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Lab 06 ONLINE
LESSON
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If viewing this lesson in Powerpoint
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Do take notes as we peruse through this
lesson…
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Plate Tectonics
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Plate Tectonics is a geologic idea that states
the surface of the planet is covered by a series of
rigid plates that move…
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These plates move away each other
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These plates move toward each other
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These plates move past each other
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Plate Tectonics is driven by heat within the interior
of the planet…
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A current theory suggests that radioactive materials are
the source for the earth’s internal heat…
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This heat melts the surrounding rock
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Melted rock (magma) rises to the surface and
pushes the plates…
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There are three types of plate boundaries
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Divergent, Convergent and
Transform
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Divergent boundary: the plates move away from
each other
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Convergent boundary: the plates move toward
each other
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Transform boundary: the plates move past each
other
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A transform boundary: cuts across a divergent
boundary…
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A divergent boundary is also referred to as a spreading center,
such as the Mid Atlantic Ridge…
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A divergent boundary is a part of the earth’s
surface where new crust is formed…
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A convergent boundary is also
known as a subduction zone…
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Subduction is the process of pushing
seafloor crust into the interior of the
planet…
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A convergent boundary is where
crust is destroyed and massive earthquakes
occur…
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A transform boundary is also known as a
fracture zone or fault…
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The San Andreas Fault is a well known transform fault in this area…
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Earthquakes occur at all of these
boundaries because solid rock is moving against solid rock…
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The bigger earthquakes occur at the convergent and
transform boundaries…
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But small and shallow earthquakes can
occur at transform and divergent boundaries…
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Shallow earthquakes occur at divergent
boundaries because the crust is thin…
5 -10 km thick…
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The following is a map of many
divergent, convergent and transform boundaries…
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Plate Tectonics can be thought of as a
grand unifying theory in geology…
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Meaning that many geologic phenomena are associated with
Plate Tectonics
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And can be explained by Plate Tectonics
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At convergent boundaries …volcanoes,
earthquakes and mountains and deep sea
trenches can be formed…
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Right click to play
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Also at convergent boundaries …the deepest
earthquakes occur
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Subducted seafloor is pushed into the interior of the
planet….
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As much as 650 kilometers
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At divergent boundaries …heat,
volcanoes, earthquakes and new
seafloor can be formed…
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Since new seafloor is formed at the divergent
boundaries…the notion of seafloor spreading can
also be observed…
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Seafloor crust is made primarily of iron rich (MAFIC)
minerals
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These MAFIC minerals are subject to the earth’s
magnetic field…
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Magma rises up from the interior of the planet…
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And punches through the ocean crust to form new
crust…
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The newly formed MAFIC crust can record the
prevailing magnetic field
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The earth’s magnetic field has changed direction over the course of the life of the
planet
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North has become south and the other way around…
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These magnetic reversals have been recorded in the
seafloor crust
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These records can tell us such things as the rate of movement of the plates…
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Each recorded event is a time marker…
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The newest crust is at the point where magma rises from the
interior of our planet…
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The older crust is further away…
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Oceanic crust as old as 200,000,000 years old can
be detected…
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How can spreading rates be determined from magnetic
reversals?
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Here is a section of the ocean floor’s magnetic
reversals…
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Seafloor spreading begins here…
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And ends up here…
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The distance of seafloor movement is read here…in
this case…1425 kilometers…
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The time is read here…in this case…78,000,000 years…
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Spreading rates are always noted in
cm/year
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1425 km = 142,500,000 cm
142,500,000 cm
78,000,000 years
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So the spreading rate is 1.83 cm/year
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Hot Spots are places on the planet where magma rises up to produce pinpoint
volcanic eruptions…
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There are about 40 hotspots on the planet…
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A hotspot can be described as a plume of magma rising up and punching through the crust…
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The Hawaiian Islands are an example of a hotspot…
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The hotspot plume is currently under the main island of
Hawaii…
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The Pacific Plate is moving northwest…
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The plates move while the plume is stationary…
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END
L06
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