Metamorphism and Metamorphic Rocks
A. Metamorphic rocks: Form at conditions
between igneous and sedimentary rocks
Common Metamorphic Rocks
Definition
Protolith: parent rock, what
the rock was before it was
metamorphosed
Common Metamorphic Rocks
A. Foliated: mineral grains are
aligned produced by directed
pressure
1. Slate: first product of
metamorphism of shale.
Temperature: 200-350C
Relatively low temperature and
pressure
2. Phyllite: next product of
shale
Temperature: 350-500C
Shiny rock with wavy layers
Low-intermediate temperature
and pressure
Metamorphism and Metamorphic Rocks
A. Foliated—mineral grains
are aligned (produced by
directed pressure)
3. Schist: next product of shale
Temperature: 500-650C
Shiny rock with individual mica
flakes now visible to the
unaided eye
Intermediate-high temp and
pressure
4. Gneiss: next product of
shale, felsic igneous rocks
Temperature > 650C
Minerals separate into lightand dark-colored layers
High temp and pressure
Metamorphism and Metamorphic Rocks
A. Foliated—mineral grains are
aligned (produced by directed
pressure)
5. Blueshcist: oceanic basalt
formed in subduction zones
High pressure and low
temperature
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks:
minerals aren’t aligned
Produced with high confining
Pressure (not directed
pressure)
Contact metamorphism
Parent rock is monomineralic
quartz or calcite
(limestone); not elongate
minerals
1. Marble: CaCO3
lack elongate minerals
pure limestone
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks:
minerals aren’t aligned
Produced at high confining
pressure (not directed
pressure)
Contact metamorphism
Parent rock is monomineralic
Quartz or calcite (limestone);
not elongate minerals
2. Quartzite SiO2 (quartz)
Lack elongate minerals
Pure quartz sandstone (most
sandstones, coastal
environments)
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks: minerals
aren’t aligned
Produced with high confining
pressure (not directed
pressure)
Contact metamorphism
Parent rock is monomineralic
quartz or calcite (limestone);
not elongate minerals
3. Hornfels: contact
metamorphism
High temperature, low pressure
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks: minerals
aren’t aligned
3. Hornfels: contact
metamorphism
High temperature, low pressure
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks: minerals
aren’t aligned
3. Hornfels: contact
metamorphism
High temperature, low pressure
Metamorphism and Metamorphic Rocks
B. Nonfoliated Rocks:
minerals aren’t aligned
Produced with high confining
pressure (not directed
pressure)
Contact metamorphism
Parent rock is monomineralic
quartz or calcite (limestone);
not elongate minerals
Metamorphism and Metamorphic Rocks
Metamorphism and Plate Tectonics
V. Metamorphism and Plate
Tectonics
Plate Movements create much
of the heat, pressure and hot
fluids for metamorphism
Directed pressure @
convergent plate boundaries:
Regional metamorphism
most common
Tectonic history:
Blueshists: Subduction zones
Hydrothermal metamorphosed
basalts (not foliated: ocean
basins
Metamorphism and Plate Tectonics
V. Metamorphism and Plate
Tectonics
Plate Movements create much
of the heat, pressure and hot
fluids for metamorphism
Directed pressure convergent plate
boundaries, regional
metamorphism most
common
Tectonic history:
Blueshists: subduction zones
Hydothermal metamorphosed
basalts (not foliated): ocean
basins
Metamorphism and Plate Tectonics
V. Metamorphism and Plate
Tectonics
Plate Movements create much
of the heat, pressure and
hot fluids for metamorphism
Foliation  direction of ancient
tectonic compression
Metamorphic grade (slate,
phyllite, schist, gneiss)
Burial depth & amount of
heat
Geochronology—the study of “Earth Time”
I. Types of Geological
Dating
A. Relative Dating:
compares two or more
groups of rocks to
determine which is older
and which is younger.
Non-quantitative
B. Numerical Dating:
Absolute time, how long
ago in years that a rock
was formed or an event
occurred.
Quantitative measure.