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LPC 2020 S2 - EAE1012 - Earth Science 2 > EAE 06 Rocks (10) > Flashcards

EAE 06 Rocks (10) Flashcards

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1
Q

How are Igneous rocks formed?

A

They are formed from the cooling of molten rock

EAE 7aa

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2
Q

How are Sedimentary rocks formed?

A

They are formed when weathered fragments of other rocks are buried, compressed, and cemented together, or when minerals precipitate directly from solution

EAE 7ab

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3
Q

How are Metamorphic rocks formed?

A

They are formed by alteration (e.g., heat, pressure) of a pre-existing igneous or sedimentary rock.

EAE 7ac

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4
Q

What is a rock?

A

Consolidated mixture of minerals, or mineral like substances

  • Not necessarily more than one type of mineral
  • Naturally occurring

EAE 7ad

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5
Q

Key points

Minerals

A
  • Definite chemical composition
  • Definite crystalline structure
  • Formed naturally

EAE 7ae

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6
Q

What are the 3 main types of rocks?

A

Igneous

Sedimentary

Metamorphic

EAE 7af

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7
Q

What is the difference between Magma and Lava?

A

Magma = molten rock still underground.

Lava = molten rock that has broken through the Earth’s surface.

EAE 7ag

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8
Q

What is an Igneous Rock?

A
  • Any rock that has formed out of a molten source (i.e. Magma or Lava)
  • Many types, depending on:
      * What they are made of
  * Where they cooled
  * How fast they cooled

EAE 7ah

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9
Q

How common is igneous rock?

A

95% of the Earth’s crust is made of igneous rocks

EAE 7ai

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10
Q

How do you melt a rock to make magma?

A

3 ways:

* Heat it up
* Reduce its pressure
* Add water

EAE 7aj

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11
Q

Where does magma get made?

A
  1. Heat it up
    • In subduction zones
  2. Reduce its pressure
    • At rifts
    • Within rising plumes
  3. Add Water
    • At Subduction Zones

EAE 7ak

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12
Q

Why does heating rocks up happen?

A
  • Add enough heat, eventually everything will melt
  • Hot stuff reduces in density, becomes more buoyant
  • Rises through its denser surrounding rock usually through cracks, but can melt through if a long lived heat source is present.

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13
Q

How does magma get made through reducing pressure?

A

“Decompression melting”

  • Solids (minerals in rocks) are stable at certain temperatures and pressures
  • Change the pressure, and you change how stable they are
  • Reduce the pressure, and the minerals/rocks melt
  • Produces a magma, which is buoyant

EAE 7am

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14
Q

How does magma get made through adding water?

A

Hydration Melting

Adding water (OH) changes the stability of minerals/rocks, even if the pressure does not change

The more water (OH) you add, the lower the temperature they melt

Subducting rocks lose water into the mantle above them, which melts the mantle and adds water to the magma

Produces a magma, which is buoyant…

EAE 7an

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15
Q

What happens as the magma rises up through the crust?

A
  • Hot liquid magma melts surrounding rocks and they add to magma - may change magma composition if surrounding (country) rocks are chemically different to magma
  • Surrounding rocks are cooler magma freezes (cools/chills) SLOWLY within them to become rock made of minerals → INTRUSIVE rock
  • Some magma makes its way to the surface now called “Lava” where it freezes RAPIDLY → EXTRUSIVE rock

EAE 7ao

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16
Q

What sort of rocks can you make?

A

Depends on three things:

What you started off with

The material that has been added to it (or subtracted from it)

How fast it cools

EAE 7ap

17
Q

Core Term

Igneous rock that cools slowly within crust

A

Intrusive = Plutonic

EAE 7aq

18
Q

What is igneous rock with big crystals, due to a long time for minerals to grow?

A

Phaneritic

Coarse grained

EAE 7ar

19
Q

What is igneous rock that has cooled quickly at the surface?

A

Extrusive
= Volcanic

EAE 7as

20
Q

What is rock with only a short time for minerals to grow?

A

small crystals
Aphanitic
fine grained

EAE 7at

21
Q

What is rock that has cooled too fast for minerals to grow?

A

Glass

EAE 7au

22
Q

What is rock that has cooled slowly, then quickly?

Initial slow cooling within crust, then quickly at surface.

A

Porphyritic = two crystal sizes

EAE 7av

23
Q

What are phenocrysts?

A

Coarse grains in prophyritic rock

EAE 7aw

24
Q

What is groundmass?

A

Fine grained minerals in porphyritic rock.

EAE 7ax

25
Q

What type of rock is

Granite

A

Phaneritic (coars grained)

EAE 7ay

26
Q

What type of rock is

Basalt

A

Aphanitic (fine grained)

EAE 7az

27
Q

What type of rock is

Obsidian

A

Glassy

EAE 7ba

28
Q

What rock forms at

Mid Ocean Ridges

A

At ridges, the mantle decompresses (decompression melting) and then solidifies at the surface

It is essentially mantle material that has simply moved to the surface

Mantle = olivine + pyroxene + plagioclase feldspar = Basalt or Gabbro

EAE 7bb

29
Q

What rock forms at

Rift Zones

A
  • On Land Early stage rifts
  • Basalt from mantle mixes with granite from continental crust
  • All sorts of magmas, depending on how old the rift is
  • Young = more granitic = rhyolites to dacites
  • Old = more basaltic = andesites to basalts

EAE 7bc

30
Q

What rock forms at

Subduction Zones

A
  • Subducting slab loses water (OH) into overlying mantle dehydrates
  • Water lowers melting point of mantle rocks, AND allows new minerals to form from mantle hydration melting
  • Amphibole, Biotite , Muscovite, Quartz
  • Andesites (low water) to Granites (water rich)
  • Plutonic (intrusive due to thick crust) and Volcanic (extrusive) rocks

EAE 7bd

31
Q

What rock forms at

Hot Spots

A
  • At hot spots, mantle ‘melts’ through the crust, and may incorporate overlying rocks
  • Basalts to granites, depending on what composition of rock overlies the hot spot
  • Old hot spots = basalts
  • New hot spots on continents = granites
  • Middle aged hot spots = mixed (intermediate)
  • Magmas = andesites

EAE 7be

32
Q

What is a Plutonic rock?

A

Igneous rock that cools slowly within crust
Intrusive rock

EAE 8aa

33
Q

What is phaneritic rock?

A

Igneous rock with big crystals, due to a long time for minerals to grow

Coarse grained

EAE 8ab

34
Q

What is extrusive rock?

A

Igneous rock that has cooled quickly at the surface

= Volcanic

EAE 8ac

35
Q

What is an Aphanitic rock?

A

Rock with only a short time for minerals to grow.
→ small crystals or fine grained

EAE 8ad

36
Q

What is natural glass?

A

Rock that has cooled too fast for minerals to grow

EAE 8ae

37
Q

What is porphyritic rock?

A

Rock that has cooled slowly, then quickly → 2 crystal sizes

Initial slow cooling within crust, then quickly at surface.

EAE 8af

LPC 2020 S2 - EAE1012 - Earth Science 2 (18 decks)

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