Transcript plate boundaries

The Changing Earth
Chapter Eleven: Plate Tectonics
• 11.1 Pangaea
• 11.2 Sea Floor Spreading
• 11.3 Plate Boundaries
11.3 Plate boundaries
•
•
Divergent boundaries (the trailing edge
of a plate) = plates moving away from each
other (this type of boundary is found over
the rising part of a convection cell)
Convergent boundaries (the leading
edge of a plate) = plates that collide with
other plates
11.3 Plate boundaries
• An edge of a
lithospheric plate
that slides by
another plate is
called a transform
fault boundary.
11.3 Divergent boundaries
•
•
•
Divergent boundaries are found in the
ocean as mid-ocean ridges.
A divergent boundary is the line between
two plates where they are moving apart.
This type of boundary is found over the
rising plume of a mantle convection cell.
11.3 Divergent boundaries
• Divergent boundaries can
also be found on continents
as rift valleys.
• When a rift valley forms on
land, it may eventually split
the landmass.
11.3 Convergent boundaries
•
•
When oceanic plates collide, the “older” plate
subducts under the “younger” plate because it
is more dense.
This forms a valley in the ocean floor called a
deep-ocean trench.
11.3 Convergent boundaries
•
What happens if an oceanic plate and
a continental plate collide?
– The oceanic plate must subduct
under the continental plate. A
continental plate is simply too
buoyant and too thick to subduct
under an oceanic plate.
11.3 Mountains and convergent
boundaries
•
When an oceanic plate with a continent on it
collides with a continental plate;
– The oceanic part of the plate subducts
under the continental plate, but the
continental part of the plate cannot be
sucked into the trench because the granite
rock continents are made of is less dense.
The two continents collide and form a
mountain range.
11.3 Mountains and convergent
boundaries
•
Mountain ranges are formed when
continents collide.
11.3 Transform fault boundaries
•
A good clue for
locating transform
faults is offsetting.
When seen from
above, the feature
will appear to make
a zigzag.
11.3 Slickenslides, evidence of
plate boundaries
• The effect of rock
moving against rock
is evidence of plate
boundaries.
(slickensides)
• The rock surface
moving to the right is
called slickensides
because it is smooth
11.3 Earth’s lithospheric plates
•
Can you identify the three types of plate
boundaries labeled A, B, and C?.
Geology Connection
Where to go for
Volcanoes
• There are many
volcanoes on the
mainland of the United
States.
• In the recorded history
of Earth, more than 500
volcanoes have erupted.
Activity
Make a Plate Tectonics Book
• Your book will recount
part of the plate
tectonics story.
• Use the graphic on
this page and others in
Chapter 11 to help you
outline your story.