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BSc Environmental Science > LEC.172 Geology > Flashcards

LEC.172 Geology Flashcards

1
Q

Define igneous rock with an example

A

Form by cooling + solidification of molten rock and have quartz/feldspar/mica minerals, granite

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2
Q

Define sedimentary rock with an example

A

Form by hardening + cementation of layers of sediment deposited at Earth’s surface, sandstone

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3
Q

Define metamorphic rock with an example

A

Form from pre-existing rocks by transformation in solid state under intense heat + pressure, marble

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4
Q

What are the 4 principles of relative dating?

A
  1. Original horizontality
  2. Superposition (each layer of sedimentary rock in tectonically undisturbed sequence younger than one beneath it)
  3. Cross-cutting relationships (igneous intrusion must be younger than rocks it intrudes)
  4. Faunal succession (sedimentary strata contain fossils in a definite sequence)
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5
Q

When do solid solutions form + example?

A

When cations of similar sizes substitute for each other, olivine is a solid solution of Fe and Mg

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6
Q

Which is the only major silicate group to not show some degree of solid solution?

A

Quartz

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7
Q

What is natural glass and how is it formed?

A

Obsidian, formed when lava cools too quickly to form crystals (atoms randomly arranged in silica tetrahedra)

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8
Q

What are the different kinds of crystal structures that a chemical substance can form called + example?

A

Polymorphs, CaCO3 can form calcite or aragonite, pure C can form graphite or diamond

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9
Q

What are 5 diagnostic features of minerals?

A
  1. Habit (shape/morphology)
  2. Cleavage + fracture
  3. Specific gravity
  4. Colour
  5. Hardness
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10
Q

What are 2 ways of examining thin sections under a microscope?

A
  1. PPL (Plain Polarised Light)
  2. XPL (Cross Polarised Light)
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11
Q

Define magma and lava

A

Magma = molten rock beneath Earth’s surface
Lava = molten rock at Earth’s surface

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12
Q

What are the 3 types of pyroclast?

A
  1. Ash (<2 mm)
  2. Lapilli (2-64 mm)
  3. Volcanic bombs (>64 mm)
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13
Q

What are 4 components of ash?

A
  1. Pumice/scoria (fragments of vesicular lava)
  2. Lithics (rock fragments)
  3. Crystals (individual + broken)
  4. Glass shards (chilled magma with vesicle walls)
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14
Q

What does vesicular mean?

A

Gas trapped in melt at time of solidification (bubbles)

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15
Q

Define pyroclastic fall

A

Sedimentation of particles from a volcanic plume (forms pyroclastic fall deposit)

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16
Q

Define pyroclastic density current

A

Gravity flow of hot gases/particles which flow down flanks of volcano

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17
Q

Define lahar

A

Flow of mixture of water (from melting or rainfall) + volcanic material (forms lahar deposit)

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18
Q

Define debris avalanche

A

Flow of landslide material down flanks of volcano (forms debris avalanche deposit)

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19
Q

Define phreatic eruption

A

Steam eruption (no deposit)

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20
Q

Define kettle hole

A

Block of ice in lahar deposit has melted

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21
Q

Define batholiths

A

Solidified magma chambers

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22
Q

Define plutons

A

Smaller body of intrusive magma

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23
Q

What is the difference between sills and dykes (igneous intrusions)?

A

Sills = horizontal
Dykes = vertical

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24
Q

What 4 things are igneous rocks classified by?

A
  1. Magma type
  2. Silica content (% weight)
  3. Volcanic (<1 mm, fine-grained, extrusive)
  4. Plutonic (>5 mm, coarse-grained, intrusive)
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25
Q

What are the properties of ultramafic magma?

A

<45% silica
Plutonic rock: Peridotite

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26
Q

What are the properties of mafic magma?

A

45-52% silica
Volcanic: Basalt
Plutonic: Gabbro

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27
Q

What are the properties of intermediate magma?

A

52-65% silica
Volcanic: Andesite
Plutonic: Diorite

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28
Q

What are the properties of felsic magma?

A

> 65% silica
Volcanic: Rhyolite
Plutonic: Granite

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29
Q

What are the 2 types of chemically similar basaltic lava?

A
  1. Aa (blocky)
  2. Pahoehoe (ropy)
30
Q

When are lava ‘pillows’ formed?

A

When basalt erupts into water and rapidly cools

31
Q

From basalt –> andesite –> rhyolite, how do eruption temp and viscosity change?

A

Eruption temp decreases, viscosity increases

32
Q

What is the magma composition of calderas and craters?

A

Mafic-felsic

33
Q

What is the difference between a caldera and a crater?

A

Both topographic depressions, caldera diameter = >1 km, crater diameter = <1 km

34
Q

How is a caldera formed and what is an example of a caldera?

A
  1. Magma fills magma chamber –> volcanic eruption
  2. Magma chamber partly depleted
  3. Summit collapses into chamber
    E.g. Sollipulli, Chile
35
Q

What is an example of a crater?

A

Poas, Costa Rica

36
Q

What is the magma composition of composite volcanoes (stratovolcanoes) and an example?

A

Intermediate-felsic
E.g. Mount Rainier, Washington

37
Q

What is the magma composition of lava domes, why are they dangerous, and an example?

A

Viscous intermediate-felsic
Slow extrusion of viscous lava so gases build up –> explosive eruption
E.g. Volcan de Colima, Mexico 2009

38
Q

What is the magma composition of shield volcanoes and an example?

A

Low viscosity mafic
E.g. Mauna Loa, Hawaii

39
Q

What are fissures, what viscosity is the lava at fissures, and an example?

