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Earth Systems 3209

Earth Systems 3209. Reference: Chapters 2, 3, 6, 7; Appendix A & B. Unit: 3 Earth’s Materials. Unit 3: Topic 5.1. Metamorphism - Overview. Focus on . . . defining and describing the processes involved in metamorphism. outlining the agents of metamorphism.

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Earth Systems 3209

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  1. Earth Systems 3209 Reference: Chapters 2, 3, 6, 7; Appendix A & B Unit: 3Earth’s Materials

  2. Unit 3: Topic 5.1 Metamorphism - Overview Focus on . . . • defining and describing the processes involved in metamorphism. • outlining the agents of metamorphism. • distinguishing between high and low grade metamorphism.

  3. Metamorphism - Overview • Metamorphism literally means to “change form.” • Metamorphism causes a change in the rock’smineral composition and texture. • What causes the changes? (i.e. Change Agents) • Heat/Temperature • Pressure • Hot Chemical Fluids (e.g. Water) • These changes occur at various depths beneath Earth’s surface, from 2 -3 km depth to the crust - mantle boundary (MOHO).

  4. Metamorphism - Overview • All three types of rocks (i.e. igneous, sedimentary, and metamorphic) can be metamorphosed. • Example: Granite (Ign.) “changes to” Gneiss (Met.) • Example: Sandstone (Sed.) “changes to” Quartzite (Met.) • Example: Slate (Met.) “changes to” Phyllite(Met.) • Metamorphism DOES NOT involve a melt and there IS NO recrystallization of minerals from such a melt. • It is the hot chemical fluids that serve to dissolve away previous minerals and serve as the medium for the crystallization of NEW MINERALS.

  5. Metamorphism - Overview Metamorphism can cause CHANGES in: Texture: Two types of textures: A) Foliated and B) Non-foliated. Volume: The volume of a metamorphic rock isless than the volume of the parent rock. This is due to the metamorphic agent called pressure. Chemical Change: New minerals are often the result.These minerals are different from the minerals that werepresent in the parent rock. Note: Hot chemical fluids are often essential as a transport medium for the movement of ions and the formation of new minerals.

  6. Metamorphism - Overview • Three Metamorphic agents cause rocks to change: • Increased heat • Increased pressure • Chemically active fluids

  7. Metamorphism - Overview • Metamorphism most often occurs in one of two geologic environments: • during mountain building(regional metamorphism) • surrounding masses of molten rock(contact metamorphism.)

  8. Metamorphism - Overview • Metamorphism of rocks can vary in degree from a rock that is slightly changed, low grade metamorphism (Shale to Slate), to a rock that undergoes great change, high grade metamorphism (Granite to Gneiss). • Low-Grade Metamorphism • Rocks are subjected to small changes in temperatures and pressures which result in slight changes to the rock. • Example: Shale changes to form slate.

  9. Metamorphism - Overview • Metamorphism of rocks can vary in degree from a rock that is slightly changed, low grade metamorphism (Shale to Slate), to a rock that undergoes great change, high grade metamorphism (Granite to Gneiss). • High-Grade Metamorphism • Rocks are subjected to extreme temperatures and pressures (close to that at which rocks melt) which result in great changes to the rock. • Example: Granite changes to form Gneiss.

  10. Example 1: If rock “X” is changed by heat, pressure and chemical action of fluids to form rock “Y”, then rock “Y” is said to be which rock type? igneous (B) metamorphic natural (D) sedimentary Which are the main factors causing metamorphism? chemical fluids and mineral composition (B) mineral composition and heat heat and pressure (D) pressure and density

  11. Example 2: Which is the correct sequence for a rock being metamorphosed? (A) gneiss changes to phyllite limestone changes to marble (C) quartzite changes to sandstone slate changes to shale Metamorphism of which rock will form quartzite? (A) basalt (B) conglomerate (C) granite (D) sandstone

  12. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: Which rock has been subjected to the highest temperature and pressure conditions? gneiss (B) phyllite shale (D) slate

  13. Solutions . . . Question: Which rock has been subjected to the highest temperature and pressure conditions? gneiss (B) phyllite shale (D) slate

  14. Summary . . . Overview of Points covered: • Agents of Metamorphism • Pressure • Heat • Chemical Active Fluids • Metamorphic Environments • Mountains (Regional) • Molten Rock (Contact) • High and Low Grade Metamorphic rocks

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