PLATE BOUNDARIES

DESTRUCTIVE (CONVERGENT)

OCEANIC - CONTINENTAL

  • Different densities - denser oceanic plate forced under the continental plate (SUBDUCTION)

  • Deepedning o the ocean at the plate boundary and forms an ocean trench

  • Ocean trench marks the zone of subducation where the ocean crust descends into the asthenosphere

  • Continental crust is buckled and uplifted - vast amounts of materials are injected into it

  • Mountains chains form

  • As the oceanic plate comes under intense pressure, fauling and fracturing occur in the Benioff zone - releases energy causes earthquakes

  • As rising material is less dense than surroundings, it rises towards the surface may create fold mountains

  • Where magma reaches the surface it forms volcanoes

  • Example - Andes

OCEANIC - OCEANIC

  • Slightly denser one will subduct under the other creating a trench

  • Plate melts and magma rises forming chains of volcanoes known as island arcs

  • Nothwest zone of the 'Pacific Rim of Fire’ contains island arcs

CONTINENTAL - CONTINENTAL

  • Little if any subduction occurs - two plates have similar densities

  • Collision of the African and Eurasian plate over past years has created the Alps

CONSERVATIVE PLATE MARGIN

  • Tectonic plates netierh diverge nor converge but slide past each other

  • Volcanic activity is absent

  • Fricitinal resisitance often causes pressure to build up

  • Pressures can cause rocks to fracture, releasing energy causing earthquakes

  • Not associated with landforms

  • Example - San Andreas fault system where Noth American and Pacific plates slide past each other

CONSTRUCTIVE (DIVERGENT)

OCEANIC - OCEANIC

  • Ocean crust is created along mid-ocean ridges

  • Ocean grows wider through sea floor spreading as more lava is erupted

  • Plates pull apart magma is produced by decompression of undrelying zone

  • If magma erupts onto surface of sea floor it is termed a basaltic lava flow

  • Example - Mid-Atlantic Ridge

CONTINENTAL - CONTINENTAL

  • Spreading apart of the surface which is subsequently further deepend by the forces of erosion

  • Tensional forces are strong enough to cause plate to split apart

  • Raised area either side are known as Horsts

  • Drop of centre creates nearly parallel steeply dipping walls of a rift valley

  • Valley widens until it becomes a large basin that fills with sediment from the rift walls of the surrounding area

  • Example - East African Rift Zone