Chapter 9 (part I): Metamorphic Rocks - PowerPoint PPT Presentation

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Chapter 9 (part I): Metamorphic Rocks

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Title: Chapter 9 (part I): Metamorphic Rocks


1
Chapter 9 (part I) Metamorphic Rocks
  • Study Help for Chapter 9
  • Definition of metamorphism, its causes, and the
    agents of metamorphism.
  • Textures of metamorphic rocks, rock cleavage,
    foliation. The most common metamorphic rocks and
    what they are formed from (parent rock).
  • Understand the main types/environments of
    metamorphism, which are the most/least common,
    where do they occur? How are they related to
    plate tectonics?
  • Know the slate ? gneiss progression of
    metamorphism
  • Progressive regional metamorphism and index
    minerals (Figure Story 9.7)

2
Chapter 9 (part I) Metamorphic Rocks
  • Introduction
  • Metamorphic environments
  • Agents of metamorphism

3
1) Introduction
Recall
3 fundamental rock types
  • Igneous
  • Sedimentary
  • Metamorphic

4
1) Introduction
Recall
3 fundamental rock types
  • Igneous
  • Sedimentary
  • Metamorphic

crystallization
5
1) Introduction
Recall
3 fundamental rock types
  • Igneous
  • Sedimentary
  • Metamorphic

crystallization
deposition
6
1) Introduction
Recall
3 fundamental rock types
metamorphism
Lit. change form
7
2) Metamorphic environments
Contact metamorphism Hydrothermal
metamorphism Regional metamorphism
Fig. 9.3
8
3) Agents of metamorphism
9
3) Agents of metamorphism
  • Heat
  • The most important agent
  • Recrystallization results in new, stable minerals
  • Two sources of heat
  • Contact metamorphism rocks are baked by heat
    from magma
  • An increase in temperature with depth due to the
    geothermal gradient (20-30 C per km in upper
    crust)

See Fig. 9.1
10
3) Agents of metamorphism
  • Pressure (stress)
  • Increases with depth (300-400 bar/km)
  • Confining pressure applies forces equally in all
    directions
  • Rocks may also be subjected to differential
    stress which is unequal in different directions

See Fig. 9.1
11
Origin of pressure in metamorphism
3) Agents of metamorphism
12
3) Agents of metamorphism
  • Pressure/Stress

13
3) Agents of metamorphism
  • Pressure/Stress

14
3) Agents of metamorphism
  • Pressure/Stress

15
3) Agents of metamorphism
  • Pressure/Stress

near surface deformation brittle
shearing force
16
3) Agents of metamorphism
  • Pressure/Stress

Deep crust/mantle deformation ductile
shearing force
17
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18
3) Agents of metamorphism
  • Chemically active fluids hydrothermal fluids
  • Mainly water with other volatile components
  • Enhances migration of ions
  • Aids in recrystallization of existing minerals
  • Where is the water from from?
  • Squeezed out of pore spaces of sedimentary rocks
  • Squeezed out of fractures in igneous rocks
  • Hydrated minerals such as clays and micas

19
4) How metamorphism alters rocks
3) Agents of metamorphism
  • Hydrothermal fluids cause mineralogical changes

20
3) Agents of metamorphism
  • The importance of parent rock
  • Most metamorphic rocks have the same overall
    chemical composition as the parent rock from
    which they formed
  • Mineral makeup determines, to a large extent, the
    degree to which each metamorphic agent will cause
    change
  • e.g., in shale, clays recrystallize to micas, but
    quartz and feldspars remain largely unaltered

21
3) Agents of metamorphism
Important parent rock mineralogy
Example magma intrudes rock host rock
alteration quartz sandstone
not much limestone
lots
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