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SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
•  Monday before class
•  folders outside of lecture hall
•  submit by first letter of FAMILY NAME
•  email submissions not accepted!
•  Q&A blog on Coursera!!
HOMEWORK PAGE
•  emailed questions on weekends may not
be answered
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
Why do continents have roots?
What keeps the lithosphere afloat?
SIO15-16: Lecture 4 Plate Tectonics
2 counteracting forces
•  gravity
•  buoyancy
isostatic equilibrium
•  forces are balanced
•  body floats
Image: S. Marshak “Earth, Portrait of a Planet”
!  rigid lithosphere floats on soft asthenosphere
!  asthenosphere reacts to imbalance (flows)
SIO15-16: Lecture 4 Plate Tectonics
•  lithosphere is broken up
into 12 major plates
•  move about (a few cm per year)
•  driven by mantle convection
•  divergent
•  convergent
•  transform
Mendocino
Triple Junction
SIO15-16: Lecture 4 Plate Tectonics
Image: P. Abbott “Natural Disasters”
•  lith. formed at MORs
•  lith. consumed in subduction zones
•  same rate
•  plates move a few cm/yr
•  earthquakes
•  volcanism
•  mountain building and other features on Earth’s surface
SIO15-16: Lecture 4 Plate Tectonics
ridge push
slab pull
slab pull more dominant
SIO15-16: Lecture 4 Plate Tectonics
SIO15-16: Lecture 4 Plate Tectonics
slab pull
How do we know that plates move sideways?
•  Alfred Wegener, 1915
•  continents like jigsaw puzzle
•  fossil records match across oceans
•  geologic units match across oceans
•  apparent polar wander curves
don’t match
SIO15-16: Lecture 4 Plate Tectonics
•  magnetic north 2000 at:
81.5ºN, 111.4ºW
Shape:
like that of bar magnet (dipole)
Observables:
strength, declination, inclination
Origin:
currents in metallic liquid outer core
-> magnetic dynamo
Time Evolution:
changing field; reversals
SIO15-16: Lecture 4 Plate Tectonics
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