boundaries

• Boundary between two plates

that are moving apart or rifting

� �� �

• RIFTING causes SEAFLOOR

SPREADING

• Divergent boundaries are also present

– under continents during the early stages

– of continental breakup

Divergent BoundariesDivergent Boundaries

�� Beneath a Beneath a continent, continent, continent, continent,

�� magma wells magma wells up, and up, and

�� the crust is the crust is initially initially �� elevated, elevated,

�� stretched stretched

�� and thinnedand thinned

• The stretching produces fractures and rift valleys.

Rift ValleyRift Valley

�� During this During this stage, stage,

�� magma typicallymagma typically�� magma typicallymagma typically

�� intrudes into the intrudes into the fracturesfractures

�� and flows onto and flows onto the valley floorthe valley floor

�� Example: East Example: East African Rift African Rift ValleyValley

Features of Divergent Features of Divergent

BoundariesBoundaries• Mid-ocean ridges

• rift valleys

• fissure volcanoes• fissure volcanoes

Divergent Boundaries

• Spreading ridges

– As plates move apart new material is erupted to

fill the gap

Convergent BoundariesConvergent Boundaries

• Boundaries between two

plates that are colliding

� �� �

• There are 3 types…

ContinentContinent--Continent BoundaryContinent Boundary

• Two approaching continents are initially – separated by ocean floor that is being

subducted

– under one of them, which, thus, has a volcanic arc

• When the 2 continents collide �� Its density Its density • When the 2 continents collide

– the continental lithosphere cannot subduct�� Its density Its density is too low,is too low,

�� although although one one continent continent may partly may partly slide under slide under the otherthe other

Type 1Type 1

• Ocean plate colliding with a less dense continental plate

• Subduction Zone: where the less dense plate slides under less dense plate slides under the more dense plate

• VOLCANOES occur at subduction zones

Andes Mountains, Andes Mountains,

South AmericaSouth America

Type 2Type 2

• Ocean plate colliding with

another ocean plate

• The less dense plate slides • The less dense plate slides

under the more 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:• Have Collision Zones:

–a place where folded and thrust

faulted mountains form.

The 6,000-km-plus journey of the India

CARTOON SECTION SHOWING INDIA ASIA COLLISION

Island Arc-Continent Collision Mountain BuildingCollision Belts

Continent-Continent Collision Mountain Building

Transform Fault BoundariesTransform Fault Boundaries

• Boundary between two plates

that are sliding past each other

• EARTHQUAKES along faults• EARTHQUAKES along faults

San Andreas Fault, CASan Andreas Fault, CA

Causes of Plate Causes of Plate

TectonicsTectonicsTectonicsTectonics

Convection CurrentsConvection Currents

• Hot magma in the Earth

moves toward the surface,

cools, then sinks again.cools, then sinks again.

• Creates convection currents

beneath the plates that cause

the plates to move.

Plate MovementPlate Movement

• “Plates” of lithosphere are moved around by

the underlying hot mantle convection cells