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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
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–2
Convection Currents: The movement of a fluid, caused by differences in temperature, that transfers heat from one part of the fluid to another
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–3
• 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.
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–4
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
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–5
Figure 1-13 Transform Motion
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–6
Geology at a Glance Plate Boundaries (cont'd)
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–7
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
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–8
Geology at a Glance Plate Boundaries (cont'd)
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–9
Figure 1-12a Continental Collision
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–10
Figure 1-12b Continental Collision (cont'd)
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–11
Figure 1-11 Plate Subduction
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–12
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
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–13
Geology at a Glance Plate Boundaries (cont’d)
Copyright © Houghton Mifflin Company. All rights reserved. Essentials of Geology, 1b–14
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
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Major Plates
• Six major plates:– Eurasian– African– Indo-Australian– Pacific– North American– South American
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