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rowan study decks > geology midterm 2 > Flashcards

geology midterm 2 Flashcards

1
Q

physical/mechanical weathering

A

Where the rocks are physically broken/fractured into smaller pieces

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2
Q

frost wedging

A

Frost wedging -accomplished when water that seeps into the cracks of rocks expands when it freezes, and this expansion causes the crack to wedge farther apart. Multiple freeze and thaw events can cause cracks to get so big that they connect, and rocks are broken loose from the bedrock.

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3
Q

Salt wedging

A

occurs when salt crystal grow as salt water that lands on rock near the coast (commonly from ocean spray) evaporates. As the salt crystals grow larger, they can wedge existing fractures in the rock apart

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4
Q

Biogenic wedging

A

trees and plants wedge their roots in between crystals of rock

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5
Q

Unloading - sub-horizontal fractures

A

-unloading/exfoliation: the type of fractures seen on half-domes. Rocks on top unload, taking pressure off rock below, allowing that rock to expand.

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6
Q

Abrasion

A

water carves through rock, water has other pieces of rock and sand that are used as a tool by the water to abrade the bedrock

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7
Q

Chemical weathering

A

The bonds that are holding the atoms together in minerals are being attacked.
-dissolution, hydrolysis, oxidation

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8
Q

chemical weathering: Dissolution

A

is when minerals dissolve in weakly acidic water

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9
Q

chemical weathering: Hydrolysis

A

Hydrolysis is the process by which water and weak acids attack the bonds in minerals to produce clay minerals (which have water in their crystalline structure and are aluminum‐ rich) as well as ions dissolved in water

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10
Q

chemical weathering: oxidation

A

Oxidation is the chemical process in which ions in the mineral structure leave the crystalline lattice to bond with oxygen atoms from the atmosphere

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11
Q

climate & weathering

A

Wet, warm environments favor chemical weathering processes, cold and dry environments tend to favor physical weathering processes.

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12
Q

Products of weathering:

A

Clasts - Weathering produces clasts (pieces of rock that can range in size from boulders to pebbles to sand and microscopic mud) and ions dissolved in water.
Ions - dissolved in rainwater, moved into streams, transported to oceans - making it more salty

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13
Q

soil

A

Soil - Weathering is also closely tied to the production of soil. Soils are often rich in clay minerals.
Soil profile: rock that’s been weathered and mixed with plant debris

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14
Q

clastic sedimentary rocks

A

Rivers deposit bits and pieces of rocks, turning them into clastic sedimentary rock.

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15
Q

bedding

A

Bedding
When sedimentary beds are tilted, we can infer that the beds must have been deformed after they were deposited.
Sometimes sedimentary beds can get so deformed that they are turned upside‐down! Sedimentary structures can help inform geologists of the original direction of ‘up.’ Original ‘up’ is important because up indicates the age of the rocks: older on the bottom, younger on the top

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16
Q

graded bed

A

A bed that gradually changed from coarse to fine. This is how you check if the bed is right side up. It should be fine grained on top.

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17
Q

sedimentary provenance

A

where the clasts came from. Tells us about areas around the basin.

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18
Q

chemical sedimentary rock:

A

when water evaporates and leaves behind minerals like salt, forming chemical sedimentary rock

Chemical sedimentary rocks: formed by ions

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19
Q

chemical sedimentary rock: evaporite

A

inorganic. A chemical sedimentary rock that forms when dissolved ions precipitate because the water evaporates.

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20
Q

chemical sedimentary rock: limestone (reef):

A

organic. Formed when biologic processes cause dissolved ions to precipitate from water. For example, many plants and animals in coral reefs use ions from sea water to form their shells/tests.

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21
Q

chemical sedimentary rock: deep sea life

A

organic chemical sedimentary rocks can form in deep ocean environments where the primary lifeform that accumulates on the ocean floor are plankton tests (shells.) Foraminifera make their tests out of calcite. Diatoms and radiolarians make their shells out of silica.

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22
Q

Sedimentary lithification:

A

The process of taking loosely consolidated clasts or chemical precipitates and turning them into sedimentary rocks. This is a two step process.
1) Compaction: as the rocks get buried deeper, the rocks at the bottom get squished and compacted, sticking sand grains together
2) Cementation: reducing the space between the grains, cementing them together so they can’t come apart

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23
Q

depositional setting:

A

the environment in which the loose grains are being deposited.

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24
Q

depositional setting: fluvial/river

A

-associated with alternating layers of conglomerate, sandstone, mudstone, and sometimes coal.

