Transcript Plate Tectonics

The Theory of Plate Tectonics
Earth’s Interior and Surface Plate Movements
13 –
 Time for Change
 Chapter
1
The guy who started it all:
Alfred Lothar Wegener
1880-1930
Learning Targets
I
will summarize the theory of
plate tectonics.
 I will identify and describe the
three types of plate boundaries.
 I will list and describe three
causes of plate movement.
2
1960’s
• Evidence supporting
continental drift and seafloor spreading lead to
the development of a
theory called plate
tectonics, the theory that
explains why and how
continents move.
How Continents Move

Earth’s crust and
the rigid, upper
part of the mantle
form a layer
called…..
The Lithosphere

The thin outer shell
that is broken into
blocks, called
tectonic plates, that
ride on top of…….
The Asthenosphere

A layer of solid
rock that acts like
a plastic, it flows
like Sillyputty when
put under
pressure.
Two Types of Crust
• Oceanic: Thin,
dense, high in iron
(Fe) and magnesium
(Mg).
• Continental:
Thicker, less dense,
high in silica (SiO2).
• Tectonic plates can
consist of only one
Tectonic Plates
 About 15 currently
known.
 While some can be
identified by features
easy to see (mountain
ranges or ocean
trenches), some cannot
be.
 We can identify plate
boundaries by…….
Earthquakes
 When plates
move, they
produce
earthquakes, so
we can say that 2
or more plates
meet in that area.
Volcanoes
Plate motions can
form magma that
erupts on the
Earth’s surface as
lava.
Best Example

11
The “Pacific Ring
of Fire”, an active
zone of both
volcanoes and
earthquakes,
indicating plate
boundaries.
Types of Plate Boundaries
• Three main types, each associated with a
characteristic type of geologic activity.
Divergent Boundaries

Magma rising to the surface forces plates
to move apart. Since the newly formed
rock is warmer and lighter it sits higher
than the surrounding rock. This forms
the…….
Mid-Ocean Ridges

The undersea
mountain ranges
where new oceanic
lithosphere is
created. Down the
center of the ridge
is a rift valley, a
narrow valley
formed where the
plates separate.
Thingvellir fissure
The rift valley (in
shadow), the onland exposure of
the Mid-Atlantic
Ridge in Iceland.
Can Occur On Continental Plates

The East African
Rift system is
where Africa is
currently breaking
up, and has
already formed the
Red Sea by the
separation of the
African and
Arabian plates.
Convergent Boundaries
• Formed where
two plates
collide. Three
types of
collisions can
happen.
Oceanic to Continental
Collision
 Because oceanic
lithosphere is
denser, it
subducts, or sinks
below the
continental plate.
The area is called
a subduction
zone.
Deep Ocean Trenches
 These form at
subduction zones. The
oceanic plate is heated
and releases fluids into
the overlying mantle,
causing magma
formation, which rises
to the surface to form
volcanoes.
Continent to Continent Collision
Neither plate
subducts, rather
the edges
crumple and
thicken, causing
the formation of
large mountain
ranges.
Oceanic to Oceanic Collisions

21
One subducts under
the other. Again, a
trench is formed
and magma rises to
the surface to form
an island arc, a
chain of volcanic
islands.
Transform Boundaries
Francois Gohier
Where two
plates slide past
each other
horizontally.
They do not slide
smoothly,
producing
earthquakes.