A

Mafic lava rapidly flows away from fissures
Low viscosity
E.g. Kilaeua, Hawaii 1979

40
Q

What are cinder cones, what is their magma composition, and an example?

A

Steep/conical/symmetrical formed by explosive eruptions
Mafic pyroclastic material
E.g. SP Crater, USA

41
Q

What are 3 ways deformation can be studied?

A
  1. Field experiments
  2. Lab experiments
  3. Satellite observations
42
Q

What is stress (deformation)?

A

Pressure

43
Q

What are the 6 types of stress?

A
  1. Compression stress (shortens object)
  2. Tension stress (lengthens object)
  3. Normal stress (perpendicular to surface, either compression/tension)
  4. Shear stress (acts parallel to surface)
  5. Hydrostatic/uniform stress (uniform in all directions)
  6. Directed/differential stress (not uniform in all directions)
44
Q

Define strain

A

Measure of the extent of deformation (change in shape/volume due to stress)

45
Q

What do plastic and brittle deformation result in?

A

Plastic: folding e.g. folded dyke
Brittle: fracturing

46
Q

What 3 things does stress depend on?

A
  1. Temperature and pressure
  2. Mineral/rock type
  3. Strain rate
47
Q

At which temperatures and pressures do minerals/rocks deform most easily at?

A

Higher temperature and low pressure

48
Q

Which minerals/rock types fault and fold?

A

Hard igneous/metamorphic rocks behave as brittle material = faulting, softer sedimentary rocks deform in a ductile manner = folding

49
Q

How does strain rate affect whether a mineral/rock is faulted or folded?

A

Rapid deformation = brittle faulting, slow deformation = plastic folding

50
Q

Define dip

A

Measure of maximum angular deviation of an inclined plane from the horizontal (perpendicular to strike direction)

51
Q

What are the 8 types of folding?

A
  1. Monocline (step-like)
  2. Syncline/anticline
  3. Symmetrical (vertical axial plane + each limb dips at same angle)
  4. Asymmetrical (inclined axial plane + limbs dip at diff. angles)
  5. Overturned (1 limb rotated to be upside down)
  6. Recumbent (axial plane is horizontal)
  7. Non-plunging and plunging (inclined fold axis)
  8. Domes and basins
52
Q

Define joint

A

Fracture along which little/no movement has occurred, perpendicular to fracture surface

53
Q

Define fault

A

Fracture along which blocks on opposite sides of fracture plane have moved

54
Q

What do GPS and LPS mean in terms of faulting/stress?

A

GPS = Greatest Principal Stress axis
LPS = Least Principal Stress axis

55
Q

What are the 3 types of faults?

A
  1. Normal (GPS vertical, LPS horizontal)
  2. Reverse (GPS horizontal, LPS vertical)
  3. Transcurrent (GPS and LPS horizontal)
56
Q

What do metamorphic rocks result from and in what state does this take place?

A

Transformation of other rocks beneath Earth’s surface, solid state

57
Q

What are the 3 factors affecting transformation into metamorphic rocks?

A
  1. Temperature
  2. Pressure
  3. Fluid activity
58
Q

How does temperature affect transformation into metamorphic rocks and what are the metamorphic minerals?

A

Increasing temp. increases rate that chemical reactions that produce new mineral assemblages, geothermometers

59
Q

What is the increase in temperature with depth called and how does it vary with plate tectonic setting?

A

Geothermal gradient, continental plate extension = high, ancient continental plate = low

60
Q

How does pressure affect transformation into metamorphic rocks, what are the metamorphic minerals, and at what rate does pressure increase at?

A

Increasing pressure increases rate that chemical reactions produce new mineral assemblages, geobarometers, 0.3-0.4 kilobars/km

61
Q

What type of metamorphic rocks do uniform and differential stress produce?

A

Uniform stress: non-foliated
Differential stress: foliated

62
Q

How does fluid activity affect transformation into metamorphic rocks?

A

Increase rate of chemical reactions, carry chemical substances, + change rock’s composition via metasomatism

63
Q

Where does regional metamorphism occur and what does it result from?

A

Convergent plate boundaries (volcanic mountain belts) + cores of mountain chains formed by continental collision, results from high temp., high pressure, + extreme deformation in Earth’s crust

64
Q

What increases from low to high grade metamorphic rocks and give examples of rocks from high to low grade?

A

Temp. and pressure, slate –> phyllite –> schist –> gneiss

65
Q

What are metamorphic zones?

A

Zones based on distinctive silicate mineral assemblages

66
Q

What are index minerals?

A

Characterise metamorphic rocks and are used to map metamorphic zones

67
Q

What are the index minerals for clay-rich metamorphic rocks from low to high metamorphic grade?

A

Chlorite –> biotite –> garnet –> kyanite –> sillimanite

68
Q

What is an isograd?

A

Line of equal metamorphic intensity (patterns of isograds follow faults + folds)

69
Q

What are polymorphs?

A

The different structures formed when a chemical substance forms more than 1 kind of crystal structure

70
Q

What are metamorphic facies and what do they provide clues to?

A

Groups of rocks characterised by specific mineral assemblage formed under the same broad T and P conditions from diff. parent rocks, plate tectonic processes responsible for metamorphism

71
Q

When does contact metamorphism occur, what does it form, and what do mineral assemblages reflect?

A

When rock intruded by hot magma (high T and low P zones of metamorphism surround intrusion), hornfels and metamorphic aureoles, decreasing temp. with distance from intrusion

72
Q

Where does dynamic metamorphism occur and what does it form?

A

Along fault zones (rocks subjected to high P), mylonites (formed by accumulation of high strain rates in ductile zones)

BSc Environmental Science (11 decks)

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