Metamorphic Rocks

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Metamorphic Rocks

• Mr. Ahearn
• Earth Science 2010

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What are Metamorphic Rocks?

• Form at conditions between those that produce
  igneous and sedimentary rocks
• Most found under thousands of meters sed. rx

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Conditions Promoting Metamorphism

• Heat
• Pressure
• Circulating Fluids

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Types of Metamorphism

• Regional
• Contact
• Other
• Hydrothermal
• Fault
• Shock
• Pyrometamorphism

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Regional Metamorphism

• Large belts of regional metamorphism are produced
  when high temperature and pressure affect large
  regions of Earths crust.
• can be low grade, intermediate grade, and high
  grade.

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Regional Metamorphism

• Some key minerals are used to map metamorphic
  zones.

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Contact Metamorphism

• contact metamorphism occurs when molten rocks,
  such as those in an igneous intrusion, come in
  contact with solid rock. (small scale)
• High temperature and moderate-to-low pressure
  form the mineral assemblages that are
  characteristic of contact metamorphism.

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Contact Metamorphism

• temperature decreases with distance from an
  intrusion, metamorphic effects also decrease with
  distance.
• limited to thin zones.

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Metamorphic Textures

• Foliated metamorphic rocks are characterized by
  wavy layers and bands of minerals.
• High pressure during metamorphism causes minerals
  with flat or needlelike crystals to form with
  their long axes perpendicular to the pressure.

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Metamorphic Textures

• Nonfoliated metamorphic rocks lack mineral grains
  with long axes in one direction.
• Nonfoliated rocks are composed mainly of minerals
  that form with blocky crystal shapes.
• Ex. ? Quartzite and marble.

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Common Metamorphic Rocks

• Foliated
• Slate
• Phyllite
• Schist
• Gneiss
• Nonfoliated
• Marble
• Quartzite
• Hornfels

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Amphibolite
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Gneiss
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Slate
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Hornsfels
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Phylite
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Marble
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Quartzite
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Schist
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Metamorphic Facies and Plate Tectonics

• Metamorphic Facies assemblages of different
  minerals that are commonly found together
• Indicate specific temp pressure conditions
• Indicators of ancient subduction zones
• Low temp/ high pressure
• High temp/ high pressure
• High temp/ low pressure

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Metamorphic Rock Uses

• Strength and Stability
• Building materials
• Valued highly for appearance
• Sculptors- marble, serpentinite
• Talc- powder, flame resistant asbestos
• Garnet- abrasive
• Minerals associated with meta rx
• Zinc, lead, copper, iron, gold

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The End