Transcript ESC101 Ch 4 Plate Tectonics

PLATE TECTONICS
Objectives
• Explain how paleomagnetism provided the
definitive evidence for continental drift.
• Define seafloor spreading.
• Define theory of plate tectonics.
• Describe the different types of plate margins.
• Explain the role of mantle convection in plate
tectonics.
A Revolution in Geology
• Continental drift
• Proposed by Alfred
Wegener
• Slow, lateral
movement of
continents along
Earth’s surface
• The puzzle piece
argument
• Pangaea
• Continental shelf
• Continental slope
Matching Geology
• Matching rocks
• What is the “true” edge of a continent?
Matching Geology
• Matching rocks
• How well do the
continents fit?
Matching Geology
• Matching rocks
• How well do the ages match?
Matching Geology
Matching Geology
• Matching rocks
• What evidence did the glaciers leave?
Matching Geology
• Matching fossils
• What evidence did
the glaciers leave?
• Glossopteris: ancient
tree with large seeds
found on several
continents
• Mesosaurus: small
reptile found in Brazil
and S. Africa
Matching Geology
Apparent Polar Wandering
Paths
• Paleomagnetism
– Apparent polar
wandering
• Magnetic poles
wandered
– Used to indicate
America and Europe
were a single
continent
Apparent Polar Wandering
Paths
Seafloor Spreading
• The missing clue
– Seafloor spreading
• The process by which the seafloor splits and moves apart
along a midocean ridge
• New oceanic crust forms along the ridge
– Global Positioning Systems (GPS) valuable tool
The Plate Tectonic Model
• Plate tectonic
– The movement and interactions of large fragments of
Earth’s lithosphere (i.e. plates)
– Below lithosphere- asthenosphere
• Weak due to hot temperature (near melting point)
– Relationship between lithosphere and asthenosphere
is isostasy
• Fault
– A fracture in Earth’s crust along which movement has
occurred
The Plate Tectonic Model
Types of plate margins
• Divergent
margins
– A boundary along
which two plates
move apart from
one another
Types of plate margins
• Convergent margin
– A boundary along which two plates come together
Types of plate margins
• Subduction zone
– A boundary along which one lithosphere plate plunges
into the mantle beneath another plate
• “Collision zone” between continents
– Deep oceanic trenches
– Arcs of volcanoes
Types of plate margins
• Transform vault
– A fracture in the
lithosphere where
two plates slide
past each other
Earthquake and plate margins
• Earthquake
– Tectonic movement produce pressure and friction.
– Friction is overcome, the block slips and pent up energy releases
with a huge “snap”
– Focus
• Where earthquake begins
– Epicenter
• Point on earth’s center directly over the focus
The search for a mechanism
• Earth’s internal heat
– Conduction
• Slow release of heat
– Convection
• A form of heat transfer
in which hot material
circulates from hotter to
colder regions, looses
its heat, and then
repeats the cycle
The tectonic cycle
• Tectonic cycle
– Movements/ interactions by which rocks are cycled from the mantle to
the crust and back
– Includes earthquakes, volcanism, and plate motion, driven by
convection in the mantle
– As a result, seafloor recycles itself every 200 million years
The tectonic cycle
Hawaiian Islands
Critical Thinking
• What are some of the important questions about
plate tectonics that remain unanswered today?
• Why do geologists call plate tectonics a “unifying
theory”?
• As Africa slowly separated from Arabia, and the sea
began to enter the rift, what kind of sediment would
you expect to be deposited?