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petrology > Exam > Flashcards

Exam Flashcards

1
Q

What is petrology, petrography, and petrogenesis?

A

Petrology: branch of geology that deals with the origin, occurrence, structure, and history of rocks

– Petrography: description and classification of rock types

– Petrogenesis: processes that form/modify rocks

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2
Q

what are some uses of petrology?

A

Resources
Environment Reclamation
Climate Change - Remediation
Engineering

Hazards:
- Geophysical/Geomechanical Aspects Rocks
-Volcanic rock types and their properties.
* Viscosity, gas content of different rock types all contribute to the degree of risk to environments nearby

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3
Q

What are the dominant minerals in felsic, intermediate, mafic, and ultramafic rocks?

A

Felsic: orthoclase, na-rich plagioclase, quartz, biotite, muscovite
(Si, O, Al, Na, K)

Intermediate: Quartz, mix of Na and Ca rich plag, biotite, amphibole, minimal pyroxene

Mafic: Ca rich plag, amphibole, pyroxene, minimal olivine
(Mg, Fe)

Ultramafic: Pyroxene, olivine

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4
Q

What are some rocks of mixed origin?

A
  • Ash fall deposits (Tuff or Tuffaceous Rocks)
    – sedimentary or volcanic
  • Serpentinites
    – igneous or metamorphic
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5
Q

Abundance of rock types with time? Surface vs interior

A

Earth’s surface
– Overall, 75% is sedimentary
– Remainder is igneous and
metamorphic
– Most of the ocean floor is sedimentary

-abundance decreases with age
-> erosion, metamorphism

-felsic (crustal rocks) less prone to weathering than mafic/ultramafic (mantle rocks)

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6
Q

Condensation vs Accretion

A

Condensation
Solar system - hot centre, cold edges
Hot nebular gases cool and solidify into solid grains of dust
- Refractory elements solidify near sun, form small rocky planets
- Solar winds drive volatiles to the outer solar system, form large gas giants

Accretion
Dust grains join to become planets
-silicates grabbed oxygen during accretion

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7
Q

What is the importance of Si to planetary life?

A

The importance of Si to planetary life is that O is required for life. O is volatile so would have gone with gas giants instead of rocky, but O was captured by Si (SiO4) and stayed with Earth. Oxides & silicates

Weathering by microbial life release O from the rocks

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8
Q

What are the 4 most common elements?

A

Fe, O, Mg, Si

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9
Q

Mechanisms of Heat Transfer & rheological properties
(convection vs conduction)

A

Conduction:
-Static
-Shallow Earth
-Brittle rocks (dont flow)
-Not as efficient as Convection

Convection:
-Active
-movement of hot rock or magma flow
- more heat = less dense = more buoyant

Lithosphere:
-Mainly conduction but poor
- brittle rocks so no flow
-Silicate rocks (poor conductors)

Asthenosphere and Mesosphere
A: Upper part of upper mantle
M: rest of mantle
- Ductile silicate rich rocks, can flow
- Convection (efficient)
- Hotter material expands, becomes less dense/buoyant and Rises

  • Liquid outer core:
    Convection and conduction

Solid inner core
-Metals -> efficient conduction

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10
Q

Slab pull vs ridge push

A

Ridge Push
Buoyant magma pushes up, driving plates apart
-Mantle heated internally (+radioactive decay & primordial heat)
-heat transfer by convection,
-hot rocks are buoyant and less dense

Slab Pull
Old dense oceanic plate sinks back into the mantle at subduction zones pulling crust

“Slab Pull” is far more effective than “Ridge Push” as a force for plate tectonics and mantle convection.

