PLATE TECTONICS chapter 7

Interior of Earth 4 Core –Inner Solid Fe; under pressure –Outer Liquid Fe 4 Mantle –Solid; plastic 4 Crust –Solid; brittle –Si, O 2

Plates 4 Lithosphere- rigid 4 Asthenosphere- rock that flows 4 Ocean plate- basalt, dense, thin 4 Continental plate- granite, less dense, thick

What is a plate?

How do we know what is inside the earth?

core 4 Outer- no S waves; liquid 4 Magnetic field flip supports liquid outer core 4 Overall density based on orbit 4 Magnetic field= iron

Mantle 4 Tomography- look at how temp. differs 4 Volcanoes give us a “peek”

Crust 4 Directly sample (drill cores) 4 Sonograms (sound waves)

What moves the plates? 4 Convection currents

ALFRED WEGENER Father of Plate Tectonics

4 Studied Greenland’s weather 4 meteorologist

EVIDENCE FOR “CONTINENTAL DRIFT” 4 Shapes of continents 4 Identical fossils separated by oceans 4 glacial deposits in tropics 4 Mt. ranges with exact geology separated by oceans

EVIDENCE FOR “CONTINENTAL DRIFT” 4 Shapes of continents

Same rock layers match across continents

Ancient climates

No one believed him- why not? 4 Didn’t know what moved the plates – (still questionable) 4 Didn’t know where the edge of plates were

4 Last photo of Wegner 4 Died lost in Greenland- 1930

NEW EVIDENCE 4 Sonar (1960’s)- mapped ocean floor –age of ocean floor is young –Mirror images of ages on each side of ridges

More “new” evidence 4 Pattern of earthquakes- outline edges of plates

Maybe Wegner was right! 4 “New” theory (1968) called PLATE TECTONIC THEORY Included: –“new” way plates move –“new” ocean evidence

Plate tectonics explains so much! 4 Location of… –Volcanoes –Earthquakes –Igneous rocks –Metamorphic rocks –Mountains –Folds and faults

PLATE BOUNDARIES Where plates meet

DIVERGENT 4 Move apart 4 rifts 4 most under the sea- Mid Ocean Ridge, Red Sea 4 some continental- East African rift

Divergent boundaries

Fissure eruption

CONVERGENT BOUNDARIES 4 Move together

Ocean-ocean 4 Volcanoes form on ocean floor- create island arcs (volcanoes off coast) 4 trenches

Japan

Ocean-continental (subduction) 4 trenches 4 composite volcanoes 4 Volcanoes form on continent

Mt. St. Helens

Continental-continental 4 Folded mountains- non-volcanic!

Himalayas 4 Mt. Everest

TRANSFORM(strike-slip) 4 Plates slide past each other 4 shallow earthquakes

San Andreas Fault

What moves the plates? 4 Convection currents

Who gives a schist? 4 Predict earthquake areas 4 Source for geothermal energy 4 Find areas of mineral resources 4 Predict future?