Download Part III (Ig Rocks)

Part III: Rocks
A. Igneous Rocks
B. Sedimentary Rocks
C. Metamorphic Rocks
- Rock = a collection of minerals "glued" together
- Ig = form from lava = molten rock {gran/bas}
- Sed = form from sediments = dirt {ss/carb}
- Met = from from existing rocks by increases ion P & T
{bent}
Concept of "Rocks"
- Classification
- Processes of rock formation
- Petrography vs Petrology
- Classification: Ig, Sed, Met - based upon formation
process, next split by composition & texture
- Process: volcanos, streams (mud), P-T changes
- Petrography = description & classification of rocks
identification - splitting
- Petrology = origin & occurrence of rocks
interpretation - lumping
Rock Cycle
melting
Magma
Metamorphic
rock
crystallization
metamorphism
Igneous
rock
weathering
Sediment
lithification
Sedimentary
rock
- Three rocks types
- Two non-rock types
- 5 processes
- 2 destroy (melting & weathering)
- 2 make (crystallization & lithification)
- 1 alters (metamorphism)
A. Igneous Rocks: Two main types
- Based on Petrology (where they formed)
1. Extrusive
2. Intrusive
- Based on Petrography (what they look like)
1. Aphanitic
2. Phaneritic
In general, what rocks look like gives us clues how they form.
- Ex = igneous rx that form at or near the Earth's surface
- In = igneous rocks that form deep in the Earth
- Ap = minerals to small to see (< 60 mic)
(no-see-ums) (A - implies without)
- Ph = minerals large enough to see (>60 mic)
(see-ums)
Nomenclature & "Synonyms"
Where they formed:
Extrusive or Intrusive
How they formed:
Volcanic or Plutonic
What they look like:
Aphanitic or Phaneritic
- Location - process - appearance
- Show map of Idaho (ig ex/in & sed)
Classification:
Based on composition & texture.
- Texture: aphanitic or phaneritic
- Composition: the minerals present
- ap -> one classification based on composition
- ph -> another classification based on composition
- Show overhead of lab classification
1. Extrusive igneous rocks
a. Processes
b. Rock types (classification)
a. Processes
molten rock
- lava: magma at the surface
- magma composition: Expand
- magma:
- volcano types or how magma becomes lava:
- relation of magma composition, "volcano" type
(i.e., composition of lava & eruptive style), and
plate tectonics:
Integrate
Expand
More minerals: p 41
quartz: SiO2 (most common)
feldspars: orthocloase K - Al - Si - O
plagioclase Ca-Na-Al-Si-O
micas:muscovite
biotite
K Al-Si-O-OH
K-Mg-Fe Si-O-OH
chain silicates:
pyroxene
Ca-Mg-Fe-Si-O
amphibole Ca-Mg-Fe-Si-O-OH
olivine:(Mg,Fe)2SiO4
ferro-magnesian vs. non-ferro-magnesian silicates
Fe&Mg = dark
- Magma composition & rock type
- Magma is composed of different elements
plus water & gases.
high in Fe & Mg low in Si (basalt)
2. intermediate:
(andesite)
low in Fe & Mg high in Si (rhyolite)
3. felsic:
1. mafic:
more viscous
- mafic: olivine, amp, pyr, Ca-plag (dark minerals)
ferromagnesians - Fe-Mg minerals
- intermediate: Ca/Na plag, less Fe-Mg minerals
- felsic: qtz, K-feld, Na-plag (light minerals)
- more viscous (=thick)
viscosity = f(T, X)
e.g.,
oil: hot vs cold
oil: different grades
oil & water
- Ways magma becomes lava becomes rx.
(don't write!)
1. Mid-oceanic ridges:
2. Flood basalts:
3. Shield volcano:
4. Composite volcano:
5. Cinder cones:
6. Volcanic domes:
- Descriptive aspect (details) -> understand (concept)
1. Mid-oceanic ridges:
- Characteristics:
- Eruption:
- Rock type:
- Minerals:
- Example:
2. Flood (plateau) basalts:
- Characteristics:
(p13, P&M)
- Eruption:
- Rock type:
- Minerals:
- Example:
(p567, P&S)
- Eruption: very calm
- Rock type: ocean basalts
- Minerals: Ca-Plag, Fe-Mg
- Example: Atlantic ocean ridge
- Eruption: very calm
- Rock type: continental basalts
- Minerals: Ca-plag, Fe-Mg
- Example: Columbia River Basalts (example rock)
Flood basalts (cont.)