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25
Q

depositional setting: deep marine

A

-associated with alternating layers of mudstone and plankton shells (diatomite/chert/ chalk)

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26
Q

depositional setting: shallow marine

A

-associated with sandstone that is deposited at the beach, mudstone that is deposited just beyond the breaking waves, and limestone that forms on the outer/deepest portion of the shallow marine setting.

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27
Q

sedimentary basin

A

-sedimentary basin: the low point where all of the sediment collects and layers

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28
Q

rift basin

A

subsidence in rift basins occurs in extensional settings (divergent boundaries) as the crust thins and the surface sinks.

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29
Q

flexural basin

A

subsidence in flexural basins occurs at convergent boundaries as the land is bent (or flexes) downward due to the weight of growing mountain belts, making space for the sediment to come in.

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30
Q

transgressions

A

-Sea level rises
-Transgressions that form as sea level rises are documented by stratigraphic columns of shallow marine rocks that indicate increasing water depths with time (e.g., sandstone below mudstone below limestone).

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31
Q

regression

A

-Sea level falls
-Regressions that form as seal falls are documented by stratigraphic columns of shallow marine rocks that indicate decreasing water depths with time (e.g., limestone below mudstone below sandstone).

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32
Q

metamorphic rocks

A

are rocks that have changed mineralogy and/or texture due to changes in pressure and temperatures.
Driving force: temperature
Forces water out of the crystalline structure
Increased temperature forms new minerals that have no water in their crystalline structure (composition)
Causes minerals to grow bigger (texture)
High temperature favors larger crystals
Mineralogical change: water out
The metamorphic process starts the wet-melting process for igneous rocks

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33
Q

protolith & metamorphic rocks

A

-Metamorphic protolith refers to the composition of a metamorphic rock before it was metamorphosed.
-Because different rocks have widely variable initial compositions, metamorphism of adjacent rocks with different protoliths but at the same pressure and temperature conditions will yield visibly different metamorphic rocks
-Two protoliths that are particularly important for the study of metamorphic rocks are mafic protoliths (e.g., basalt and gabbro), and pelites (mudstone).

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34
Q

geotherm

A

describes the temperature and pressure as they increase deeper into our planet. Temp and pressure are the two main variables determining when a rock melts

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35
Q

metamorphic rock: slate

A

-200 degrees Celsius
-Solid rock
-Slate is a fine‐grained metamorphic rock with strong layering (foliation).
-We can infer that it formed at relatively low metamorphic temperatures due to the fine‐grained texture.

36
Q

metamorphic rock: schist

A

-400 degrees celsius
-Wavy texture
-Lots of mica
-Solid rock
-Schist describes rocks with a wavy texture associated with relatively coarse‐grained micas that warp around other large minerals in the rock.
-The relatively coarse‐grained nature of this rock indicates that it formed at medium metamorphic temperatures.

37
Q

metamorphic rock: gneiss

A

-400-600 degrees celsius
-Dark and light layers
-Fewer micas
-Solid rock
-Gneiss is a metamorphic rock with coarse crystals that form alternating light and dark layers.
-It has fewer micas than schist, and is generally associated with high metamorphic temperatures and/or metamorphosed igneous rocks

38
Q

metamorphic rocks: migmatite

A

-700-900 degrees celsius
-Dark and light layers
-Migmatites are gneisses that got so hot during metamorphism that they partially melted.
-Partial melt - Melt zones

39
Q

foliation

A

-Foliation describes metamorphic rocks that have layers in the rock that are formed by minerals with a strong preferred orientation formed by differential stress.
-can form rock cleavage - When rocks break along foliation planes associated with a strong preferred mineral orientation, it is called rock cleavage
-Easy to break rock where the fine grains are meeting
-Weak foliation =No differential stress
More common near surface

40
Q

causes of metamorphism:

A
  1. Impact metamorphism
  2. Hydrothermal metamorphism
  3. Contact metamorphism
  4. Regional metamorphism
41
Q

impact metamorphism:

A

During a meteor impact pressure and temperatures get very high - new minerals form

42
Q

hydrothermal metamorphism:

A

-Rock is getting heated up by hot water
-Water brings new elements which can change the composition of the rock as well
-Commom at MORs and near tye surface of the earth where hot water circulates through cracks and pores in rocks

43
Q

contact metamorphism:

A

-When a rock comes into contact with something very hot (ex: magma)
-Typically have weak foliation because this happens relatively shallow in the crust

44
Q

regional metamorphism

A

-Happens over huge areas
-Regional or dynamothermal metamorphism occurs when rocks are heated up during tectonic burial of large regions or terranes. This type of metamorphism is associated with higher pressures than contact metamorphism due to burial to great depths in the Earth’s crust

45
Q

index minerals

A

Index minerals are metamorphic minerals that form at specific temperatures and pressures. Different protoliths are associated with different index minerals. For example, for pelitic protoliths, chlorite is only stable at low temperatures and sillimanite is only stable at high temperatures.