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11
Q

Plate boundaries, magma types

A

Transform
-Sliding boundaries, Brittle Deformation, Cataclastic Rocks

Divergent
ultramafic magma makes mafic rock
-Create Oceanic Crust
Oceanic:
-ascending mantle magma (mafic), hot buoyant, spreading, Wilson Cycle
Continental, Rifts:
-magmas interact with continental crust

Convergent
mafic magma makes felsic/intermed rocks
-Create Continental Crust
Subduction zones:
-metamorphism,
-volcanic types vary due to host rocks,
partial melts&contamination, volatiles

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12
Q

Mantle Plumes and Hot Spots

A

Hot, less dense magma, rises as Diapiric structure
-(buoyant, deformable material rises through surrounding rocks, forming a blob-like structure)

hits lithosphere
-spreads out on boundary
-incorporates host rocks:
mantle mafic (basalt) + ocean or continent

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13
Q

Regions of Magma Generation and
Formation of Igneous Rocks

A
  1. Mid-Ocean Ridges:
  2. Continental Rifts:
  3. Island Arcs and 4. Continental Arcs:
  4. Back-Arc Basins:
  5. Ocean Islands:
  6. Continental Hot Spots:
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14
Q

Wilson Cycle

A
  1. tectonic break Continent
  2. Ocean Basin open
    -sedimentation and Rifting
  3. Ridge Push results in Slab Pull
  4. Ocean Basin closes, Tectonic Orogeny
  5. Continental Collisions, metamorphism,
    weathering = sedimentation, igneous melts/rifts
  6. Stable Continent. Sedimentation of all types.
  7. Back to 1 and Repeat
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15
Q

Head sources - primordial vs radioactive (where?)

A

Two Heat Sources (Impact on Crustal Processes)

  1. “Primordial” Heat: (Slowly Running Out)
    * From Earth’s initial accretion and differentiation
    * up to a quarter of total surface/shallow heat flux
  2. Decay of Radioactive Isotopes
    * Concentrated in the crust and mantle
    * >3 quarters of total surface/shallow heat flux
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16
Q

Making a melt - explain - ways it can happen

A

1) Raise the Temperature
Move Geotherm to right

  • Ocean and continental hot spots
  • Subduction zones:
    heat from hot mafic magmas ponding below the crust
  • Lower the Pressure
    Move the Geotherm Path to right
    -mid-ocean ridges, back-arc basins, and intracontinental rifts
    -decompression melting
    -angle of geotherm=%of melt
  • Add Volatiles (H2O)
  • Subduction zones: dehydrate minerals in subducted plate
    -releases water into overlying mantle wedge, which partially melts (flux melting)

composition of melt:
1. Composition / mineralogy of the original rock
2. Percent of original rock that is partially melted – the temperature
3. Presence/absence of volatiles (H 2 O, CO2 ) and the lithostatic pressure also exert an influence

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17
Q

RCMP felsic vs mafic

What promotes liquid separation

A

surface tension prevents melts from separating, so there is a minimum % of melt required

Rheological critical melt percentage (RCMP):

percent of melt when crystal framework is replaced by melt dominated crystal mush

– Higher for more viscous silica-rich (felsic) magmas
 RCMP = 1-7% for mafic magmas
 RCMP = 15-30% for felsic magmas

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18
Q

Rock diversity - 8 mechanisms and processes

A
  1. Fractional Crystallization
    -u know this
  2. Filter differentiation
    Magma flows in fractures, crystals in magma too large & filtered out
  3. flow segregation
    -thin veins/pipes
    -early formed crystals collect in center of the pipe
    -slow flow in middle
  4. Zoning (solid solution)
    -melt and mineral not in equilibrium
    -Cooling rates important
  5. Liquid Immiscibility
  6. Ultramafic/mafic vs felsic
    * Felsic melt separate from mafic or ultramafic melts
  7. Silicate-sulphide (why are there Ore Deposits)
    separation of sulphide liquid (Dense)
  8. Alkaline, CO2-rich systems
    * Silica and alkali-rich liquid separates from a carbonate-rich liquid
  9. Fluids
  10. Heat:
  11. Fluid-bearing magma rises to shallower depth
  12. Late-stage crystallization
  13. Assimilation
    Melting wall/roof rocks will alter magma’s composition
  14. Magma Mixing
    Injection of hot mafic magma into shallower felsic magma chamber
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19
Q

pigionite vs inverted pigionite

A

in case c on the diagram, the melt hits the liquidus to the right of the inversion curve with cpx composition

upon slow cooling the melt crosses the inversion curve to opx and becomes opx with cpx lamellae
->inverted pigionite

