Plate Tectonics

Plate Tectonics

Where plates meet, distinct boundaries form. There are three types of boundaries that form between plates.

Divergent Boundaries

• Divergent Boundaries are also called constructive margins and form when two plates are moving apart and new crust material rises up from the mantle creating new crust.
• Some prominent divergent boundaries are found along the oceanic ridge system.
  • This system is found running through all major oceans.
  • These ridges can be 1000 to 4000km wide.
• The mechanism responsible for creating new seafloor along the oceanic ridges is called seafloor spreading.
• The rate of seafloor spreading varies with location
  • From 2cm per year in the North Atlantic to 15cm per year in the East Pacific Rise
• Future divergent boundaries are formed from continental rift systems.
  • A rift system develops when a continent is centered over a hot spot of the mantle.
  • The increased heat causes the continental crust to expand and form a dome
  • As expansion increases, faulting of the rock occurs and volcanoes result.
  • The rift, over time, will break the plate into smaller plates.
  • Typical rift systems have 3 arms, or spread in 3 directions.
  • Examples:
    • East African Rift Valley
    • Baikal Rift in South Central Siberia
    • Rhine Valley in Northwest Europe
    • Rio Grande Rift

Convergent Boundaries

Convergent boundaries, also known as destructive margins, occur where two plates collide together. If two plates that are carrying continental crust collide, mountain ranges result.

If two plates carrying oceanic crust collide, one plate will subduct under the other forming a subduction zone resulting in a trench, under water volcanoes and/or volcanic island arcs.

When one plate carrying continental crust collides with a plate carrying oceanic crust, the oceanic plate will subduct under the continental crust plate. This sometimes results in the formation of continental volcanic arcs.

Transform Boundaries

Transform boundaries are called conservative margins. These boundaries form where two plates grind past each other without producing or destroying lithosphere.