Partial Melting

• Decompression Melting


  Occurs beneath Mid Ocean Ridges

  Pressure is reduced by thinning of the lithosphere and covection brings hot mantle material up

  Increases the geothermal gradient
• Flux Melting

  Occurs at Covergent Plate Boundry

  water or CO2 is are added - the melting temp is lowered

  By lowering the melting temp rock could partially melt to generate magma
• Magma Types

  Ultra-Mafic, Mafic, Intermediate, Silic
• Ultra-Mafic & Mafic = Shield Volcano

  Intermediate & Silic = Stratovolcano
• Mantle

  Ultra-Mafic
• Divergent Plate Boundary

  Decompression Melting, Mafic Melt = Shield Volcanoes
• Ocean Lithosphere

  Mafic
• Convergent Plate Boundary

  Flux Melting, Intermediate Melt = Startovolcano
• Continental Lithosphere

  Silic
• Exsolution of Volatites

  Reduction of pressure allows dissolved gases to exsolve forming bubbles -> Increase the pressure in the magma chamber and can trigger an eruption
• 1. In Silic magma the expansion of magma to gas is resisted causing explosive eruptions
  2. In Mafic magma expansion is easy due to less viscous magma