Metamorphic Rocks

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Metamorphic Rocks

• Metamorphism is the alteration of a preexisting
  rock (the parent rock) due to heat and pressure
  caused by burial in the earth. The parent rock
  must adapt to the new conditions and it does so
  by changing mineral composition and texture.

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Metamorphic Texture

• 2 types
• Non-foliated (granular)
• Foliated

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Non-foliated (granular) texture

• uniform in composition they are all one mineral
  so the minerals do not segregate into layers -
  like the picture to the right.
• Examples
• quartz quartzite
• calcite marble
• exception hornfels)

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Examples
Quartz quartzite
Calcite marble
Exception Hornfels can have any of a wide
diversity of microscopic minerals, all too small
to see or identify without thinsection and a
specialized microscope.
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Non-foliated

• We must be careful not to confuse mineral
  layering with color banding in some rocks color
  banding looks superficially like mineral
  layering, but color banding without mineral
  layering is not foliation for example in this
  serpentinite.)

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Foliated Texture

• results when the new metamorphic minerals (many
  of which are platy micas such as biotite and
  muscovite) line up producing a distinct layering
  in the rock.

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Foliated textue

• The layering produces three distinctly different
  looking rocks those with slaty cleavage (e.g.
  slate), schistosity (e.g. schist), and mineral
  banding (or gneiss texture). Metamorphic rocks
  are identified on these textures

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Examples
Schistocity Schist
Slaty cleavage Slate
Mineral banding gneiss
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Kinds of Metamorphism

• There are 5 kinds of metamorphism
• Focus on 2
• Barrovian (regional)
• Contact

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Barrovian Metamorphism

• takes place during mountain building events when
  very large areas of sedimentary rocks are buried,
  squeezed, and heated.
• Sometimes the metamorphism occurs just because
  the burial is deep enough, but often it is also
  associated with major igneous intrusions that
  supply most of the heat.

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Contact Metamorphism

• Contact metamorphism occurs in the " country
  rock" (the rock intruded by and surrounding an
  igneous intrusion). Rocks are " baked" into a
  ceramic from heat escaping from intrusives, often
  enhanced by hot fluids.
• pressure is not a significant factor in the
  contact process

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