IGNEOUS PETROLOGY (CONCEPTS) Flashcards
1
Q
What is a magma?
A
A molten rock due to the partial melting of the mantle and of the crust; composed of varying proportions of Melt, Crystal, Dissolved Gases, and rock fragments controled by Temp, Pres and Chemical conditions
2
Q
At which temp will the magma be enriched in liquid and dissolved gases?
A
> 1200 deg cel
3
Q
These are magma chambers of various sizes, shapes, and depths that store magma within earth
A
Plutons
4
Q
What is the mechanism of Lava extrusion?
A
Magma is less denser than the surrounding rock and magmatic gases tends to provide additional force propelling magma upward
5
Q
Wt% silica Ultra Basic?
A
<45%
6
Q
Wt% silica Basic?
A
45-52%
7
Q
Wt% silica intermediate?
A
52-66%
8
Q
wt% Silicic or Acidic?
A
> 66%
9
Q
?very darkcolored rock,
?depleted in SIO2,
?enriched in pyx, oli, and amph, and ca-plag.
?ultramafic plutonic rock occurs in Earth’s Mantle
?”Mantle Rocks”
A
Peridodite
10
Q
The ultramafic volcanic rock that is rare
A
Komatiite
11
Q
?dark clored SiO2 poor volcanic rocks
? rich in plag, pyx, and oliv
? encompasses few km of the oceanic crust
A
Basalt
12
Q
?Dark colored SiO2 poor which
?cyrstallizes more slowly at depths in the
?LOWER CRUST of Ocean Basins
A
Gabbro
13
Q
?Gray colored to salt and pepper colored volcanic rocks rich in ?hbld, plag, biot qtz and is
?common volcanic rock around the pacific ring of fire with ?more than half to almost 2/3rds Silica (<2/3 SiO2)
A
Andesite
14
Q
?Intermediate plutonic rocks with
?characteristis salt and pepper appearance which
?usually underlie andesitic volcanoes
A
Diorite
15
Q
?Felsic volcanic rock with approx 2/3 silica rich in
?plag, alkali felds, qtz and minute hornblende and biotite =2/3 SiO2
A
Dacite
16
Q
?Felsic plutonic rocks that underlies andesitic-dacitic volcanoes
A
Granodiorite
17
Q
?Light colored rocks with more than 2/3 SiO2 and
?rich in Kfelds, qtz, and small percentages of plag and biot. ?This usually erupts in thick, continental crust >2/3 SiO2
A
Rhyolite
18
Q
?Felsic plutonic rocks which usually occur in continental crust
A
Granite
19
Q
Frothy vesicular rocks that are felsic
A
Pumice
20
Q
Frothy vesicular mafic rock
A
Scoria
21
Q
Non-crystalline with glassy txture, conchoidal fracture, Black
A
Obsidian
22
Q
Other name for pyroclastic/volcanic rocks
A
Fragmentals
23
Q
Ash to gravel sized fragmental rocks
A
Volcanic Tuff
24
Q
larger than gravel size
A
Volcanic Breccia
25
In terms of grain size and identification, differentiate volcanic and plutonic rocks?
Volcanic have very fine grains that are too small to be identified with the eye while plutonic rocks alllow for large crystal identiftcation and characterization
26
this represents the initial crystallization temperature below which crystals and liquids coexits
Liquidus
27
this is the term used to described temp below the liquidus
Subliquidus
28
This represents the separation betwen a highr temp field containing liquids and solid crystals from a lower temp in which only crystals exist
Solidus
29
In Subliquidus, Crystal Size depends on
1)Crystal Nucleation rate
2) Crystal Growth Rate
30
This pertains to formation of new crystals, nuclei or seed crystals, large enough to persists and grow into larger crystals
Crystal Nucleation
31
Crystal nucelation rate is expressed in?
Crystal nucleation rate = nuclei/ cc/ s
32
What factors affect crystal nucleaction?
1)Rate of Undercooling
2) availability of necessary ions and
3) ease of ion migration
33
This occurs when liquids are cooled to temp below liquidus line
Undercooling
34
When does nucleation rate decrease and approach to zero?
during large degree of undercoling because of magma viscosity which impedes assembly of nuclei
35
This is a measure of increase in crystal radius overtime
Crystal growth rate
36
what governs crystal growth rate?
rate of undercooling
availability of elements
magma viscoity
37
What would be the resulting crystal growth and nucleaction under temperatires just below the liquidus temp and experience prolonged small levels of undercooling
Low nucleation
High Crystal growth
38
What types of texture are produced by prolonged low degrees of undercooling?
Phaneritic, porphyrtic or pegmatitic with euhedral to subhedral crystals
39
What would be the result of crystal growth and nucleation rate under temperatires with high degrees undercooling well bellow the liquidus line
High Nucleation and Low Crystal Growth rate
40
What textures are produced by high degrees of undercooling well below the liquidus line?
Aphanitic , skeltal or dendritic
41
this are the textures produced by failure of crystal nucleation produced by extremely rapid cooling
non-crystaline , spherulitic
42
High Degrees of Undercooling:Crystal Nucleation = Low Degrees of Undercooling: Crystal Growth
crystal growth:Coarse=Crystal Nucleation:Fine
43
This refers to the availability of ions that can fill specific ionic sites in a crystal lattice structure
Ion availability (the more the ions available the larger the crystal will be)
44
why are zircon and apatite crystals small?
Because their mineral growth are impeded by the limited ion availability of the minor and trace elements phosphorous and zirconium
45
This pertains to the rate at which elements migrate through the magma
Diffusion
46
the resistance of fluid to shear stress or resistance to flow
Viscosity
47
a force applied parallel to the surface of an object
Shear Stress
48
a time-dependent change in the shape of an object in response to shear stress
Shear Strain rate
49
formula for viscoity
V = Shear Stress / Shear Strain Rate or the abillity to flow
50
What is the effect of viscosity to ion diffusion and crystal growth?
