EOS 120 > Lab 5 > Flashcards

Lab 5 Flashcards

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1
Q

Why are metamorphic rocks important

A
  1. they mark the positions of plate collisions that took place millions of years ago
  2. They make up most of earth’s interior and the cores of every continent and mountain belt, thus they record conditions and processes that we cannot see or measure directly
  3. A number of economically valuable products (e.g. marble, slate, and talc; ores of tin and tungsten) are derived from metamorphic rocks
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2
Q

What does metamorphism refer to

A

Metamorphism refers to changes in a rock’s appearance and mineral composition due to changes in temperature and pressure in the environment.

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3
Q

What determines the type of metamorphic rock that forms

A

the content of the original rock (“parent rock” or protolith) and also on the intensity of the conditions to which he rock is subjected

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4
Q

What brings about metamorphic changes

A

increased temperatures, pressures, and or reaction with hot fluids deep in the crust

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5
Q

What are some processes that cause metamorphism

A

There are a wide variety of processes that cause metamorphism, including the intrusion of an igneous body, burial (and heating) of thick sedimentary sequences, and rare meteorite impacts. Most occurs within the crust adjacent to active plate margins

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6
Q

How are metamorphic rocks classified

A

Classified based on granular or foliated textures. texture refers to grain size, shape, and orientation

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7
Q

What is foliated texture

A

Foliation (Leafy appearance) refers to the planar structures that result from flattening of mineral grains (like mica) or banding of minerals in concentrations

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8
Q

how does deformation occur with metamorphism

A

Deformation (alignment) of mineral grains occurs during metamorphism by directed stresses that cause minerals to be physically reoriented or rotated, giving a layered or “leafy” appearance to the rock. Direction of foliation is perpendicular to the direction of the greatest stress which acted upon the rock

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9
Q

What is slaty cleavage

A

Slaty cleavage - parallel foliation of fine grained minerals (chlorite), producing the rocks slate and phyllite

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10
Q

What is Schistose foliation

A

Schistose - parallel arrangement of visible coarse-grained minerals (biotite, mica) and may contain a variety of other minerals (quartz, felspars, garnet, sillimanite) and produces schist

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11
Q

What is Gneissic foliation

A

Gneissic - most intense form of foliation where banding occurs: granular minerals (quartz and feldspar) alternate with platy or elongate minerals to form gneiss

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12
Q

How can foliation vary

A

Foliation can be subtle or pronounced depending on the degree of metamorphism

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13
Q

What is Lineation

A

a linear textural element that may occur in either foliated or non foliated rocks. May be formed by elongate minerals with a preferred orientation, or of orientated mineral aggregates such as a stretched-pebble conglomerate or metaconglomerate.

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14
Q

What are crenulations

A

Fold axes or parallel sets of tiny folds called crenelations can also form a type of lineation

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15
Q

What are Metamorphic rocks

A

Rocks that have changed their composition and or texture. The original chemical composition of the rock before metamorphism controls what minerals can form. Thus we may group the parent rock types (or protoliths) into four general categories based on mineralogical composition

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16
Q

What are Shales

A

Shales are composed of clay minerals rich in aluminum, silicon, iron, magnesium, and potassium

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17
Q

What are Calcareous rocks

A

Limestones, dolostones rich in calcium, carbon, and oxygen, with less iron and magnesium and only a little aluminum

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18
Q

what are mafic rocks

A

Basalts and gabbros rich in calcium, aluminum, iron, and magnesium

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19
Q

What are Felsic (or Quartz/Felspar-rich) Rocks

A

Igneous rocks like granite and rhyolite, or clastic sedimentary rocks such as quartz sandstone and arkose. These contain abundant silicon, potassium, aluminium, and sodium, with minor iron or magnesium

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20
Q

What are the categories of metamorphic rocks

A

Shales
Calcareous Rocks
Mafic Rocks
Felsic (or Quartz/Feldspar-rich) Rocks

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21
Q

How do mineral changes occur in rocks that are metamorphosed

A

New minerals that appear represent a crystalline configuration which is more stable at the increase temperature and or pressure

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22
Q

What are the most common mineral changes

A

Recrystallization occurs when small crystals of a mineral slowly convert to fewer, larger crystals of the same mineral without melting of the rock

Neomorphism occurs when new minerals are formed from the minerals that are present in the parent rock with or without the addition of elements from circulating fluids

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23
Q

What process does Slate go through

A

Slate -> Shale -> Phyllite -> Schist -> Gneiss

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24
Q

What is Slate like

A

Mostly clay with some mica growth, flat and smooth, breaks along flat planes, more lustre than shale (Low metamorphic grade)

