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