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Plate Tectonics - Download Now PowerPoint

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					Plate Tectonics
What is plate Tectonics?

• Plate tectonics is the study of how the Earth's plates are
  driven and shaped by geological forces that keep them
  in constant motion.

• About twenty separate, cool plates of rock of various
  sizes make up the earth's crust. The size and position
  of these plates change over time. The plates float
  above fiery magma, whose heat makes them come
  together, move apart, and slide past each other.

• The edges of these plates, where they move against
  each other, are sites of intense geologic activity, such
  as earthquakes, volcanoes, and mountain building…
ALFRED WEGENER
(1880-1930)
German climatologist and
geophysicist who, in 1915,
published as expanded
version of his 1912 book The
Origin of Continents and
Oceans. This work was one
of the first to suggest
continental drift and plate
tectonics. He suggested that
a supercontinent he called
Pangaea had existed in the
past, broke up starting 200
million years ago, and that the
pieces “drifted'' to their
present positions.

     The theory of plate tectonics became widely accepted by scientists in
     the 1960s and 1970s. It revolutionized our understanding of the Earth
     and unified the Earth sciences, from the study of fossils (paleontology)
     to the study of earthquakes (seismology).
Currently there are 14 main plates.
The main plates are:
                       •   Pacific plate
                       •   Juan de Fuca plate
                       •   North American plate
                       •   South American plate
                       •   Caribbean plate
                       •   Cocos plate
                       •   Nazca plate
                       •   Scotia plate
                       •   Antarctica plate
                       •   African plate
                       •   Arabian plate
                       •   Eurasian plate
                       •   Indian-Australian plate
                       •   Philippine plate
• The Earth’s tectonic plates can move apart, collide, or slide
  past each other. The Mid-Ocean Ridge system (the Earth’s
  underwater mountain range) arises where the plates are
  moving apart.

• As the plates part, the seafloor cracks. Cold seawater seeps
  down into these cracks, becomes super-heated by magma,
  and then bursts back out into the ocean, forming
  hydrothermal vents.


                                              As mountains
                                              build…..
                                              Sea floor
                                              spreading
                                              occurs!
              Sea floor spreading
• When the plates under the ocean
  move apart, magma rises, often
  violently, from inside the earth's
  mantle to fill the gap, solidifies
  quickly in the icy sea water, and
  forms new crust. This process is
  called seafloor spreading.

     •Tectonic plates move 1.27 to 15 cm a year, but the
     movement occurs in bursts, and different plates move in
     different motions at different speeds.
     •For example, in the the Pacific plate moves west at 13
     cm per year.
     And the Nazca plate is shifting east about 7.6 cm per
     year.
Subduction
• Conversely, when tectonic
  plates meet, the force
  causes mountains to rise
  and deep trenches to form.
  When the edge of one
  plate is forced under
  another — a process
  called subduction — it
  causes intense vibrations
  in the Earth’s crust,
  producing an earthquake.
  One of the most violent
  earthquakes related to       Volcanic arcs and oceanic trenches partly
  plate tectonics struck       encircling the Pacific Basin form the so-called
  northeast China in 1976.     Ring of Fire, a zone of frequent earthquakes
  The disastrous Tangshan      and volcanic eruptions.
  quake, registering 7.8 on    The trenches are shown in blue-green.
  the Richter scale, killed
  more than 240,000 people.
        So what about Galapagos??
•   the Galapagos are thought to be the
    product of a mantle plume. Mantle
    plumes are columns of hot rock,
    roughly 100 km in diameter, that rise
    from deep within the Earth. These
    plumes rise because they are hotter
    (by perhaps as much as 200 degrees
    centigrade) and therefore less dense,
    than the surrounding rock. The rate
    of ascent is about 10 cm/year or so.
•   As plumes near the surface, they
    begin to melt. The melting occurs as    The upward motion of the mantle
    a result of decompression rather than   plumes pushes the overlying
    any heating. Melting probably begins    lithosphere upward. This, together
    at a depth of 150 km or so and          with magmatic thickening of the
    continues until the plume is            crust, is responsible for the
    prevented from further rise by the      Galapagos Platform, an
    overlying lithosphere.                  anomalously shallow region of the
                                            ocean upon which the Galapagos
                                            Islands sit.
continued…
• Mid-ocean ridges are often offset by fracture zones or transform
  faults.
• A major transform fault is located just north of the Galapagos at
  91° W. Subduction zones occur where plates collide.
• A major subduction zone is located along the west coast of Central
  and South America, where the Nazca and Cocos Plates are
  subducting beneath the South American and Carribean plates.
  Subduction zones are marked by deep trenches and overlying
  chains of volcanoes.

 As a lithospheric plate moves over a mantle plume, a
 chain of volcanoes is created. The volcanoes get older in
 the direction of plate motion. The Hawaiian mantle plume
 has created a chain of volcanic islands and seamounts.
 continued..
• The Galapagos Islands are located beneath the Nazca Plate, which
  is moving east-southeast.
• The Galapagos plumes has not produced such as simple linear
  chain as the Hawaiian Islands or the Society Islands.
• The islands do get older to the south-southeast and it has produced
  a chain of seamounts known as the Carnegie Ridge

   A second seamount chain, the Cocos Ridge, extends
   northeast from the Galapagos Spreading Center. This ridge
   was also produced by the Galapagos plume because up until
   about 5 million years ago, the Galapagos Spreading Center
   was located directly over the Galapagos mantle plume. This a
   chain of volcanos was produced on both the Cocos and
   Nazca plates. The Galapagos Spreading Center has since
   migrated to the north.
  continued..
• Motion of the lithosphere eventually carries a volcano away from the
  plume and its magma source, so the volcano then becomes extinct.

• The volcano and the lithosphere beneath it begins to cool. As it
  cools it contracts. As a result of this contraction, the volcano slowly
  sinks beneath the sea.

• Many scientists believe that the Galapagos mantle plume is
  responsible for the abundant volcanic rocks of Creteceous age that
  occur in the Carribean and on the northwest margin of South
  America.

• The Galapagos mantle plume could be as old as 90 million years
  and there may have been islands in this locality this long. This is of
  great importance in understanding the origin and evolution of the
  unique animals that occur on the Galapagos.
Plumes seem to be stable over
many millions of years.
With time, they burn through the
crust to form an underwater
volcano which may eventually
grow big enough to become an
island.
But, because the plates are in
constant motion, and so the island
will eventually move off of the hot
spot—making room for a second
volcanic island. And a third, and a
fourth
Thus are archipelagos like the
Galápagos formed.
works cited
•   http://venturedeepocean.org/
•
•   http://www.neptune.washington.edu/vents/video.html
•
•   http://oceanexplorer.noaa.gov/explorations/02galapagos/background/education/.html
•
•   http://www.divediscover.whoi.edu/hottopics/galapagos.html
•
•   http://www.ucmp.berkeley.edu/geology/tectonics.html
•
•   http://www.seismo.unr.edu/ftp/pub/louie/class/100/plate-tectonics.html
•
•   http://www.cet.edu/ete/modules/msese/earthsysflr/plates1.html
•
•   http://csep10.phys.utk.edu/astr161/lect/earth/tectonics.html
•
•   http://www.hartrao.ac.za/geodesy/tectonics.html
•
•   http://www.ucmp.berkeley.edu/geology/techist.html

				
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