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25
What is phyllite like
Clays and micas, pearly lustre from fine grained but abundant micas, may have wavy appearance, soapy feel if talc present, may have chlorite (Low metamorphic grade)
26
What is Schist like
Abundant large micas, quartz and feldspars, glassy lustre from micas and quartz, wavy structure, often have large crystals of garnet, kyanite, magnetite (intermediate grade metamorphism)
27
What is Gneiss from shale like
Micas are largely gone, dominated by quartz, feldspars, and ferromagnesian; light and dark minerals in bands. sometimes graphite. (high grade metamorphism)
28
What is Gneiss from Diorite or Granite like
Quartz, feldspars, and ferromagnesians; banded light and dark minerals. Sometimes graphite (high metamorphic grade)
29
What is Greenstone/Greenschist like
Forms from Basalt Fine-grained, dense; looks like a green basalt; contains epidote, chlorite, and green amphibole (low to intermediate grade metamorphism) Greenschist if foliation developed
30
What is Eclogite like
Formed from Basalt and Gabbro Fine to coarse grained,; contains a green pyroxene, garnet, quartz, also possibly pyrite, kyanite, amphibole (high grade metamorphism)
31
What is Quartzite like
forms from Quartz Sandstone Recrystallization of existing quartz sand grains. Difficult to tell grade unless accessory minerals like biotite are present (all possible metamorphic grades)
32
What is marble like
Formed from limestone or Dolostone Interlocking calcite grains. Difficult to tell grade, unless accessory minerals like biotite are present (all possible metamorphic grades)
33
What is the mineral graphite like
Forms from coal 100% carbon, greasy feel, metallic grey colour All possible metamorphic grades
34
What conditions does metamorphism occur under
200-800ºC 1-10 kilobits of pressure (1 bar = atmospheric pressure)
35
How do we assign metamorphic grade
Assigned based on pressure and temperature applied to rock. Low, intermediate, or high. We can determine it based on grain size and mineral content
36
What does grain size tell us about metamorphism
Increasing metamorphic conditions generally cause grain sizes to become larger
37
What does Mineral content tell us about metamorphism
Different minerals form only under certain temperatures and pressure
38
What are the four types of metamorphism
Burial metamorphism Regional metamorphism contact metamorphism Subduction zone metamorphism
39
What is Burial Metamorphism
Burial Metamorphism occurs when sediments and water are gradually buried, compressed and heated. An example is a passive continental margin such as the east coast or Brazil where the amazon deposits huge quantities of sediment. The weight of sediment actually causes the crust to sink, thus creating a sedimentary depression which can build up to many kilometres thick
40
what is regional metamorphism
Occurs over large areas associated with convergent plate boundaries which exhibit extremely high pressures, much greater than is caused by simple burial. This metamorphism is characterized by a relatively even increase in pressure and temperature
41
What is contact metamorphism
Contact metamorphism occurs wherever molten rock comes into contact with other rock, either within the crust near intrusive bodies such as batholiths, or neared the surface, beneath lava flows. This metamorphism tends to be very high temperature but lower pressure
42
What is subduction zone metamorphism
Occurs in the rocks surrounding the contact between the subduction plate and the over-riding plate. This metamorphism is unusual because the rocks go very deep quite quickly, but tend to be slow to heat up and involve abundant hot water. So high pressure but low temp
43
what can tell you that you have a marble
a vigorous acid reaction will tell you that you have a marble. Differ from limestone by being coarser grained, having a glassy lustre, and not containing any trace of fossils
44
What does a soapy or greasy feel tell us
Phyllites often contain talc or graphite and have a greasy or soapy feel to it
45
What does green colour indicate
A green colour may be due to an abundance of chlorite, epidote, or green amphibole, all indicative of low to intermediate grade metamorphism
46
What do dark red "geodesic-dome" shaped minerals indicate
these are likely garnets and indicate intermediate to high grade rocks
47
What does muscovite indicate
a low grade metamorphic rock
48
what does pyroxene or hornblende indicate
high grade metamorphic rock
49
what does biotite indicate
an intermediate metamorphic grade rock
50
what does pyrite crystals indicate
low and intermediate grade rocks
51
What do pyramid shaped magnetic porphyroblasts indicate
indicate high metamorphic grade, may be identified with magnet
52
What does a blueish colour indicate
the presence of glaucophane, a blue amphibole, and tells you that the rock you are looking at is a blue schist (low temp, high pressure metamorphic rock)
53
What four minerals are only found in metamorphic rocks
Chlorite, Talc, Graphite, and Epidote
54
What is up with Chlorite
Low to intermediate metamorphic grade Found in greenstone, greenschist, and Chlorite schist
55
What is up with talc
low metamorphic grade found in phyllite
56
What is up with Graphite
all possible metamorphic grades, commonly in phyllite and gneiss
57
What is up with Epidote
low to intermediate metamorphic grade found in Greenstone, Greenschist, and schist
58
What are 7 minerals commonly found in metamorphic rocks, and other rocks
Quartz, Biotite, Muscovite, Hornblende, Pyroxene (not the light green version), Plagioclase, Garnet
59
What is up with Quartz
All metamorphic grades found in quartzite, along with schists, gneiss and Eclogite
60
What is up with Biotite
Intermediate metamorphic grade Found in phyllite, schists, and maybe quartzite and marble
61
What is up with Muscovite
Low metamorphic grade found in Schist, and maybe Gneiss, Marble, and Quartzite
62
What is up with Hornblende
High metamorphic grade found in Amphiboles, eclogite, and gneiss
63
What is up with Pyroxene
High metamorphic grade, found in amphibole, eclogite, and gneiss
64
what is up with Plagioclase
all metamorphic grades found especially in schists and gneiss
65
what is up with Garnet
intermediate to high metamorphic grade found in Eclogite and Schist
66
How do you calculate the depth a mineral was formed in
approximate by diving pressure in Pa by 2800 Kg/m^3 (which is crustal density times gravity)
67
what processes does shale go through
shale - slate - phyllite - schist - gneiss
68
what process does granite or diorite go through
Felsic igneous rock - gneiss
69
what does Peridotite become
serpentinite (low metamorphic grade)
70
What do Mafic igneous rocks become
Greenstone (low) - Greenschist (intermediate) - Eclogite (high)
71
what does sandstone become
Quartzite (all metamorphic grades)
72
What does Limestone become
Marble (all metamorphic grades)
73
what does coal become
Graphite then Diamond
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