metamorphic rocks a.evidence of metamorphism b.the ingredients of metamorphism c.classifying...
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Metamorphic Rocks
A. Evidence of metamorphism
B. The ingredients of metamorphism
C. Classifying metamorphic rocks
D. Metamorphism of shale (& other parent rocks!)
E. Metamorphic minerals
The Rock Cycle
Rock
Metamorphism (Increased T & P)
Meta- morphic rock
Partial Melting
Magma
Geological Materials
Transformation Processes
MetamorphismMetamorphic Rocks
Definition Re-crystallization of
minerals While still solid Into minerals that are
stable at different temperatures and
Different pressures
MetamorphismMetamorphic Rocks
WHY??? do the minerals recrystallize? To reach chemical
equilibrium!!!
Animation of metamorphic rock formation
A. Evidence of Metamorphism
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
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
Shale
Gneiss
Evidence of Metamorphism
Differential pressure “squashes” rock and included features
2. Flattened Pebbles
Conglomerate
Metaconglomerate
3. Crystalline Texture Minerals tightly interlocking
due to recrystallization under pressure
Evidence of Metamorphism
Quartz Sandstone
Quartzite
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
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 Metamorphism
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
0 600 1200Temp. (ºC)
A B C
A C B
Recipe of metamorphism: Heat Geotherm: Geotherm: Temperature increases
with depth beneath Earth’s surface Typical: 30° C/km
Igneous intrusions: Igneous intrusions: Localized increases in temperature
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
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 High grade
(High P & T)
Low grade (Low P & T)
Intensity of Metamorphism:Intensity of Metamorphism:
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
Fig. Story 9.7b
Metamorphic Rocks of other Parent Rocks
Limestone Marble
Bioclastic calcite Crystalline calcite
Nonfoliated
Metamorphic Rocks of other Parent Rocks
Quartz Sandstone Quartzite
Granular quartz Crystalline quartz
Nonfoliated
Metamorphic Rocks of other Parent Rocks
Basalt Amphibole Schist Granite Gneiss
Uniform texture Foliation (schistosity and
gneissic banding)
Characteristic Metamorphic Minerals
For more images: http://skywalker.cochise.edu/wellerr/mineral/
kyanite
andalusite
sillimanite
staurolite garnet
Distinct Mineral Assemblages
GradeGrade
GradeGrade
Distinct Mineral Assemblages
Index Minerals
Define the metamorphic conditions or zones
Give information about the “metamorphic grade”
Fig. Story 9.7a
SummaryA. Evidence of metamorphism
A. Deformed layers, flattened pebbles, crystalline texture, & new mineral assemblages
B. The ingredients of metamorphismA. Parent rock, heat, pressure, fluids, & time
C. Classifying metamorphic rocksA. Low grade --> high grade & facies
D. Metamorphism of shale (& other parent rocks!)A. Shale --> Gneiss, Sandstone --> Quartzite, Limestone -->
Marble
E. Metamorphic mineralsA. Muscovite and Garnet = Index minerals
To think about… Metamorphic Rocks & Plate Tectonics Tracing changes in pressure and
temperature conditions that a rock experienced …
… gives insight into plate tectonic settings!!
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