Download Lab 506-Plate Tectonics

Lab 506
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LESSON
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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
L506
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