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Metamorphic Rocks

Metamorphic Rocks. Ch 4 S4. 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

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Metamorphic Rocks

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  1. Metamorphic Rocks Ch 4 S4

  2. 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

  3. 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

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

  5. Regional Metamorphism • Occurs when pressure builds up in rock buried under other rock formations or when Earth’s crust collides • Occurs over thousands of km3 within the rocks crust • Found beneath continental rock formations

  6. Regional & Contact Metamorphism

  7. Composition of Metamorphic Rock • Metamorphism occurs when temperature & pressure inside the Earth’s 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

  8. Recrystallization & Index Minerals

  9. Textures of Metamorphic Rock • 2 textures • Foliated • Nonfoliated

  10. 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

  11. 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

  12. 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

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