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Metamorphic Rocks. Evidence of metamorphism The ingredients of metamorphism Classifying metamorphic rocks Metamorphism of shale (& other parent rocks!) Metamorphic minerals. Geological Materials Transformation Processes. The Rock Cycle. Rock Metamorphism (Increased T & P)

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metamorphic rocks

Metamorphic Rocks

Evidence of metamorphism

The ingredients of metamorphism

Classifying metamorphic rocks

Metamorphism of shale (& other parent rocks!)

Metamorphic minerals

the rock cycle

Geological Materials

Transformation Processes

The Rock Cycle
  • Rock

Metamorphism

(Increased T & P)

  • Meta-

morphic

rock

Partial Melting

  • Magma
metamorphism metamorphic rocks
MetamorphismMetamorphic Rocks

Definition

  • Re-crystallization of minerals
  • While still solid
  • Into minerals that are stable at different temperatures and
  • Different pressures
metamorphism metamorphic rocks4
MetamorphismMetamorphic Rocks

WHY??? do the minerals recrystallize?

  • To reach chemical equilibrium!!!

Animation of metamorphic rock formation

a evidence of metamorphism
A. Evidence of Metamorphism

Shale

For example…

Sedimentary Rocks

    • Made of minerals derived from weathering of a parent rock
    • Stable at atmospheric temperatures and pressures (low T & P)
    • Originally horizontal, continuous and uniform layers
  • 1.Bent (deformed) layers

Gneiss

evidence of metamorphism
Differential pressure “squashes” rock and included features

2. Flattened Pebbles

Evidence of Metamorphism

Conglomerate

Metaconglomerate

evidence of metamorphism7
Evidence of Metamorphism
  • 3.Crystalline Texture

Minerals tightly interlocking due to recrystallization under pressure

Quartz Sandstone

Quartzite

evidence of metamorphism8
Evidence of Metamorphism
  • 4. New mineral

assemblages

Example:

Shale: Clay minerals

(some quartz) 

Metamorphism

(Mid-grade)

  • Forms Schist: Mica, Feldspar and other silicate minerals 
b recipe of metamorphism
B. Recipe of Metamorphism
  • 1.Parent Rock
    • Even though minerals will change
    • Most elements are provided by parent rock
    • Except water and some dissolved ions

Shale

Schist

b recipe of metamorphism10
B. Recipe of Metamorphism

Temp. (ºC)

0

C

600

1200

A

B

  • 2.Heat
    • Geothermal gradient: more pressure = more heat!!
    • Minerals stable at lower temperatures converted to
    • minerals stable at higher temperatures
    • Solid state chemical reactions are accelerated

A

B

C

recipe of metamorphism heat
Recipe of metamorphism: Heat
  • Geotherm: Temperature increases with depth beneath Earth’s surface
    • Typical: 30° C/km
  • Igneous intrusions: Localized increases in temperature
recipe of metamorphism
Recipe of Metamorphism
  • 3.Increased Pressure & Stress
    • Increased Confining Pressure as rocks are buried
    • Compression at convergent plate boundary or
    • Sheared as plates slide past each other
results of stress
Compressive Stress

Shear Stress

Causes Foliation

Results of Stress
ingredients of metamorphism
Ingredients of Metamorphism
  • 4.Addition or removal of fluids (and elements)
    • Water (and other fluids) within rocks and minerals
    • Moving during metamorphism
    • Accelerates solid-state chemical reactions and
    • May change rock composition
  • 5.Time  Millions of years!
metamorphic grade
Metamorphic Grade
  • Intensity of Metamorphism:
  • High grade (High P & T)
  • Low grade (Low P & T)
metamorphic facies
Metamorphic Facies
  • The minerals in a rock are clues to the (pressure and temperature) history of the rock
  • Facies = a set of metamorphic conditions
  • Each facies is characteristic of its
    • Tectonic environment
    • Source rocks in the environment (like shale)
metamorphism of shale
Metamorphism of Shale

not found

in

nature

Fig. Story 9.7b

metamorphic rocks of other parent rocks
Metamorphic Rocks of other Parent Rocks
  • Limestone  Marble
  • Bioclastic calcite  Crystalline calcite

Nonfoliated

metamorphic rocks of other parent rocks19
Metamorphic Rocks of other Parent Rocks
  • Quartz Sandstone  Quartzite
  • Granular quartz  Crystalline quartz

Nonfoliated

metamorphic rocks of other parent rocks20
Metamorphic Rocks of other Parent Rocks
  • Basalt  Amphibole Schist
  • Granite  Gneiss
  • Uniform texture  Foliation (schistosity and

gneissic banding)

characteristic metamorphic minerals
Characteristic Metamorphic Minerals

sillimanite

kyanite

staurolite

garnet

andalusite

For more images: http://skywalker.cochise.edu/wellerr/mineral/

slide24

garnet - the index mineral

Sedimentary

parent rock

Igneous

parent rock

index minerals
Index Minerals
  • Define the metamorphic conditions or zones
  • Give information about the “metamorphic grade”

Fig. Story 9.7a

summary
Summary
  • Evidence of metamorphism
    • Deformed layers, flattened pebbles, crystalline texture, & new mineral assemblages
  • The ingredients of metamorphism
    • Parent rock, heat, pressure, fluids, & time
  • Classifying metamorphic rocks
    • Low grade --> high grade & facies
  • Metamorphism of shale (& other parent rocks!)
    • Shale --> Gneiss, Sandstone --> Quartzite, Limestone --> Marble
  • Metamorphic minerals
    • Muscovite and Garnet = Index minerals
to think about metamorphic rocks plate tectonics
To think about… Metamorphic Rocks & Plate Tectonics
  • Tracing changes in pressure and temperature conditions that a rock experienced …
  • … gives insight into plate tectonic settings!!