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Metamorphism and Metamorphic Rocks

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Metamorphism and Metamorphic Rocks ... Gneiss Rock Cycle Regional Revisited Slate Phyllite Schist, Gneiss Magma Nonfoliated - Marble metamorphosed limestone ... – PowerPoint PPT presentation

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Title: Metamorphism and Metamorphic Rocks


1
Metamorphism and Metamorphic Rocks

2
Daily Question
  • Correctly place the following
  • statements in the Venn Diagram.
  • Occurs at divergent boundaries
  • Occurs at convergent boundaries
  • Forms as a result of melting (magma)
  • Temperature is an agent
  • Pressure is an agent
  • Generates foliated rocks
  • Forms as a result of being near an intrusion of
    magma
  • Found in mountain belts
  • May have been originally been a metamorphic rock
  • Form at temperatures above 200 oC
  • May underlie several adjacent states

3
Definitions
  • Metamorphism mineralogical, chemical, and
    physical changes that occur in solid rocks.
  • Occurs at depths greater than that of
    lithification (Diagenesis).
  • Solid state recrystallization changes that
    occur without the rock melting (rocks that melt
    are igneous).

4
Factors influencing Metamorphism
  • Temperature
  • Pressure
  • Fluid
  • Time

Agents of Metamorphism
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6
Factors influencing Metamorphism
  • Temperature
  • below about 150oC, most minerals are stable
    (little or no metamorphism)
  • above 150oC, reaction rate increases as
    temperature increases, new minerals begin to form
  • above 600oC, some minerals begin to melt
    (transition to igneous rocks)
  • Temperature a function of depth within the Earth
    and the presence of a magma

7
Factors influencing Metamorphism
  • Pressure
  • as pressure increases, pore spaces reduced and
    density increases, pore fluids are expelled
  • Minerals recrystallize and begin to realign
  • Differential stress
  • pressure is greater in one direction than in
    another

8
Temperature, Pressure and Rock Type
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10
Effects of Stress
Uniform
Differential
11
Factors influencing Metamorphism
  • Pore fluids (water and carbon dioxide)
  • as pressure increases, pore fluids are expelled
  • Pore fluids increase the rate of metamorphic
    reactions by
  • storing ions involved in reactions
  • moving ions from one place to another
  • Chemical Fluids from Magmas
  • Carry ions from the melt
  • Fluids increase the temperature in the rock

12
Veins
  • Solutions are deposited in fractures and joints

13
Factors influencing Metamorphism
  • Time
  • solid state recrystallization is a slow process
  • in general, size of minerals increases with time

14
Types of Metamorphism
  • Burial Metamorphism
  • 2. Contact Metamorphism
  • 3. Regional Metamorphism

15
Metamorphism Plate Tectonics
16
Types of Metamorphism
  • Burial Metamorphism
  • most common type, occurs where crust is greater
    than 5 km thick
  • Relatively low temperature and pressure (low
    grade metamorphism)
  • Maximum stress vertical, foliation parallel to
    ground surface

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18
Types of Metamorphism
  • Contact metamorphism
  • Occurs in rocks around a magma body
  • High temperature (heat from magma) bakes the
    rock around the magma creating an alternation
  • High temperature fluid primary agents, little
    to no pressure (occurs at shallow depths in the
    crust)

19
Non-foliated Metamorphic Rocks
  • Granular texture
  • Interlocking grains
  • Composed primarily of one mineral
  • Uniform grain size

20
Contact Metamorphism
21
Contact Metamorphism
22
Types of Metamorphism
  • Regional metamorphism
  • Large scale large volume of rock is affected
  • Associated with convergent plate margins and
    mountain building
  • Folding and faulting increase thickness of the
    crust
  • Occurs over a range of temperatures and pressures
  • Fluids are also present
  • Low grade to high grade metamorphism
  • Will have zones of contact metamorphism

23
Regional Metamorphism
24
Metamorphic Grade
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26
Metamorphic Grade
  • As pressure and/or temperature increases, the
    grade of metamorphism increases

27
Low Grade Metamorphism
  • Example Slate
  • Rocks become more dense and compact
  • forms at low temperature and pressure
  • microscopic crystals
  • dull luster
  • clay and mica minerals
  • foliated

28
Low Grade - Slate
29
Metamorphic Grade
30
Intermediate Grade Metamorphism
  • Example Phyllite
  • intermediate temperature and pressure
  • small crystals
  • shiny luster
  • mostly mica minerals
  • foliated

31
Intermediate Grade Phyllite
32
Metamorphic Grade
33
High Grade Metamorphism
  • Example Schist
  • high temperature and pressure
  • large crystals
  • mica-rich
  • foliated

34
High Grade - Schist
35
Metamorphic Grade
36
High Grade Metamorphism
  • Example Gneiss
  • high temperature and pressure
  • large crystals
  • mica-poor
  • foliated

37
High Grade - Gneiss
38
Rock Cycle
39
Regional Revisited
Slate
Phyllite
Schist, Gneiss
Magma
40
Nonfoliated - Marble
  • metamorphosed limestone (CaCO3)
  • bedding and fossils obliterated

41
Nonfoliated - Quartzite
  • metamorphosed quartz-rich sandstone
  • Pore spaces filled with SiO2

42
Metamorphic Facies
  • Different minerals form at different temperatures
    and pressures
  • Group of stable minerals define a facies
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