Metamorphism and Metamorphic Rocks

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Metamorphism and Metamorphic Rocks
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Rock Cycle
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Metamorphic Rocks

• Mineral composition or texture of the rock is
  changed by heat, pressure, or fluid

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Agents of Metamorphism

• Heat
• Pressure
• Fluid activity

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Pressure

• Lithostatic pressure
• Pressure caused by weight of material above
• P rgd
• r is density, g is gravity, d is depth
• Implies the deeper you are, the pressure increases

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Metamorphism Changes Rocks in Two Ways

• Composition
• New minerals stable at higher temperatures or
  pressures (for example clays are changed to
  micas) Chlorite, Garnet
• Texture
• Foliation

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Classification of Metamorphic Rocks

• Texture
• Minerals
• Grain size
• Metamorphic grade (how much rock has been
  altered)
• Low, medium, high

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Types of Metamorphism

• Contact metamorphism
• Dynamic metamorphism
• Regional metamorphism

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meta aureole
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Contact metamorphism

• Alteration around intrusion
• shale to hornfels

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Regional metamorphic rocks

• foliated
• Slate
• Phyllite
• Schist
• Gneiss

• nonfoliated
• Quartzite
• Marble

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Foliated Metamorphic Rocks

• platy minerals
• Slates --slaty cleavage, mostly clays
• Phyllites -- phyllitic sheen, tiny mica crystals
• Schists --schistocity flakiness large mica
  crystals.
• Gneisses have bands of different minerals.

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foliation
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Mylonite
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slate
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slate 2
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schist
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gneiss
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migmatite
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Nonfoliated metamorphic rocks

• Marble from limestone.
• Quartzite from sandstone

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nonfoliated texture
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Marble
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Sandstone
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Quartzite
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Metamorphic facies

• low grade -- high grade
• Blueschist (blue mineral glaucophane)
• Low Temp, High Pressure
• Greenschist (has chlorite green)
• Low Pressure, Higher Temp
• Granulite
• High Temp

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metamorphic facies
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Michigan metas
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Metamorphic Rocks and Plate Tectonics

• High-Pressure and Low Temp in Trenches
• High-Pressure and High Temp, Deep and in
  Collisions
• High-Temp and Low Pressure near volcanoes

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Meta facies plate tect
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Important Minerals

• Asbestos
• Serpentine (Chrysotile from serpentine)
• Fibrous, curly form
• Bulk of commercial asbestos (95)
• Non-toxic
• Amphibole (Crocidolite from slates, schists)
• Long,course, spinning fiber
• Toxic
• EPA treats all asbestos as the same Huge
  economic impact

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Contact Metamorphic Minerals

• Many formed by fluid interactions
• Copper, iron, lead, tin, talc, graphite
• Garnet and corundum used as abrasives or
  gemstones
• Andalusite, silliminate, kyanite used for hi-temp
  porcelains (sparkplugs furnace linings)

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Group Exercise

• What type of environment do you think the
  following rocks were formed (temp and pressure)
• Where would they occur in a subduction zone?
• If you could change one thing in this class, what
  would it be? (BESIDES THE INSTRUCTOR!)

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