Plate Tectonics

Plate Tectonics:  Unifying geological theory which explains almost all geological processes on Earth by the interaction of lithospheric plates driven by convection currents in the mantle, which in turn are driven by the heat flow from the Earth's still hot interior.

Lithospheric Plate Interactions:

1.  Mid-oceanic ridge:  seafloor spreading zone where new oceanic crust material (basalt) wells up as two oceanic plates spread apart.  example:  mid-atlantic ridge

2.  Oceanic trench with island arcs:  subduction zone where two oceanic plates converge.  One plate is subducted and melts producing a more viscous magma material (andesite) which gives rise to explosive volcanos forming island arcs.  example:  Japanese islands and associated trench

3.  Oceanic trench with costal volcanic mountain range:  subduction zone where an oceanic plate is subducted below a continental plate.  The oceanic plate melts the upwelling of andesitic magma produces explosive volcanos which form a costal volcanic mountain range.  example:  Cascade range in N. America (northwest)

4.  Uplifted mountain range:  convergence zone where two continental plates converge.  Neather plate subducts and the resulting slow intense compression causes the rock layers to fold and uplift into mountain ranges.  example:  Himalayan mountain range

5.  Rift valley:  spreading zone beginning in a continental plate, eventually becomes a mid-oceanic ridge.  example:  eastern African rift valley

6.  Volcanic islands not associated with subduction zones:  islands formed by volcanic eruption of balsaltic lava over a mantle hot spot under the central area of an oceanic plate.  A mantle hot spot and its associated magma chambers produce shield volcanos at the surface that build volcanic islands over the hot spot.  As the plate moves over the mantle hot spot the island volcanos are disconected from their magma sources and begin to erode back to sea level by the action of wind and waves.  example:  Hawaiian island chain

7.  Earthquake fault zone (note "in-out" arrows in diagram):  two lithospheric plates move parallel to each other at their boundries.  As the two plates "stick" and "slip" pass one another, major earthquakes may be generated.  example:  San Andreas fault in southern California