Plate Tectonics

Objectives

• Summarize the theory of plate tectonics• Identify and describe the three types of plate

boundaries• List and describe three causes of plate

movement.

Warm-Up Question

• Where was the majority of Pangaea located compared to the equator?

• What were the southern portions of today’s land masses of S. America, Africa, India, and Australia covered with?

• What was used to map the ocean floor?

Plate Tectonics

• Plate Tectonics is the theory that explains why and how continents move and is the study of the formation of features in Earth’s crust.

• It turns out that the upper section of the mantle (asthenosphere)is stuck to the underside side of the lithosphere to form what we call tectonic plates

Plate TectonicsPlate Tectonics

Tectonic Plates

• 15 major tectonic plates• Many are bordered by major surface features,

such as mountain ranges or deep trenches in the ocean, the boundaries of the plates are not always easy to identify.

• Some boundaries are located within continents far from mountain ranges.

Tectonic PlatesTectonic Plates

Boundaries

• Identified from studying data from earthquakes.

• When plates move, sudden shifts can occur along their boundaries

• This sudden movement is called an earthquake.• Frequent earthquakes in given zones are

evidence that two or more plates may meet in an area.

Boundaries

• Volcanoes can also help to identify boundaries.

• Some volcanoes form when plate motions generate magma that erupts on Earth’s surface.

Where are we going?Where are we going?

We appear to be headed for another super continent (Pangaea Ultima) as North America,

South America, Asia and Australia converge in the ever shrinking Pacific Ocean

Plate BoundariesPlate Boundaries• Convergent – plates move toward one

another

• Divergent – plates move away from each other

• Transform – plates slide past each other

Convergent Plate Boundaries

• Plates collide as they move toward each other.• Three Types– Suduction zone – Oceanic lithosphere collides with

continental lithosphere. The oceanic lithosphere sinks under the continental lithosphere. Causing trenches and volcanic arcs.

Convergent Boundaries

– Continental lithosphere collides with continental lithosphere. This causes the two sides to crumple and uplift. They then form large mountain ranges.

– Oceanic lithosphere collides with oceanic lithosphere. This causes causes trenches to form and magma to be released and rise to the surface so to form an Island Arc or chain of volcanic islands.

Convergent PlatesConvergent Plates

Divergent Plate Boundaries

• Plates move away from each other, allowing magma from the asthenosphere to rise to the surface.

• The magma then cools and forms new oceanic lithosphere.

Divergent Boundaries

• Magma from the asthenosphere rises to the surface as the plates move apart. Forms mid ocean ridges with rift valley’s in the middle.

• Mostly located on the ocean floor.

Divergent PlatesDivergent Plates

Transform Plate Boundaries

• The boundary at which two plates slide past each other horizontally.

• The edges typically do not slide along smoothly. Instead, they scrape against each other in a series of sudden spurts of motion that are felt as earthquakes.

• Do not produce magma.

Transform boundaries

• Facture zones are a type of transform boundary.

Transform PlatesTransform Plates

Transform PlatesTransform Plates

San Andreas Fault

In Summary…In Summary…

Why do the Plates Move?Why do the Plates Move?• No single idea explains everything but we can

identify several forces that contribute to the movement of the plates.– Slab pull

• The sinking of the cooled dense oceanic plates pulls on the rest of the plate

– Ridge push• The material deposited on the top of the ridge slides downs from

the rift pushing on the plate– Convection

• Movement within the mantle could be part of the driving force behind the motion of the plates.

Why do the Plates Move?Why do the Plates Move?

Homework:

• Read Pages 247 -254• Answer Questions 1-7