Plate Tectonics

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Plate Tectonics

• Rearranging Earths Surface

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Tectonic Processes

• GOAL To understand the processes behind the
  distribution of Earths continents and oceans

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Tectonic Processes

• Alfred Wegener and how a scientific paradigm
  operates
• Structure of Earth allows continents to move
• Types of Plate Interactions
• Divergence
• Convergence
• Transform
• 4. Hot Spots

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1. Alfred Wegener and how a scientific paradigm
operates
"Scientists still do not appear to understand
sufficiently that all earth sciences must
contribute evidence toward unveiling the state of
our planet in earlier times, and that the truth
of the matter can only be reached by combing all
this evidence. . . It is only by combing the
information furnished by all the earth sciences
that we can hope to determine 'truth' here, that
is to say, to find the picture that sets out all
the known facts in the best arrangement and that
therefore has the highest degree of probability.
Further, we have to be prepared always for the
possibility that each new discovery, no matter
what science furnishes it, may modify the
conclusions we draw." Alfred Wegener. The Origins
of Continents and Oceans (4th edition)
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Field work Atlantic once closed
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Shape MatchRocks MatchFossils MatchLifetime of
work
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Theory of Continental Drift

• Meteorologist proposes
• to change geology

1st edition 1915
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Earlier, Sir Francis Bacon

• Wondered about similar shape of South America and
  Africa coastline

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Until 1960s Utter Rejection by Geologists
Dr. Rollin T. Chamberlin of the University of
Chicago said, "Wegener's hypothesis in general is
of the footloose type, in that it takes
considerable liberty with our globe, and is less
bound by restrictions or tied down by awkward,
ugly facts than most of its rival theories."
American Association of Petroleum Geologists
organized a symposium specifically in opposition
to the continental drift hypothesis.
"Utter, damned rot!" W.B. Scott, President of
the American Philosophical Society
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Today We Map Tectonic Plates
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Classroom Resources Folder
Today We Accept that most Earthquakes and
Volcanoes occur along boundaries of Tectonic
Plates
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Today We Accept Plate Movement
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Today We Accept Pangaeaand its breakup
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Resources
Pangaea Breakup

• Earth in the Future

Animation of Drift Over Time
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Online Video Presentations
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Why the opposition shift?

• An example of how a discipline can get locked
  into a pathway of mental thinking for decades
  (paradigm), rejecting the idea of moving
  continents.
• An example of how a discipline protects its
  turf rejecting the thoughts of a
  meteorologist.
• Enough time for the opponents to die, and a bunch
  of new geologists in the 1960s to challenge the
  establishment.
• Reminder throughout this class that ideas shift
  and much depends on the mental framework of the
  scientist

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2. Structure of Earth allows continents to move

• Wegener could not answer a fundamental question
  of HOW continents could move.

But geology advanced to the point to begin to
understand Earths internal structure how it
allows continental drift
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Structure and Internal Energy  

• Knowledge of Earths Interior is incomplete
  weve only explored about 1/1000 of Earths
  radius
• Inferential knowledge through monitoring of
  shockwaves transmitted through Earth from
  earthquakes or human-made explosions
• Four main zones of the Earths Interior
• Earths Core Deepest part of the Earth
• Inner Core supposedly solid, dense (iron/nickel
  or iron/silicate
• Outer Core (molten) liquid shell beneath the
  mantle that encloses the inner core

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Structure and Internal Energy (cont.)

• Earth in Cross Section
• 3. Earths Mantle Surrounds the outer core,
  largest of all four shells believe 3 zones
  within mantle
• Lithosphere uppermost zone of mantle crust
  together
• Asthenosphere plastic layer below lithosphere
• Mesosphere rigid part of mantle below
  asthenosphere
• 4. Earths Crust outermost layer mixed rock
  types
• Mohorovicic discontinuity (Moho) boundary
  between earths crust mantle

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Earth in Cross Section
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Earths Interior
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Earths Interior
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Core to Crust
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Earths Structure
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Brittle Crust Floats on Flowing Asthenosphere
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Different Crusts 5/6th submerged(isostatic
balance)

• Ocean Crust Continental Crust
• Dense (sima) Lighter (sial)
  

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ISOSTACYCrust adjusts to create a balance
(equilibrium)
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Human Induced Change
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2 continental plates under Tibet

• To reach isostatic
• balance, Tibet
• Plateau
• rises

Too thick, so get uplift
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Effects Of Erosion on Isostacy
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Earth oozes at different rates

• Asthenosphere flows

Even the crust adjusts
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Reason for Movement

• Excess heat from radioactive decay creates liquid
  outer core (and magnetic field), and forces
  mantle to have convection

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Exactly how mantle moves?

