GEOLOGY 101

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GEOLOGY 101

• Today Chapter 4
• The Way the Earth Works Plate Tectonics

Instructor Professor Matt Fouch Email
fouch101_at_asu.edu Office PSF-540 Phone x5-9292
TA Kara Krelove Email kara.krelove_at_asu.edu Offic
e PSF-209
Course Website http//fouch101.asu.edu
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Continental drift and paleomagnetism
PLATE TECTONICS
Sea floor spreading
Harry Hess and Bob Dietz, in the early 1960s
proposed

• ocean ridges are above mantle upwellings, which
  cause seafloor to spread, like a conveyor belt
• magma replaces seafloor as it moves away,
  becoming new oceanic crust
• deep ocean trenches are locations where oceanic
  crust dives back into planet

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Continental drift and paleomagnetism
PLATE TECTONICS
Seafloor magnetic stripes

• 1963, Vine Matthews connected seafloor
  spreading continental drift, from magnetic
  field reversals recorded in cooling lavas of new
  seafloor
• symmetric patterns (stripes) on either side of
  spreading center (mid-ocean ridge)
• changes in width of a given stripe indicate
  changes in spreading rate.

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Continental drift and paleomagnetism
PLATE TECTONICS
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Modern ideas
PLATE TECTONICS
Plate tectonics theory

• In 1965, J. Tuzo Wilson recognized plates
• In 1968, Isacks, Oliver, and Sykes created a new
  list of global earthquake locations, and showed
  how their distribution explains motion/behavior
  of Earths lithosphere
• explains mechanisms of continental drift,
  seafloor spreading, and subduction
• explains global patterns of earthquakes,
  including deep subduction zone quakes

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Modern ideas
PLATE TECTONICS
Plate tectonics

• about a dozen plates

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Earths Major Plates(about a dozen major plates)
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3 types

• divergent boundaries
• convergent boundaries
• transform fault boundaries

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Basic Plate Boundaries

• Geologists define three types of plate boundary,
  based simply on the relative motions of the
  plates on either side of the boundary.
• Animation gtgt

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• Divergent boundaries

Mostly mid-ocean ridges (seafloor spreading)
Typical spreading rates 5 cm/year (1-20
cm/year range) As oceanic moves away from ridge,
it cools, becomes denser Also found where
continents break apart Example Red Sea
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Fig.4.07
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Fig.4.08
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Fig.4.10
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Fig.4.11a
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Deploying ALVIN
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Fig.4.09
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Life Near Mid-Ocean Ridges
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The Process of Rifting

• Rifting is the process by which a continent
  splits and separates to form a new divergent
  boundary. This animation shows the progressive
  formation and evolution of a continental rift,
  and the formation of a mid-ocean ridge.
• Animation gtgt

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Plate boundaries
PLATE TECTONICS
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The Gulf of California Formed by Rifting of Baja
California from Mainland Mexico
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Plate boundaries
PLATE TECTONICS

• Convergent boundaries

Subduction zones ocean-continent ocean-ocean
continent-continent
- Accretionary wedge Examples W. coast of
S. America
- Volcanic island arcs Examples Marianas,
Aleutians, Tonga
- Continental crust shortens/thickens
Examples Himalayas, Alps, Appalachians
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ocean-continent ocean-ocean
continent-continent
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The Process of Subduction

•  At convergent plate boundaries or convergent
  margins, two plates move toward each other.
• Rather than butting each other like angry rams,
  one oceanic plate bends and begins to sink down
  into the asthenosphere beneath the other plate.
• This sinking process is termed subduction.
• Animation gtgt

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Formation of Accretionary Prisms
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Convergent MarginsAlaskan Volcanoes
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Fig.4.15b
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Plate boundaries
PLATE TECTONICS

• Transform fault boundaries

Strike-slip faulting Plates slide past each
other no production/destruction of
material they connect mid-ocean ridge segments

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Spreading Centers Offset by Transform Boundary
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The Process of Subduction

•   This animation shows the development of a
  transform fault along a divergent plate boundary.
• Plates slide past one another along a transform
  fault without the formation of new plate or the
  consumption of old plate.
• As this process occurs, new sea floor forms along
  the mid ocean ridge.
• Animation gtgt

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San Andreas Fault