INTRO TO PLATE TECHTONICS!

OBJECTIVES FOR THE DAY: AFTER TODAY, YOU SHOULD BE ABLE TO:

• Describe the evidence that first let people to consider that the continents may have been joined together.

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• State Wegener’s four main ideas that support his theory of continental drift.

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• Explain why most geologists did not accept his theory.

SECTION 1 VOCAB

• Continental Drift
• Pangea

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PLEASE READ TO YOUR SELF

• Page 133. Unit 6 section 1.
• Find the answers to these questions (Please be sure to write down the answers):�
• What was the earliest evidence that suggested that the Earth’s continents have moved?
• What were the four things that Wagener used to argue continental drift?
• Why was his thought rejected?

• What was the earliest evidence that suggested that the Earth’s continents have moved?

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• The continents seem to fit together

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• What were the four things that Wagener used to argue continental drift?

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• The fit of the continents
• Fossil evidence
• Similarity of rock types
• Ice age deposits

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WHY WAS HIS THOUGHT REJECTED?�

• There was no explanation of how they moved.

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PLATES

A plate is one of numerous rigid sections of the lithosphere

PLATE TECTONICS

◆ Divergent boundaries (also called spreading centers) are the place where two plates move apart.

◆ Convergent boundaries form where two plates move together.

◆ Transform fault boundaries are margins where two plates grind past each other without the production or destruction of the lithosphere.

ACTIONS AT PLATE BOUNDARIES

• Divergent Boundaries
• ◆ Continental Rifts
• • When spreading centers develop within a continent, the landmass may split into two or more smaller segments, forming a rift.

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ACTIONS AT PLATE BOUNDARIES

◆ A subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate.

• Denser oceanic slab sinks into the asthenosphere.

◆ Oceanic-Continental

• Pockets of magma develop and rise.

• Continental volcanic arcs form in part by volcanic activity caused by the subduction of oceanic lithosphere beneath a continent.

• Examples include the Andes, Cascades, and �the Sierra Nevadas.

Convergent

ACTIONS AT PLATE BOUNDARIES

ACTIONS AT PLATE BOUNDARIES

• Two oceanic slabs converge and one descends � beneath the other.

◆ Oceanic-Oceanic

• This kind of boundary often forms volcanoes on the ocean floor.

• Volcanic island arcs form as volcanoes emerge � from the sea.

• Examples include the Aleutian, Mariana, and �Tonga islands.

9.3 ACTIONS AT PLATE BOUNDARIES

• When subducting plates contain continental � material, two continents collide.

◆ Continental-Continental

• This kind of boundary can produce new mountain ranges, such as the Himalayas.

THE PLATES

EARTHQUAKES

EARTHQUAKES

9.3 ACTIONS AT PLATE BOUNDARIES

◆ At a transform fault boundary, plates grind past each other without destroying the lithosphere.

◆ Transform faults

• Most join two segments of a mid-ocean ridge.

• At the time of formation, they roughly parallel the direction of plate movement.

• They aid the movement of oceanic crustal material.

TRANSFORM FAULT BOUNDARY

TESTING PLATE TECTONICS

◆ Paleomagnetism is the natural remnant magnetism in rock bodies; this permanent magnetization acquired by rock can be used to determine the location of the magnetic poles at the time the rock became magnetized.

• Normal polarity—when rocks show the same magnetism as the present magnetism field

• Reverse polarity—when rocks show the opposite magnetism as the present magnetism field

PALEOMAGNETISM PRESERVED �IN LAVA FLOWS

TESTING PLATE TECTONICS

◆ The discovery of strips of alternating polarity, which lie as mirror images across the ocean ridges, is among the strongest evidence of seafloor spreading.

POLARITY OF THE OCEAN CRUST

HOT SPOT

HOT SPOT

HOT SPOT

MOUNTAINS

• Several ways mountains from
• Volcanoes
• Erosion of softer materials
• Plate tectonics.

FOLDING

• When plates converge, a large amount of force is applied to the rocks of the plate. We call this Stress. Low amount cause the rocks to bend, and may become contorted. High amounts of stress can cause them to fracture.

• Compression: squeezed by stress coming in opposite directions.
• Fold: a bend in a rock layer

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• Anticline: Top of the fold of a rock
• Syncline: Bottom of the fold

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• Monocline: step in the rock caused by a fold

FAULTING

• Compressional stress causes rocks to fold if small, but if it is to powerful it causes it to break. We call the breaks in rocks Faults, but only if movement has occurred.
• Some more vocab words.
• Fracture: a break where the rock did not move.
• Tension: a pulling force
• Hanging wall: the rocks above the fault.
• Foot wall: the rocks below the fault
• Normal wall: where the hanging wall is moving down
• Reverse fault: the hanging wall is moving up.
• Thrust fault: a reverse fault that is a low angle.
• Strike slip fault: movement along the fault I shorizontal

• Strike slip fault

• Folded mountains vs Fault block mountains.
• Fault block mountains: caused by large blocks of the crust to rise or sink due to compression or stress.
• Horst: uplifted blocks
• Graben: downthrown blocks

MOUNTAIN BUILDING PROJECT

• Your assignment is to create a model of mountain building. You can recreate it using any medium you wish to (within reason). Please include both folding and faulting in your presentation.
• Label your model with the following terms:
• Stress
• Tension
• Hanging wall
• Foot wall
• Horst
• Graben
• Anticline
• Syncline

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Please submit your final work in the form of a photograph