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Geo 1 > Quiz 3 > Flashcards

Quiz 3 Flashcards

1
Q

Metamorphism

A

To change from one form to another (metamorphic rocks have undergone solid state changes in texture/mineralogy/chemical composition)

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2
Q

Protolith

A

Parent rock

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3
Q

Relationship between metamorphic rocks and their parent rock

A

Most metamorphic rocks have the same overall composition as the parent rock (in terms of what minerals are in it). The exception: if water/gases are added, they are carrying dissolved ions within them that can add new elements or remove some (another way to put it: possible loss/accumulation of volatiles like water and carbon dioxide)

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4
Q

Four principle factors that drive metamorphism

A

Temperature, pressure, fluids, and parent rock composition

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5
Q

Geothermal gradient

A

Rate at which temperature increases as you go further into the crust

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6
Q

General effects of temperature on metamorphic rocks

A

Affects a rock’s texture and mineralogy, breaks chemical bonds and alters crystal structure, atoms and ions re-crystallize into new mineral assemblages, many new crystals will grow larger than they were in the parent rock.
Given a specific set of minerals in a metamorphic rock, you can infer the temperature at which the metamorphic rock formed (for index minerals) because the metamorphic changes that occur with temperature follow a predictable and repeatable path

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7
Q

Recrystallization

A

Mineral grains recrystallize to form new, interlocking grains of the same mineral (and grains typically get larger)

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8
Q

Neocrystallization

A

Chemical reactions change the original assemblage of minerals into a new, metamorphic assemblage of minerals. This means new minerals, same chemical composition

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9
Q

Confining pressure

A

Pressure in all directions; produces compact rocks with a greater density because it closes the spaces between mineral grains, but doesn’t cause deformities

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10
Q

Differential stress

A

Pressure applied more in one or two directions; compression, tension, and thus deformities (folds, faults, foliation; shape of the mineral changes: compressed, stretched, rotated)

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11
Q

Metaconglomerate

A

Pebbles flattened, elongated, and aligned. Can tell what way stress was applied based on the alignment of the mineral grains

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12
Q

Shearing

A

Pressure applied in opposite directions, giving an “S” or sigma-shaped grain

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13
Q

Foliation

A

Alignment of minerals, which happens with minerals that have cleavage. Requires a platey (muscovite, biotite) or elongate (amphibole, pyroxene) cleavage

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14
Q

General effects of pressure on metamorphic rocks

A

Changes a rock’s mineralogy and texture in a predictable manner. Metamorphic minerals can be compressed, elongated, and/or rotated by being forced into preferred orientations

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15
Q

General effects of fluids on metamorphic rocks

A

The only way that you can add or remove components during metamorphism, as fluids can carry dissolved ions or remove ions.
Water acts as a catalyst during metamorphism to increase the likelihood of metamorphism (as it makes it easier to break bonds).
Water aids in the exchange of ions between growing crystals.

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16
Q

Four main criteria of metamorphism

A

Size of their crystals (minerals), how the mineral grain shape is changed, the degree to which minerals are segregated into light and dark bands, and metamorphic grade

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17
Q

Metamorphic grade

A

How much temperature and pressure a rock experience/how much metamorphic changes rocks have undergone

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18
Q

Differences between low grade, intermediate grade, and high grade metamorphic rocks. Include the location and conditions in which the rocks form.

A

Low grade: formed in shallower, crustal regions under low temperature and/or low pressure
Intermediate grade: in between the two
High-grade: formed in deeper crustal regions, perhaps as deep as the upper mantle, under high temperature and/or high pressure

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19
Q

Foliated rocks in order of increasing grade

A

Slate: fine-grained, parent rock is shale
Phyllite: grain size is barely visible, but has a higher proportion of micas (shinier). Parent rock is mud-/clay-rich sedimentary rocks
Schist: medium to course grain, many of them are platey/flakey from mica/muscovite/biotite. Derived from clay and mud sedimentary rocks, passed through a process involving the production of shales, slates, and phyllites as intermediate steps
Gneiss: light-and-dark banding, parent rock can be shale or granite
Migmatite: boundary between metamorphic and igneous due to partial remelting

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20
Q

Isograds

A

Boundaries between zones in regional metamorphism

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21
Q

What makes non-foliated rocks the way they are?

A

They don’t experience differential pressure and/or are composed of only one mineral. This means no deformation, large recrystallization

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22
Q

Another name for non-foliated rocks

A

Granoblastic rock

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23
Q

Examples of non-foliated rocks

A

Quartzite, marble, hornfels, greenstones, and amphibole

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24
Q

Contact/thermal metamorphism

A

A hot, igneous body (like a magma chamber or contact with hot groundwater) bakes the surrounding rocks. Has no differential pressure; doesn’t produce foliated rocks

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25
Q

Hydrothermal metamorphism

A

Hydrothermal fluids can carry dissolved calcium dioxide, sodium, silica, copper, and zinc. Ascending hydrothermal fluids can react with overlying rock, creating new minerals (which may have great economic value).
Can happen in the ocean at mid-ocean ridge zones (where plates are moving apart) where there’s hot, mineral-rich water that can interact with rocks experiencing pressure and temperature changes from the magma upwelling (while the plates move apart).

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26
Q

Burial metamorphism

A

Happens as a plate subducts (goes underneath another plate), and rocks are metamorphosed due to increase in temperature and pressure as they descend.
Can lead to changes in minerology, texture, composition, and foliation (depending on the stresses as that plate is subducting).
High temperature, high pressure.

