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GLE 2024 (Day 2) > IGNEOUS PETROLOGY (CONCEPTS) > Flashcards

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

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2
Q

At which temp will the magma be enriched in liquid and dissolved gases?

A

> 1200 deg cel

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3
Q

These are magma chambers of various sizes, shapes, and depths that store magma within earth

A

Plutons

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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

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5
Q

Wt% silica Ultra Basic?

A

<45%

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6
Q

Wt% silica Basic?

A

45-52%

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7
Q

Wt% silica intermediate?

A

52-66%

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8
Q

wt% Silicic or Acidic?

A

> 66%

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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

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10
Q

The ultramafic volcanic rock that is rare

A

Komatiite

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11
Q

?dark clored SiO2 poor volcanic rocks
? rich in plag, pyx, and oliv
? encompasses few km of the oceanic crust

A

Basalt

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12
Q

?Dark colored SiO2 poor which
?cyrstallizes more slowly at depths in the
?LOWER CRUST of Ocean Basins

A

Gabbro

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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

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14
Q

?Intermediate plutonic rocks with
?characteristis salt and pepper appearance which
?usually underlie andesitic volcanoes

A

Diorite

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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

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16
Q

?Felsic plutonic rocks that underlies andesitic-dacitic volcanoes

A

Granodiorite

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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

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18
Q

?Felsic plutonic rocks which usually occur in continental crust

A

Granite

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19
Q

Frothy vesicular rocks that are felsic

A

Pumice

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20
Q

Frothy vesicular mafic rock

A

Scoria

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21
Q

Non-crystalline with glassy txture, conchoidal fracture, Black

A

Obsidian

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22
Q

Other name for pyroclastic/volcanic rocks

A

Fragmentals

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23
Q

Ash to gravel sized fragmental rocks

A

Volcanic Tuff

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24
Q

larger than gravel size

A

Volcanic Breccia

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25
Q

In terms of grain size and identification, differentiate volcanic and plutonic rocks?

A

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

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26
Q

this represents the initial crystallization temperature below which crystals and liquids coexits

A

Liquidus

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27
Q

this is the term used to described temp below the liquidus

A

Subliquidus

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28
Q

This represents the separation betwen a highr temp field containing liquids and solid crystals from a lower temp in which only crystals exist

A

Solidus

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29
Q

In Subliquidus, Crystal Size depends on

A

1)Crystal Nucleation rate
2) Crystal Growth Rate

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30
Q

This pertains to formation of new crystals, nuclei or seed crystals, large enough to persists and grow into larger crystals

A

Crystal Nucleation

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31
Q

Crystal nucelation rate is expressed in?

A

Crystal nucleation rate = nuclei/ cc/ s

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32
Q

What factors affect crystal nucleaction?

A

1)Rate of Undercooling
2) availability of necessary ions and
3) ease of ion migration

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33
Q

This occurs when liquids are cooled to temp below liquidus line

A

Undercooling

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34
Q

When does nucleation rate decrease and approach to zero?

A

during large degree of undercoling because of magma viscosity which impedes assembly of nuclei

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35
Q

This is a measure of increase in crystal radius overtime

A

Crystal growth rate

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36
Q

what governs crystal growth rate?

A

rate of undercooling
availability of elements
magma viscoity

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37
Q

What would be the resulting crystal growth and nucleaction under temperatires just below the liquidus temp and experience prolonged small levels of undercooling

A

Low nucleation
High Crystal growth

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38
Q

What types of texture are produced by prolonged low degrees of undercooling?

A

Phaneritic, porphyrtic or pegmatitic with euhedral to subhedral crystals

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39
Q

What would be the result of crystal growth and nucleation rate under temperatires with high degrees undercooling well bellow the liquidus line

A

High Nucleation and Low Crystal Growth rate

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40
Q

What textures are produced by high degrees of undercooling well below the liquidus line?

A

Aphanitic , skeltal or dendritic

41
Q

this are the textures produced by failure of crystal nucleation produced by extremely rapid cooling

A

non-crystaline , spherulitic

42
Q

High Degrees of Undercooling:Crystal Nucleation = Low Degrees of Undercooling: Crystal Growth

A

crystal growth:Coarse=Crystal Nucleation:Fine

43
Q

This refers to the availability of ions that can fill specific ionic sites in a crystal lattice structure

A

Ion availability (the more the ions available the larger the crystal will be)

44
Q

why are zircon and apatite crystals small?

A

Because their mineral growth are impeded by the limited ion availability of the minor and trace elements phosphorous and zirconium

45
Q

This pertains to the rate at which elements migrate through the magma

A

Diffusion

46
Q

the resistance of fluid to shear stress or resistance to flow

A

Viscosity

47
Q

a force applied parallel to the surface of an object

A

Shear Stress

48
Q

a time-dependent change in the shape of an object in response to shear stress

A

Shear Strain rate

49
Q

formula for viscoity

A

V = Shear Stress / Shear Strain Rate or the abillity to flow

50
Q

What is the effect of viscosity to ion diffusion and crystal growth?

A

Low viscosity (Mas Fluid) increases diffusion rate thus increases crystal growth rate

51
Q

What influences viscosity of magma?

