Chapter 2 plate tectonics
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Chapter 2: Plate Tectonics. Tectonic Plates of Earth. Pangaea. Pangaea: Pan = all Gaea = Earth Panthalassa Thalassa = sea AKA Tethys Sea. Continental Drift. Progressive breakup of Pangaea into modern continents Similar to sea ice. Wegner’s Evidence.

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Pangaea
Pangaea

  • Pangaea:

    • Pan = all

    • Gaea = Earth

  • Panthalassa

    • Thalassa = sea

    • AKA Tethys Sea


Continental drift
Continental Drift

  • Progressive breakup of Pangaea into modern continents

  • Similar to sea ice


Wegner s evidence
Wegner’s Evidence

  • Present-day shorelines fit like puzzle pieces

  • Better fit from continental shelves


Fossil evidence
Fossil Evidence

  • Identical fossils present in S. Amer. & Africa

  • e.g. Mesosaurus

  • e.g. Glossopteris

  • e.g. Marsupials


Geologic evidence
Geologic Evidence

  • Identical rocks on different continents

    • e.g. 2.2Ga igneous rocks in Brazil & Africa

  • Similar Mountain Ranges

    • e.g. Appalachian Mts ~ Caledonian Mts


Mesozoic supergroup

Identical package of rocks & fossils found in S.Amer., Africa, Australia & Antarctica

Mesozoic Supergroup


Paleoclimatic evidence
Paleoclimatic Evidence Africa, Australia & Antarctica

  • Paleo = ancient

  • Climate = weather conditions

  • Glacially transported sediments

  • Glacial striations


Rejection of continental drift hypothesis
Rejection of Continental Drift Hypothesis Africa, Australia & Antarctica

  • No evidence of continents “breaking through” oceanic crust

  • Tidal forces necessary would halt Earth’s rotation

  • Danish scientists found no astronomical evidence of drift from 1927-1948


Earth s magnetic field
Earth’s Magnetic Field Africa, Australia & Antarctica

  • Similar to bar magnet

  • Magnetic materials align themselves to magnetic field


N s orientation dip

Magnetic orientation has 2 dimensions Africa, Australia & Antarctica

North-South

Dip angle (Inclination)

Curie point (T)

Fossil Magnetism / Paleomagnetism

N-S Orientation & Dip


Magnetic inclination

Magnetization = degrees from N pole Africa, Australia & Antarctica

Magnetization + Latitude = 90°

e.g. Lavas from Puerto Rico show 75 ° from N pole & Puerto Rico = 15 ° from equator

Magnetic Inclination


Apparent polar wander
Apparent Polar Wander Africa, Australia & Antarctica


Seafloor spreading
Seafloor Spreading Africa, Australia & Antarctica


Paleomagnetism
Paleomagnetism Africa, Australia & Antarctica


Progression of seafloor spreading
Progression of Seafloor Spreading Africa, Australia & Antarctica


Plate boundaries
Plate Boundaries Africa, Australia & Antarctica


Plate boundaries1
Plate Boundaries Africa, Australia & Antarctica

  • Corresponds to Earthquakes & Volcanoes


Plate boundaries2
Plate Boundaries Africa, Australia & Antarctica

  • Three Types

    • Divergent

      • AKA Rift

    • Convergent

      • AKA Subduction

    • Transform

      • AKA Strike-slip


Divergent boundaries
Divergent Boundaries Africa, Australia & Antarctica

  • AKA Spreading Centers

  • AKA Rifts

  • Largest mountain chains

  • Plates move apart due to eruption of lava

    • New lava = new oceanic crust

  • Oldest oceanic crust 180Ma


Pillow basalts
Pillow Basalts Africa, Australia & Antarctica

  • Form when lava extruded under water

  • Immediately outer layer freezes

  • New material pushes through like toothpaste


Continental rifting

Rifts also can form in continental settings Africa, Australia & Antarctica

Linear depressions

Lakes, valleys, etc.

Asthenosphere thins due to tension

e.g. East Africa Rift Zone, Mt. Kilimanjaro

Continental Rifting


Continental rifting con t
Continental Rifting (con’t) Africa, Australia & Antarctica

  • If tension continues, eventually continental rift develops into oceanic spreading

  • e.g. Red Sea, Sea of Cortez


Convergent boundaries
Convergent Boundaries Africa, Australia & Antarctica

  • Old oceanic crust dense & heavy

  • Heavy vs. light => subduction

  • AKA destructive margins

  • Large earthquake & explosive volcanoes

  • Melting triggered at ~100km depth


Oceanic oceanic convergence
Oceanic-Oceanic Convergence Africa, Australia & Antarctica

e.g. Virgin Islands, Japan, Philippines


Oceanic continental
Oceanic-Continental Africa, Australia & Antarctica

e.g. Andes, MesoAmerica, Italy


Continental continental
Continental-Continental Africa, Australia & Antarctica

e.g. India


Hot spots
Hot Spots Africa, Australia & Antarctica

  • Caused by mantle plumes

  • Plumes do not move, plates do

  • Bend at 40Ma

    • Major change in plate motion


Relative plate motions
Relative Plate Motions Africa, Australia & Antarctica

  • Relative to Hot Spots & other plates

  • Measure motions with Paleo-magnetism


Forces driving plate motions
Forces Driving Plate Motions Africa, Australia & Antarctica

  • Convection of Mantle

  • Upwelling Mantle

    • Ridge-push

  • Slab Suction

    • AKA Slab-pull


Layer cake model
Layer-Cake Model Africa, Australia & Antarctica

  • Two zones of convection, above & below ~660km

  • Explains why mid-ocean ridge basalt different than hot spot basalt


Whole mantle convection
Whole Mantle Convection Africa, Australia & Antarctica

  • Cold oceanic crust descend to bottom of mantle, “stirring” it

  • Hot plumes rise from core-mantle boundary

    • Bring “primitive” mantle to surface

  • Not popular b/c complete mixing in 100s Ma


Deep layer model
Deep Layer Model Africa, Australia & Antarctica

  • Heat from Earth’s interior causes two layers to shrink & swell

    • Similar to lava lamp

  • Small amt of material rises to surface to create hot spots

  • Little seismic evidence to support this model


Importance of plate tectonics
Importance of Plate Tectonics Africa, Australia & Antarctica

  • First theory to provide comprehensive view & explain:

    • Earth’s major surficial processes

    • Geologic distribution of earthquakes, volcanoes & mountain ranges

    • Distribution of mineral resources & ancient organisms


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