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Metamorphic RocksMetamorphic Rocks form beneath the Earth’s surfaceform beneath the Earth’s surface
– heat, pressure and/or fluids on pre-existing heat, pressure and/or fluids on pre-existing rocksrocks
– exhumed by uplift and erosionexhumed by uplift and erosion– Don’t Create / changeDon’t Create / change
metamorphism can be:metamorphism can be:– regionalregional– fault-related (beside seismic zones)fault-related (beside seismic zones)– contact (adjacent to igneous rocks)contact (adjacent to igneous rocks)
Metamorphic rocks Metamorphic rocks
"Changed form" rocks "Changed form" rocks Produced from preexistingProduced from preexisting
• Igneous rocksIgneous rocks• Sedimentary rocksSedimentary rocks• Other metamorphic rocks Other metamorphic rocks
MetamorphismMetamorphism
Original minerals become Original minerals become unstableunstable
new stable minerals formnew stable minerals form graphite ---> diamond (MR)graphite ---> diamond (MR) no change in chemistryno change in chemistry all changes occur in the all changes occur in the
solid state (no liquid solid state (no liquid involved)involved)
Figure 3.2
The rock cycle
““Shields” of the Shields” of the worldworld
Canadian Shield ~ 1-3 BaExposed now but once must have been 10-30 km below
Origin of pressure in Origin of pressure in metamorphismmetamorphism
Figure 3.20
Directed stress
Gneiss typically Gneiss typically displays displays a banded a banded
appearanceappearance
Figure 3.24
End night classEnd night class
Metamorphic RocksMetamorphic Rocks
form beneath the Earth’s surfaceform beneath the Earth’s surface– heat, pressure and/or fluids on pre-existing heat, pressure and/or fluids on pre-existing
rocksrocks– exhumed by uplift and erosionexhumed by uplift and erosion
metamorphism can be:metamorphism can be:– regionalregional– contact (adjacent to igneous rocks)contact (adjacent to igneous rocks)– fault-related (beside seismic zones)fault-related (beside seismic zones)
Measuring stress Measuring stress directionsdirections
Figure 3.22
Marble – a nonfoliated Marble – a nonfoliated metamorphic rock metamorphic rock
Figure 3.24
Less directed stress
Metamorphic rocks Metamorphic rocks
Common metamorphic rocks Common metamorphic rocks • Nonfoliated rocksNonfoliated rocks
• Marble Marble • Used as a building stone Used as a building stone • Variety of colors Variety of colors
• Quartzite Quartzite • Parent rock – quartz sandstoneParent rock – quartz sandstone• Quartz grains are fusedQuartz grains are fused
Metamorphic rocks Metamorphic rocks
Metamorphic textures Metamorphic textures • FoliatedFoliated texture texture
• Minerals are in a parallel alignment Minerals are in a parallel alignment • Minerals are perpendicular to the Minerals are perpendicular to the
compressional force compressional force
• Nonfoliated texture Nonfoliated texture • Contain equidimensional crystals Contain equidimensional crystals • Resembles a coarse-grained igneous rock Resembles a coarse-grained igneous rock
Metamorphism and Metamorphism and DeformationDeformation
Metamorphism = Metamorphism = new minerals new minerals replacing older onesreplacing older ones
under these conditions, under these conditions, the the rocks may behave plasticallyrocks may behave plastically
they flow to form foldsthey flow to form folds metamorphism and metamorphism and
deformation are “siblings”deformation are “siblings”
Rock deformationRock deformation
Flowing
New Minerals
Folded veinsFolded veins
metamorphism can be:metamorphism can be:– regionalregional– fault-related (beside seismic zones)fault-related (beside seismic zones)– contact (adjacent to igneous rocks)contact (adjacent to igneous rocks)
REGIONAL REGIONAL METAMORPHISMMETAMORPHISM
Metamorphism and platesMetamorphism and plates
Continental collisionContinental collision
Rock deformationRock deformation
Flowing
New Minerals
CONTACT METAMORPHISMCONTACT METAMORPHISM
CONTACT METAMORPHISMCONTACT METAMORPHISM
FAULT-RELATED FAULT-RELATED METAMORPHISMMETAMORPHISM
Fault surfaceFault surface
Metamorphic Metamorphic mineralsminerals
•Minerals reflect conditions of Minerals reflect conditions of metamorphismmetamorphism
•Mineral content reveal Mineral content reveal processes occurring within processes occurring within the Earth’s crustthe Earth’s crust
•Diamond / graphiteDiamond / graphite•Reaction rates slow with Reaction rates slow with temptemp
High pressures
Low pressures
High T
All minerals = Al2Si05
Water
Increasing Increasing metamorphismmetamorphism
Increasing grain size, Increasing grain size, increasing temperature increasing temperature
slate (very fine grained)slate (very fine grained) schist (visible crystals, schist (visible crystals,
coarse grained)coarse grained)
Fault-relatedFault-related
Smearing-MyloniteSmearing-Mylonite
AndesAndes
DEFORMATIONDEFORMATIONaccompanies metamorphism
change in shape, geometry minerals oriented into minerals oriented into
“fabrics”“fabrics” folds and fracture on all scales
outcrop to global scale
UNUSEDUNUSED
MeltingMelting
Classification of Classification of metamorphic rocksmetamorphic rocks
Figure 3.23