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1. In your own words describe Continental Drift Hypothesis
2. How did Wegener support his hypothesis?
3. Why do you think he chose this type of information?
4. Why was the continental drift hypothesis rejected?
5. What is the difference between the Theory of
Continental Drift and the Theory of Plate Tectonics?
(c) McGraw Hill Ryerson 2007
III. Layers of the Earth
•
•
•
•
Crust
Mantle
Outer core
Inner core
Crust
• Outermost layer,
• relatively solid, brittle rock layer
Continental crust
– approx. 50 km thick
– made from less dense type of rock called granite
Oceanic crust
– approx. 10 km thick
– made from dense rock called basalt
Mantle
•
•
•
•
Thickest layer: 2900 km thick
Iron, magnesium and silicon
Upper Mantle: solid, more cool and brittle
Lower Mantle: molten rock, solid, dense
– Flows like toothpaste
Outer Core
• 2200 km thick
• Made up of liquid iron and nickel
Inner Core
• 1200 km thick
• solid iron and nickel (due to tremendous
pressure)
• Extremely hot 5,500°C
Tectonic Plate Layers
LITHOSPHERE:
• Outer layer of rock composed of crust
and part of upper mantle.
• Makes up the
tectonic plates
• 65-100 km thick
ASTHENOSPHERE:
• Makes up molten layer beneath plates
• Lower Mantle
• So hot it behaves like plastic, less rigid, flows
like toothpaste
Tectonic Plates
•
•
•
•
12 major plates and many smaller ones.
Oceanic Plates – contain dense basalt
Continental Plates – granite
Interactions between lithosphere and
asthenosphere help explain plate tectonics
because the hotter, plastic mantle material
(asthenosphere) beneath can flow enabling
plates (lithosphere) to move.
Questions
1. Tectonic plates are composed of which parts
of Earth’s layer?
2. What are two types of tectonic plates?
3. Describe two features of each.
V. Plate Interactions : Boundaries
• Plate boundaries are marked by earthquakes,
volcanoes, mountain ranges and ocean
trenches
• There are three main types of plate
boundaries:
• Divergent
• Convergent
• Transform
• Melting crust rises beneath the subduction
zone, forming volcanoes parallel to the plate
boundary;
• trenches are found beneath the ocean where
the oceanic crust subducts;
1) Divergent Boundaries
• When two plates separate and create new
oceanic crust.
• Sea floor spreads along a mid-ocean ridge.
• Can also occur in middle of continents
(continental rifting)
• Mid-Atlantic ridge –
• largest mountain range
Divergent Boundaries
• Mid-Atlantic ridge
Divergent Boundaries
Endeavour hydrothermal vents were created as
the Juan de Fuca plate moves away from the
Pacific plate
Diverging Plates
• Diverging plates at the East African Rift are
slowly breaking Africa into pieces
Convergent Boundaries
• Where two plates collide
• Denser crust eventually goes below the lessdense crust (subduction), causing deep sea
trenches to form
• Volcanoes and Mountains form, earthquakes
common
• variable results depending on the plates
involved
a) Continental-Oceanic Plates
• When dense oceanic plates collide with
continental plates, the oceanic plate will sink
under the continental plate and be pushed
into the mantle (subducted).
• Continental crust is less dense than oceanic
crust and never subducts
• Cone-shaped
volcanoes of West
Coast of North
America are result
of oceanic –
continental
convergence
between Juan de
Fuca Plate
(oceanic) and
North American
Plate (continental).
• Cascade Mountain
Range
• Mount Garibaldi – result
of the Juan de Fuca plate
subducting under the
North American plate
• Mount Meager
c) Oceanic-Oceanic Plates
• When two oceanic plates collide, usually one
plate subducts beneath the other.
• Volcanic Island Arcs form above the nonsubducting plate.
• Islands of Japan
and Indonesia
and the Aleutian
Island of Alaska
Pacific Ring of Fire
Pacific Ring of Fire
• The Ring of Fire is a major area in the basin of
the Pacific Ocean where a large number of
earthquakes and volcanic eruptions occur.
(c) McGraw Hill Ryerson 2007
c) Continental-Continental Plate Convergence
• When continental plates collide, neither plate
is dense enough to be pushed down, so the
land buckles like a car hood in a car crash
(“uplifting”), forming mountain ranges;
Himalayan Mountain Range
• Himalayas formed from Indian continent
colliding with Asian continent.
• Continue to increase in elevation by several
cm per year
3) Transform Boundaries
• Where two plates slide by each other
• Results in frequent earthquakes and faults
• Fault – breaks in rock layers due to movement
on either side
3) Transform Boundaries
• First identified by Canadian geologist, John
Tuzo Wilson.
• Earthquakes are common at these boundaries
• Oct 2012, an earthquake of magnitude of 7.7
originated from movement along the Queen
Charlotte Fault.
Transform Boundary
• San Andreas
Fault
Plate Boundary Symbols
III. Plate Motion
• Tectonic plates make up the lithosphere (crust
and upper portion of mantle), which floats on
the asthenosphere (molten, lower mantle).
• Tectonic plates are all moving at the same
time
III. Plate Movement
• Variable temperature causes convection currents
See pages 520 - 522
(c) McGraw Hill Ryerson 2007
Mantle Convection
• Molten rock called magma in the mantle is heated up
near the core of the earth and becomes less dense
and buoyant.
• Warmer, less dense material rises and cooler, denser
material sinks, causing convection current.
• As magma moves,
it drags the tectonic
plates above with it.
• Rising magma pushes plates apart at
spreading centers in oceans
• Colder, dense magma near the surface sinks.
• The rotation causes movement of the plates.
The Earth’s Temperature
• As you go deeper into the Earth’s crust, the
temperature increases about 1oC for every 40
m of depth
• Beneath the crust, this temperature rise
gradually slows, until a core temperature of
about 7000oC is reached.
• The Earth’s heat comes from:
• radioactive element decay (uranium,
potassium, thorium);
• friction between rock masses in the crust
and mantle;
• heat left over from planetary formation.
Two other processes affecting plate
movement
Ridge Push – rising material spread out as it
reaches the upper mantle. This cause the
lithosphere to lift and push tectonic plates apart
at divergent plate boundaries.
Slab Pull
• Slab Pull – as the leading edge of a subducting
plate sinks, it pulls the rest of the plate with it
at convergent plate boundaries. Gravity and
convection assist this movement.
1. Name and draw three main types of tectonic
plate boundaries.
2. Why does subduction not occur at some
kinds of tectonic plate boundaries?
3. Describe the process that results in a volcanic
island arc.
4. Name a mountain range produced by
continental-continental plate convergence.