Low viscosity (Mas Fluid) increases diffusion rate thus increases crystal growth rate
51
What influences viscosity of magma?
1)SiO2-Content, (Higher more viscous)
2)Temp (Lower more viscous)
3)dissolved gases
52
Describe the relation of viscosity with molecular bonding in the fluid?
Higher molecular bonding - Higher SiO2, Highr viscosity (Mas madaming SiO2 Mas Crowded)
53
Elements that tend to increase molecular linkage, thereby increasing viscosity
Network formers
54
these are elements that decrease molecular linkage, thereby decreasing viscosity
Network modifiers
55
Relationship of temperature to viscosity and molecular bonding?
Inversely proportional
56
What happens when temp increases?
Incerase in molecular vibrations which breaks bond and decrease in molecular linkage
57
Is crystal nucleation exothermic or endothermic?
Exothermic
58
What happens to crystal growth as temperature and diffusion rate decreases?
decreases and viscosity increases
59
Temp Up, Diffusion Up, Crystal growth Up, Gas Up Water Content Up
Viscosity Down
60
What is the role of gases in terms of viscosity?
Gases are network modifiers thus lowering viscosity
61
Max wt% of volatile gases in the magma
7%
62
result of high water vapor pressure in magma?
reduction in viscoity and increasse in diffusion and crystal growth rates this leadung to low nucelation and high growth rate forming small numbers of large crystals
63
Textural product of high water vapor pressure?
Small numbers of large crystals (Pegmatitic)
64
Which type of magma are usually affected by high water vapor pressure?
Silicic (>66% SiO2)
65
What is the effect of unsually high H2O vapors (3-7%) to silicic magmas?
results to the production of pegmatites such as granite pegmatites, and granodiorite pegmatites
66
water vapor content of basic magmas (<52%)
contain <1%
67
Differentiate earlier and later formed granites
earlier formed granite: pegmatitic textures
later formed : cross-cutting veins which may contain finegrained textures (Aplitic)
68
Fine grained granitic textures usually in cross cutting veins
Aplitic
69
What explains aplitic texture?
As silici magma rises toward the surface, confining pressure decreases enhancing exsolution of gases out of the magma thus loweing water vapor which accelerates magma viscosity and thus inhibiting crystal growth
70
supercooled solids
Glass
71
Differentiate Quenching and Rapid gas loss as mechanism for glass formation
Quenching - contact of the melt with liquid water (basic glasses) or air
Rapid Loss of Dissolved Gas from solution which rapidly lowers H2O. The rate is so fast that it inhibits crystal nucleation and crystal growth.
72
What model explains forming of obsidian?
Obsidian is rather assoociated with silic magma and is formed due to rapid reduction of volatile gas
73
What do microlites and cryptocrystalline grains represent?
Incipient crystal nucleation in a nearly solid magma of extremely high viscosity
74
Rocks with porphyrytic (May malalaking crystals) glass texture
Vitrophyres
75
This may occur when glasses crystallize in the solid state by growing on preexisting microlitic or cryptocrystalline nuclei
Devitrification
76
This is produced when crystallization proceed outward from nuclei and produced rounded mass of radiating crystals
Spherulites
77
Cristobalite seed crystals which grow into white snowflake forms within black glass obsididan
Snowflake obsidian
78
Glassy SiO2 rich volcanic rocks with higher water content that obsidian
Perlite
79
Differentiate Obsidian from perlite
Perlite have cloudy apperance (white) and curved or subspherical cooling cracks called perlitic cracks
80
This occurs above the level of exsolution where volatiles nucleate as small bubbles
Vesiculation
81
This is where bubbles constitute 70-80% of the magma volume and changes from liquid with suspended gas bubbles to a buoyant gaseous mixture containing liquid blobs
Fragmentation surface
82
A rock with >30% vesicles by volume and is white to gray colored solidified as a frothy glass from silicic lava
Pumice
83
A rock with >30% vesicles by volume and is brownish red to black color derived from basaltic to intermediate lava and may be hypocyrstalline
Scoria
84
Rocks which contain 5-30% vesicles?
Vesicular + rocks
85
If the rock has <5% vesicle?
Vesicle Bearing + rock
86
Common secondary amygdules
qtz, calcite, epidote, zeolites and metals
87
Literal meaning of pyroclasts?
Fiery Fragment
88
These are pyroclasts which contain fragments of rocks
Lithic Fragments
89
Pyroclasts composed of glassy fragments commonly of pumice or scoria shards
Vitric
90
Pyroclasts consist of minerals
Crystals
91
pyroclasts >64mm and angular
Blocks
92
>64mm pyroclasts and rounded
Bombs
93
This consist primarily of hot gases, lithic clasts, crystals, and pumice shards and fragments which creates tuffs and lapilli tuffs
Pyroclastic flows
94
This is the result when fragments become progressively fused together as porosity decreases during compaction in a pyroclastic flow or eruption
Welding
95
What explains the draping of shards and fragments around rigid crystals and lithic fragments?
Differential cooling rate which allows shards and pumic to remain plastic and bend around more rigid crystals
96
A welded pyroclastic rocks characterized by abundant flattened juvenile clasts usually of pumice
Ignimbrite or Welded Tuff
97
These are structures often found in welded tuff and ignimbrites that are characterized by small dark lenses of glassy materials (pumice) that were softened and compressed into tuff during welding episode
Fiamme
98
A name which can be used for a flame bearing tuff
Piperino or peperine
