Plate TectonicsPlate Tectonics

Alfred WegenerAlfred Wegener

• German Scientist

• Ph.D in astronomy, interested in meteorology and climatology

• Served in German Army weather service

• Proposed supercontinent Pangea separated 200 mya

Evidence for his theoryEvidence for his theory

1) Similar coastlines (jigsaw puzzle)

Evidence for his theoryEvidence for his theory

2) Identical fossils along joining coasts– Ex. South America and Africa

Evidence for his theoryEvidence for his theory

3) Identical age and rock types along joining coasts– Ex. Brazil and West Africa

4) Similar mountain chains across joining coasts– Ex. Appalachians and mountains in Scotland and Northern

Europe

5) Climactic changes in geologic record– Pangea over south pole = glaciers in South Africa and South

America– Tropic or subtropic swamps in NA = coal deposits in WV and

WY

Wegener’s ProblemWegener’s Problem

• No mechanism to cause continental drift

• Proposed continents were moving through the ocean’s crust by centrifugal and tidal forces

• If so, continents would be deformed• There isn’t enough force from either to move continents

• His theory was not accepted until after his death

Later SupportLater Support

6) Sea floor spreading– Found young rocks along Mid-Atlantic ridge in 1947– Ridge is a break in Earth’s crust– Ocean floor is separating and new crust is forming– Ocean floor moving = continents moving

• Animation: http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm

http://wrgis.wr.usgs.gov/docs/parks/animate/A48.gif

Later SupportLater Support

7) Paleomagnetism– Earth as a giant magnet– Arrangement of minerals along mid-ocean ridges– Bands of rock oriented toward N or S pole– Dating rocks supports EM reversals in the past– His hypothesis was fully supported

Plate Tectonics Plate Tectonics

• Continental crusts and oceanic crust

• Lithosphere – crust and upper mantle-The lithospheric plates float on the

asthenosphere, carrying the continents with them

• There are 8 large plates and 9 small plates

• Some are moving towards each other, some away and some are sliding past each other– This movement has made most major surface features on the

earth• Ex. Mountains ranges, trenches

Plate BoundariesPlate Boundaries

• 3 Types– Divergent – Convergent– Transform

DivergentDivergent

• Where plates move in opposite directions– Sea floor spreading (ocean ridges)– Creates Rift Zones, on land they’re called rift

valleys– Asthenosphere rises to take up the space

• Ex. Mid-Atlantic ridge; Rift Valley, Africa

Divergent BoundaryDivergent Boundary

Convergent Boundaries Convergent Boundaries

• Where two plates are colliding – Located on the opposite side of plates from

divergent boundaries

• 3 Types– Oceanic – Continental– Continental – Continental– Oceanic – Oceanic

Oceanic - ContinentalOceanic - Continental

• Creates a Subduction Zone– Oceanic crust is denser and pushed beneath continental

crust (subduction)• Forms a trench

• Oceanic crust heats up, releases water, and causes the mantle to melt

• Magma produced then rises and forms volcanic mountains– Ex. Andes Mountains, South America

Subduction ZoneSubduction Zone

Continental - ContinentalContinental - Continental

• Plates have same density, so neither is subducted

• Are crumpled and uplifted

• Forms mountains– Ex. Himalayas

Oceanic - OceanicOceanic - Oceanic

• One plate is subducted

• Forms a trench

• Subducted oceanic crust melts, releases water and causes magma to rise and make a chain of volcanic islands

(Island Arc)

Transform Boundaries Transform Boundaries

• Where plates slide past one another

• Grind as they pass each other in short quick movements, causing earth quakes– Ex. San Andreas Fault, CA

Carrizo Plain, CA (san Andrea Fault)Carrizo Plain, CA (san Andrea Fault)

Causes for plate motion Causes for plate motion

• Convection– Seen in boiling water– Movement of material due to temperature

differences– Act like conveyor belts that the plates ride on

Microplate Terranes (Suspect Microplate Terranes (Suspect Terranes) Terranes)

• Continents made of a variety of lithospheric chunks, each with a different geologic history

Theory of Continental DriftTheory of Continental Drift

• Alfred Wegener (German Scientist)– Proposed hypothesis that all the continents

were once part of one large land mass called Pangaea (all lands)

• 200 MYA they started to separate and have led to the world we see today

EvidenceEvidence

• Coastlines fit together like a jigsaw • Identical fossils found along joining coasts

– Ex. South American and Africa

• Age and rock types along joining coasts– Ex. Brazil and West Africa

• Similar mountain chains – Appalachians and mountains in Scotland and Northern Europe

• Climactic changes seen in the geologic record– Thought that Pangaea was once positioned over the South Pole

• Ex. Glaciers in southern Africa and South America, • Coal deposits in North America (land was once covered with tropical

or subtropical swamps)

http://upload.wikimedia.org/wikipedia/commons/8/8e/Pangea_animation_03.gif

Seafloor SpreadingSeafloor Spreading

• Areas along sea floor where plates are separating

• Cause a underwater mountain range

• Actually is a rift, or break in the crust

• New magma rises to fill the gap– Mid-Atlantic Ridge

PaleomagnetismPaleomagnetism

• Earth is one giant magnet

• As minerals rise and solidify in crust, they orient themselves toward the N pole

• Found rock bands along these ridges that were oriented toward the S pole

• Suggests that the Earth’s magnetic poles have switched throughout history

SourcesSources

• http://www.platetectonics.com/book/images/Pangaea.gif• http://www.geo.lsa.umich.edu/~crlb/COURSES/270/Lec12/spreexamples.jpeg• http://www.windows.ucar.edu/earth/images/seafloor_spreading.jpg• http://www.physicalgeography.net/fundamentals/images/seafloor_spreading.gif• http://www.msu.edu/~bausemic/geo/seafloor.jpg• http://quake06.stanford.edu/centennial/tour/images/11-04-fig4.jpg• http://www.howard.k12.md.us/res/beginnings/pangea.jpeg• http://www.calstatela.edu/faculty/acolvil/plates/magnetic_field.jpg• http://www.noc.soton.ac.uk/gg/classroom@sea/general_science/images/plates_map_lge.jpg• http://www.livescience.com/images/050104_cascadia_subduction_03.gif• http://geology.uprm.edu/Morelock/1_image/volmtn.jpg• http://www.100gogo.com/cya.jpg• http://geology.com/records/ocean-trench.gif• http://pubs.usgs.gov/gip/earthq1/san_andreas.gif• http://sepwww.stanford.edu/oldsep/joe/fault_images/FT02.3.gif• http://www.geo.lsa.umich.edu/~crlb/COURSES/107-EQandVolcanoes/Lec5/transform.jpeg• http://www.heritage.nf.ca/environment/images/cell.gif• http://energy.usgs.gov/images/geothermal/geothermal_lithoplatesLG.gif