Download Theory of Plate Tectonics

Plate Tectonics
Plate Boundaries
Causes of Plate Tectonics
 The
Earth’s crust and rigid
upper mantle are broken into
sections called plates
 Plates move around on top of
the asthenosphere like ships
 The
crust and rigid part of the
upper mantle = lithosphere
 100
km thick
 Less dense than the material
below it so it “floats”
 The
plastic-like layer below
the lithosphere =
asthenosphere
 The plates of the lithosphere
float on the asthenosphere
 Ocean
plates - plates below
the oceans – denser basalt
 Continental plates - plates
below the continents
What is the theory of plate
tectonics?
 What is the lithosphere?
 What is the asthenosphere?
 What is the connection between
the two?
 What are the two types of plates?

 Boundary
between two plates
that are moving apart or
rifting

 RIFTING
causes SEAFLOOR
SPREADING
 Mid-ocean
ridges
 Rift valleys
 Fissure volcanoes
Lava Fountains, Krafla Volcano
Thingvellir Fissure Zone,
Iceland
Erte Ale Summit Crater, Ethiopia
Oldoinyo Lengai, East African Rift
Zone [

Map of East Africa showing
some of the historically active
volcanoes(red triangles) and the
Afar Triangle (shaded, center) - a so-called triple junction (or
triple point), where three
plates are pulling away from
one another: the Arabian Plate,
and the two parts of the African
Plate (the Nubian and the
Somalian) splitting along the
East African Rift Zone.
USGS website

This image shows
several fault scarps
that are
progressively farther
away. Essentially we
are looking at the
edges of several
horst (risen) blocks
from within a
graben (valley) that
contains Lake
Baringo.
 Boundaries
between two
plates that are colliding
 
 There
are 3 types…
 Ocean
plate colliding with a
less dense continental plate
 Subduction Zone: where the
more dense plate slides under
the less dense plate
 VOLCANOES occur at
subduction zones; trenches
Subduction –
Process by
which the ocean
floor sinks
beneath a deepocean trench
and back into
the mantle;
allows part of
the ocean floor
to sink back
into the mantle
Deep-Ocean
Trench –
Occurs at
subduction
zones. Deep
underwater
canyons form
where oceanic
crust bends
downward
 Ocean
plate colliding with
another ocean plate
 The more dense plate slides
under the less dense plate
creating a subduction zone
called a TRENCH
Map of Alaska
A
continental plate colliding
with another continental plate
 Have Collision Zones:
a
place where folded and thrust
faulted mountains form.

click here

click here
 Boundary
between two plates
that are sliding past each
other
 EARTHQUAKES along faults
What are the three types of
boundaries?
 What direction do plates go for
each?
 Which boundary has a
subduction zone…what occurs
at a subduction zone?

 Hot
magma in the Earth
moves toward the surface,
cools, then sinks again.
 Creates convection currents
beneath the plates that cause
the plates to move.


Slab pull - Cold, sinking lithosphere at the
edges of a tectonic plate pulls the rest of the
plate across earth’s surface.
Ridge push – Gravity pulls newly formed
lithosphere downward and away from the
mid-ocean ridge. The rest of the plate moves
because of this force.

click here for interactive map

BBC video click here


Japan’s Tsunami
click here
What causes plates to move?
 How is a convection current
formed?
 Explain slab pull
 Explain ridge push
