Metamorphic Rocks

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Metamorphic Rocks

• Ch 4 S4

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Introduction

• Rocks can go through process of metamorphism
• Metamorphism a change in the constitution of
  rock specifically a pronounced change effected
  by pressure, heat, and water that results in a
  more compact and more highly crystalline
  condition
• Metamorphic rocks are rocks in which the
  structure, texture, or composition has been
  changed
• Can be changed by heat, pressure, or both

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Origins of Metamorphic Rock

• Texture/mineral composition can change (?) when
  surroundings change (?)
• Occurs between 50ºC 1,000ºC
• Can occur over 1000ºC
• Metamorphic change takes place more than 2 km
  beneath the surface of the Earth

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Contact Metamorphism

• Occurs near igneous intrusions
• Occurs near bodies of magma
• Rock is heated and changed by the nearby magma

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Regional Metamorphism

• Occurs when pressure builds up in rock buried
  under other rock formations or when Earths crust
  collides
• Occurs over thousands of km3 within the rocks
  crust
• Found beneath continental rock formations

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Regional Contact Metamorphism
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Composition of Metamorphic Rock

• Metamorphism occurs when temperature pressure
  inside the Earths crust change
• Minerals change into different minerals that are
  more stable in the new environment
• Index minerals minerals that form only at
  certain temperatures pressures
• Used to measure temperature, depth, pressure at
  which a rock undergoes metamorphosis
• Include biotite mica, chlorite, and garnet

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Recrystallization Index Minerals
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Textures of Metamorphic Rock

• 2 textures
• Foliated
• Nonfoliated

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Foliated Metamorphic Rock

• Texture mineral grains are arranged in planes or
  bands
• Contains aligned grains of flat minerals
• Diagram shows a sedimentary rock transforming via
  metamorphism

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Nonfoliated Metamorphic Rock

• Texture mineral grains are not arranged in
  planes or bands
• Made of one or only a few minerals
• Mineral crystals may change in size or mineral
  may change in composition

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Metamorphic Rock Structures

• Deformation a change in the shape of a rock due
  to a force placed on it
• Rock may be squeezed or stretched
• Bends in the rock are indicators