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Lab 06 ONLINE

LESSON

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lesson…

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Plate Tectonics

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Plate Tectonics is a geologic idea that states

the surface of the planet is covered by a series of

rigid plates that move…

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These plates move away each other

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These plates move toward each other

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These plates move past each other

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Plate Tectonics is driven by heat within the interior

of the planet…

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A current theory suggests that radioactive materials are

the source for the earth’s internal heat…

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This heat melts the surrounding rock

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Melted rock (magma) rises to the surface and

pushes the plates…

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There are three types of plate boundaries

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Divergent, Convergent and

Transform

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Divergent boundary: the plates move away from

each other

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Convergent boundary: the plates move toward

each other

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Transform boundary: the plates move past each

other

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A transform boundary: cuts across a divergent

boundary…

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A divergent boundary is also referred to as a spreading center,

such as the Mid Atlantic Ridge…

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A divergent boundary is a part of the earth’s

surface where new crust is formed…

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A convergent boundary is also

known as a subduction zone…

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Subduction is the process of pushing

seafloor crust into the interior of the

planet…

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A convergent boundary is where

crust is destroyed and massive earthquakes

occur…

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A transform boundary is also known as a

fracture zone or fault…

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The San Andreas Fault is a well known transform fault in this area…

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Earthquakes occur at all of these

boundaries because solid rock is moving against solid rock…

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The bigger earthquakes occur at the convergent and

transform boundaries…

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But small and shallow earthquakes can

occur at transform and divergent boundaries…

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Shallow earthquakes occur at divergent

boundaries because the crust is thin…

5 -10 km thick…

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The following is a map of many

divergent, convergent and transform boundaries…

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Plate Tectonics can be thought of as a

grand unifying theory in geology…

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Meaning that many geologic phenomena are associated with

Plate Tectonics

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And can be explained by Plate Tectonics

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At convergent boundaries …volcanoes,

earthquakes and mountains and deep sea

trenches can be formed…

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Right click to play

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Also at convergent boundaries …the deepest

earthquakes occur

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Subducted seafloor is pushed into the interior of the

planet….

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As much as 650 kilometers

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At divergent boundaries …heat,

volcanoes, earthquakes and new

seafloor can be formed…

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Since new seafloor is formed at the divergent

boundaries…the notion of seafloor spreading can

also be observed…

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Seafloor crust is made primarily of iron rich (MAFIC)

minerals

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These MAFIC minerals are subject to the earth’s

magnetic field…

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Magma rises up from the interior of the planet…

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And punches through the ocean crust to form new

crust…

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The newly formed MAFIC crust can record the

prevailing magnetic field

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The earth’s magnetic field has changed direction over the course of the life of the

planet

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North has become south and the other way around…

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These magnetic reversals have been recorded in the

seafloor crust

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These records can tell us such things as the rate of movement of the plates…

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Each recorded event is a time marker…

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The newest crust is at the point where magma rises from the

interior of our planet…

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The older crust is further away…

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Oceanic crust as old as 200,000,000 years old can

be detected…

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How can spreading rates be determined from magnetic

reversals?

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Here is a section of the ocean floor’s magnetic

reversals…

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Seafloor spreading begins here…

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And ends up here…

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The distance of seafloor movement is read here…in

this case…1425 kilometers…

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The time is read here…in this case…78,000,000 years…

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Spreading rates are always noted in

cm/year

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1425 km = 142,500,000 cm

142,500,000 cm

78,000,000 years

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So the spreading rate is 1.83 cm/year

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Hot Spots are places on the planet where magma rises up to produce pinpoint

volcanic eruptions…

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There are about 40 hotspots on the planet…

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A hotspot can be described as a plume of magma rising up and punching through the crust…

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The Hawaiian Islands are an example of a hotspot…

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The hotspot plume is currently under the main island of

Hawaii…

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The Pacific Plate is moving northwest…

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The plates move while the plume is stationary…

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END

L06