• ASU view

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Classroom Resources

• Animation of a theoretical model showing sinking
  crust and rising hot plumes all in the mantle

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3. TYPES OF PLATE INTERACTION

• Stream Systems on
• Dynamic Earth

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3. Type of Plate Interactionsa. Divergent
Boundaries

• Mid-ocean
• ridges are
• places of
• plate divergence

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Mid-Atlantic Ridge is the Icon
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• Mid
• Atlantic
• Ridge

• East
• Pacific
• Rise

• Mid Indian
• Ridge

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Why a ridge? Why not a Valley?

• Heat makes the large structure rise up, but at
  the axis there is a rift valley from spreading

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Sea Floor Spreading Key to Rejecting the Old Ways

• Plate Tectonics continental drift sea-floor
  spreading
• Rename the theory with new evidence
• Potassium-Argon dating
• Paleomagnetism

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Potassium - Argon Dating

• Discovery middle of ocean ridges youngest

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• Millions of years before present

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Classroom Resources

• Animation showing ages of ocean crust getting
  older away from spreading

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Paleomagnetism
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Classroom Resources

• Visualizing reversals of magnetic field and how
  this creates a mirror image on the two sides of a
  spreading center

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• Lava has minerals that record the magnetic field

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Paleomagnetism in Symmetry

• Conclusion
• was that
• Sea floors
• Spreading
• apart

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Source for Latest Info

• Website

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Continents can also spread

• Atlantic Opened up

Africa is Rifting
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Obvious question with making new sea floor, why
isnt Earth expanding?

• Old ocean plates undergo subduction

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3. Type of Plate Interactionsb. Convergent
Boundaries
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Oceanic-Continental Convergence

• Denser Oceanic Crust Subducts
• Trench Forms
• Volcanoes Form
• Lithosphere Subducts Into Asthenosphere
• Earthquakes Common All Along Boundary

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Andes
Cartoon

• Nazca plate collide with South American Plate

Recent Research from Nature
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Classroom Resources

• Visualizations about the Andes Mtns as from
  Convergence of Ocean Continental Plates

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• From the East-Pacific Rise, the Pacific plate
  moves towards subduction in the Aleutian Trench

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• Ocean-Cont.
• Convergence
• in Pacific
• Northwest

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Island Arcs from Ocean-Ocean Convergence
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Convergence of 2 continental plates

• Example of Himalaya

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Classroom Resources

• Animations of Himalaya Formation

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Formation of Appalachian Mountains resulted from
the collision of the African and European Plates
with North American Plate prior to 300 million
years ago.
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Ural Mountains
Formation of the Ural Mountains related to
collision tectonics prior to 300 Mya ago.
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Convergence Tsunami
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Effects Of Plate Locking
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EQ (or landslide or volcanic eruption) movement
generates the wave that travels about 500 mph
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Classroom Resources

• Shows how Tsunami can be made from subduction

Shows time sequence in Tsunami destroying coastal
city in Alaska
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Animated gif
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Mega-Quake Set off 2004 Tsunami will happen
again

• Energy ripple

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Sri Lanka
Sumatra Uplift
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Indonesia
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Indonesia
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Has Happened, Will Happen Again
In Classroom Resources Folder, Animation of Chile
EQ generating Tsunami that destroyed Hilo in 1960

• Hilo, 1960

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3. Type of Plate Interactionsc. Transform
Boundaries

• Side-by-side motion
• along San Andreas zone

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Transform motion of the San Andreas Fault can be
seen by offset of streams that cross the fault
zone.
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California Wont Fall into the Ocean

• Continent is 5/6ths submerged, so it is anchored
  very tight

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Classroom Resource

• Animation showing how there used to be
  convergence along the California coast, but it
  turned into a transform boundary

Animation of San Francisco Peninsula Topography
shows the gash of the San Andreas fault zone
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Other Transform Boundaries
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4. Hot Spots
Focus here on Hawaii
Often in the middle of a plate
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Hawaiian Hotspot
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Classroom Resources

• Animation of Hawaii as moves over Hot Spot

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Trail of the Hot Spot

• Note change in direction 43 myr ago

Change in direction 43 myr ago
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Alternative Hypothesis
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Online Visualizations

• Tsunami Visualizations
• http//serc.carleton.edu/NAGTWorkshops/visualizati
  on/collections/tsunami.html
• Plate Tectonic Movement Visualizations
• http//serc.carleton.edu/NAGTWorkshops/visualizati
  on/PTMovements.html
• Isostacy
• http//serc.carleton.edu/NAGTWorkshops/visualizati
  on/collections/IsoGrav.html
• Mountain Uplift
• http//serc.carleton.edu/NAGTWorkshops/visualizati
  on/collections/mouneros.html
• Earth History
• http//serc.carleton.edu/NAGTWorkshops/visualizati
  on/collections/geotime.html
• Mountain Building
• http//serc.carleton.edu/NAGTWorkshops/visualizati
  on/collections/orogeny.html