The Theory of Plate Tectonics

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The Theory of Plate Tectonics
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Levels of Scientific Understanding

• Observation
• Idea
• Hypothesis
• Theory
• Fact

• round moon, sun,
  planets
• could the earth be
  round?
• curved horizon,
  different stars
• astronomers
  navigators
• Magellan, space
  flight

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History of Plate Tectonics Theory

• Early Ideas
• Continental Drift Hypothesis
• Atlantic Ocean Discoveries
• Theory of Sea Floor Spreading
• Role of Benioff Zones
• Theory of Plate Tectonics
• Is it a Fact?

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Early Ideas

• Similar shoreline geometry of South
• America and Africa
• Were they connected at one time?
• Impossible!

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Continental Drift Hypothesis

• Alfred Wegener (about 1912)
• Jigsaw puzzle fit of continents
• Similar structures at connection points
• Similar ancient rock sequences
• Similar fossil species
• Changing climate patterns
• How could continents possibly move?

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Atlantic Ocean Discoveries

• 1950's - Exploration of the Atlantic for
• military and economic purposes
• Discovery of the Mid-Atlantic Ridge
• Sediment thickness patterns
• Type of bedrock
• Age of bedrock

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Theory of Seafloor Spreading

• 1960 by Hess and Deitz
• The Mid-Atlantic Ridge is being pulled apart by a
  series of fissure eruptions. Each pull-apart
  creates new lithosphere and makes the Atlantic a
  little wider.
• The continents on either side of the Atlantic are
  moving apart!

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Role of Benioff Zones

• Discovered in 1927 by Benioff but applied to
• the Plate Tectonic Theory in the 1960's
• Explained the crustal balance problem created
• by the Theory of Seafloor Spreading
• Zone of progressively deeper earthquakes along
• continent margins and island arcs

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Theory of Plate Tectonics

• Earth's structure (crust, mantle, core)
• The Plates (lithosphere/asthenosphere)
• Convection as the driving force
• Plate Boundaries (convergent, divergent,
• transform)

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Theory of Plate Tectonics

• The lithosphere is divided into a series of
  plates that move and interact with one another to
  generate earthquakes, volcanoes, ocean trenches,
  mountain ranges, and the creation of new
  lithosphere.

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Plate Boundary Types

• Divergent (oceanic)
• Divergent (continental)
• Convergent (oceanic - continental)
• Convergent (oceanic - oceanic)
• Convergent (continental - continental)
• Transform

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Divergent (oceanic)

• Examples Mid-Atlantic Ridge
• other mid-ocean ridges
• Effects volcanoes (fissure eruptions)
• earthquakes
• creation of new lithosphere
• widening ocean basin

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Divergent (continental)

• Examples East Africa
• Red Sea
• Effects earthquakes
• faulting / rift valley
• lake / sea / ocean basin
• some volcanic activity

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Convergent (oceanic - continental)

• Examples Washington/Oregon Coast
• Andes
  
• Effects volcanoes
• earthquakes
• ocean trench
• mountain building
• lithosphere destroyed

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Convergent (oceanic - oceanic)

• Examples Japan
• Aleutian Islands
  
• Effects earthquakes
• volcanoes
• island chain
• ocean trench
• lithosphere destroyed

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Convergent (continental - continental)

• Examples Himalaya Mountain Range
• Appalachian Mountain
  Range
• Effects crustal deformation
• mountain building
• faulting
• earthquakes
• rare volcanoes

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Transform

• Example San Andreas Fault Zone
• Effects recurrent earthquakes
• faulting