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Plate Tectonics Notes
Term
crust
continental
crust
oceanic crust
mantle
Definition or Information Diagram/Picture
Earth’s outermost layer
 made of relatively light
and brittle rocks
 Earth’s thinnest layer--ranging from about 5
km to about 100 km
thick
 makes up only about 1
% of Earth’s mass
 main elements--oxygen, silicon,
aluminum
 average density of the
crust ranges from
about 2.7 g/cm3 to 3.0
g/cm3
 lighter, older, and
thicker part of the crust,
which makes up the
continents
 granite
 the rock that makes up
the ocean floor (basalt)
 oceanic crust has
nearly twice as much
iron, magnesium, and
calcium as the
continental crust
 these elements make it
much denser
 the layer of Earth
beneath the crust
 about 2,900 km thick
and makes up nearly 67
% of Earth’s mass
 density ranging from
3.3 g/cm3 to 6 g/cm3
 uppermost part is solid
 tremendous heat and
pressure make the
middle act more like a
very thick liquid
 In the lowest part of the
mantle, the pressure is
so great that it keeps
the rock from melting.
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Plate Tectonics Notes
lithosphere
crust and the rigid and
immovable part of the
mantle
 resembles a giant
jigsaw puzzle---each
piece of the puzzle is a
tectonic plate
 rigid layer
 about 100km thick
 less dense than lower
layers
asthenosphere denser, semi-molten layer
of Earth
 hot and flowing
 plastic-like rock layer
of the mantle below the
lithosphere
 soft layer within the
mantle that flows like a
very thick liquid
convection
 circular path of heating
current
and cooling by
temperature differences
 moves the tectonic
plates

Alfred
Wegener
stated a hypothesis
about Earth’s surface
(1912)
 proposed the Theory of
Continental Drift
 his ideas were not well
received (skepticism)
Pangaea




that continents were
joined
evidence to support
theory---similar rocks
and fossils on separate
continents
similar mountain ranges
puzzle
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Plate Tectonics Notes
tectonic plate


plate
boundary





divergent
boundary



large section of
lithosphere that is in
slow but constant
motion (sometimes
referred to as
lithospheric plates)
plates are able to move
because they float on
the asthenosphere
region where two
tectonic plates meet
Earthquakes (faults)
and volcanic eruptions
most often occur near
plate boundaries.
Active volcanoes are
most likely to form at
convergent boundaries
(oceanic-continental
boundaries).
Mountain ranges form
when two continental
plates collide.
Volcanoes and
earthquakes
boundary between two
plates that are moving
apart
2 continental plates
moving away from each
other forming a rift
valley
2 oceanic plates
diverging form a
mid-ocean ridge
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Plate Tectonics Notes
convergent
boundary



transform
boundary
mid-ocean
ridges

two plates move
together
mountain range forms
similar rock densities at
convergent boundaries
will form a mountain
range
where two plates slide
past or grind past one
another
 move in opposite
directions or same
direction at different
rates
 when this happens
suddenly---an
earthquake occurs
 mountains chains at the
bottom of the oceans
between continents
 great deal of volcanic
activity
 result of the formation of
new ocean floor
 the older rocks are farther
away from the ridge
 youngest rocks are
located near mid-ocean
ridge
 creation of mid-ocean
ridges take the same
amount of time as
mountain formation
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Plate Tectonics Notes
seafloor
spreading



rift valley
when magma squeezes
up through boundaries
between oceanic plates
plates move apart
new crust forms on the
seabed
 magma rises between two
continental plates
 deep crack and new crust
appears in the valley
 where two continental
plates pull apart
(divergent)
 The Great Rift Valley on
the continent of Africa
causes volcanic eruptions
and earthquakes. The
future will probably
create an inland sea.
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Plate Tectonics Notes
folded
mountains



trench



form where two plates
made of continental
crust collide (at
continental-continental
plate boundaries)
rock layers are
squeezed together and
pushed upward to form
folds, or ripples in the
crust
highest mountains in
world (Himalayas of
Asia; Alps of Europe;
Ural Mountains in
Russia; Great Smoky
Mountains in U.S.)
deep canyon forms in
the ocean floor where
the two plates meet
oceanic-oceanic
boundaries collide
one plate is subducted,
or pushed under the
other
subduction
zone

region where one plate
slides under another
plate
volcano

opening in Earth’s
surface
magma is released
magma cools and
hardens on ocean floor
that makes a chain of
volcanic mountains
An island arc is a long,
curved chain of islands
that form from volcanic
activity. (Aleutian
Islands of Alaska)



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Plate Tectonics Notes
shield
volcano




cinder cone
volcano


composite
volcano


Ring of Fire




thick layers of lava pour
out of a vent and harden
on top of previous
layers
gradually building a
wide, gently sloping
mountain
least explosive
example---Hawaiian
Islands
ash, cinders, and bombs
build up around the
vent in a steep, coneshaped hill or small
mountain
example---Paricutin in
Mexico
tall, cone-shaped
mountains in which
layers of lava alternate
with layers of ash
examples---Mount Fuji
in Japan and Mount St.
Helens in Washington
State
edge of the Pacific
Ocean
zone of frequent
volcanic eruptions that
circles the Pacific Basin
contains more than 75
% of all volcanoes
an arc that reaches from
New Zealand, north
along the eastern edge
of Asia, across the
Aleutian Island and
south along the west
coasts of North and
South America
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Plate Tectonics Notes
hot spot



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seismic wave




seismology

seismographs



volcanic activity near
middle of a tectonic
plate
located beneath a plate
remains in one place as
plate above it moves
creates chain of small
volcanoes
no longer active when
not over the hot spot
Hawaiian Islands--different ages of islands
a wave of energy that
travels away from the
center of an earthquake
in all directions
increase going into
Earth because they are
moving from less dense
material to more dense
material
most common where
plates slide by each
other
fault--- break, or crack,
in Earth’s surface along
which rock has moved
branch of science
concerned with
earthquakes
measure the speed and
intensity of seismic
waves
recordings from these
instruments are
seismograms
Richter scale ---rating
of an earthquake’s
magnitude based on the
size of the earthquake’s
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Plate Tectonics Notes
P waves
(primary
waves)



S waves
(secondary
waves)


surface waves 


seismic waves
first waves to arrive
compress and expand
the ground like an
accordion
travel through both
solids and liquids
vibrate from side to side
as well as up and down
S waves cannot move
through liquids
When P and S waves
reach the surface
move more slowly than
P waves and S waves
can produce severe
ground movements
focus
the place inside Earth
where an earthquake occurs
epicenter
Located directly above the
focus on the surface of the
Earth
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Plate Tectonics Notes
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Plate Tectonics Notes
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