Ig Exam Flashcards
(100 cards)
1
Q
- Difference between MORB and OIB basalts.
A
2
Q
What are the three big questions of Petrology?
A
What is this rock?
How are they related?
How are they related to tectonic processes?
3
Q
What do all Igneous rocks have in common?
A
Form from a melt and end up solid
4
Q
Where does melt come from?
A
Temperature, Pressure, forms at depth
5
Q
What does petrology tell us?
A
- What layers of the planet look like and how they formed
- Why rocks and landforms end up the way they do
What temp and how fast, what pressure, which fluids, and when our planet underwent massive changes.
6
Q
Igneous rock definition
A
Forms from the cooling and solidification of magma or lava
7
Q
Oceanic Crust
A
Thin: 10km deep
Ophiolite suite:
- oceanic sediments
- pillow basalts
- sheeted dikes
- more massive gabbro
- ultramafics
8
Q
What are the layers of Earth?
A
Crust, lithosphere, asthenosphere, inner and outer mantle, outer and inner core.
9
Q
What is the Moho?
A
Discontinuity in the Mantle, changes wave speed where the speed increases at deeper depths
- caused from the orientation of rock
10
Q
Ultramafics
A
Undergo lots of fluids, causing intense serpentinization.
11
Q
Continential Crust
A
20-90km thick, average 35 km thick. Average rock: granodiorite
12
Q
Plutonic rock
A
coarse or medium grain sizes and have crystallized deep in the crust. Interconnected.
13
Q
Hypabyssal
A
Fine-grained to glassy, shallow depths less than a kilometer, fine.
13
Q
- Major-element geochemistry
A
determine whether a suite of rocks is related through a process such as magmatic differentiation or mixing
13
Q
- Trace-element geochemistry
A
is used to identify the role various minerals may have played as either crystallizing phases or residual phases in a suite of rocks
13
Q
Mafic
A
Ferromagnesian minerals
14
Q
Isotope geochemistry
A
which can involve both radiogenic and stable isotopes, can determine whether a suite of rocks formed from a single magma, or whether a more complex, multisource process was involved.
14
Q
Volcanic
A
Fine grained to glassy, formed at surface. Interconnected.
14
Q
Classification of ig rocks
A
- A rock can be classified either according to the minerals that make it up or by its chemical composition
14
Q
Felsic
A
Rich in quartz, feldspars, or feldspathoids
14
Q
Ultramafic
A
No felsic minerals
15
Q
Mantle composition
A
Peridotite. Upper 410 km olivine and spinel, low vel layer is 60-220km.
16
Q
Mafic mienrals
A
olivines, pyrozenes, amphiboles, micas, opaques, zircon, apatite, sphene, allanite, garnet, carbonate
17
Q
QAPF
A
Felsic, intermediate, mafic. Quartz, Alkali, Plag, Feldspar/. Ultramafics have their own classification.
18
Rock Classification
I/M/S? -Origin
Color - chem chomp
Grain Size- Solidification
19
Earth rock composition giong into core
Granodiorite, olivine+ pyrox+ garn, spinel+ major, pervoskite+ ferropericlase. +post-pervoskites+ ferropericlase, liquid iron-allow, solid iron.
20
The Mantle
Peridotite, ultramafic
Low velocity layer (60-220km), olivine-> spinel
Transition Zone (velocity increases rapidly) spinel- perov 660km
Lower Mantle has more gradual increase
21
What is magma made of?
Usually SiO4
- Rarely carbonate or others
- Dissolved gas: H20, CL, CO2, Fl
22
What effects magma viscosity?
A mixture of silicate liquid, crystals, and bubbles
23
What is glass?
Silicate liquid
24
SiO2
All silicate minerals
25
TiO2
Oxides (pyroxene, hornblende, biotite)
26
Al2O3
Feldspars, hornblende, mica, pyrox
27
Fe2O
Oxides
28
FeO
Oxdies, ferromagnesian minerals
29
Ferromagnesian mienrals
Olivines, pyroxenes, amphiboles, micas
30
Potassium minerals
Feldspar, biotite, muscovite, amphibole
31
MgO
Ferromagnesian
32
CaO
Plag, pyrox, horn
33
Na2O
Feldspar
34
P2O5
Apatite
35
H2O fugitive
hornblende, mica
36
physical properties of magma, abundant structure
Silicate tetrahedra, isolated/chains
37
How fluids move
Phenocrysts: visc increases above 40%
Bubbles: visc may increase or decrease
38
Bubbles
Stiffening and shearing effects
39
Rehology
Shear stress v shear rate
Newtonian
- deforms at eql rate no matter force
Bingham
- deforms at eql rate no matter force after certain threshold is achieved
Dilatant
- strain rate decreases w/increased stress
Psuedoplastic
- strain rate incr w/incr stress
40
Density
between 2.3 *10^3- 3.0 * 10^3 kgm^-3
41
Dense constituents
fe, mg, ti, ca
42
Light constituents
Si, Al, Na, K, H2o
43
Geothermal gradient
deeper, hotter, different rates. Continents are colder than the ocean. Primordial, tidal, radioactive heating.
44
Geobaric gradient
Pressure increases with depth.
P(swirly equal sign) DpG
P= pressure, D= depth,, p= density, g=gravity
45
Heat transfers
Advection, convection, conduction, radiation
46
Will rocks melt at geothermal gradient?
No.
47
What compound is abundant in zeolites, micas, amphiboles, and ocean sediments
water
48
Partial melting
Lower melting point components prefer liquid
part melt determines what gets in the magma
fractional crustallization determines the out
49
Eutectic
Lowest energy part of solidus and liquidus coming together
50
Peritectic
point that gets stuck
51
Why do rocks melt?
