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GEOLOGY > Igneous rock formation > Flashcards

Igneous rock formation Flashcards

2.1-2.4

1
Q

igneous rocks are formed from

A

the solidification of a melt

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2
Q

a melt is

A

molten rock

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3
Q

what’s the difference between lava and magma

A

magma below ground lava above ground

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4
Q

extrusive is

A

above ground

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5
Q

intrusive is

A

below ground

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6
Q

the crust and athenosphere are mostly in what state

A

solid

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7
Q

melts occur in what areas

A

localized

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8
Q

the earth has been cooling by

A

radiating heat out to space

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9
Q

the uppermost layer of the earth froze to form

A

the crust

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10
Q

how thick is the mantle

A

2800 km

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11
Q

temp increases or decreases with depth

A

increases

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12
Q

almost all solid rock is

A

peridotite

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13
Q

lithosphere thickness

A

100-150km

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14
Q

lithosphere is the

A

crust and upper mantle

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15
Q

athenosphere thickness

A

100-350km

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16
Q

athenosphere is a part of the

A

mantle

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17
Q

melts occur because of

A

decrease in pressure (decompression)

introduction of volatiles’ (flux)

heat transfer (heat transfer)

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18
Q

what happens in decompression melting

A

P decreases but T remains constant

temperature is high enough to melt rock at surface but pressure keeps them solid

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19
Q

how does pressure decrease to allow decompression melting

A

a volume of hot asthenosphere rises by a mantle plume or divergent plate boundaries

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20
Q

decompression melting creates M/F material

A

mafic

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21
Q

what kind of melt created hawaii

A

decompression

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22
Q

what happens in flux melting

A

volatiles help break chemical bonds, creating a melt

h2o or co2 mi with hot dry rock and help break the chemical bonds

this lowers the melting point of the rock

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23
Q

where does flux melting happen

A

subduction zones

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24
Q

flux melting creates M/F material

A

Felsic

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25
Q

Heat transfer melting happens when

A

heat from magma melts adjacent rocks

hot mantle rises up and brings heat with it

this melts existing crustal rock that has a lower melting point

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26
Q

volcanic ars along plate boundaries come from what type of melting

A

heat transfer melting

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27
Q

melt composition is defined by

A

the proportion of different oxides

SILICA SiO2
IRON OXIDE FeO and Fe2O3
MAGNESIUM OXIDE MgO

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28
Q

a dry melt has

A

no volatiles

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29
Q

a wet melt has

A

volatiles

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30
Q

What are the four major compositional groups of magma

A

felsic (silicic). 67-76% silica
intermediate. 53-66% silica
mafic. 46-52% silica
ultramafic. 38-45% silica

31
Q

felsic magma is what percent silica

A

67-76%

32
Q

intermediate magma is what percent silica

A

53-66%

33
Q

mafic magma is what percent silica

A

46-52%

34
Q

ultramafic magma is what percent silica

A

38-45%

35
Q

the four major compositional groups of magma is the percent

A

magma weight that is silica

36
Q

the four major compositional groups of solid rock

A

are dependent on the proportion of silica relative to the combination of magnesium and iron oxide

37
Q

diorite is _ I/S/M and _ F/M

A

igneous intermediate

38
Q

rhyolite I/S/M and F/M

A

felsic igneous

39
Q

gabbro I/S/M F/M

A

igneous mafic

40
Q

why do melts vary

A

source rock dictates the initial melt composition

41
Q

what is magma mixing

A

different magmas from different source rocks mix in the magma chamber changing the magma composition

42
Q

what is assimilation / contamination

A

heat provided by magma partially melts wall rock

the new magma the mixes with the original magma

blocks of wall rock can dissolve in the original magma and that wall rock may chemically react with the magma

changes the melts composition

43
Q

what is partial melting

A

only a fraction of a source rock will melt at an achievable P and T

some minerals melt at lower temps than others

44
Q

in partial melting liquid magma

A

migrates away from the source rock before the entire rock can melt

45
Q

partial melting produces a rock with

A

higher silica content

46
Q

how does molten rock flow

A

melts migrate toward the surface due to their relatively low density

47
Q

viscosity of molten rock depends on

A

temperature, volatile content, and silica percent content

48
Q

Low viscosity magma is

A

Hotter
more mafic
has less volatiles

49
Q

high viscosity magma is

A

cooler
more felsic
has more volatiles

50
Q

mafic melts are ___ viscous than felsic melts. why

A

less

more silica tetrahedra in felsic magma. they link together and don’t like to flow

51
Q

how does a melt become a rock

A

it freezes

migrates towards the surface

loses heat to surrounding rock or erupts onto surface

looses volatiles

52
Q

the time a melt takes to cool depends on how

A

well insulated it is

53
Q

wall rock is a ____insulator than water or air

A

better

54
Q

melts cool ___ at the surface than underground

A

faster

55
Q

the deeper magma is the hotter

A

the wall rock will be

56
Q

a larger intrusion will cool _____ than a small intrusion at the same depth

A

slower

57
Q

interaction with ground water can cool a melt _____ as water

A

faster

as water can carry away heat but also introduce volatiles

58
Q

thing lava flows cool ____ than thick ones

A

faster

59
Q

lava immersed in water cools _____ than water immersed in air

A

faster

60
Q

what is fractional crystallization

A

when a melt cools some minerals form earlier than others due to their melting points

this results in sequential crystal formation

61
Q

fractional crystallization creates a more

A

felsic melt

62
Q

in crystal fractionalization the material that solidifies out is

A

more mafic

olivine and calcium rich plagioclase

63
Q

In bowens reaction series Low temperature corresponds to

A

last minerals to crystallize
felsic materials

64
Q

in bowens reaction series high the first minerals to crystallize

A

do so at high temperatures
are ultramafic

65
Q

What are tabular intrusions

A

Sills and Dikes

underground solidified melts

66
Q

Dikes are ___ to rock layers

A

perpendicular

67
Q

Sills are ___ to rock layers

A

parralell

68
Q

most sills result in a

A

change in land elevation of the surface

69
Q

dikes spread in what way

A

sideways

70
Q

what is a lacolith

A

when magma that cannot spread accumulates in a blister shaped intrusion

71
Q

what is a pluton

A

a solid igneous intrusion

72
Q

what is a batholith

A

a large solid igneous intrusion larger than 100km^2

73
Q

what is a xenolith

A

a piece of rock in an igneous rock that is not derived from the original magma that showed up from elsewhere

74
Q

what is unroofing

A

when intrusive igneous features are exposed over a long period of time

GEOLOGY (12 decks)

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