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220 > Igneous Rocks > Flashcards

Igneous Rocks Flashcards

1
Q

How are igneous rocks formed

A

by the cooling of magma

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2
Q

what are the three types of magma

A

Mafic/Basaltic magma, intermediate magma and felsic/basaltic magma

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3
Q

how is mafic magma formed

A

two methods: decompression melting and flux melting

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4
Q

what is decompression melting

A

convection currents in the mantle can take chunks of the mantle with them. As the mantle rises the pressure drops, allowing the molecules to move faster resulting in the melting of that chunk. this process has minimal temperature change and is the largest source of mafic magma

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5
Q

what is flux melting

A

when two tectonic plates collide, the heavier plate is driven down into the mantle. the increased pressure and temperature drives out volatiles in the crust and when they come into contact with the mantle they lower the melting temperature of mantle.

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6
Q

what is heat transfer

A

rising basaltic magma if unable to rise to the earths surface pools underneath the crust. the heat generated by the pool melts the surrounding crust

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7
Q

what is the dominant component of lava

A

silica

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8
Q

what are properties of mafic/basaltic magma

A

low silica, dark coloured, low viscosity, high temp, volatile poor. mafic minerals dominate

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9
Q

what are the properties of andesitic magma

A

as a mix of basaltic and felsic magma, properties are in between

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10
Q

what are the properties of rhyolitic magma

A

formed from crustal material, high silica, light coloured, high viscosity, low temp, volatile rich, very sticky

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11
Q

what can mafic magma form

A

olivine and pyroxene

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12
Q

what can andesitic magma form

A

pyroxene, amphibole, biotite

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13
Q

what can rhyolitic magma form

A

biotite, quartz, muscovite and feldspars

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14
Q

how are igneous rocks classified

A

based on the rock texture, mineral composition

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15
Q

how many igneous rock textures are there and what are they

A

3, aphantic, phaneritic and porhyritic

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16
Q

how are intrusive igneous rocks formed

A

slow cooled in the earths crust e.g. gabbro and granite

17
Q

how are extrusive igneous rocks formed

A

fast cooling after reaching the earths surface e.g. basalts and obsidian

18
Q

why are unaltered intrusive and extrusive igneous rocks suitable for engineering applications

A

strength due to interlocking crystals, stable overall at most dip angles and have little water flow

19
Q

why aren’t volcaniclastic rocks suitable for engineering purposes

A

weathers easily and decreases strength

20
Q

what are the two main groups of igneous rocks

A

volcanic/extrusive and plutonic/intrusive

21
Q

what is hot spot volcanism

A

when a moving tectonic plate moves over a stationary hotspot. creating intrusive and extrusive basalt

22
Q

what is plate divergence

A

when 2 plates move away from each other and rising magma fills the gap forming both intrusive or extrusive basalt

23
Q

what is island arc plate subduction

A

when an oceanic plate is subducted beneath another oceanic plate. creating mafic to intermediate extrusives and intrusives

24
Q

what is continental plate subduction

A

when an oceanic plate collides with a continental plate with the oceanic plate being subducted. creating mafic to felsic intrusives and extrusives

25
Q

what are the properties of basalts

A

extrusive, dark coloured and aphanitic, silica content 47-53%

26
Q

what are the properties of andesites

A

intermediate extrusive rock, medium grey colour, porphyritic with phenocrysts normally feldspars, proxene. silica content 53-63%

27
Q

what are the properties of dacite

A

intermediate extrusive rock, colour medium grey, with phenocrysts normally feldspars. silica content 63-70%

28
Q

what are the properties of rhyolite

A

extrusive rock, light colour due to high silica content of 70-78%. porphyritic with phenocrysts normally feldspar

29
Q

what are the properties of gabbro

A

intrusive rock, dark in colour, dense with a phanertic texture with crystals feldspar, pyroxene silica content 47-53%

30
Q

what are the properties of diorite

A

intrusive intermediate rock, speckled black and white with a phaneritic texture crystals normally feldspar, silica content ranging from 53-70%

31
Q

what are the properties of granite

A

intrusive rock with pinkish white colour, phaneritic texture with crystals of feldspar and quartz, silica content 70-78%

220 (9 decks)

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