A

1)SiO2-Content, (Higher more viscous)
2)Temp (Lower more viscous)
3)dissolved gases

52
Q

Describe the relation of viscosity with molecular bonding in the fluid?

A

Higher molecular bonding - Higher SiO2, Highr viscosity (Mas madaming SiO2 Mas Crowded)

53
Q

Elements that tend to increase molecular linkage, thereby increasing viscosity

A

Network formers

54
Q

these are elements that decrease molecular linkage, thereby decreasing viscosity

A

Network modifiers

55
Q

Relationship of temperature to viscosity and molecular bonding?

A

Inversely proportional

56
Q

What happens when temp increases?

A

Incerase in molecular vibrations which breaks bond and decrease in molecular linkage

57
Q

Is crystal nucleation exothermic or endothermic?

A

Exothermic

58
Q

What happens to crystal growth as temperature and diffusion rate decreases?

A

decreases and viscosity increases

59
Q

Temp Up, Diffusion Up, Crystal growth Up, Gas Up Water Content Up

A

Viscosity Down

60
Q

What is the role of gases in terms of viscosity?

A

Gases are network modifiers thus lowering viscosity

61
Q

Max wt% of volatile gases in the magma

A

7%

62
Q

result of high water vapor pressure in magma?

A

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
Q

Textural product of high water vapor pressure?

A

Small numbers of large crystals (Pegmatitic)

64
Q

Which type of magma are usually affected by high water vapor pressure?

A

Silicic (>66% SiO2)

65
Q

What is the effect of unsually high H2O vapors (3-7%) to silicic magmas?

A

results to the production of pegmatites such as granite pegmatites, and granodiorite pegmatites

66
Q

water vapor content of basic magmas (<52%)

A

contain <1%

67
Q

Differentiate earlier and later formed granites

A

earlier formed granite: pegmatitic textures
later formed : cross-cutting veins which may contain finegrained textures (Aplitic)

68
Q

Fine grained granitic textures usually in cross cutting veins

A

Aplitic

69
Q

What explains aplitic texture?

A

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
Q

supercooled solids

A

Glass

71
Q

Differentiate Quenching and Rapid gas loss as mechanism for glass formation

A

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
Q

What model explains forming of obsidian?

A

Obsidian is rather assoociated with silic magma and is formed due to rapid reduction of volatile gas

73
Q

What do microlites and cryptocrystalline grains represent?

A

Incipient crystal nucleation in a nearly solid magma of extremely high viscosity

74
Q

Rocks with porphyrytic (May malalaking crystals) glass texture

A

Vitrophyres

75
Q

This may occur when glasses crystallize in the solid state by growing on preexisting microlitic or cryptocrystalline nuclei

A

Devitrification

76
Q

This is produced when crystallization proceed outward from nuclei and produced rounded mass of radiating crystals

A

Spherulites

77
Q

Cristobalite seed crystals which grow into white snowflake forms within black glass obsididan

A

Snowflake obsidian

78
Q

Glassy SiO2 rich volcanic rocks with higher water content that obsidian

A

Perlite

79
Q

Differentiate Obsidian from perlite

A

Perlite have cloudy apperance (white) and curved or subspherical cooling cracks called perlitic cracks

80
Q

This occurs above the level of exsolution where volatiles nucleate as small bubbles

A

Vesiculation

81
Q

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

A

Fragmentation surface

82
Q

A rock with >30% vesicles by volume and is white to gray colored solidified as a frothy glass from silicic lava

A

Pumice

83
Q

A rock with >30% vesicles by volume and is brownish red to black color derived from basaltic to intermediate lava and may be hypocyrstalline

A

Scoria

84
Q

Rocks which contain 5-30% vesicles?

A

Vesicular + rocks

85
Q

If the rock has <5% vesicle?

A

Vesicle Bearing + rock

86
Q

Common secondary amygdules

A

qtz, calcite, epidote, zeolites and metals

87
Q

Literal meaning of pyroclasts?

A

Fiery Fragment

88
Q

These are pyroclasts which contain fragments of rocks

A

Lithic Fragments

89
Q

Pyroclasts composed of glassy fragments commonly of pumice or scoria shards

A

Vitric

90
Q

Pyroclasts consist of minerals

A

Crystals

91
Q

pyroclasts >64mm and angular

A

Blocks

92
Q

> 64mm pyroclasts and rounded

A

Bombs

93
Q

This consist primarily of hot gases, lithic clasts, crystals, and pumice shards and fragments which creates tuffs and lapilli tuffs

A

Pyroclastic flows

94
Q

This is the result when fragments become progressively fused together as porosity decreases during compaction in a pyroclastic flow or eruption

A

Welding

95
Q

What explains the draping of shards and fragments around rigid crystals and lithic fragments?

A

Differential cooling rate which allows shards and pumic to remain plastic and bend around more rigid crystals

96
Q

A welded pyroclastic rocks characterized by abundant flattened juvenile clasts usually of pumice

A

Ignimbrite or Welded Tuff

97
Q

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

A

Fiamme

98
Q

A name which can be used for a flame bearing tuff

A

Piperino or peperine

GLE 2024 (Day 2) (41 decks)

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