Download Metamorphic Rocks - Ms. Sheehans Geology Class

Metamorphic Rocks
Bell ringer:
Looking at the pictures, what do you
think metamorphic rocks are?
What are Metamorphic Rocks?
• Metamorphism means “to change form”.
• Metamorphic rocks are rocks that form when
existing rocks are changed by heat and
pressure.
• The existing rocks that are changed can be any
of the 3 rock types: igneous, sedimentary, &
even other metamorphic rocks.
What determines which metamorphic
rock will form?
1. Starting minerals in the parent rock
(protolith)
2. The agent(s) of metamorphism acting upon
the rock.
3 Agents of Metamorphism
1. Heat
1. Pressure
3. Fluids (Hydrothermal Solutions)
Heat
• Two main sources:
1. Heat from magma, (“bakes” the rock)
2. Heat from increasing temperature due to
increasing depth.
• Heat can cause recrystallization and chemical
reactions, which can cause new minerals to form.
Pressure
• Causes
1. Burial of rock
2. Pressure due to tectonic plates.
• Effects
Usually heat and pressure work together, because both
increase as you go deeper in the Earth.
At high temperatures and pressures, most rocks break
down and change into a different arrangement of
minerals that are stable in the new conditions.
Mineral grains get squeezed together with pressure and
become more compact (thus more dense). Pressure
can orient minerals into layers (foliation).
Write your questions:
Level 1
Define
Describe
Identify
List
Name
Level 2
Compare
Contrast
Group
Sequence
Explain
Classify/Categorize
Give the relationship
Cause/Effect
2 “Level 1” Questions & 2 “Level 2” Questions
Foliation vs. Stratification
• Don’t get foliation confused with stratification.
Stratification is a characteristic of sedimentary
rocks, whereas foliation is a characteristic of
metamorphic rock.
Stratification
(SEDIMENTARY rocks)
• When sediments are deposited, they are laid
down in layers.
Stratification
Sketch in your
notebook
(Sedimentary Rock)
Foliation
(METAMORPHIC rocks)
• Some metamorphic rocks
become foliated when
exposed to heat and pressure.
• This happens when pressure
forces the mineral grains to
grow and line up in parallel
layers. The rock’s minerals
become layered in sheets or
the rock can appear banded.
Foliation
(Metamorphic Rock)
Sketch in your
notebook
Fluids
(Hydrothermal Solutions)
• Many chemical reactions require
water.
• Water contains dissolved minerals and/or
dissolved ions, which can be exchanged between
the solution and the rock.
• This changes a rock's chemistry (chemical
makeup) rather than just the way the minerals
are arranged.
Types of Metamorphism
1. Regional Metamorphism
2. Contact Metamorphism
Write your questions:
Level 1
Define
Describe
Identify
List
Name
Level 2
Compare
Contrast
Group
Sequence
Explain
Classify/Categorize
Give the relationship
Cause/Effect
2 “Level 1” Questions & 2 “Level 2” Questions
Regional Metamorphism
• Occurs over a wide area or region.
- mainly along convergent plate boundaries
where mountains are built or where volcanoes
form.
- During the process of mountain building,
there is a lot of heat and pressure. It is this
combination of heat and pressure that creates
metamorphic rocks.
Sketch in your
notebook
Contact Metamorphism
• Occurs in specific locations through contact
with magma.
• Occurs near igneous intrusions, where hot
magma forces itself into sedimentary strata.
The rocks next to the invading magma are
baked.
Sketch in your
notebook
Classification of Metamorphic Rocks
• Foliated Metamorphic Rocks
• Nonfoliated Metamorphic Rocks
Foliated Metamorphic Rocks
• Foliated: Layered or banded texture due to
minerals aligning in the same direction due to
pressure.
Sketch in
your
notebook
Banded Texture of Gneiss
Layered Texture of Schist
Nonfoliated Metamorphic Rocks
• Nonfoliated: no banded texture. Most contain
only one mineral. For example Limestone
(Protolith or parent rock) metamorphoses into
Marble. Both are made of Calcite.
Limestone’s calcite crystals combine to form larger interlocking
crystals thus forming marble
Write your questions:
Level 1
Define
Describe
Identify
List
Name
Level 2
Compare
Contrast
Group
Sequence
Explain
Classify/Categorize
Give the relationship
Cause/Effect
2 “Level 1” Questions & 2 “Level 2” Questions
Guided Summary
• FIRST Identify the 2 factors that will determine
what exact metamorphic rock will form.
(example: why will marble form in some
situations and gneiss form in others?)
• SECOND Have your teacher check your answer
before moving on to the next task.
• THIRD Summarize what all determines what
specific metamorphic rock will form.
Example of notes follow in the next
few slides