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20
Q

clinopyroxenes + water

A

water vapour pressure and partial pressure of oxygen important to aegirine-acmite formation

increase volatiles, more oxic, get iron

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21
Q

cotectic line

A

Cotectic Line:
Boundary Line in a Ternary Phase Diagram,

the intersection of the Liquidus surfaces for Two Phases;

-one of two crystalline phases present can react with the melt upon decreasing the temperature to form the other crystalline phase.

22
Q

amphiboles, types, families

A

Anthophyllite-Cummingtonite
(Ca+Na≅0) (Fe+Mg amphiboles)

Calcium Amphiboles (Ca>Na)
Alkali Amphiboles (Na>Ca)

Within these groups there are several continuous series

orthoamphibole
clinoamphibole
hornblende
Kaersutite
Alkali Amphiboles

There are both orthorhombic and monoclinic amphiboles

typical series:
tremolite -> actinolite -> ferro-actinolite

23
Q

sanadine vs microcline

A

sanadine is high temp, monoclinic, al is randomly distributed, carlsbad twinning
microcline is triclinic and al is ordered in the structure, tartan twinning

24
Q

perthite vs antiperthite - how formed

A

slow cooling rate causes separation into 2 crystals

medium causes lamellae

fast no unmixing

  • Slow cooling rate:
    complete separation into 2 crystals
  • Intermediate cooling rate:
    lamellae form in a host

perthite is k-spar with albite lamellae

Antiperthite is albite with k-spar lamellae

25
Q

k - na system - role solvus
phase

A

2 loops joined at eutectic

Solvus Curve:
at high temps, k and na mix
(a) At higher Temperatures the

(b)
at low temps separate so K and Na = Exsolution Lamellae or Perthitic
Textures

26
Q

p increase water
leucite
k - na system
phase

A

melt contains H 2O
i. The leucite field disappears with increasing H2O pressure.
ii. Crystallization temperatures are reduced.
iii. Composition changes continuously along liquidus-solidus during cooling.

27
Q

Eskola experiment slide z lec 7c

A

Added SiO2 to Ca plag and heated

result:
-much of the plag had converted to albite.

-in many low temperature and metamorphic rocks, albite is a stable end member.

Ca plag is the high
temperature end member

28
Q

color igneous rocks
leuco vs meso

A
  • Felsic rock: dominated by felsic minerals
    – Generally leucocratic: light-colored
  • Mafic rock: dominated by mafic minerals
    – Melanocratic: dark-colored
    – Ultramafic rock: >90% mafic minerals

– Volume % of dark minerals
– < 30% = leucocratic,
30-60% = mesotype,
>60% = melanocratic

29
Q

SiO2%
felsic acid vs
rock types

A

Acidic rocks are usually felsic rocks
-Basic rocks are usually mafic rocks
Ultrabasic rocks are usually ultramafic rocks

this is determined by SiO2 %

30
Q

silica saturation - oversaturated vs undersaturated minerals

A

undersaturated with respect to SiO2:

-minerals can react with free silica to form more silica-rich minerals.

-minerals can stably co-exist with free silica
-oversaturated with respect to SiO2

31
Q

Alumina saturation
periluminous, perialkaline

A

Peraluminous:
Al2O3 exceeds the sum of CaO, Na2O, and K2O.

Peralkaline:
Al2O3 is less than the sum of Na2O and K2O.

Metaluminous:
Al2 O3 exceeds the sum of Na2O and K2O, but is less than the sum of Na2 O, K2O, and CaO.
Subaluminous: molecular proportion of Al2O3 is approximately equal to the sum of Na2O and K2O.

