Transcript Metamorphism - Faculty Server Contact

Chapter 10: Metamorphism: New
Rocks from Old
La Pietra by
Michelangelo, carved
from Carrera marble
© 2012 John Wiley & Sons, Inc. All rights reserved.
Learning Objectives
What is metamorphism?
• Describe the conditions necessary for
metamorphism.
Metamorphic rock
• Identify the metamorphic products of shale and
basalt.
Metamorphic processes
• Describe different types of metamorphism and
their tectonic settings.
Metamorphic facies
• Describe metamorphic zones and the types of
facies they produce.
© 2012 John Wiley & Sons, Inc. All rights reserved.
What Is Metamorphism?
Metamorphism
• The mineralogical,
textural, chemical, and
structural changes that
occur in rocks
• A result of exposure to
elevated temperatures
and/or pressure
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What Is Metamorphism?
The Limits of Metamorphism
Low-grade
•Rocks metamorphosed under temperature and pressure
conditions up to 400°C and 400 MPa
High-grade
•Rocks metamorphosed under temperature and pressure
conditions higher than about 400°C and 400 MPa
Figure 10.2 Temperature and pressure conditions for metamorphism
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What Is Metamorphism?
Factors Influencing Metamorphism
Temperature and pressure
Figure 10.3 From shale to gneiss
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What a Geologist Sees—
At the roadside
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What Is Metamorphism?
Pore fluid
• Pore fluids
influence
metamorphism.
• Pores are open
spaces.
Figure 10.4 Quartz vein
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What Is Metamorphism?
Factors Influencing Metamorphism
Stress
• Foliation
• A planar arrangement of textural features in a
metamorphic rock
• Gives rock a layered or banded appearance
Figure 10.5 Effects of uniform and differential stress
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What Is Metamorphism?
Factors Influencing Metamorphism
Foliation
•Slaty cleavage
• Foliation in low-grade
metamorphic rocks
that causes such rock
to break into flat,
plate like fragments
•Schistosity
• Foliation in coarsegrained metamorphic
rocks
Figure 10.6 Foliation under the microscope
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What Is Metamorphism?
Figure 10.7 Slaty cleavage
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Metamorphism and Billiards
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What Is Metamorphism?
Factors Influencing Metamorphism
• Duration
• Rate of metamorphism
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Metamorphic Rock
Rock with Foliation
Slate
A very fine-grained metamorphic rock with slaty
cleavage; the metamorphic product of shale
Phyllite
• A fine-grained metamorphic rock with pronounced
foliation, produced by further metamorphism of
slate
•
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Metamorphic
Rock
Figure 10.8 Schistosity versus
slaty cleavage
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Metamorphic Rock
Figure 10.9 Metamorphism of basalt
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Metamorphic Rock
Figure 10.9 Metamorphism of basalt
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Metamorphic Rock
Rock Without Foliation
Quartzite
• The product formed by recrystallization of
sandstone
Figure 10.10 Nonfoliated metamorphic rocks: Quartzite
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Metamorphic Rock
Rock Without Foliation
Marble
•The product formed by recrystallization of limestone
Figure 10.10 Nonfoliated metamorphic rocks: Marble
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Metamorphic Processes
Processes that cause changes in texture and mineral
assemblages in metamorphic rock
• Mechanical deformation
• Grinding, crushing, bending and fracturing
Figure 10.11 Mechanical deformation
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Metamorphic Processes
Processes that cause changes
in texture and mineral
assemblages in metamorphic
rock
• Chemical recrystallization
• Changes in mineral
composition, growth of
new minerals,
recrystallization of old
minerals, and changes
in amount of pore fluid
• Typically caused by
heating and squeezing
of rock
Figure 10.12 Contact metamorphic
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Metamorphic Processes
Types of Metamorphism
Regional metamorphism
•Metamorphism of an
extensive area of the crust
•Associated with plate
convergence, collision, and
subduction
Other types of metamorphism
occasionally occur in geologic
settings where high
temperature and/or elevated
pressure or stress exists.
Figure 10.13 Tectonics and metamorphism
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Metamorphic Processes
Types of Metamorphism
•
•
Contact metamorphism
• Rocks are heated and
chemically changed
adjacent to an
intruded body of hot
magma.
Burial metamorphism
• Occurs after
diagenesis; is a result
of the burial of
sediments in deep
sedimentary basins.
Figure 10.14 Quick pressure, slow heat
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Metamorphic Processes
Types of Metamorphism
Figure 10.15 Instantaneous metamorphism
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Metamorphic Processes
Metasomatism
Metasomatism
•The process whereby the
chemical composition of a
rock is altered by the
addition or removal of
material by solution in
fluids:
• Frequently water or
carbon dioxide
Figure 10.16 Metasomatism
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Metamorphic Facies
Metamorphic facies
• The set of metamorphic
mineral assemblages
• Form in rocks of
different compositions
• Form under similar
temperature and stress
conditions
Figure 10.17 Regional metamorphism in Scotland
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Metamorphic Facies
Figure 10.18 Metamorphic facies
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Critical Thinking
• Compare the concept of metamorphic facies to
that of sedimentary facies. In what ways are
they similar? In what ways are they different?
• Museum curators obviously can’t shave off
pieces from valuable art. How do you think they
manage to identify the rocks and minerals?
• Briefly explain how pressure and temperature
might change over time in rocks being subjected
to contact, burial, and subduction-related
regional metamorphism.
© 2012 John Wiley & Sons, Inc. All rights reserved.