PLATE TECTONICS!

CONVERGENT

DIVERGENT

• OCEAN-OCEAN
  • old sea floor subducted
  • ex: ocean trenches ie Aleutian Trench
  • volcanic activity, shallow to deep earthquakes
• OCEAN-CONTINENT
  • old sea floor subducted
  • ex. continental volcanic arc ie Peru-Chile
  • volcanic activity, shallow to deep earthquakes
• CONTINENT-CONTINENT
  • mountain building
  • ex. mountain ranges ie the Alps
  • no volcanic activity, shallow to intermediate earthquakes

• OCEAN-OCEAN
  • new sea floor created
  • ex. mid-ocean ridges ie Mid-Atlantic Ridge
  • volcanic activity, shallow earthquakes
• CONTINENT-CONTINENT
  • continents break apart
  • ex. continental rifts & shallow seas ie the Red Sea
  • volcanic activity, shallow earthquakes

• OCEAN-OCEAN
  • transform faults, fracture zones
  • ex. Clipperton Transform Zone
  • no volcanic activity, earthquakes
• CONTINENT-CONTINENT
  • transform faults, fracture zones
  • ex. San Andres Fault
  • no volcanic activity, earthquakes

MECHANISMS

• weight of cold dense downgoing slab pulls plate down & away

• friction between lithosphere & asthenosphere drag plate along convection cell and down & away

ALSO

• age-depth relationship
• lithosphere cools->sinks lower in ductile asthenosphere
• can estimate sea floor age from depth (distance traveled/age=spreading rate)

• volcanoes or geothermal action not on a plate boundary (often form island chains ie Hawaii)
• hotspots appear stationary relative to center of Earth
• thus as plates travel across the hotspots island chains are formed
• islands can be aged by knowing plate direction, distances between, and/or age
• source of hotspots still controversial