The Theory of Plate Tectonics

Plate Tectonics Plate tectonics is the theory that the Earth’s lithosphere is divided into tectonic plates that move around the top of the asthenosphere. Plate boundaries – a place where tectonic plates touch: collide, separate, or slide past each other.

Three types of plate boundary Convergent Divergent Transform

Convergent Boundaries Convergent boundaries - the boundary formed by the collision of two lithospheric plates. There are three styles/types of convergent plate boundaries Continent-continent boundaries Continent-oceanic boundaries Ocean-ocean boundaries

Continent-Continent Collision Continent-Continent Collision - when the two plates collide, they buckle and thicken, which pushes the continental crust upward Forms mountains, e.g. European Alps, Himalayas

Himalayas

Continent-Oceanic Crust Collision Continent-Oceanic Crust Collision - the denser oceanic crust sinks below the continental crust where it is remelted and recycled Called subduction zone; can form volcanoes

Subduction

Ocean-Ocean Plate Collision Ocean- Ocean Plate Collision - when two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone. The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench. The worlds deepest parts of the ocean are found along trenches.

Age of Oceanic Crust Courtesy of www.ngdc.noaa.gov

Divergent Boundaries - The boundary between two tectonic plates moving away from each other As the plates move apart, magma rises to fill the gap; can cause volcanic activity Mid-ocean ridges are the most common type

Iceland Iceland has a divergent plate boundary running through its middle

Transform Boundaries Two tectonic plates slide past each other horizontally Above: View of the San Andreas transform fault

San Andreas Fault, CA