6.2 The Theory of Plate Tectonics

How is water in a pot that is held over a flame become heated throughout, even though the flame touches only the bottom of the pot?

Plate tectonics The theory that Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere.

Tectonic plates Pieces of the lithosphere that move around on the top of the asthenosphere Tectonic plates float on the asthenosphere like ice cubes float in juice.

Tectonic Plate Boundaries A boundary is a place where tectonic plates meet. Locations of earthquakes, volcanoes, and landforms.

Why do tectonic plates made of continental lithosphere displace more asthenosphere than tectonic plates made of oceanic lithosphere do ? Continental lithosphere has a greater thickness and displaces more asthenosphere than thin oceanic lithosphere does.

Plate Tectonics

Convergent Boundaries The boundary where two tectonic plates collide.

Three Types Two continental plates collide which forms a mountain range. An oceanic plate collides with a continental plate which causes the more dense oceanic plate to sink (subduction). Subduction can cause a chain of volcanoes to form parallel to the plate boundary.

Two oceanic plates collide Two oceanic plates collide. The denser plate subducts which causes series of volcanic islands, called an island arc.

Divergent Boundaries The boundary where two tectonics plates separate. Some boundaries happen on land (Iceland and eastern Africa)

Divergent Boundaries Some boundaries happen on the sea floor. As the plates pull apart fractures form on the ocean floor. Magma solidifies to form new lithosphere.

Transform Boundaries The boundary at which two tectonic plates slide past one another horizontally. Occurs mostly in the sea floor at the mid-ocean ridge. Another example is San Andreas fault.

Compare the three types of plate boundaries. At convergent boundaries, tectonic plates are colliding. When these collisions occur, mountain ranges or a chain of volcanoes or volcanic islands may form. At divergent boundaries, a series of fractures forms in the lithosphere as plates separate. Magma rises through these fractures to form new lithosphere. At transform boundaries, two tectonic plates slide past each other horizontally.

Tectonic Plate Motion Plate movement happens because of the difference in density caused by the flow of heat within the Earth.

Convection occurs in the Earth’s core and mantle moving the heat. Convection currents is the process where hot, less dense rock rises and at the surface cold, dense rock subducts.

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What is the theory of plate tectonics? Review Questions What is the theory of plate tectonics? The theory of plate tectonics is the theory that explains how tectonic plates move and change shape. Describe the three types of plate boundaries. At convergent plate boundaries, tectonic plates collide. At divergent boundaries, tectonic plates separate. At transform boundaries, two plates slide past each other horizontally.

How does the motion of tectonic plates relate to continental drift? The continents are carried along as passengers on the moving tectonic plates. 4. How do mountain building and volcanoes relate to plate motion at convergent boundaries? Volcanoes form at convergent and divergent plate boundaries. Mountains form where two plates of continental lithosphere collide.

Quiz 6.2 Review convergent boundaries Divergent boundaries Transform boundaries Convection in mantle Plate tectonics Tectonic plates Boundary Flow of heat (warmer to cooler) Sea-floor spreading