2 Metamorphic Rocks

Question 1

Metamorphisis

Answer 1

Change of State

Question 2

Unseen Metamorphism

Answer 2

Occurs deep in the crust
How can we see it?
Erosion and uplift

Question 3

Metamorphic rock formation

Answer 3

Formed from pre-existing rocks
Protolith
SOLID state recrystallization
From changes in the temperature, pressure, or chemically active fluids
New minerals from old
+ TIME

Formed from pre-existing rocks
Protolith
SOLID state recrystallization
Temperature
Pressure
Directional or uniform
Chemically active fluids
+ TIME
This is a S-L-O-W process (usually)
Millions of years

Question 4

Solid State Recrystallization: Clay into Ceramic

Answer 4

Atoms of a mineral are reorganized and rearranged
Particles of clay are fused and quartz recrystallizes
Water, carbon, and sulfur will be driven off
New minerals are formed

Question 5

Minerology and texture

Answer 5

Protolith to metamorphic rock:

Protolith: Red Shale
quartz, clay, iron oxide
Metamorphic rock: Gneiss
quartz, felspar, biotite, garnet

Protolith: Fossiliferous limestone
fossil fragments, shells, etc
Metamorphic rock: Marble
interlocking grains of intergrown calcite

Question 6

metamorphic processes

Answer 6

Recrystallization
Size and shape change, composition does not
Neocrystallization
New minerals grow through chemical reactions
Plastic deformation
Mineral grains soften and deform, no breakage: affects entire grain whole thing deformed
Pressure solution
Grains partially dissolve where surfaces touch: middle of the grain remains untouched like a jawbreaker

Question 7

Contact Metamorphism

Answer 7

Around hot igneous intrusions
Narrow bands (thin halo around igneous rocks) of altered/baked not melted rocks
Between 1 m – 100s m thick
Notch Peak, Utah

Question 8

Dynamic Metamorphism

Answer 8

Fault zones
Shallow
Brittle, no metamorphism
Deep (+15km)
Ductile, smear like taffy
Forms a metamorphic rock called mylonite
rock becomes long and skinny streaks because it is being squashed and smeared

Question 9

Regional Metamorphism

Answer 9

The biggest deal to us
Deep in the crust
Usually convergent plate boundaries
Mountain building events
Appalachians, Himalaya
Wide, deep, extensive
Directional stress, two plates coming together to form mountains
Exposed Continental shields
Roots of folded mountain belts

Question 10

orogeny

Answer 10

mountain building events that gives us clues about what has happened in the past

Question 11

Metamorphic classification

Answer 11

Once again: Texture and Composition

Texture
Non-foliated Rocks (be able to turn in circles and not be able to see the switch in directionality in it)
Foliated Rocks (directional, lineation on rock)

Foliation
Visible direction of mineral growth
- Alignment of platy minerals or alternating light/dark bands
“Layers”
- But not sedimentary strata!
Subjected to differential stress

Question 12

foliated Metamorphic Rocks: Slate

Answer 12

from shale
Slate
Fine grained rock
Micas grow in response to stress (they are being squashed in a certain direction of growth, breaks like the pages of a book)
Low grade metamorphism

Question 13

foliated Metamorphic Rocks: schist

Answer 13

from slate
Schist
Strongly foliated
“Schistosity”=Shimmer of platy minerals (micas)
Mid-grade metamorphism

Platy minerals (bioite and muscovite micas) aligned with each other=shiny under a microscope and without sometimes

Question 14

foliated Metamorphic Rocks: gneiss

Answer 14

from schist

Gneiss
Extremely foliated (gneissic banding)
Light and dark minerals group together (mafic and felsic)(through stress and chemical/physical weathering)
Quartz & Feldspar together
Amphibole and biotite together
High metamorphic grade

Question 15

foliated Metamorphic Rocks: Migmatite

Answer 15

from gneiss

Migmatite
Extremely foliated
Actual melting of certain minerals: Quartz & Feldspar
Not melted: mafic
Igneous and metamorphic mixed
creates ribbons of melted rock in the metamorphic rock

Question 16

foliated Metamorphic Rocks: stretched pebble conglomerates

Answer 16

Metamorphism of a conglomerate
“Stretched pebble conglomerates”
Raft River Mountains
round river rocks Flattened by pressure solution and plastic deformation

Question 17

Non-foliated Metamorphic Rocks: marble

Answer 17

Marble
Interlocking large grains of calcite
Recrystallization of limestone
Organic carbon either cooked out, or concentrated into dark veins
looks kind of foliated, but it’s not

Question 18

Non-foliated Metamorphic Rocks: Quartzite

Answer 18

Quartzite
Metamorphism of quartz sandstone
Entire rock recrystallized
Sometimes, sedimentary features can still be seen
Used in buildings, flagstones, patios, fireplaces…very durable and sturdy

Question 19

Metamorphic Fact #1: You can’t make something from nothing:

Answer 19

You can’t make something from nothing: (sand grains=quartz)
Composition of the protolith dictates the type of metamorphic rock
If the original rock is sandstone, then what is it made of?
What do we have to make new minerals?

Question 20

Metamorphic Fact #2: Heat Matters

Answer 20

Temperature change causes metamorphism
-High temperatures causes different minerals to be stable
-May also allow minerals to grow bigger

Causes of temperature change
-Geothermal gradient: shove down into the earth
-Upwelling hot magma: hot stuff around it

Question 21

Metamorphic Fact #3: pressure causes change

Answer 21

Higher pressure causes
-metamorphism
High pressures causes different minerals to be stable
-New minerals will be more dense

Causes of pressure
-The deeper, the more pressure
-Directional stress
Newly formed minerals will be elongated

Question 22

Metamorphic Fact #4: hot fluids are super reactive

Answer 22

Chemically active fluids cause metamorphism
Mostly water and carbon dioxide
Carries ions through the rock to create new minerals

Sources of water
Trapped in sedimentary protolith
Given off by cooling intrusive rocks
rain

Can create ore deposits
Kennecott Copper

Question 23

Metamorphic Fact #5: geologic time is needed

Answer 23

None of these conditional changes happen fast
Long periods of time are needed

Question 24

Environments of Metamorphism: contact metamorphism

Answer 24

Contact Metamorphism:
High temperature
Low pressure
Fluids

Question 25

Environments of Metamorphism: Seafloor metamorphism

Answer 25

Seafloor Metamorphism
Moderately high temperature
Low pressure
Fluids playing the biggest role in temp change and formation

Question 26

Environements of metamorphism: regional metamorphism

Answer 26

Regional Metamorphism
Need convergent (continental) plate boundaries High temperature
High pressure
Fluids
“Roots” of mountains
Location of most intense metamorphism
Intensity of metamorphism decreases away from the mountains