Plate Tectonics

Plate Tectonics

PANGEA

• In 1912 Alfred Wegener thought that all of the continents were connected as one supercontinent called PANGEA. This was about 300 million years ago and over time they drifted apart.

Continental Drift Theory

• http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm#1

The Structure of Earth

• The Earth is made up different types of layers.

• The Lithosphere is divided into large plates.

• Convection currents in the asthenosphere move the plates.

Layers of the Earth

• Crust: Rigid surface of the Earth. It can be between 0-100 km thick, depending on where it is. 2 Types:

• Continental Crust: Thicker parts of the crust (above the ocean)

• Oceanic Crust: Thinner parts of the crust. Under the oceans.

• Mantle: Between the crust and the core. Largest volume of the earth. Mg, Fe, O, Si

• Upper Mantle: Solid part of the mantle

• Lithosphere: Crust and upper mantle.

• Lower mantle: Loose moving due to heat from the core.

• Core: Outer part is liquid and about

2300km thick.

Inner is solid and mostly nickle and iron. *Believed to control the Earth’s magnetic field.

Tectonic Plates

• The lithosphere is broken into 9 large, rigid pieces called plates.

• The plates are all moving in different directions and at different speeds (from 2 cm to10 cm per year)

Plates meet at Plate Boundaries

• There are 3 main plate boundaries:

• 1) Convergent Boundary• 2) Divergent Boundary• 3) Transform Boundary

1. Convergent Boundaries

• Occurs when 2 plates collide.

Oceanic plate is more dense and is forced under the continental plate.

Some of the rock in the Oceanic plate melts as the plate sinks. The melted rock rises up causing earthquakes and volcanic eruptions.

• Where they collide is called a SUBDUCTION ZONE.

• When a continental plate has crashed into a continental plate:

The 2 continental plates are the same density. This causes folding and bending of the plates as

well as earthquakes.Continental plates are folded into mountains.

Example of a Convergent Plate Boundary

• South America: • Oceanic Nazca Plate collides

into the South America plate.

• Formed the Andes Mountains (volcanoes along the mountain crest)

• Formed a deep trench off the

coast in the Pacific Ocean.

• SUBDUCTION AT A PLATE BOUNDARY Animation

Divergent Plate Boundaries• Plates are being pulled apart by

convection currents in the mantle.

• As the plates separate along the boundary, the block between the faults cracks .

• Magma from the mantle rises through the cracks.

• This cools and new crust is formed along the boundary.

• Earthquakes occur along the faults, and volcanoes form where the magma reaches the surface.

Mid Atlantic Ridge

• Mid-Atlantic Ridge is a Divergent Plate Boundary.

• Over 15000 km long.• Average height of 3km.• Sea-Floor Spreading

Animation.• Formation of Oceanic

Crust Animation.

Example of a Divergent Plate Boundary

http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm#1 The Process of Rifting

Transform Boundary• Places where plates slide past

each other.

• Transform boundaries are not marked by spectacular surface features, their sliding motion causes lots of earthquakes.

• Example: San Andreas Fault, shown in the drawing to the right.

• The slice of California to the west of the fault is slowly moving north relative to the rest of California.

HOT SPOT VOLCANOES

• http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm#1 Animation