Plate TectonicsPlate Tectonics

DefinitionDefinition

Plate: Tectonic:

Rigid, rocky outer surface of the Earth

To build or destroy

The processes by which the rocky plates of the planet move

and interact with each other

Internal Structure of the EarthInternal Structure of the Earth

lithosphere

mantle

inner core

outer core

plates

solid iron

hot dense rock

liquid iron

Lithospheric PlatesLithospheric PlatesOceanic:

thin, heavy, mostly lava flows

Continental:

thick, light, mostly granite

Asthenosphere

Weak, plastic upper mantle

Lithospheric PlatesLithospheric Plates

Diverging Plate BoundariesDiverging Plate BoundariesWhere plates pull apart from each other

Stretching & thinning

High heat flow

(New Crust Created)

Diverging Plate BoundariesDiverging Plate BoundariesKey landform: mid-oceanic ridges

volcanic mt. ranges

1000’s miles long

1-2 miles tall

axial valley

Converging Plate BoundariesConverging Plate Boundaries

Where plates collide

Subduction zone: collision between oceanic and continental lithosphere

(Crust Destroyed)

Subduction zonesSubduction zonesKey landforms:

trenches & volcanic arcs

Transform Plate BoundariesTransform Plate Boundaries

Where plates slide side by side

Key landform: faults

(Crust neither destroyed or created)

Driving ForceDriving Forcethermal convection / convection currents

hot rock

plates spread away

cold rock

pushes up at ridges

plate sinks and subducts

Volcanism: C, D

Earthquakes: C, D, T

Rock Deformation: C, D, T

Geologic activity at plate marginsGeologic activity at plate margins

Evidence: shape of continentsEvidence: shape of continents

SouthAmerica

Africa

The margins of some continents

look like they could fit together

First proposed by Alfred Wegner

Fossil EvidenceFossil Evidence

Evidence: volcanoesEvidence: volcanoes

Nonrandom occurrence of volcanic activity

Evidence: earthquakesEvidence: earthquakes

x xx

x xx

xx x

x

Nonrandom occurrence of earthquakes

deep at converging margins

Shallow at diverging margins

Evidence: hot spotsEvidence: hot spotsStationary upwellings of heat away

from plate margins

Evidence: hot spotsEvidence: hot spots

As plates move, the volcanoes are carried away from the hot spot

Can determine direction and speed of the plate motion

Only volcanoes near the hot spot are are active

Evidence: age of seafloor rocksEvidence: age of seafloor rocks

Youngest rocks are found at the mid oceanic ridges

Oldest rock are found farthest from the ridge

Evidence: paleomagnetismEvidence: paleomagnetism

Earth has a strong magnetic field

Iron rich volcanic rocks record Earth’s magnetic field at the time

they form

seafloor paleomagnetic recordseafloor paleomagnetic record

Bands of alternating polarity

Symmetrical about the mid oceanic ridges

seafloor paleomagnetic recordseafloor paleomagnetic record

lava forming at the ridges picks up the current magnetism, then gets pushed out

of the way as newer lava forms

Records of the growth and spreading of the

seafloor

seafloor paleomagnetic recordseafloor paleomagnetic record

The alternating polarity represents complete reversals of Earth’s

magnetic field

The location of magnetic poles on The location of magnetic poles on separate continents appear to wander separate continents appear to wander

with timewith time

continental paleomagnetic recordcontinental paleomagnetic record

If the poles haven’t moved significantly, then the continents

didUse overlapping poles to reconstruct the past positions of the continents

Plate Tectonics in the PNWPlate Tectonics in the PNW

0 20 0

k m

M t M e a g e r

M t C ay le y

M t G ar ib al d i

M t B ak er

G la cie r P ea k

M t R ai n ier

M t A d a m sM t S t H e l e n s

M t H o o d

M t J e f fe rs o n

T h r e eS is te r s

C ra ter L a ke

M t M c L o u g h in

M t S h as ta

L as s e n P e ak

Sa n

And

reasFa ul t

Juan

deFu

caNorth American

Pacific

Cascadia subduction

zone

Plate Tectonics in the PNWPlate Tectonics in the PNW

HighCascadesvolcanoes Western

CascadesWillamette valley

CoastRange

Deschutes basin

ocean

subducting oceanic plate

partialmelting

60 miles

150 milesWest East

Pacific

Cross section of the Cascadia Subduction zone

Cascades volcanic arc

Plate Tectonics in the PNWPlate Tectonics in the PNW

0 20 0

k m

M t M e a g e r

M t C ay le y

M t G ar ib al d i

M t B ak er

G la cie r P ea k

M t R ai n ier

M t A d a m sM t S t H e l e n s

M t H o o d

M t J e f fe rs o n

T h r e eS is te r s

C ra ter L a ke

M t M c L o u g h in

M t S h as ta

L as s e n P e ak

Sa n

And reas

Fa ul t

Juan

deFu

caNorth American

Pacific

Juan de Fuca & Gorda mid ocean

ridges

Plate Tectonics in the PNWPlate Tectonics in the PNW

0 20 0

k m

M t M e a g e r

M t C ay le y

M t G ar ib al d i

M t B ak er

G la cie r P ea k

M t R ai n ier

M t A d a m sM t S t H e l e n s

M t H o o d

M t J e f fe rs o n

T h r e eS is te r s

C ra ter L a ke

M t M c L o u g h in

M t S h as ta

L as s e n P e ak

Sa n

An

d reasFa ul t

Juan

deFuca

North American

Pacific

Blanco & Medocino

fracture zones

Plate Tectonics in the PNWPlate Tectonics in the PNW

“exotic terranes

islands carried by the plates

Attached to the North America continent

seafloor paleomagnetic recordseafloor paleomagnetic record

Bands of alternating polarity

Symmetrical about the mid oceanic ridges

Evidence: paleo-environmentsEvidence: paleo-environments

deserts

glacial

coral reefs

deserts

glacial

desert

desert

glacial

tropics

Evidence: distribution of mountainsEvidence: distribution of mountains

Importance of Plate TectonicsImportance of Plate Tectonics