Lake City Community College Earth Science, 11e

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Lake City Community CollegeEarth Science, 11e

• Edward J. Tarbuck Frederick K. Lutgens

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Plate TectonicsChapter 8

• Earth Science, 11e
• Stan Hatfield and Ken Pinzke
• Modified by Dr. Kane

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Continental drift It started it all

• Alfred Wegener
• First proposed hypothesis, 1915
• Published The Origin of Continents and Oceans
• Continental drift hypothesis
• Supercontinent called Pangaea began breaking
  apart about 200 million years ago
• Continents "drifted" to present positions
• Continents "broke" through the ocean crust

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Did you know?

• The Appalachian Mountain formed 300 million years
  ago during the formation of Pangaea

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Pangaea approximately 200 million years ago
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Continental drift an idea before its time

• Wegener's continental drift hypothesis
• Evidence used by Wegener
• Fit of South America and Africa
• Fossils match across the seas
• Rock types and structures match
• Ancient climates

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Wegeners matching of mountain ranges on
different continents
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Paleoclimatic evidence for Continental Drift
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Was Wegener a visionary or a dreamer?

• Would you object or agree with Wegeners idea?
• If you had a chance what question would you ask
  Wegener?

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What was missing?

• Main objection to Wegener's proposal was its
  inability to provide a mechanism

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Then came Harry Hess

• Used fathometer to explore the ocean floor
• Discovered the ocean crust is made of basalt not
  granite
• Discovered the mid-ocean ridge
• Found that the seafloor grows from the mid ocean
  ridge (seafloor spreading)
• Found that the continental plates drift from the
  mid-ocean ridge over the mantle

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Did Hess explain it all?

• Did Hess provide the mechanism to support
  Wegeners idea of Continental Drift?
• How?

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Then came Vine and Matthews

• Used Paleomagnetic reversals to confirm seafloor
  spreading
• Used age of seafloor rocks to confirm seafloor
  spreading (seafloor rocks get older as you move
  away from the mid-ocean ridge)
• Discovered Polar Wandering

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Paleomagnetic reversals recorded by basalt flows
at mid-ocean ridges
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Apparent polar-wandering paths for Eurasia and
North America
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The Unified Theory

• Unifying Continental Drift and Seafloor Spreading
  into on theory The Plate Tectonics Theory. It
  says
• The lithosphere is broken into plates that move
  over the Asthenosphere
• Whats the lithosphere?

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Plate tectonics the new paradigm

• The lithosphere consists of several plates
• Plates are moving slowly over the mantle
• Largest plate is the Pacific plate
• Many plates are beneath the ocean
• Earthquakes, volcanoes, mountains are the results
  of plate motion

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Directions and rates of plate motions
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Plate Boundaries

• Plate boundaries
• All major interactions among plates occur along
  the 3 major plate boundaries
• - Convergent (destructive margin)
• - Divergent (constructive margin)
• - Transform Fault

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A - Divergent plate boundaries

• Divergent plate boundaries (constructive margins)
  
• Continental rifts within a continent, i.e. East
  African rift
• Mid-Ocean ridges in the middle of ocean floor

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Divergent Plate Boundary

• Divergent plate boundaries (continued)
• Two plates move apart
• Mantle material upwells to create new seafloor
• Ocean ridges and seafloor spreading
• Oceanic ridges develop along well-developed
  boundaries
• Along ridges, seafloor spreading creates new
  seafloor

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Divergent boundaries are located mainly along
oceanic ridges
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The East African rift a divergent boundary on
land
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Types of Plate Boundaries

• Convergent plate boundaries (destructive margins)
• Plates collide, an ocean trench forms and
  lithosphere is subducted into the mantle, it
  melts and produces volcanic arcs

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B - Convergent Plate Boundary

• Convergent plate boundaries (destructive margins)
• Three types of Convergent Plate Boundary
• Oceanic-continental convergence
• Denser oceanic slab sinks into the asthenosphere
• Pockets of magma develop and rise
• Continental volcanic arcs form
• Examples include the Andes mountains in South
  America,

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An oceanic-continental convergent plate boundary
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Plate Boundaries

• Convergent plate boundaries (destructive margins)
• Oceanic-oceanic convergence
• Two oceanic slabs converge and one descends
  beneath the other
• Often forms volcanoes on the ocean floor
• Volcanic island arcs forms as volcanoes emerge
  from the sea
• Examples include the Aleutian Islands in Alaska,

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An oceanic-oceanic convergent plate boundary
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Plate Boundaries

