Metamorphic Rocks
Earth Science
Chapter 3 Section 3
BELLWORK:
Explain how igneous rocks and
sedimentary rocks are related.
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TODAY’S OBJECTIVES:
Describe the agents of metamorphism.
List the criteria used to classify metamorphic
rocks.
List the names, textures, and environments
of formation for the most common
metamorphic rocks.
METAMORPHIC ROCKS
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Definitions
“Meta” = change
●“Morph” = shape
●A rock that has been changed from its original
form by heat, pressure, and fluid activity into a
new rock
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Original form = “parent”
●New form = “daughter”
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METAMORPHIC ROCKS
Rocks that have changed form
●Produced from preexisting
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Igneous rocks
●Sedimentary rocks
●Other Metamorphic rocks
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METAMORPHISM
Takes place where preexisting rock is
subjected to temperatures and pressures
unlike those in which it formed
●Degrees of metamorphism
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Exhibited in the rock’s texture and mineralogy
●Types
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Low-grade (eg. Shale becomes slate)
●High-grade (causes the original features to be
obliterated)
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HEAT
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Sources include…
Magma
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Temperature of magma
●Composition of magma
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Geothermal Gradient
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Temperature increases with depth of burial
●Core of Earth is warmer than outer crust
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**METAMORPHIC SETTINGS
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1. Contact, or thermal metamorphism
Near a mass of magma
●Change is driven by a rise in temperature
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Vein of magma
Contact
Metamorphism
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2. Regional metamorphism
Result of directed pressures and high
temperatures during mountain building
●Produces the greatest volume of
metamorphic rock
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Regional metamorphism
occurs here
The tremendous pressure heat and pressure
may cause rocks to buckle and fold.
Pressure
Pressure
METAMORPHIC AGENTS
Heat
●Pressure (stress)
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From burial (confining pressure)
●From differential stress during mountain
building (best place to find meta. rock)
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Chemically active fluids
Mainly water and other volatiles
●Promote recrystallization by enhancing ion
migration
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METAMORPHIC TEXTURES
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Foliated texture
Minerals in a parallel alignment
●Minerals perpendicular to the
compressional force
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Non-foliated texture
Contains equi-dimensional crystals
●Resembles coarse-grained igneous
rock
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COMMON METAMORPHIC ROCKS
Foliated rocks
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Slate
fine-grained
●splits easily
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Schists
strongly foliated
●“Platy”
●Types based on composition (eg, mica schist)
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Gneiss
Strong segregation of silicate minerals
●“Banded” texture
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COMMON METAMORPHIC ROCKS
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Non-foliated rocks
Marble
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Parent rock – limestone
●Large, interlocking calcite crystals
●Used as a building stone
●Variety of colors
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Quartzite
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Parent rock – quartz sandstone
●Quartz grains are fused
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