Download Plate Tectonics

Lumberton High
Sci Vis II
V205.03
 The surface of the Earth is
broken into large pieces of earth
called plates.
 These plates float over an inner molten layer.
 The size and position of these plates change over
time.
 Example - the idea of a super
continent called Pangaea that
existed millions of years ago.
 Evidence suggests that the
separate continents we know
today migrated from this one
large land mass.
 The edges of these plates are
sites of intense geologic
activity.
 Earthquakes, volcanoes, and
mountain building can occur
when they move against each
other.
 Plate tectonics are a combination of
two earlier ideas, continental drift
and sea-floor spreading.
 Continental drift is the movement of continents over the
Earth's surface and their change in position relative to each
other.
 Sea-floor spreading is the creation of new oceanic crust at
mid-ocean ridges and movement of the crust away from the
mid-ocean ridges.
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Many changes and movements
in the earth’s crust originate
along Lithospheric plate
boundaries.
These boundaries are not
always easy to identify.
The familiar outlines of the
continents and oceans
depicted on maps may not
resemble the outlines made by
the plate boundaries.
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Plate boundaries can be
in the middle of the
ocean floor, around the
edges of continents, or
within continents.
There are several types of
plate boundaries, each of
which is associated with a
characteristic type of
geologic activity.
 Divergent boundaries are two
plates moving apart from each
other.
 Also known as spreading boundary,
a divergent boundary occurs where
two plates move apart, allowing
magma, or molten rock, to rise
from the Earth's interior to fill in
the gap.
 The two plates move away from
each other like two conveyor belts
moving in opposite directions.
 The process by which the
plates move apart can also
be referred to as sea floor
spreading.
 At this type of boundary, new
oceanic crust is formed in the
gap between two diverging
plates.
 Plate area is increased as the
plates move apart.
 Plate movement takes place
laterally away from the plate
boundary, which is normally
marked by a rise or a ridge.
The ridge or rise may be
offset by a transform fault.
 Presently, most divergent
margins occur along the
central zone of the world’s
major ocean basins. The MidAtlantic Ridge and East Pacific
Rise provide good examples
of this type of plate margin.
 Convergent boundaries are the direct
collision of one plate with another.
 As seafloor spreading pulls plates
apart at one boundary, those plates
push into neighboring plates at other
boundaries.
 The direct collision of one plate with
another type of plate is called a
convergent boundary.
 Three types of collisions can occur at
convergent boundaries.
Oceanic-continental
convergence –
 One type occurs when a plate
with oceanic crust at its leading
edge collides with a plate with
continental crust at its edge.
 oceanic crust is denser, it is
subducted, or forced under the
less dense continental crust.
 Scientist refer to the region along a plate
boundary where one plate moves under
another plate as a subduction zone.
 A deep oceanic trench generally forms
along a subduction zone.
 As the oceanic plate moves down into a
subduction zone, it melts and becomes
part of the mantle material.
 Some of the magma formed rises to the
surface through the continental crust and
produces volcanic mountains.
 Continent-continent convergence -- A
second type of collision occurs when two
plates with continental crust at their leading
edges come together.
 During this type of collision, neither plate is
conducted because they both have the same
density.
 Instead, the colliding edges are crumpled
and uplifted, producing large mountain
ranges.
 Scientist are convinced that the Himalayas
were formed by this type of collision
Oceanic-oceanic convergent
 The third type of collision along
convergent boundaries occurs
between oceanic crust and oceanic
crust.
 A deep ocean trench also forms
when one of these plates is
subducted.
 Part of the subducted plate melts,
and the resulting molten rock rise to
the surface along the trench to form
a chain of volcanic islands called an
island arc.
Transform fault boundaries
 occur were two plates are grinding
past each other.
 Transform boundaries neither create
nor consume crust.
 Rather, two plates move against
each other building up tension and
then releasing the tension in a
sudden and often violent jerk.
 This sudden jerk creates an
earthquake.
 The San Andreas Fault is undoubtedly the
most famous transform boundary in the
world.
 To the west of the fault is the Pacific plate,
which is moving northwest.
 To the east is the North American Plate,
which is moving southeast.
 Los Angeles, located on the Pacific plate, is
now 340 miles south of San Francisco,
located on the North American plate.
 In 16 million years, the plates will have
moved so much that Los Angeles will be
north of San Francisco!
 Global Positioning System
(GPS) is a constellation of 24
satellites which are used for
navigation and precise
geodetic position
measurements.
 They can also be used to plot
global velocities.
 Satellite Laser Ranging (SLR)
determines round-trip time
of light from ground-based
lasers at widely separated
points on the earth to
mirrors on satellites.
 Very Long Baseline
Interferometry (VLBI) uses
the difference in time at
widely separated places of
received quasar-emitted
radio signals and can also be
used to obtain plate
movement.
 Volcanic and earthquake
activity can also be measured
to help determine plate
movement.
 The “Ring of Fire” (area of
volcanic activity) in the
Pacific Ocean helped map
out certain oceanic plates.