Download PLATE TECTONICS 2

PLATE TECTONICS
What is plate tectonics?
• Theory based on the idea that the lithosphere
is composed of a # of segments (plates) that
move independently of one another, at
varying speeds over Earth’s surface.
• Based on the principle of buoyancy – that
something less dense (wood) floats on
something denser (water).
EARTH’S INNER FURNACE
Source: http://observe.arc.nasa.gov/nasa/earth/tectonics/Tectonics2_and_a_quarter.html
Isostacy
• Theory which holds that the Earth’s crust
floats on the denser layers beneath, like a
boat floats on water.
• Where the load is greater, the crust rides
lower in the asthenosphere.
• Where the load is lighter, the crust rides
higher.
http://geology.er.usgs.gov/eastern/plates.html
Divergent Plate Boundaries
• Crustal plates are
spread apart = rifting
• Molten material wells
up b/wn separated
plates, hardens, and
forms ridges.
• = new sea floor; aka
sea-floor spreading.
• Ex: Mid-Atlantic Ridge
http://observe.arc.nasa.gov/nasa/earth/tectonics/Tectonics3.html
Convergent Plate Boundaries
• “Collision zones”;
continental and oceanic
crust collide.
• Subduction = when the
edge of the heavier plate
sinks under the crust on
the lighter plate
– Deep ocean trenches
– Mountain chain as the
lighter plate is pushed up
• Example: western edge
of South America
http://observe.arc.nasa.gov/nasa/earth/tectonics/Tectonics3.html
Transform Plate Boundaries
• Occur where plates
slide laterally past one
another at right angles
to a sea-floor spreading
center.
• They neither diverge
nor converge.
• No volcanic eruptions.
http://observe.arc.nasa.gov/nasa/earth/tectonics/Tectonics3.html
http://pubs.usgs.gov/publications/text/Vigil.html