Ocean / Continental Divergence

  • Oceanic crust is denser than continental crust, when plates collide the oceanic crust is subducted into the upper mantle, asthenosphere.
  • Subduction creates several features characteristic of destructive margins. As the ocean crust descends, friction with the overlying continental crust builds up and causes major earthquakes in the Benioff Zone, the zone of earthquake formation.
  • Destructive margins are some of the most seismically active zones in the world, with shallow to deep focus earthquakes charting the descend of subducted crust into the mantle.
  • Rocks scraped off the descending plate and folding of the continental crust help to create young fold mountains, such as the Andes along the west coast of South America.
  • Deep ocean trenches are found along the seaward edge of destructive margins. The deepest point of the Peru-Chile trench is 8,065m deep.
  • The friction created by the descending slab of ocean floor generates enormous heat, leading to partial melting of the crust.
  • This allows the release of gases, including carbon dioxide trapped within the descending ocean crust, causing a build-up of pressure in the upper layers of the asthenosphere.
  • Magma derived from the melting of old ocean floor basalts are less dense than the mantle; they try to rise through fissures and by burning their way through overlying rock until they reach the surface.

Vulcanicity is a key feature of subduction zones; around 80% of all active volcanoes are found above subduction zones.