Igneous Rocks

• What makes up large parts of the continent and oceanic rocks?

  Igneous Rocks
• The common rocks are igneous rocks
• Igneous rocks indicate plate boundaries and hot spots.
• What is a magma?

  A molten rock below the earth’s surface.
• Magma solidifies into plutonic/intrusive igneous rock.
• Magma erupts as either lava/pyroclastic materials. Pyroclastic materials and lava cool to form volcanic (extrusive) igneous rocks.
• What is viscosity?

  Resistance to flow.
• What controls viscosity?

  Primarily controlled by temperature and composition.
• Higher temperature=lower viscosity. Lowe temperature=higher viscosity.
• UMIF

  Ultramafic have the least silica and high Fe and Mg

  Mafic have less silica and Fe and Mg Rich

  Intermediate is between felsic and mafic

  Felsic is silica-rich and low in Fe and Mg
• Low viscosity (mafic) is runny because of higher temperature and less silica content.

  High viscosity (felsic) is thick because of lower temperature and higher silica content.
• Patrial melting is a magma that is less mafic than the parent rock.
• Composition of a rock is ruled by the source area.

  Melting mantle = mafic magma

  melting crust = felsic/intermediate magma
• Magma mixing = similar viscosities
• Magma mingling = diff viscosities
• Grain size determines the cooling speed of the rock.
• Rocks that are fine-grained cooled fast. Rocks that are coarse-grained cooled slow.
• Volcanic (extrusive) rocks are fine-grained with aphanitic texture.
• Plutonic (intrusive) rocks are coarse-grained.


  Coarse-grained = phaneritic texture

  Extremely coarse pegmatitic texture

  Complex/non-uniform = porphyritic

  holes = vesicular

  ash = pyroclastic

  no grains = glassy
• Welded tuff are formed when particles are buried before cooling down.
• Non-welded tuff (rhyolitic tuff) forms when particles cooled before burying.
• Plutons are bodies of igneous rocks which have intruded on country rock