PLATE TECTONICSchapter 7

Interior of Earth

Core– Inner

• Solid Fe; under pressure

– Outer• Liquid Fe

Mantle– Solid; plastic

Crust– Solid; brittle– Si, O2

Plates

Lithosphere- rigid Asthenosphere- rock

that flows

Ocean plate- basalt, dense, thin

Continental plate- granite, less dense, thick

What is a plate?

How do we know what is inside the earth?

core

Outer- no S waves; liquid Magnetic field flip supports liquid outer core Overall density based on orbit Magnetic field= iron

Mantle

Tomography- look at how temp. differs

Volcanoes give us a “peek”

Crust

Directly sample (drill cores)

Sonograms (sound waves)

What moves the plates?

Convection currents

ALFRED WEGENERFather of Plate Tectonics

1880-1930

Studied Greenland’s weather

meteorologist

EVIDENCE FOR “CONTINENTAL DRIFT”

Shapes of continentsIdentical fossils separated by

oceansglacial deposits in tropicsMt. ranges with exact geology

separated by oceans

EVIDENCE FOR “CONTINENTAL DRIFT”

Shapes of continents

Same rock layers match across continents

Ancient climates

No one believed him- why not?

Didn’t know what moved the plates – (still questionable)

Didn’t know where the edge of plates were

Last photo of Wegner Died lost in

Greenland- 1930

NEW EVIDENCE Sonar (1960’s)-

mapped ocean floor

– age of ocean floor is young

– Mirror images of ages on each side of ridges

More “new” evidence

Pattern of earthquakes- outline edges of plates

Maybe Wegner was right!

“New” theory (1968) called

PLATE TECTONIC THEORY

Included:– “new” way plates

move

– “new” ocean evidence

Plate tectonics explains so much!

Location of…– Volcanoes– Earthquakes– Igneous rocks– Metamorphic rocks– Mountains– Folds and faults

PLATE BOUNDARIES

Where plates meet

DIVERGENT

Move apart rifts most under the sea- Mid Ocean Ridge, Red

Sea some continental- East African rift

Divergent boundaries

Fissure eruption

CONVERGENT BOUNDARIES

Move together

Ocean-ocean

Volcanoes form on ocean floor- create island arcs (volcanoes off coast)

trenches

Japan

Ocean-continental (subduction)

trenches composite volcanoes Volcanoes form on

continent

Mt. St. Helens

Continental-continental

Folded mountains- non-volcanic!

Himalayas

Mt. Everest

TRANSFORM(strike-slip)

Plates slide past each other shallow earthquakes

San Andreas Fault

What moves the plates?

Convection currents

Who gives a schist?

Predict earthquake areas Source for geothermal energy Find areas of mineral resources Predict future?