CONTINENTAL DRIFT AND PLATE TECTONICS

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CONTINENTAL DRIFT AND
PLATE TECTONICS
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DRIFT AND PLATES

• Continental drift concept
• Introduction
• did continents originate at their present
  locations or did they move to where they are
  today?
• drift concept supplied information to aid in the
  formulation of rock plate or tectonic plate
  concept
• a solid lithosphere floating on top of the
  asthenosphere gives an idea of how plates can
  float
• Accretion of continental material took place

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DRIFT AND PLATES

• convection cells in Earths interior is the force
  which split the lithosphere and are the driving
  force in continental separation

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DRIFT AND PLATES
Accretion of Continental Materials during
Drift---Western USA
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DRIFT AND PLATES

• who was the first to observe this map fit?
• Alfred Wegener was the first to publish a
  summary of ideas about continental drift in 1912.
• some ideas in the publication were 1) the
  protocontinent or supercontinent was named
  Pangaea 2) southern section was named Gondwana
  or Gondwanaland and northern section, Laurasia
  3) the protocontinent broke in pieces about
  150-200 million years ago

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DRIFT AND PLATES

• Some important data confirming continental drift
• map fit--already mentioned
• mountain chains formed on continents with
  longitudinal axes perpendicular to movement of
  the continents--examples Himalayan, Rocky
  Mountain and Andes Mountain chains
• same fossils (in rocks),same rocks , mountain
  ranges, and glacial features located on different
  continents in areas representing prejoined
  positions prior to continental drift

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DRIFT AND PLATES

• Initial ideas of continental drift
• jig saw puzzle or map fit of continents

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Matching of Fossils from Common Locations on
Separated Continents
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Matching of Mountain Chains from Common
Locations on Separated
Continents
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Matching of Glacial Deposits from Common
Locations on Separated Continents
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DRIFT AND PLATES

• presence and shape of global ocean ridge
• a ridge is a raised region on ocean basin which
  is believed to represent prejoined or splitting
  area of separated continents--the shape of the
  ridge contours shape of coast lines of separated
  continents--- this is most evident in the mid
  Atlantic ocean

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Global Ocean Ridge
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DRIFT AND PLATES

• seafloor spreading
• age of rocks located on equivalent positions on
  both sides of the ridge are the same--rocks
  progressively increase in age away from the ridge
• magnetic intensities in the rocks are found to be
  the same on equivalent sides of the ridge--on
  both sides of ridge magnetic intensity alternates
  between normal(high intensity) and abnormal(low
  intensity)

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DRIFT AND PLATES
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Magnetic Intensities and Sea Floor Spreading
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DRIFT AND PLATES

• Lithospheric plates and plate tectonics
• where are the spreading continents going?
• the answer was important in initiating the rock
  plate concept
• rock sections or plates which diverge from
  spreading zones move towards or converge on
  subduction zones
• Rock plates
• ocean basin and continental sections float in the
  asthenosphere, some plates diverge, some converge
  and some move parallel (to each other)

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DRIFT AND PLATES

• Classification of rock plate boundaries
• volcanism and seismic activity are abundantly
  associated with plate boundaries
• boundaries are classified as divergent,
  convergent, or transformed boundaries
• divergent boundary--includes all ridges and
  rifts--tensional forces caused by convection
  cells drive the plates apart

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DIVERGENT PLATE BOUNDARY
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DRIFT AND PLATES

• kinds of divergent plate boundaries--1)ocean
  basin to ocean basin boundary

example is the mid ocean ridge
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DRIFT AND PLATES

• 2) continental to continental boundary

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DRIFT AND PLATES

• convergent boundaries--includes all subduction
  boundaries--compressional forces caused by
  convection cells drive plates towards each
  other--volcanic arcs are associated with
  convergent boundaries

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Convergent Plate boundary
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3 types of convergent plate boundaries
1) Ocean basin to continental boundary
(Example is the Cascade Mountain chain)
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2) Ocean basin to ocean basin boundary
(Examples are Aleutian Islands and Japan)
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Aleutian Islands and Japan
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3) Continental to continental plate boundary
(Example is India and Asian continent boundary)
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(No Transcript)
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DRIFT AND PLATES

• transformed boundary--plates move parallel to
  boundary

Example are those off the Coast of Western U.S.A.
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DRIFT AND PLATES

• Major Plates on Earth and Movement Rates

Movement rates are about as fast as your
fingernails grow