lecture 3 plate tectonics (cont.d) © 2011 pearson education, inc. earthquakes as evidence most...
TRANSCRIPT
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Lecture 3
Plate Tectonics (cont.d)
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Earthquakes As Evidence
• Most large earthquakes occur at subduction zones.
• Earthquake activity mirrors tectonic plate boundaries.
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Global Distribution of Earthquakes
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Global Plate Boundaries
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Plate Tectonics Theory
• Lithosphere – tectonic plates that float on ductile asthenosphere
• Large scale geologic features occur at plate boundaries
• Two major tectonic forces– Slab pull– Slab suction
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Types of Plate Boundaries
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Examples of Plate Boundaries
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Divergent Boundary Features
• Plates move apart• Mid-ocean ridge
– Rift valley• New ocean floor
created• Shallow focus
earthquakes
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Generation of a Divergent Boundary
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Types of Spreading Centers• Oceanic rise
– Fast-spreading– Gentle slopes– East Pacific
• Oceanic ridge– Slow-spreading– Steep slopes– Mid-Atlantic
• Ultra-slow– Deep rift valley– Widely scattered volcanoes– Arctic and southwest India
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Types of Spreading Centers
East Pacific Rise
Mid-Atlantic Ridge
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Convergent Boundary Features
• Plates move toward each other• Oceanic crust destroyed
– Ocean trench– Volcanic arc
• Deep focus earthquakes
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Three Types of Convergent Boundaries
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Types of Convergent Boundaries
• Oceanic-Continental Convergence– Ocean plate is
subducted– Continental arcs
generated– Explosive andesitic
volcanic eruptions
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Types of Convergent Boundaries
• Oceanic-Oceanic Convergence– Denser plate is subducted– Deep trenches generated– Volcanic island arcs generated
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Types of Convergent Boundaries
• Continental-Continental Convergence– No subduction– Tall mountains uplifted
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Transform Boundary Features
• Offsets oriented perpendicular to mid-ocean ridge– Segments of plates slide past
each other
• Offsets permit mid-ocean ridge to move apart at different rates
• Shallow but strong earthquakes
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Transform Boundary Features• Oceanic Transform Fault – ocean floor only• Continental Transform Fault – cuts across
continent• All transform faults
occur between mid-ocean ridge segments.
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Plate Interior (non-plate boundary)Topography Formation:
• Mantle Plumes and Hotspots– Intraplate features
• Volcanic islands within a plate• Island chains
• Record ancient plate motions– Hotspot Track
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Global Hotspot Locations
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Hawaiian Island – Emperor Seamount Hotspot Track
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Plate Tectonics and Intraplate Features
• Seamounts – Rounded tops
• Tablemounts– Flattened tops
• Subsidence of flanks of mid-ocean ridge• Wave erosion may flatten seamount
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Coral Reef Development
• Fringing reefs – develop along margin of landmass
• Barrier reefs – separated from landmass by lagoon
• Atolls – reefs continue to grow after volcanoes are submerged
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Coral Reef Development
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Detecting Plate Motion with Satellites
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Paleogeography
• Paleogeography – study of ancient continents
• Continental accretion– Continental material added to edges of
continents through plate motion
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Paleogeographic Reconstructions
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Future Predictions
• Future positions of continents and oceans– Assume same direction and rate of plate
motions as now
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World Map 50 million Years in Future
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Wilson cycle
• John Tuzo Wilson
• Life cycle of ocean basins–Formation
–Growth
–Destruction
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Wilson cycleWilson cycle