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Metamorphic Rx
“meta” = change; “morphos” = shape/form
Parent Rock = pre-existing rock that undergoes metamorphism
Metamorphism
Caused by:- increase in pressure- increase in temperature- exposure to chemically active
fluid
Metamorphism
Occurs within Earth’s crust- minerals change until they are
stable under the new conditions
Types of pressure
a) Differential pressure - applied unequally from different
directions- produces foliated texture
Foliation
Linear arrangement of minerals- creates a layered appearance- associated w/mountain building
Types of pressure
b) Confining pressure- applied equally from all sides- associated with deep burial- produces nonfoliated texture
Metamorphic Conditions
2) Increasing temperatureNOTE: Temperature cannot
exceed the melting point of all minerals in rock
Why?
Increasing temperature
Two methods:a) deep burial
- geothermal gradient- increases 30o C per km
b) magma intrusion
Increasing temperature
Changes to parent rock:a) Compositional change- unstable minerals either melt or
rearrange into new minerals
Increasing temperature
b) Textural Change- partial melting allows minerals to
recrystallize- produces nonfoliated texture
Metamorphic Conditions
3) Chemically active fluid- superheated water with ions in
solution- “hydrothermal solution”- occurs near magma chambers
Metamorphic Rock Classification
Foliated textures - in order of increasing
metamorphic intensity (temperature, pressure)
Nonfoliated textures
Composition controlled by parent rock
Parent Rock Meta. Rock Sandstone Quartzite Limestone Marble
Metamorphic Settings
1) Contact Metamorphism- caused by contact with magma- heat from magma partially melts
minerals- minerals recrystallize into
nonfoliated texture
Contact Metamorphism
Metamorphic zone is narrow (1’-10’ wide)
Zone of contact metamorphism referred to as a “baked zone”
Metamorphic Settings
2) Regional Metamorphism- associated w/mountain building- large-scale metamorphism (100’s
miles wide)- produces foliated textures