plate tectonics. sea-floor spreading process by which new oceanic lithosphere is created as older...
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Plate Tectonics
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Sea-Floor Spreading
• Process by which new oceanic lithosphere is created as older materials are pulled away
• Creates Mid-Ocean Ridges– Underwater Mountain Chains
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Theory of Plate Tectonics• Theory that both continental and oceanic
crust move• Theory states:– Earth’s lithosphere is divided into tectonic plates
that move around on top of the asthenosphere
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Causes of Motion• Heat and Gravity• Convection– Hot material rises and cooler
material sinks. Drags tectonic plates sideways
• Slab Pull– Oceanic lithosphere is denser
than the asthenosphere.– Oceanic plate sinks and pulls the rest of the plate with it
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Tectonic Plate Boundaries• Convergent – Two plates push into another – Result depends on what type of crust• Continental / continental– Push crust upward
• Continental / Oceanic–Oceanic plate slides under
• Oceanic / Oceanic–One of the plates slides under
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Tectonic Plate Boundaries• Divergent – Two plates move away from each other– Examples:• Sea-floor spreading• Mid-ocean ridges are the most common• Can be found on continents
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Sea-Floor Spreading Process• Plates move away from each other• Creates a gap in the sea floor• Magma rises to fill gap• Magma cools and forms underwater
mountains
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• Newer Crust = At the Mid-ocean crust• Older Crust = Edges of continents
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Tectonic Plate Boundaries• Transform– Two plates slide past each other
horizontally– Plates are smooth so they grind and jerk• Cause Earthquakes
– Example• San Andreas Fault in California
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Tracking Plate Motion
• Slow and Gradual• Measured in centimeters per year• Measure using GPS– Global Positioning System