PLATE TECTONICS What is plate tectonics Theory based

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/Tectonics 2_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/Tectonics 3. 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/Tectonics 3. 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/Tectonics 3. html

http: //pubs. usgs. gov/publications/text/Vigil. html