Metamorphism in Geology

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Questions and Answers

What process is primarily involved in changing a rock into a metamorphic rock?

  • Changes caused by heat and pressure without melting (correct)
  • Melting due to high temperatures
  • Sedimentation from volcanic ash
  • Chemical alteration due to weathering

Which of the following is NOT a cause of metamorphism?

  • Heat from nearby igneous intrusions
  • Deep burial of rocks
  • Exposure to surface conditions (correct)
  • Pressure from tectonic movements

What ultimately supplies the high temperatures needed for metamorphism?

  • Surface volcanic activity
  • Chemical reactions in the earth's crust
  • Earth's internal heat and igneous intrusions (correct)
  • Solar radiation

What kind of changes occur during metamorphism?

<p>Alterations in texture, mineral composition, and chemical composition (D)</p> Signup and view all the answers

Which factor contributes to the pressure conditions required for metamorphism?

<p>Compression from tectonic movements (D)</p> Signup and view all the answers

What characterizes foliated metamorphic rocks?

<p>Layers and bands of minerals caused by high pressure (A)</p> Signup and view all the answers

What process describes the change of existing crystal size and shape in metamorphic rocks?

<p>Recrystallization (D)</p> Signup and view all the answers

What happens to minerals during metamorphism under new temperature and pressure conditions?

<p>They undergo solid-state alterations (B)</p> Signup and view all the answers

How does foliation develop in metamorphic rocks?

<p>Through the application of pressure from opposite directions (A)</p> Signup and view all the answers

The recombination of elements in existing minerals results in what outcome during metamorphism?

<p>Formation of new and stable minerals (C)</p> Signup and view all the answers

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Study Notes

Metamorphism

  • Occurs when rocks are altered by heat, pressure, or fluids.
  • Changes the texture, mineral composition, and chemical composition of rocks without melting them.
  • Derived from Earth's heat, buried under layers of rocks or adjacent to igneous intrusions.
  • The pressure required for metamorphism is from either deep burial or tectonic plate compression.

Directed Stress

  • Results in shearing and compressive stress.
  • Causes rocks to deform and change shape.

Metamorphic Minerals

  • Minerals in rocks undergo solid-state alterations.
  • Change into new minerals that are more stable under the new temperature and pressure conditions.

Effects of Metamorphism

  • Mineralogical Changes: Minerals change to reflect the new pressure and temperature equilibrium conditions.
    • Recrystallization: Existing crystals change in size and shape to form layers or interlocking crystals.
    • Recombination: Elements in pre-existing minerals recombine to form stable new minerals.
    • Addition/Subtraction of ions: Common in the presence of fluids during metamorphism.
  • Metamorphic Textures:
    • Foliated metamorphic rocks are characterized by layers and bands of minerals due to pressure during metamorphism.
    • Foliation develops perpendicular to the direction of the pressure.
    • Nonfoliated metamorphic rocks have blocky crystal shapes with no layering.
    • Increasing grain size parallels changes in composition and development of foliation. This is not a factor for nonfoliated rocks.

Grades of Metamorphism

  • Different combinations of temperature and pressure produce different grades: low, intermediate, and high.
  • Each grade is associated with a specific set of minerals and textures.
  • Metamorphism of shale produces the colorful minerals observed in slate.
  • Prograde metamorphism: A series of increasing changes in mineral composition and textures as the temperature and pressure increases. Example: slate → phyllite → schist → gneiss → migmatite

Types of Metamorphism

  • Regional Metamorphism: Occurs when high temperatures and pressures affect large regions of Earth's crust.
    • Produces large belts of metamorphism that range from low to high grade.
    • Results in mineral and rock type changes, folding, and deformation of rock layers.
  • Contact Metamorphism: Occurs when molten material, such as in igneous intrusions, comes in contact with solid rock.
    • High temperatures and moderate-to-low pressure result in specific mineral assemblages.
  • Hydrothermal Metamorphism: Occurs when very hot water reacts with rock, altering its chemical and mineral composition.
    • Commonly occurs near igneous intrusions and active volcanoes.
    • Chemical changes are common.

Economic Importance of Metamorphic Rocks and Minerals

  • Many economic mineral resources are produced by metamorphic processes.
  • Metallic Mineral Resources: Many metallic deposits are precipitated from hydrothermal solutions.
  • Nonmetallic Mineral Resources: Metamorphism produces resources such as talc, asbestos, and graphite.

The Rock Cycle

  • Igneous Rocks: Crystallize from magma.
  • Sedimentary Rocks: Form from cemented or precipitated sediments.
  • Metamorphic Rocks: Form from changes in temperature and pressure.

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