Pangaea
Colliding Plates
• Objectives
– Explain how plate tectonics accounts for the
movement of continents
– Compare and contrast divergent, convergent
and transform plate boundaries.
– Explain how convection currents inside Earth
might be the cause of plate tectonics
• Key Terms
– plate tectonics, lithosphere, divergent
boundary
– Convergent boundary, transform fault boundary
Plate Tectonics
• Tectonic plates
– Think of the hypotheses of continental drift and
sea-floor spreading as clues to a mystery.
– How can the two hypotheses be explained?
• In the 1960’s, geologists developed a new theory to
explain the apparent movement of the continents.
• The theory of plate tectonics suggests that Earth’s
crust and upper mantle are broken into sections
called plates (that move).
• But, what are they made of and how do they move??
• We already know that the Earth’s crust is a
layer of solid rock.
• The uppermost portion of the mantle is
also solid
– Together, these two areas are known as the
lithosphere
• We also know that there is an area in the
mantle that is less solid. Here, the material
acts more like a putty; it’s a solid that can
flow.
– This putty-like layer is called the
asthenosphere
Plates
• Divergent Boundaries
– The boundary between two tectonic plates
that are moving away from each other
• Magma is forced upward between the two plates,
creating a new crust, thus making….
• Mid-ocean ridges are divergent boundaries
Divergent Boundary
Learning Check
• The theory that suggests that Earth’s crust and
upper mantle are broken into sections called plates
(that move) is known as…
– plate tectonics
• Together, the Earth’s crust is a layer of solid rock
and the uppermost portion of the mantle is also
solid are known as
– Lithosphere
• The boundary between two tectonic plates that are
moving away from each other is known as…
– Divergent boundary
• Convergent Boundaries
– Crustal material can be
destroyed where 2 plates meet head on.
– This type of boundary is called a
convergent boundary
– What do you think happens when two
plates containing continental crust collide?
• The two plates crumple forming mountain
ranges!
• The Himalaya Mountains formed when the
Indian Plate collided with the southern part of
the Eurasia plate.
Himalayas
Convergent Boundaries
• There are three styles of convergent
plate boundaries
– Continent-continent collision
– Continent-oceanic crust collision
– Ocean-ocean collision
Convergent Boundary
• Transform Fault Boundaries
– A third type of boundary that is formed
when two plates slide past one another in
opposite directions.
• Think about the San Andreas Fault in California
– This is where the North America and the
Pacific plate slide past one another!
• Along this boundary, the Pacific plate moves
NW relative to the North American plate at an
average rate of 2 cm per year.
Transform Fault Boundary
Transform Fault Bound. Cause
Earthquakes!
• Causes of Plate Tectonics
– How does the theory of plate tectonics explain
the cause of plate movements?
• The driving force behind this movement is
HEAT!
• A material that is hot is less dense than the
same material that is cold
• This is because the same mass takes up
more volume (space) when the material is
heated.
• This helps us explain the process of
convection currents…
Convection Currents in the Earth
• Convection Currents
– C.C.’s within the Mantle
cause the various plates
in Earth’s lithosphere to
move around.
– As the plates bump into
each other, boundaries
form!
– Plates move in different
directions because there
are many conv. cells
within the Mantle!
Learning Check!
• A type of boundary that is formed when two
plates slide past one another in opposite
directions is known as
– Transform Fault Boundary
• Boundary where crustal material can be
destroyed where 2 plates meet head on is
– Convergent Boundary
• Mountain Ranges
– Convergent
• Earthquakes
– Transform Fault
Convergent Boundaries
Continent-Continent Collision
• Forms mountains, e.g. European Alps, Himalayas
Continent-Oceanic Crust Collision
• Called SUBDUCTION
Subduction
• Oceanic lithosphere
subducts underneath the
continental lithosphere
• Oceanic lithosphere heats
and dehydrates as it
subsides
• The melt rises forming
volcanism
• E.g. The Andes
Ocean-Ocean Plate Collision
• When two oceanic plates collide, one runs over
the other which causes it to sink into the mantle
forming a subduction zone.
• The subducting plate is bent downward to form a
very deep depression in the ocean floor called a
trench.
• The worlds deepest parts of the ocean are found
along trenches.
– E.g. The Mariana Trench is 11 km deep!
Convergent Boundary