3. Shield volcano:
- Characteristics:
- Eruption:
- Rock type:
- Minerals:
- Example:
4. Composite volcano:
- Characteristics:
- Eruption:
- Rock type:
- Minerals:
- Example:
- Eruption: calm, 2-10 slope
- Rock type: basalt
- Minerals: Ca-Plag, Fe-Mg
- Example: Hawaii
- Eruption: very explosive (500 atomic bombs)
- Rock type: andesite & ash
- Minerals: Na/Ca plag, Fe-Mg, biotite
- Example: Mt. St. Helens & The Ring-of-Fire
5. Cinder cone:
- Characteristics:
- Eruption:
- Rock type:
- Minerals:
- Example:
6. Volcanic dome:
- Characteristics:
- Eruption:
- Rock type:
- Minerals:
- Example:
- Eruption: explosive, ash & bombs, 30 slope, less common
- Rock type: tuffs & breccias
- Minerals: no-see-ums
- Example: Craters of the Moon
- Eruption: erupts rk, very violent if, less common
- Rock type: rhyolite
- Minerals: quartz, Na-plag
- Example: inside Mt. St. Helens
b. Rock types
Names
Color
Minerals
Chemsitry
rhyolite
lightish qtz, K-feld
andesite
grayish feld, Ca/Na-feld medium
basalt
darkish Ca-plag, Fe-Mg low Si, high Fe & Mg
high Si, low Fe & Mg
assorted rock types
very rapid cooled (rhyolite)
pumice: radid cooling with much trapped gas
scoria: rock with "tubes"
obsidian:
ejectile: ash, pyroclastics, bombs -> tuffs, breccia:
- memorial bomb
- granite & basalt most common
- Ig pets & why & hows of magmas?
2. Intrusive igneous rocks
a. Processes
b. Rock types (classification)
a. Processes
expand
- why magma compositions differ: expand
- underground magma bodies:
- relation of magma bodies to plate tectonics:
integrate
- underground magma bodies
country rock, pluton, batholith
- country rock = rock that is being intruded
- intrusions = crystallized magmas in country rock
- pluton = "spherical" intrusion
- batholith = big pluton (Idaho batholith)
dike & sill
- dike = intrusion that parallels country rock
- sill = intrusion that cuts country rock
- magma formation: melting rocks
Rocks melt by adding heat (increase in T) or
reducing pressure (decreasing P).
- increase T: (heat sources)
- geothermal gradient (25C/km)
- radioactivity
- friction
- hot spots
- decrease P:
- remove material from above
- adding water lowering melting point
- melting - increases in T or decreases in P
- inside Earth - molten interior
- 120F/mi
- add water -> mix water & antifreeze
- reduce P on coke freeze -> release of gas
- why magma compositions differ
& how magma forms
Theory: Bowen's reaction series:
Processes: (don't write)
1. crystal settling:
2. assimilation:
3. partial melting:
4. magma mixing:
- Bowen-> how magmas crystallize & how rock melt.
(add heat or reduce pressure)
- Bowen's reaction series
discontinuous
high T
continuous
- olivine (single)
- Ca feldspar (fr..)
- pyroxene (chain)
- amphibole (chain)
- biotite (sheet)
- Na feldspar (framework)
- muscovite (sheet)
- K-feldspar (framework)
- quartz (framework)
low T
- Explains the crystallization order of minerals in
a cooling magma.
- Explains how rock would melt
- Explains relative mineralogy stability
- important concept
magma type & mineral stability
- display outside lab
- Processes that form different magmas:
1. crystal settling:
2. assimilation:
-1.
- early formed crystals sink (Bowen), enriching magma
Fe-Mg forms sink, less Fe-Mg in magma
- "intellectual" enrichment HS -> College
-2.
- add country rock to magma
melt sandstone into basalt
- adding sugar into coffee
C6 H12 O6 or C17 H21 NO4
3. partial melting:
4. magma mixing:
-3.
- a magma melts another rock, melting only crystals
that have low melting points (Bowen)
- melt quartz & muscovite before olivine
enriching Si
-4.
- two separate magmas mix,
A + B A = mafic & B = felsic -> intermediate
b. Rock types
- lighter, Si
phaneritic
aphanitic
granite
rhyolite
diorite
andesite
gabbro
basalt
ultramafic
- darker, Fe-Mg
- assorted: pegmatite
very large crystals
- basalt & granite most common
Return to Bowen
olivine
Ca-feldspar
basalt
gabbro
andesite
diorite
pyroxene
amphibole
biotite
Na-feldspar
rhylolite
granite
quartz, muscovite, K-feldspar
- add T of crystallization
- add T of melting
- add resistance to weathering
The "fit" into Plate Tectonics.
- diverging plate boundary
- converging plate boundary
Igneous rocks: Conclusions
- relation between extrusive - intrusive, fine - coarse,
and volcanic - plutonic
- relate process - rock types & chemistry
- correlation of magma types with plate tectonics
Tests
1. Too long.
2. Too hard.
3. Unfair!