32
Q

Alkali-lime
calcic vs alkalic - based on?
rock type

A

-alkalinity of the rocks.
-CaO vs SiO2
-Na2 O+K2O vs SiO2

-CaO usually decreases as Na2O+K2O and SiO2 increase, the curves cross.

The SiO2 content at the point where the curves cross indicates the alkalinity of the rock suite

33
Q

anorthesite vs diorite vs gabbro

A

Phaneritic

Anorthosite
– >90% plagioclase

Diorite
– <35% mafic minerals (hornblende, biotite)
– Lighter colored

Gabbro
– >35% mafic minerals (olivine, pyroxene)
– Darker colored

34
Q

andesite vs basalt

aphanitic rock diamond

A
  • Andesite
    – Has >52% SiO2
    – lighter colored: color index < 35%
  • Basalt
    – Has <52% SiO2
    – darker colored: color index > 35%

andesite and basalt plot near p
trachyte near a

35
Q

pyroclastic triangle
block/bombs vs lapilli vs ash (tuff)

A

triangle
top
pyroclastic breccia

left
lapillistone

right
tuff
Tuff = consolidated/cemented ash

36
Q

-what are the types of metamorphism (5 - 2 are regional)

-agents of metamorphism and which are more important for each type.

A

Contact
-Heating during igneous intrusion or beneath thick flows
-mineral growth random orientations.
-Energy imparted to host intruded rock.

main agent: heat

regional
a)Orogenic:
-Batholith (large) scalemetamorphism
-mountain belts and shield areas
-result of tectonism

Main agent: deformation then p/t

b)burial:
-post diagenetic
-sedimentary rocks during burial

main agent: pressure

hydrothermal
->result of circulating fluids
a) Sea floor spreading:
b) Porphyry systems:

main agent: fluids

dynamic (faults, etc)
-high strain
-foliated, extremely
sheared/streaked and re-crystallized grains

main agent: deformation then pressure

shock
-Impact of high velocity meteorites, creates high P/T minerals at surface or shatter cones

main agent: deformation and pressure then t

37
Q

prograde vs retrograde

A

main point: can increase and decrease in grade, and do this multiple times

Prograde:
-progressive increase grade
-increase p and/or t

Retrograde:
-decreasing grade as rock cools
-after metamorphic/igneous event

  • Prograde metamorphism is typically of greater significance than retrograde metamorphism.
38
Q

high strain rocks

A

foliated
Usually results in textural change of a rock as it reacts to accommodate stress/ strain

Cataclasite – Mylonite - Gneiss

Impactite:
-category of high- strain rocks,
-extremely high- pressure silica polymorphs (eg. coesite and stishovite) -macroscopic nested cone-like structures (shatter cones)

39
Q

where does metamorphism begin and end

A
  • Metamorphism is marked by the formation of new minerals:

Lower limit : Diagenesis
* Upper limit : Migmatites – Onset of Melting

  • However, the boundary between diagenesis and metamorphism is somewhat arbitrary
  • Some minerals are considered both
    diagenetic and metamorphic
40
Q

-difference between zone and facies
pros and cons of zones

A

Zones:

-area subdivided into zones of different metamorphic conditions.
-zone boundaries ->index mineral
-new mineral that appears with a new metamorphic grade
-> based on pelitic (metamorphosed shaly) rocks

pros:
-used worldwide
-easily mappable boundaries (convenient in field)
-can be used for different protoliths
cons:
-mostly applies to pelitic rocks
-hard to relate p/t between protoliths
-doesnt account for fluid, stress/strain

Zones were defined from Pelitic rock
-Zone is very protolith composition dependent

facies:
-closed system (equilibrium)
-bulk chemistry of protolith = bulk chemistry of rock

-a set of mineral assemblages for all bulk chemistries which occur in the same narrow P/T range (regardless of protolith)

-corresponding P-T conditions
-what reactions take place

41
Q

Al2SiO5 system
limits and describe

A

polymorphs
kyanite, sillimanite, andalusite

phase diagram:
kyanite - low t high p
andalusite - low p med t
sillimanite - high t

