plate tectonics. objectives explain how paleomagnetism provided the definitive evidence for...
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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?
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