Short circuits

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