Plate Tectonics
Objectives Describe how plates move. Explain the features of plate tectonics. Describe the types of plate boundaries and the features that can form and events that can occur at each.
The Theory of Plate Tectonics The Theory of Plate Tectonics incorporates and builds on the Theory of Continental Drift and Sea-Floor Spreading. It explains the large-scale motions of the Earth s lithosphere including continental drift and sea-floor spreading.
The Theory of Plate Tectonics States that the earth s lithosphere is broken into moving plates. Plates are rigid blocks of the earth s lithosphere about 15-300 km thick.
Plates There are seven major and 18 minor plates.
How do Plates Move? Plate movement is powered by the Earth s radioactive, super-hot core. Lithospheric plates sit on top of the asthenosphere, a layer of much hotter, softer, more malleable rock.
How do Plates Move? Because of the high temperatures and immense pressure found in the uppermost part of the asthenosphere, it is deformed and flows almost plastically just beneath the lithosphere. Because the asthenosphere flows, lithospheric plates are also able to flow at about the rate human fingernails grow.
Lava Lamps
How do Plates Move? One idea that might explain the ability of the asthenosphere to flow is the idea of convection currents. When rock materials near the core are heated, they become less dense than the cooler, upper mantle rock material. The warmer rock material rises while the cooler rock material sinks, creating slow, vertical currents within the mantle.
How do Plates Move? This movement of warmer and cooler mantle rock material creates pockets of circulation within the mantle called convection cells. The circulation of these convection cells could be the force that causes the movement of tectonic plates over the asthenosphere.
Plate Boundaries Plates fit together like puzzle pieces. The places where they meet are called boundaries. Three types of boundaries
Divergent Plate Boundaries When two plates are moving apart, leaving a space between them.
Rifting Occurs when two plates are forced apart. Can split continents. Generally occurs in the oceans.
Convergent Plate Boundaries When two plates collide.
Convergent Plate Boundaries When two continental plates collide the land is buckled and lifted up to form mountains.
Convergent Plate Boundaries The Himalayas in Asia, the Andes Mountains in South America, and the Rocky Mountains in North America were all formed by convergent plate boundaries.
Subduction When a continental plate and an oceanic plate collide, the ocean plate is forced under the continental plate because the ocean plate is thinner and more dense. The continental plate is buckled to form mountains.
Subduction The ocean plate is destroyed by intense heat and pressure in the asthenosphere.
Trenches Subduction forms deep valleys in the ocean floor called trenches.
Earthquakes at Subduction Zones As the ocean plate slips beneath the continental plate, the plates can become locked, build stress, and suddenly slip causing an earthquake.
Volcanoes at Subduction Zones As the ocean plate slips underneath the continental plate, it melts forming magma. The less dense magma can rise to the surface through cracks in the crust forming volcanoes.
Transform Plate Boundaries When plates slide past one another.
Transform Plate Boundaries As plates move past each other sections of the plates may become locked. Stress builds up until the plates suddenly slip causing an earthquake.
Transform Plate Boundaries The San Andreas Fault in California is an example of a transform plate boundary.
Plotting Plate Boundaries Scientists have been able to locate plate boundaries, determine plate characteristics, and predict the movement of plates by plotting the locations of earthquakes.
Explain how earthquakes happen in Mexico and Western South America.
List the colors of the arrows where Earthquakes are likely.
Review Which type of plate boundary would most likely form a mountain range? Which type of plate boundary would most likely form a trench? Which type of plate boundary would most likely cause an earthquake?