42
Q

main sedimentary processes

A

1.Formation of sediment
– weathering, mineral grains, hard parts of organisms, or chemical precipitation

  1. Transport of sediment
    – water, wind, ice = energy for physical weathering
  2. Deposition in a variety of environments eg. basin
    – Formed by plate tectonic processes
  3. Lithification
    – compaction/cementation
43
Q

lithification vs diagenesis
compaction vs cementation

A

lithification is the process of forming and rock and involves compaction and sedimentation

diagenesis is more general and describes all processes affecting sediment after deposition (during and after lithification)

compaction refers to sediments being squeezed by weight of overlying layer

cementation occurs material precipitates in pore spaces and glues rock together

44
Q

sedimentary rock types
t-a-o %

A

Terrigenous
allochemical
orthochemical

45
Q

siliciclastic vs terrigenous rocks

A
  1. Terrigenous
    terrigenous rocks occur from erosion outside depositional area and are transported
    – Transported as solids (clastic)
    -60%
  2. Allochemical
    – Chemical precipitate outside depositional area
    – But also transported as solid
    -10%
  3. Orthochemical
    – Chemical precipitate within depositional area
    -5%
  • Combination of (1) and (2) = siliciclastic
  • Combination of (2) and (3) = chemical

siliciclastic rocks are a combination of terriginous and allochemical

triangle:
T at top
A at left
O at right

46
Q

description of components
relate to weathering and energy
- size, shape, sphericity, roundness
maturity

A

DISTANCE

Greater transport distance
->better rounding & sorting

Wind transport: rounding of sediment
* Water transport:
->slower abrasion/rounding compared
with wind

  • Glacial transport:
    ->least sorting and rounding

MATURITY
1. Immature
– >5% clay, sand poorly sorted, angular

  1. Submature
    – <5% clay, sand poorly sorted, not well rounded
  2. Mature
    – No clay, sand well sorted, not well rounded
  3. Supermature
    – No clay, sand well sorted, well rounded
47
Q

folk classifications, gravel, sand, silt, clay

A

Terrigenous Sedimentary Rocks often
classified as Grain or Matrix Supported

Folk (Mineralogy) grains
Q = Quartz = Orthoquartzite (90% Qtz)
F = Feldspar = Arkose (Feldspathic) (~25%)
R = Rock Fragments (volcanic/metamorphic)

arkokes are feldpathic rocks by folk class
arenites have fine sand, well sorted matrix by gilbert class

Gilbert (Matrix)
Wacke = appreciable fine mud, poorly sorted
Arenite = clean eg. fine sand , well sorted

48
Q

Classification Ls, micrite vs sparite vs allochems

A

Classification of Limestones

  1. Allochems (transported)
  2. Microcrystalline ooze → Micrite (carbonate mud)
  3. Sparry calcite → Sparite
    * Pore filling cement or recrystallization of micrite
49
Q

allochems = interclasts, oolites, fossils, pellets

A

Allochems
1. Intraclasts
erosion of seafloor carbonate sediments, then transported and re-deposited

  1. Oolites
    * Spherical/elliptical, carbonate accretes around central particle while being rolled around by currents
  2. Fossils
    * Broken fragments of fossils
  3. Pellets
    * Fecal pellets, well-rounded and sorted aggregates of fine
    carbonate (+ organics) with no internal structure
50
Q

Dunham vs folk classifications

A

folk: Good for thin section
classification
-intraclasts, oolites,fossils,pellets
-micrite to sparite

dunham: good for hand samples
-mudstones, wackes

51
Q

Evaporites, name at least 4 plus formulas

A

salt rocks formed in evaporating water bodies

Evaporate seawater, the
sequence would be:

  1. Calcite (not much)
    * Possibly dolomite if ancient
    seawater was Mg-rich
  2. Gypsum, anhydrite (most
    abundant)
    CaSO4 2H2O
  3. Halite (rare, requires
    90% evaporation)
  4. Sylvite (Potash minerals
    Cl – SO 4) (very rare)

petrology (1 decks)

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