Divergent Boundaries

Two plates moving AWAY from each other and forming a gap or RIFT.

• Mostly associated with OCEANIC crust[seafloor spreading = Mid-Atlantic Ridge]– as molten rock [MAGMA] from the mantle rises

the plates move apart, and fills the space between the plates.

– as it cools, it hardens onto the edges of the plates and creates new crust.

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“CONSTRUCTIVE”DIVERGENT PLATES2

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Divergent Boundaries

• Some involve the CONTINENTAL crust

– when it begins to separate, the stretched crust forms a long, narrow, depression called a RIFT VALLEY

• it is currently happening between the African and Arabian plates Red Sea is therefore widening

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DIVERGENT

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RIFT VALLEYS 6

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Mediterranean Sea

Convergent BoundariesTwo plates moving TOWARDS each other.

• Direct COLLISION of one plate with

another one.

• There are three POSSIBILITIES:– CONTINENTAL – OCEANIC– OCEANIC – OCEANIC– CONTINENTAL – CONTINENTAL

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CONTINENTAL - OCEANIC • As the plates are colliding, the denser plate will be

forced downwards

• Since the oceanic crust is denser than the continental crust, the ocean plate is pushed under continental plate. [crust destruction]The area is called a SUBDUCTION ZONE, and forms a deep-ocean trench

• As the plate sinks into the mantle, it melts and becomes magma. The magma rises through the continental plate and forms a volcanic chain

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OCEANIC CONTINENTAL

“DESTRUCTIVE”

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Mount Hood near Portland, Oregon

Cascades range11

Mount St. Helens, Washington

Cascades range

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Volcanic mountains of the Andes, (Nazca and South American Plates)

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TRENCH

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OCEANIC – OCEANIC • The more dense of the 2 will go under and form

a subduction zone / OCEAN TRENCH• The new mantle material produced from the

melting of the subducted plate will eventually resurface to produce chain of volcanic islands on the ocean floor called ISLAND ARCS

• As magma accumulates over time, the volcanoes may rise above sea level to form volcanic islands:

Mariana trench and the Mariana Islands in the west Pacific ocean

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OCEANIC-OCEANIC CONVERGENCE

“DESTRUCTIVE”

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CONVERGENT PLATES “DESTRUCTIVE”

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CONTINENTAL - CONTINENTAL• As the 2 continental plates are colliding,

neither plate is subducted i.e. neither plate goes beneath the other WHY?

– because the Continental crust is too buoyant to sink into the mantle.

• The colliding edges buckle and are pushed upward to form mountain ranges.

Indian/Australian plate collide with the Eurasian plate to form the HIMALAYAS.

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CONTINENTAL – CONTINENTAL CONVERGENCE23

The collision of India and Asia produced the Himalayas (before)

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The collision of India and Asia produced the Himalayas (after)

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Mountain Building

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Transform BoundariesTwo plates PASSING each other.

• Plates are grinding past each other and the crust is either cracked or deformed.

• Motion is not smooth but rather in spurs of sudden moves generating EARTHQUAKES*

• They are followed by periods of low or no activity San Andreas Fault

* Earthquakes can occur / are common along all boundaries27

TRANSFORMFAULT

“CONSERVATIVE”Crust is nor created nor destroyed

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Tectonic plates can include

A. only asthenosphere.

B. only oceanic crust

C. only continental crust

D. both oceanic and continental crust.

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Features found at divergent boundaries include ____.

A. ocean ridges

B. deep-sea trenches

C. crumpled mountains

D. island arc volcanoes

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Continental-continental plate collisions produce ____.

A. island arcs

B. rift valleys

C. deep-sea trenches

D. very tall mountain ranges

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The theory that explains why and how continents move is called

A. continental drift

B. paleomagnetism

C. plate tectonics

D. sea-floor spreading

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The Himalaya Mountains were formed in a collision at a

A. divergent boundary

B. convergent boundary

C. transform boundary.

D. fracture zone

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Crust is neither destroyed nor formed along which of the following

boundaries?

A. convergent

B. divergent

C. transform

D. magnetic

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SUMMARY

Direction of movement

Type of Boundary/ impact on crust

Plates involved Geological activities/features

Examples

Importance of plate tectonics

• Theory provides an explanation of Earth’s major surface processes

• Geologists have found explanations for the geologic distribution of earthquakes, volcanoes and mountains and the distributions of plants and animals fossils.

#1 MATCH

• DIVERGENT

• CONVERGENT

• TRANSFORM

• CONSERVATIVE

• DESTRUCTIVE

• CONSTRUCTIVE

What causes Plate Movement?

While several models have been proposed to explain the

DRIVING MECHANISM responsible for their movement,

there is no doubt that the Earth’s internal heat is the DRIVING

FORCE.

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DRIVING MECHANISM

Convection Currents the rising-sinking action of magma due to the heat in Earth’s core

Magma close to the core is heated, It expands, lowering its density, and then rises

Closer to the crust, the magma cools, it contracts, increasing its density, and then sinks due to gravity

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Convection currents 44

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The driving mechanism of tectonic plates movement are related to

convection currents in Earth’s ____.

A. crust

B. mantle

C. inner core

D. outer core

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The downward part of a convection current causes a sinking force that ____.

A. pulls tectonic plates toward one another

B. moves plates apart from one another

C. lifts and splits the lithosphere

D. creates a divergent boundary

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Which of the following is an example of a divergent plate boundary?

A. [Option 1]

B. [Option 2]

C. [Option 3]

D. [Option 4]

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At what type of plate boundary does sea-floor spreading occur?

A. convergent oceanic-oceanic boundaries

B. convergent oceanic-continental boundaries

C. divergent oceanic-oceanic boundaries

D. transform boundaries

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The force behind the movement of Earth’s plates is

A. cooling of magma cells that rises to the Earth’s surface

B. magnetic attraction between Earth’s iron core and its poles

C. temperature differences between Earth’s oceanic and continental plates

D. the Earth’s internal heat producing convection currents in the mantle.

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