Metamorphic Rocks

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Metamorphic Rocks
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Metamorphism

• Metamorphic rocks form from igneous or
  sedimentary rocks which have been exposed to heat
  and/or pressure.
• Metamorphism occurs when heat and pressure break
  some of the bonds in the minerals, but not enough
  to melt the rock.
• There are 3 main agents that cause metamorphism
  heat, pressure, and circulating fluids.

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Heat

• Metamorphism triggered by a change in temperature
  is caused when
• A rock moves to a greater depth (and hence,
  warmer temps) by tectonic movement or deep burial
  under sedimentary deposits, or
• Magma rises up intrusively and bakes the
  surrounding rock
• Magma creates what is known as contact
  metamorphism

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Pressure

• Metamorphism is triggered by a change in
  pressure, caused when
• A rock is deeply buried under sedimentary
  deposits, or
• Tectonic plates slide or collide, exposing rocks
  at the plate boundaries to extreme pressure
• This can create mountains and is known as
  regional metamorphism

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Pressure

• There are two kinds of pressure
• Confining pressure pushes on rocks equally from
  all directions, compressing them and reducing
  their size, or
• Directed pressure pushes on rocks greater in one
  direction than the other. This tends to bend or
  stretch the rock and align its minerals in the
  direction of the pressure. This alignment is
  called foliation.

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Confining Pressure
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Circulating Fluids

• Fluids (usually water) circulate underground and
  drive metamorphism by either speeding up the
  movement of a rocks own elements or by adding or
  removing ions to change the overall composition
  of the rock.

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Limestone is a sedimentary rock.
When exposed to heat and pressure, limestone
metamorphoses into marble.
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Shale is a sedimentary rock.
When exposed to heat and pressure, shale
metamorphoses into slate.
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Sandstone is a sedimentary rock.
When exposed to heat and pressure, sandstone
metamorphoses into quartzite.
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Coal is a sedimentary rock.
When exposed to heat and pressure, coal
metamorphoses into anthracite.
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Granite is an igneous rock.
When exposed to heat and pressure, granite
metamorphoses into gneiss.
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Talc is a silicate mineral
When exposed to heat and pressure, talc minerals
metamorphoses into soapstone.
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Basalt is an igneous rock.
When exposed to heat and pressure, basalt
metamorphoses into schist.
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3 Main Metamorphic Environments
High temperature/low pressure
Low temperature/high pressure
High temperature/high pressure