46
Q

metamorphic facies

A

pressure and temperature ranges named after index mineral assemblages in mafic metamorphic rocks. Pressure and temp conditions of metamorphism.

47
Q

green schist

A

Greenschist is basalt metamorphosed at relatively low P and T conditions where the index minerals for mafic rocks are green. ‘Greenschist facies’ thus refers to low P and T metamorphism.

48
Q

blue schist

A

Blueschist is basalt metamorphosed at relatively high P and low T conditions where the index minerals for mafic rocks are blue. ‘Blueschist facies’ thus refers to high P and low T metamorphism

49
Q

eclogite

A

Eclogite is basalt metamorphosed at relatively high P and T conditions where the index minerals for mafic rocks are red and green. ‘Eclogite facies’ thus refers to high P and T metamorphism

50
Q

amphibolite

A

Amphibolite is basalt metamorphosed at medium P and T conditions where the index minerals for mafic rocks are black and white (amphibole and plagioclase, respectively). ‘Amphibolite facies’ thus refers to medium P and T metamorphism

51
Q

granulite

A

Granulite is basalt metamorphosed at medium P and high T conditions where the index minerals for mafic black and white (pyroxene and plagioclase, respectively). ‘Granulite facies’ thus refers to medium P and high T metamorphism, and is often associated with migmatites

52
Q

differential stress

A

stress causes deformation. Rock is getting squished the same amount in all directions won’t change shape that much, but if there is more stress on one side or two sides than the others, it will change more.

53
Q

confining stress

A

A deeply buried rock is pushed down by the weight of all the material above it. Since the rock cannot move, it cannot deform. This is called confining stress.

54
Q

ductile deformation

A

When rocks get hot they can flow (ductile)

55
Q

brittle deformation

A

Break and fracture brittly

56
Q

geologic maps

A

Colors show rock type
Strike and dip symbols
Indicates the orientation of the rock layers on a map - how much the rocks have been tilted

57
Q

folds

A

-There are two general types of folds: 1) anticlines: point up in cross section (upside down U shape, like an n with Old rocks on the inside of the n) and 2) synclines: point down in cross section( U shape). Old rocks on the outside of the U, younger rocks on the inside.
-In map view, anticlines have older rocks in the axis (fold hinge) and the strike and dip symbols point away from the axis, whereas synclines have younger rocks in the axis of the fold and dips that point toward the axis.

58
Q

fold pluge

A

Plunging folds have fold axes (hinges) that tilt into the ground.

59
Q

faults

A

Faults are planes along which rocks move. Commonly, they offset rocks that were continuous prior to deformation.

60
Q

fault gouge

A

forms along brittle fault planes in the upper crust at temperatures <300 C
Fault gouge = brittle

61
Q

fault mylonite

A

At temperatures >300 C, rocks begin to flow ductiley along faults, and form mylonites, which are metamorphic rocks with a foliation formed by shearing/fault displacement
Fault mylonite = ductile

62
Q

fault types:

A

dip slip, strike slip, normal, thrust.

63
Q

dip slip faults

A

Dip slip faults have slip/displacement that is parallel to the dip in the faults surface
thus the displacement is vertical.

64
Q

strike slip faults

A

Strike‐slip faults have slip that is parallel to the strike
thus the displacement is horizontal. rock is being pushed in 2 different directions, shearing. happens at transform boundaries. causes earthquakes

65
Q

normal faults

A

Normal faults on maps are bold lines with tick marks (sometimes with barbells) on them. In cross section, it is easy to see that the faults cut the different types of layers and that the hangingwall has been offset downward relative to the footwall placing younger rocks on top of older rocks.
Normal faults are associated with horizontal extension and vertical greatest stress.

66
Q

thrust faults

A

Thrust faults are usually illustrated with bold lines with solid triangles on maps. In cross section, thrust faults put older rocks on top of younger rocks, and arrows show that the hangingwall has moved upward relative to the footwall. Thrust faults are associated with horizontal compression and horizontal greatest stress.

