plate tectonics
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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. - PowerPoint PPT PresentationTRANSCRIPT
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Plate Tectonics
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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.
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Continental Drift Theory
• http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm#1
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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.
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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
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• 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.
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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)
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Plates meet at Plate Boundaries
• There are 3 main plate boundaries:
• 1) Convergent Boundary• 2) Divergent Boundary• 3) Transform Boundary
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1. Convergent Boundaries
• Occurs when 2 plates collide.
Oceanic plate is more dense and is forced under the continental plate.
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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.
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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
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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.
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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.
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Example of a Divergent Plate Boundary
http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm#1 The Process of Rifting
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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.
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HOT SPOT VOLCANOES
• http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm#1 Animation