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Transcript
CONTINENTAL DRIFT AND
PLATE TECTONICS
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
DRIFT AND PLATES
• convection cells in Earth’s interior is the
force which split the lithosphere and are the
driving force in continental separation
DRIFT AND PLATES
Accretion of Continental Materials during Drift---Western USA
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 150200 million years ago
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
DRIFT AND PLATES
• Initial ideas of continental drift
• jig saw puzzle or map fit of continents
Matching of Fossils from Common
Locations on Separated Continents
Matching of Mountain Chains from
Common Locations on Separated
Continents
Matching of Glacial Deposits from
Common Locations on Separated
Continents
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
Global Ocean Ridge
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)
DRIFT AND PLATES
Magnetic Intensities and Sea Floor Spreading
•
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)
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
DIVERGENT PLATE BOUNDARY
DRIFT AND PLATES
• kinds of divergent plate boundaries--1)ocean
basin to ocean basin boundary;
example is the mid ocean ridge
DRIFT AND PLATES
• 2) continental to continental boundary
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
Convergent Plate boundary
3 types of convergent plate boundaries
1) Ocean basin to continental boundary
(Example is the Cascade Mountain chain)
2) Ocean basin to ocean basin boundary
(Examples are Aleutian Islands and Japan)
Aleutian Islands and Japan
3) Continental to continental plate boundary
(Example is India and Asian continent boundary)
DRIFT AND PLATES
• transformed boundary--plates move
parallel to boundary
Example are those off the Coast of Western U.S.A.
DRIFT AND PLATES
• Major Plates on Earth and Movement Rates
Movement rates are about as fast as your fingernails grow