67
Q

strike slip faults

A

-Strike‐slip faults have slip that is parallel to the strike, thus the displacement is horizontal.
-Strike slip faults have slip/displacement that is parallel to the strike of the fault – thus the displacement is horizontal.
-Strike sip faults can be either right‐lateral or left‐lateral. To determine the sense of slip, determine which direction the other side of the fault has moved.
-Strike slip faults on maps are bold lines with arrow that indicate either right‐lateral or left‐lateral displacement.

68
Q

horizontal extension

A

-Horizontal extension is associated with oceanic rifts that form mid ocean ridges (MOR) at divergent boundaries.
-Horizontal extension is also associated with continental extension. An excellent example of continental extension is the geology of Nevada, where extending crust has formed the Basin and Range province.
-Horizontal stresses are commonly greater than vertical stresses at convergent boundaries. This is associated with the development of the accretionary prism (on the trench side of the volcanic arc) and the backarc fold and thrust belt (on the continent side of the arc).

69
Q

horizontal compression

A

associated with thrust faults

70
Q

what water velocities are rocks deposited at?

A

The higher the velocity, the bigger the rocks deposits. Smaller grains deposited in lower velocity or non-moving water

71
Q

grain shape: angular clasts

A

deposited closer to the source

72
Q

beds

A

older rocks on the bottom, but sometimes there is tilt, so you need to know which way is up and which way is down

73
Q

elastic rebound theory

A
  1. stress is applied on the rocks in the Earth by the motion of tectonic plates.
  2. the rocks slowly accumulate strain over 10s to 100s of years, and the rocks deform in the area around the fault where the tectonic plates are moving past each other and applying stress.
  3. the stress on the rocks is so great, that the rocks finally fracture during the earthquake and all the accumulated strain is localized along the fracture/or fault.
  4. the rocks adjacent to the fault ‘snap’ back to their original shape
  5. repeat
74
Q

hypocenter vs epicenter

A

hypocenter: The hypocenter, or focus, of an earthquake is where slip initiates on the fault.
epicenter: The epicenter of an earthquake is the projection of the hypocenter onto the surface of the earth.

75
Q

seismic waves: P waves

A

are compressional waves with wave vibration parallel to the direction of wave travel. They travel at velocities of 6‐7 km/sec. They can travel through solids and liquids. Fastest.

76
Q

seismic waves: S waves

A

S waves are shear waves with wave vibration perpendicular to the wave transport direction. S waves travel at 3-4 km/sec. They can propagate through solids, but not liquids. 2nd fastest.

77
Q

seismic waves: surface waves

A

Surface waves are waves that travel along surfaces like the surface of the Earth as opposed to through the earth like P and S waves. They are formed when P and S waves intersect the surface. They travel at velocities of 2‐3 km/sec. slowest.

78
Q

time lag and seismographs

A
  • Because P waves travel faster than S waves, they will get to the seismograph station first – and farther away the earthquake is from the seismograph station, the P wave will get farther and farther ahead of the S wave, and the time lag between the two waves will increase. - A simple rule of thumb is that distance from the station is about equal to the time lag (in seconds) multiplied by 10 km/sec. D = 10 (km/sec) * ∆t (secs)
79
Q

Richter scale

A

Richter scale is a measure of earthquake intensity based on the S wave amplitude corrected for distance.
- It is a logarithmic scale such that an increase of 1 on the Richter Scale indicates an increase of 10 in S wave amplitude; and increase of 2 on the Richter Scale indicates an increase of 100 in S wave amplitude.

80
Q

moment magnitude

A

a more precise measurement of earthquake intensity based on the amount of energy released from the rocks during the earthquake.

81
Q

mercalli intensity scale

A

survey of people’s experiences in earthquake, how disruptive it was.

82
Q

earthquakes at transform and divergent boundaries

A

occur shallow in the earth’s crust

83
Q

earthquakes at convergent boundaries

A

occur increasing in depth away from the boundary

84
Q

Benioff zones

A

Wadati-Benioff zones: When convergent boundary earthquakes are plotted on a cross section, they define a plane dipping into the ground called the Wadati‐Benioff Zone, and which effectively outlines the shape of the subduction zone.

85
Q

igneous rocks to know

A

felsic > mafic> ultramafic
intrusive: granite, gabbro, periodite
extrusive: rhyolite, andesite, basalt

86
Q

sedimentary rocks to know

A

conglomerate, sandstone, mudstone

87
Q

metamorphic rocks to know

A

slate, schist, gneiss

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