Liquid, hot MAGMA 8'1

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Liquid, hotMAGMA8.1 8.4
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Asthenosphere

• 100-350 km deep- in the mantle
• only 1 actually molten
• most SOLID (plastic) rock
• Why?

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How does magma form?

• Increase temp.- least important
• Decrease pressure. pressure-release melting
• Add water- wet rock melts at a lower temp than
  dry rock.

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Where does magma form?

• Spreading centers
• Mantle plumes
• Subduction zones

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Spreading centers

• Pressure-release melting forms basaltic magma
• Forms new ocean crust at mid-ocean ridges.

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Mantle plumes

• hot spot
• Hotter rock is less dense, more buoyant

                                                
                                                  
                                                  
                 Revealing the plume beneath
Hawaii1. The Hawaiian Island chain was formed
by a plume of hot, buoyant rocks from the mantle,
but scientists know little about it.2. To
determine the plumes depth, width, and
temperature for the first time, scientists plan
to deploy 35 ocean-bottom seismographs.3. The
OBSs will record earthquake-generated seismic
waves traveling through the plume, revealing new
insights on how mantle plumes work.
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Subduction zones

• Addition of water (most important)
• Decreasing pressure
• Heat from friction of plates (least important)
• Ring of Fire

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Basaltic vs. granitic magma

• Mafic magma vs. felsic magma
• Granitic magma is formed when basaltic magma
  rises beneath a continent and melts the
  continental crust.
• Ex. Subduction zone (oceanic-continental),
  continental rift zone, mantle plume beneath a
  continent.

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Basaltic vs. granitic magma

• Basaltic magma
• 50 silica
• 1-2 water
• Flows easily
• Usually rises to the surface

• Granitic magma
• 70 silica
• Up to 10 water
• Thick, viscous
• Usually hardens in crust (plutons)

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Mafic (Basaltic) Lava
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Felsic (Granitic) Lava Explosive eruptions