copyright © houghton mifflin company. all rights reserved. essentials of geology, 1b–1 plate...

Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–1

Plate Tectonics

• A geological theory that states that pieces of Earth’s crust are in constant, slow motion, driven by convection currents in the mantle

• The plates of the lithosphere float on the top of the asthenosphere

• Convection currents rise in the asthenosphere and spread out beneath the lithosphere

• Geologists believe this causes plate movement


Convection Currents: The movement of a fluid, caused by differences in temperature, that transfers heat from one part of the fluid to another


• Plates are a section of the lithosphere that slowly moves, carrying pieces of continental and oceanic crust

• As plates move, they collide, pull apart, or grind past each other producing spectacular changes in the earth’s surface.


Transform Boundary

• A plate boundary where two plates move past each other in opposite directions

• Crust is neither created nor destroyed

• Fault lines are usually created in which earthquakes happen


Figure 1-13 Transform Motion


Geology at a Glance Plate Boundaries (cont'd)


Convergent Boundaries

• A plate boundary where two plates move toward each other

• Collisions can occur between:– oceanic crust and oceanic crust (subduction)

• deep ocean trenches

– oceanic crust and continental crust • volcanic eruptions

– continental crust and continental crust• mountain ranges


Geology at a Glance Plate Boundaries (cont'd)


Figure 1-12a Continental Collision


Figure 1-12b Continental Collision (cont'd)


Figure 1-11 Plate Subduction


Divergent Boundaries

• A plate boundary where two plates move away from each other

• Most divergent boundaries occur at the mid-ocean ridge

• Divergent boundaries that occur on land are called rift valleys

• Ocean Basins are usually the result of this type of movement


Geology at a Glance Plate Boundaries (cont’d)


Summary of Boundaries

• Transform– Plates slip past each other (grind)

• Convergent – Plates come together (collide)

• Divergent – Plates move apart (pull apart)

Geology at a Glance Plate Boundaries


Major Plates

• Six major plates:– Eurasian– African– Indo-Australian– Pacific– North American– South American

copyright © houghton mifflin company. all rights reserved. essentials of geology, 1b–1 plate...

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essentials of geology

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glance plate boundaries

plate subduction slide

continental collision

causes plate movement