Plate tectonics
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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.

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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.


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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


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Matching Geology

Matching rocks

What is the “true” edge of a continent?


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Matching Geology

Matching rocks

How well do the continents fit?


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Matching Geology

Matching rocks

How well do the ages match?



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Matching Geology

Matching rocks

What evidence did the glaciers leave?


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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



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Apparent Polar Wandering Paths

Paleomagnetism

Apparent polar wandering

Magnetic poles wandered

Used to indicate America and Europe were a single continent



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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


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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



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Types of plate margins

Divergent margins

A boundary along which two plates move apart from one another


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Types of plate margins

Convergent margin

A boundary along which two plates come together


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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


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Types of plate margins

Transform vault

A fracture in the lithosphere where two plates slide past each other


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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


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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


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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




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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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