Earth Science 2.4 : Metamorphic Rock


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Earth Science 2.4 : Metamorphic Rock

  1. 1. Metamorphic rock<br />Earth Science<br />Chapter 2.4<br />
  2. 2. Objectives:<br />Describe two ways a rock can undergo metamorphism.<br />Explainhow the mineral composition of rocks changes as the rocks undergo metamorphism.<br />Describe the difference between foliated and non-foliated metamorphic rock.<br />Explain how metamorphic rock structures are related to deformation.<br />
  3. 3. Origins of Metamorphic Rock<br />Metamorphic rocks <br />Rocks in which the structure, texture, or composition of the rock have changed<br />All three types of rock can be changed by heat, pressure, or a combination of both<br />A rock’s texture or mineral composition can change when its surroundings change<br />If the temperature or pressure of the new environment is different from the one in which the rock formed<br />the rock will undergo metamorphism<br />
  4. 4. Contact metamorphism<br />When magma moves through the crust, the magma heats the surrounding rock and changes it.<br />Some minerals in the surrounding rock are changed into other minerals by this increase in temperature.<br />The greatest change occurs where magma comes into direct contact with the surrounding rock.<br />
  5. 5. Regional metamorphism<br />occurs when pressure builds up in rock that is buried deep below other rock formations<br />or when large pieces of the Earth’s curst collide with each other.<br />The increased pressure and temperature causes rock to become deformed and chemically changed.<br />
  6. 6. Composition of Metamorphic Rock<br />As rocks undergo metamorphism<br />Original minerals in a rock change into new minerals that are more stable within the new pressure and temperature conditions.<br />Index minerals (form only in metamorphic rock)<br />Are used to estimate <br />Temperature<br />Depth<br />Pressure ---- at which a rock undergoes meta-morphism.<br />calcite<br />+<br />+<br />+<br />Heat and Pressure<br />=<br />quartz<br />hematite<br />Garnet<br />
  7. 7. Texture of Metamorphic Rock<br />Two types:<br />Foliated Metamorphic Rock<br />Mineral grains are arranged in planes or band<br />Usually contains aligned grains of flat minerals, such as biotite, mica or chlorite<br />Metamorphic rocks can become other metamorphic rocks if the environment changes again.<br />Nonfoliated Metamorphic Rock<br />Mineral grains are not arranged in planes or band<br />commonly made of one or only a few minerals.<br />Recrystallization<br />Process in which crystals of these minerals may change in size or the mineral may change in composition<br />
  8. 8. This shows what happens to shale, a sedimentary rock, when it is exposed to more and more heat and pressure.<br />Slate<br />Shale<br />Phylite<br />Schist<br />Gneiss<br />
  9. 9. Two examples of nonfoliated metamorphic rock<br />undergoes<br />metamorphism<br />Marble<br />limestone<br />undergoes<br />metamorphism<br />Sandstone<br />Quartzite<br />
  10. 10. Metamorphic Rock Structures<br />Metamorphic rock has features that indicates its history. These features are caused by deformation:<br />Change in the shape of a rock caused by a force placed on it.<br />These forces may cause a rock to be squeezed or stretched.<br />Folds, or bends, in metamorphic rock are structures that indicate a rock has been deformed.<br />