27
Q

Regional metamorphism

A

Large-scale metamorphism that can also happen with tectonics when there are two continental plates coming together, leading to mountain building (which leads to increased pressure and stress, with some increase in temperature).
The Andes and Himalaya mountains, as well as the Swiss and Austrian Alps, were formed this way.
Ranges from low temperature to high pressure, all the way to high temperature

28
Q

Shock/impact metamorphism

A

Occurs when an asteroid/comet impacts the earth’s surface. Moving as fast as 100k mph, the energy is transferred into heat energy and shock waves as it smashes into the earth, resulting in shocked textures and very quick metamorphism
High temperature, low pressure

29
Q

The difference between weathering and erosion

A

Both processes are major geologic processes that can significantly shape the earth’s surface; the difference between them is transport!
Both processes can act at the same time.

30
Q

Weathering

A

The general process by which rocks are broken down on the Earth’s surface (the chemical and physical breakdown of rocks).
Rocks react with the hydrosphere, atmosphere, and biosphere.

31
Q

Erosion

A

The set of processes that loosen and transport soil and rock downhill/downwind (the process that breaks down and transports)

32
Q

Regolith

A

Loose blanket of mineral grains, rock fragments, and organic matter; made from bedrock by weathering. Most of the surface of Earth is covered with this.

33
Q

Salt wedging

A

In arid climates, dissolved halite or gypsum precipitates in the small pores and joints between grains, wedging them apart on a small scale, analogously to ice.

34
Q

Types of physical weathering

A

Jointing, exfoliation, frost/salt wedging

35
Q

Jointing

A

Erosion removes material and exposes deep, crustal rocks that are hot and under high pressure. These crustal rocks cool and expand, causing fractures called “joints”

36
Q

Exfoliation

A

Buried rocks compressed by weight overlying material; when the overlying material’s removed, the rock cracks in onion-like “exfoliation” layers

37
Q

Talus/scree

A

Big piles below a cliff

38
Q

Sorting indicates what? Give an example of well-sorted and poorly-sorted environments.

A

Sorting indicates the consistency of environmental energy.
A well-sorted environment could be a beach, and a poorly-sorted environment could be an alluvial fan

39
Q

Common chemical weathering reactions

A

Dissolution, hydrolysis, and oxidation

40
Q

Factors affecting chemical weathering (and how)

A

Composition: Si-rich minerals are more stable/less prone to weathering
Water: many chemical reactions involve water
Temperature: rates of chemical reactions are faster at higher temperatures

41
Q

What does it mean for a water molecule to be polar?

A

One side is positively charged and one side is negatively charged, making it a good solvent

42
Q

Dissolution

A

Some minerals dissolve, and acidity enhances this effect. Examples: halite, gypsum, calcite
Reversing this process forms caves, as calcite precipitates

43
Q

Hydrolysis

A

Water breaks cation bonds in silicate minerals to make dissolved cations and alteration residues (like clay minerals, which are the weathering product of silicate minerals, as well as iron oxides/rust)

44
Q

Leaching

A

Dissolution of primary minerals

45
Q

Hydration shell

A

Small ions with a high charge tend to hold onto some water molecules

46
Q

Hydrolysis reaction

A

Can split a water molecule into a cation (H+) and an anion (OH-)

47
Q

Primary minerals vs secondary minerals

A

Primary minerals: minerals present in bedrock
Secondary minerals: minerals formed as a result of chemical weathering (such as Fe, Al oxides like hematite; clays)

48
Q

How do soils promote weathering?

A

Soils retain water (which promotes chemical weathering)
Soils support plant life (which promotes physical and chemical weathering)
Positive feedback system

49
Q

How can climate enhance chemical weathering and physical weathering?

A

Chemical weathering is enhanced when climate’s warm, there’s a lot of water, and there’s plants (chemical weathering hardly occurs in desert environments)
Physical weathering is enhanced when there’s more wind, there’s freeze/thaw cycles, and there’s plants

50
Q

Factors that lower and increase the geothermal gradient respectively

A

Subduction of cooler oceanic plate and rising magma

51
Q

Two factors that increase with the intensity of metamorphism

A

Crystal size and courseness of foliation

52
Q

Porphyroblasts

A

Very large crystals that may be developed during the recrystallization process. Only happens to certain minerals (like garnet, staurolite, and andalusite); other minerals (like muscovite, biotite, and quartz) typically form a large number of small crystals.
Mainly concerns schist.

53
Q

Classification of foliated rocks vs non-foliated rocks

A

Foliated rocks are classified my texture
Non-foliated rocks are classified by mineral composition

54
Q

Amphibolite’s parent rocks

A

Basalt, gabbro

55
Q

Hornfels’s parent rock and how it’s produced

A

Shale; contact metamorphism

56
Q

Metamorphic environments (types of metamorphism)

A

Contact/thermal, hydrothermal, burial, regional, shock/impact, fault zone

57
Q

Marble and quartzite can only be formed during what type of metamorphism

A

Regional metamorphism

58
Q

Bedrock

A

Solid rock attached to the crust; relatively rare to find exposed bedrock on Earth’s surface

59
Q

Sediment

A

Regolith that has been transported and deposited

60
Q

Physical weathering vs chemical weathering

A

Physical: mechanical breaking/disintegrating (busting, cracking, grinding)
Chemical: reacting with water (dissolving, making new minerals)

61
Q

Oxidation

A

Reaction in which an element combines with oxygen; important for iron-rich minerals like olivine and pyroxenes

62
Q

Biological weathering

A

Organisms like plant roots, fungi, lichens, and bacteria are often important chemical weathering agents

63
Q

Relationship between climate and weathering

A

More CO2 in atmosphere = more carbonic acid and more weathering
Increased temperatures or more exposed rocks will increase weathering and thus reduce the amount of CO2 in the atmosphere
Over millions of years, weathering is an important control of atmospheric CO2

Geo 1 (7 decks)

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