Metamorphic Rocks
Metamorphic Rocks
"Changed form" rocks
Produced from ___________
• Igneous rocks
• Sedimentary rocks
• Other metamorphic rocks
Metamorphism
• Takes place where preexisting rock is subjected to
____________ and _________ unlike those in
which it formed
• Degrees of metamorphism
• Exhibited by rock texture and mineralogy
• Low-grade (e.g., shale becomes slate)
• High-grade (obliteration of original features)
Force and Stress
Force is push or pull, expressed
as amount of acceleration
experienced by a mass
What happens if same amount of
force is applied to two wooden pillars?
Stress = force
per area
08.01.a
How Rocks Respond to Force and Stress
Small amount of stress:
block remains unchanged
08.01.b
Strain
Displacement
Rotation
Consider the structural behavior of rocks at shallow
versus deep conditions
At shallow
depths, most
rocks _____
08.01.c
Temperature and
pressure increase
with depth
Rocks
____ in
deep
conditions
Consider how minerals respond at shallow versus
deep conditions
Shallow:
minerals
may be
_________
Deep:
minerals
may
__________
08.01.c
Different Kinds of Stress
________
pressure
________
stress
Fluid pressure
counteracts
stress
08.02.a
Strength of Rock
Small
stress
Increase
stress
Too much
stress =
failure
Strength of continental
crust
08.02.b
Observe three kinds of stress and resulting structures
___________
_______
_____
Shallow levels: rocks ________
Deeper levels: rocks ____
08.02.c
Metamorphic agents
• _____
• __________ (stress)
• From burial (confining pressure)
• From differential stress during mountain building
• Chemically active ______
• Mainly _____ and other volatiles
• Promote recrystallization by enhancing ion migration
Processes that Cause Metamorphism
Burial
Subduction
Hot fluids
Change in stress
Heating
Shearing
08.09.a
Causes of
Metamorphism
Pressure
Tectonic
stress
08.08.a
Temperature
Response of Rock
Fluids
Deform
Grow larger
minerals
Cut by
Veins
Grow new
minerals
Physical Processes During Metamorphism
Deformation
of objects
Rotation
08.08.b
Folding
Shearing
Fracturing
Chemical Processes During Metamorphism
Pressure solution
Recrystallization
Remobilization
08.08.c
Types of Metamorphism
• _______, or thermal, metamorphism
• Occurs near a body of magma
• Changes are driven by a rise in temperature
• ________ metamorphism
• Directed pressures and high temperatures during
mountain building
• Produces the ________ volume of metamorphic rock
Observe how metamorphic conditions vary with depth
Heating by magma
(contact
metamorphism)
Regional
metamorphism
Subduction-zone
metamorphism
08.09.b1
Metamorphic Textures
• ________ texture
• Minerals are in a parallel alignment
• Minerals are perpendicular to the compressional force
• ___________ texture
• Contain equidimensional crystals
• Resembles a coarse-grained igneous rock
Foliation of Metamorphic Rock
Foliation Processes
Foliated Rocks
• Slate
• Fine-grained
• Splits easily
• Schist
• Strongly foliated
• "Platy"
• Types based on composition (e.g., mica
schist)
Foliated Texture
• Gneiss
• Strong segregation of silicate minerals
• "Banded" texture
Non-Foliated
• Marble
• Parent rock is limestone
• Large, interlocking calcite crystals
• Used as a building stone
• Variety of colors
• Quartzite
• Parent rock – quartz sandstone
• Quartz grains are fused
Why should I care about rocks?
Metallic mineral resources
• Gold, silver, copper, mercury, lead, etc.
• Concentrations of desirable materials are
produced by
• Igneous processes
• Metamorphic processes
Why should I care about rocks?
• Most important ore deposits are generated from
hydrothermal (hot-water) solutions
•
•
•
•
Hot
Contain metal-rich fluids
Associated with cooling magma bodies
Types of deposits include
• _____ deposits in fractures or bedding planes, and
• ___________ deposits which are distributed
throughout the rock
Why should I care about rocks?
Nonmetallic mineral resources
• Make use of the material’s
• Nonmetallic elements
• Physical or chemical properties
• Two broad groups
• Building materials (e.g., limestone, gypsum)
• Industrial minerals (e.g., fluorite, corundum, sylvite)
You use rocks and minerals from
To
Birth
Death