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Page 1: Plate Tectonics

Plate TectonicsHow the Earth moves

Page 2: Plate Tectonics

The Definition• The theory of plate

tectonics states that the Earth’s lithosphere is divided into pieces called tectonic plates that move around on top of the asthensophere

• Plates are either oceanic or continental

Page 3: Plate Tectonics

These plates drift very slowly—centimeters per year

• Once, the world had one giant supercontinent, called Pangea and one giant ocean.

• Then, over time, the supercontinent spread out, forming the 7 continents we know today—this process is described as continental drift

Page 4: Plate Tectonics

Sea-floor Spreading

• Magma rises from the mantle and solidifies—forming new oceanic lithosphere.

• Once the magma has solidified into the rocky crust, it spreads out in either direction

Page 5: Plate Tectonics

Divergent Boundary

• This is the boundary between two plates that are spreading away from one another– Like the ones found

where sea-floor spreading occurs

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Mid-Atlantic Ridge: A Divergent boundary

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Convergent Boundary

• A convergent boundary is formed where two plates collide with each other

• Three combinations exist:– Continental/continental

– Continental/oceanic

– Oceanic/oceanic

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The Three Collisions: Convergent Boundaries

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Transform Boundaries

• A transform boundary can be found where two plates are sliding past each other horizontally– The most famous of

which is the San Andreas Fault

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The San Andreas Fault—A Transform Boundary

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How Mountains Form

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Types of Mountains—Folded

• Folded mountains form at convergent boundaries where plates collide

• Rock squeezes against rock, pushing it upward

• These form the highest mountains in the world

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Types of Mountains—Fault-Block

• When the crust is tense, the rock can break along a series of faults, causing large rock blocks to drop down lower than other rocks

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Types of Mountains—Volcanic

• Volcanic mountains form when oceanic crust sinks into the asthenosphere by subduction

• These rock melts, forming magma

• This magma, under pressure, eventually rises and erupts through volcanic mountains

Page 15: Plate Tectonics

The Ring of Fire


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