• Convergent plate boundaries (destructive margins)
• Continental-continental convergence
• When subducting plates contain continental
  material, two continents collide
• Can produce new mountain ranges such as the
  Himalayas

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A continental-continental convergent plate
boundary
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The collision of India and Asia produced the
Himalayas (before)
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The collision of India and Asia produced the
Himalayas (after)
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C - Transform Fault

• Transform Fault
• Plates slide past one another
• No new crust is created
• No crust is destroyed
• i.e. San Andreas Fault, California

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Evidence for the plate tectonics model

• Paleomagnetism (ancient magnetism)
• Probably the most persuasive evidence
• Paleomagnetic records show
• Polar wandering (evidence that continents moved)
• Earth's magnetic field reversals
• Recorded in rocks as they form at oceanic ridges
  

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Evidence for the plate tectonics model

• Earthquake patterns
• Associated with plate boundaries
• Deep-focus earthquakes along trenches provide a
  method for tracking the plate's descent
• Ocean drilling
• Deep Sea Drilling Project (ship Glomar
  Challenger)

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Distribution of earthquake foci at plate
boundaries
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Earthquake foci in the vicinity of the Japan
trench
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Evidence for the plate tectonics model

• Ocean drilling (continued)
• Age of seafloor rocks
• Youngest are near the ridges
• Older are at a distance from the ridge
• Oldest Ocean floor rocks are 200 million years,
  much younger than the continent rocks

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Evidence for the plate tectonics model

• Hot spots
• Rising plumes of mantle material
• Volcanoes can form over them
• e.g., Hawaiian Island chain
• Chains of volcanoes mark plate movement over a
  stationary hot spot

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The Hawaiian Islands have formed over a
stationary hot spot
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Evidence of Plate Tectonics Model

• Measuring plate motion
• By using hot spot tracks like those of the
  Hawaiian Island - Emperor Seamount chain
• Using space-age technology to directly measure
  the relative motion of plates
• Very Long Baseline Interferometry (VLBI)
• Global Positioning System (GPS)

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Driving mechanism of plate tectonics

• No one model explains all facets of plate
  tectonics
• Earth's heat is the driving force
• Several models have been proposed
• Slab-pull and slab-push model
• Descending oceanic crust pulls the plate
• Elevated ridge system pushes the plate

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Plate tectonics the new paradigm

• Driving mechanism of plate tectonics
• Several models have been proposed
• Plate-mantle convection
• Mantle plumes extend from mantle-core boundary
  and cause convection within the mantle
• Models
• Layering at 660 kilometers
• Whole-mantle convection
• Deep-layer model

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Layering at 660 kilometers
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Whole-mantle convection
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Deep-layer model
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End of Chapter 8
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1 - What was the name of the Supercontinent?

• Gondwanaland
• Kalahari
• Pangaea
• Eurasia

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2 - Whose idea was the Continental Drift?

• A. Einstein
• A. Wegener
• H. Hess
• Vine and Matthews

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3 - Which one of these is not Wegeners Evidence
of Continental Drift?

• Fit of South America and Africa
• Fossils match across the seas
• Matching human remains in Europe and America
• Matching rock types and structures
• Ancient climates

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4 - What example of plate boundary is the East
African Rift Valley?

• Continental-continental convergent
• Divergent
• Oceanic-continental convergent
• Oceanic-oceanic convergent

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5 Ocean floor rocks get older as you move
____the ridge

• Towards
• Away from
• Parallel
• None of these
• No relation whatsoever

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6 - This is an example of a. Oceanic-oceanicb.
Ocean-continent convergence
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7 - Polar Wandering is

• Migration of Polar bears
• Another evidence of Global Warming
• Migration of the North Pole
• None of the above

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9 Plate Tectonics Theory states

• Earth crust is broken into plates
• Earth lithosphere is broken into plates
• Earth mantle is broken into plates

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10 What two continents match?

• Africa and America
• America and Europe
• Africa and South America
• India and Asia

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11 When did the Supercontinent break?

• 300 million years ago
• 200 million years ago
• 150 million years ago
• 4.6 billion years ago

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12 Age of the oldest seafloor rocks

• 4.5 billion years ago
• 200 million years ago
• 300 million years ago
• None of these

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13 The San Andreas Fault is an example of

• Convergent margin
• Divergent margin
• Mid-Ocean ridge
• Continental Island Arc
• None of the above

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14 - The Andes Mountains are an example of

• Volcanic Island arc
• Continental Volcanic arc
• Convergent margin
• None of the above
• b and c

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15 - The African Rift Valley is an Example of

• Continental volcanic arc
• Convergent margin
• Divergent margin
• None of these