Pressure, temp, deptch. Rocks no melt at geothermal gradient. Cross to melt by advection, lower pressure, lower solidus.
52
Mantle plumes
hot rock upwelling from deep interior, independent of plate motions
53
Decompression melting
up temp, down pressure
54
Where do rocks melt?
spreading centers and places of low pressure
55
ophiolite suite
ocean seds, pillow basalts, sheeted dikes, layered gabbros, ultramafics
56
Melting interval
allows for differentiation
Partial melting- up T
Fractional crystalization- down T
Assimilation/mixing
57
Bowen's reaction series
58
Lever rule
X/(X/y)*100
59
Basalt/Gabbro Ternary diagram
Olivine, pyroxene, plag
aka: Fr, Di, An
60
Compositoinal effects
compatible prefer solid phace. incom prefer liquid
61
Distribution coefficient
D > 1 compati, D < 1 incom
D unique for elements and mienrals
SiO2 incompatible
incompatieble concentration increases with differentiation
D= Cs/ Cl
62
Simple crystal settling
Stokes' Law
V=gdrhoD^2/18v
63
settling from turbulently convecting suspension
ln(1-x)=-Vt/h
64
Zoned deposit
late, hot, less evolved
early, center, more evolved
65
Closed system differentiation
fractional cryst, partial melt
- evolution occurs in relative continity
- equilibrium is maintained
66
Open system
addition of chem components messing w/evolution
mingling: viscosity is critical. Advection can be very significant. Minimal chem exchange between components, but bulk analyses may represent averages
mixing
- more complete mixing
- liquids well mixed but multiple phenocryst assemblages present
hybridization
- nearly complete
assimilation
- incorporation of solid mateiral into a magma. large thermal budget needed
- equilibrium might not be achieved. requires considerable thermal and/or mech assistance
67
Compaction
the process by which melt is initially segregated from the mantle
68
MORBS
erupt tholeiitic basalt derived from compression melting of depleted mantle; very low concentrations of trace elements that have an affinity for the melt
Basalts that erupt at subduct are enriched in k, rb, ba, pb, and other water-sol elements
69
OIB
tholeiites to nephelinites, relatively high concentrations of incompatible trace elements. very enriched.
70
Silica saturation
explains weird rocks and reflects processes/ sources
71
CIPW Norm
compares modal mineralogy of holocrystallien rock w/extrusive
identify mineralogy that's out of equilibrium w/chemistry
72
under saturated-> saturated
olivine-> hypersthene
nepheline -> albite
leucite -> orthoclase
73
Thoeliites
-hot spot
lacks olivine
low ca pyroxene
no titanaugite
rounded olivine
quartz/clear glass
74
Melt production (fertile mantle decreasing, increasing melt production)
5-phase lherzolite (ol,opx,cpx, gt/sp, phl/amph)- alkali basalt
4-phase lherzolite (ol,opx,cpx,gt/sp)
lherzolite (ol,opx,cpx)
harzburgite (ol,opx)
dunite (ol)
75
lherzolite
quick to melt, enriches
76
harzburgit
melted repeatedly
77
Granite
wet magma chamber- magnesian. Dry- ferroan
78
Subdct, MORB, OIB
alkali basaltic, MORB-like (olivine tholeiitic), quartz tholeiitic
79
Tectonic settings
silici magma evolution
MORBS
- producing, mantle depleted
VOlcanic Arcs (SRB)
- alkali basalts. water, enriched
OIB
- normal mantle
Intraplate lithospheric extension (mixture)
80
Granitoids
SiO2 >63 %, enriched in incompatible elements. most where continential crust has been thickened by continential subduction or collision of crustal massess. rare in oceanic crust. result of crustal anatexis from advection of mantle melts into crust.
water is important
81
Subduction zone magma
highly variable composition, grow in thick volcanic piles added to continent
82
Enrichment
subduction is a prinsipal means of reenriching depelted mantle
may occur if melt simply freezes on its way to the surface
83
Partial melting
the process where only a portion of a solid rock melts to form magma, leading to the differentiation of minerals within the rock
84
fractional xrystalization
stage-wise separation or removal from a melt that changes its composition
85
ferroan granites
disequilibrum in magma chamber. zenolith, xenocryst, enclaves
86
Granitic magma
crustal melting, large melt fraction, hydrous phases facilitate melting, disturbances mobilize,
87
Petrogeny's residua system
granitic melt composition controlled by ternary bias
pressure affects size and shape of phase fields
88
Granites emplaced
catazonal- great depth, migmatitic, regional metamorph, diffuse contacts
Epizonal- shallow, contact aureole, volc rocks, miarolitic cavities
mesozonal- intermediate
89
Geochemistry of granites
ferroan- dry, mafic, anhydrous, A-type granites, high T
Magnesian- wet, bio/horn
90
Granite types
I-type (metamor-ig)
- high Na/K, Ca/Al
- amphib + biotite
- 90% of granites
S-type (meta-sed)
- low Na/K, Ca/Al
- muscov, cordierite
A-typ
- high iron
- no deformation
91
Granite tectonic settins
M- subduction zone or ocean intraplate mantle
I- subduction zone, infracrustal, Ig
S- Subduction, supacrustal
A- Anorogenic stable craton rift zone , mid ocean ridge, hot spot
Cordilleran- arc magmas, manges + wet
ferroan- rift, part melt, extreme differentiation- hot spot
Caledonian- post-tectonic delam of thickened metamorphozed crust
Peraluminous leucogranites- post tect decompres
92
Alumina saturation
based on feldspar formula
Peralkaline: excess alkalis
Metaluminous: alkali + calcium = alumina
Peralum = excess alumina
- no frac xstal
- pelitic rock part melting
93
Landforms
Intrusive v extrusive
- intrusive preserved better - less incompatibles
- texture differences, size differences
- structure differences
