Metamorphism

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Metamorphism

• Changes in minerals in an existing rock
• Occurs due to heat and pressure
• Occurs in the solid state
• May include recrystallization (less severe)
  mineral crystals regrow into new forms
• May include remineralization (more severe) some
  minerals are lost, others grow out of existing
  materials

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Contact Metamorphism

• Result depends on original rock
• Extent of metamorphism depends on distance from
  hot body
• No foliation (no pressure)

Image from Peter Nelson, http//www.tulane.edu/sa
nelson/geol212/contactmeta.htm
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Regional Metamorphism

• Occurs from heat and/or pressure
• Result depends on original rock
• May produce features such as foliation and
  lineation

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Shale Sequence

• Shale (sedimentary)
• Slate (clay grains recrystallize and align
  flat)
• Phyllite (mica replaces some clay shiny)
• Schist (mica replaces almost all clay other
  minerals such as garnets grow wavy layers)
• Gneiss (igneous minerals such as feldspars
  replace others layered crystalline rock)

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Metamorphic Grade

• Simple way to classify metamorphic conditions
• Low grade lower temperature, pressure fewer
  changes in rock
• High grade higher temperature pressure more
  changes in rock

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Metamorphic facies

• Sets of temperature and pressure conditions that
  normally produce typical metamorphic rocks
• Allows easy discussion of metamorphic conditions
  and rock types
• Like a recipe for producing a given rock type

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Melanie Kelman, http//www.science.ubc.ca/geol202
/meta/metacon.html