Exam 2 Flashcards
Types of sediments
clastic, chemical, bioclastic debris
clastic sediments
cemented together clasts, solid fragments and grains of broken off preexisting rock; formed by physical and chemical weathering processes
bioclastic debris
consists of shells from organisms; processes mediated by life. EX: Coral reefs, Chalk cliffs
chemical sediments
made up of minerals directly precipitated from water; do to change in temperature and flow (when it is removed from water through evaporation)-when water is hot it can hold more minerals
sinter
chemically precipitated silica
sinter example: Yellowstone
formed on top of a hot spot; water infilitrates from surface, heats up, goes to surface and it forms geysers
travertine
chemically precipitated calcium carbonate (gets to the surface, cools, can’t carry the carbonate so it falls out)
diatoms
silica skeletons
Why do you get bioclastic build ups deep in the ocean?
Plankton shed, and it falls to the bottom; not much else accumulating here
organic sediments
consist of carbon-rich relicts of plants or other organisms
What is the most common organic sediment?
Coal
beds/strata
packets of sediment that formed from particular sediment that was deposited in a particular way
package
a bed or stratum; then collected into a set of strata
How do packages form?
Related to environmental conditions, storms carry heavy sediments, for example.
How are ripples formed?
formed by currents that pick up stuff and move it down stream
What is cross-bedding and how is it formed?
“Mega ripples” formed by winf and water flowing in a constant direction over a long period of time; can create dunes
turbidites
Deep water deposits formed by density currents resulting from underwater landslides; a sign you moved from strong currents to deeper water
density current
a submarine landslide; moves sediments from the continental shelf, builds up, becomes unstable and falls to the deep ocean.
What are graded beds due to?
larger and heavier particles settling forst at faster, current speeds
What happens when a surface loses water?
It stretches, breaks the surface (you get mud cracks)
sorting
how a conglomerate is made up (all same grain size, mixture of large and small grains); shows the distance from the source
sedimentary basin
a hole created by plate tectonics; lowered topography where sediments collect; makes an archive of Earth’s history
What is a broad area of subsiding crust that allows thick sequences of sediment to accumulate?
sedimentary basin
What is a foreland basin?
When a mountain range forms, the crust around it bows down
What is a rift basin?
Crust stretches out and gets thinner in the middle, sinking down
What is an oceanic basin?
Started as a rift basin with a passive margin which isn’t currently active
What is an intra-continental basin?
a basin away from the plate boundary related to what is going on in the mantle. The mantle is dragging it downward. Subsidence is slow, but it keeps going
What alters sedimentary environments?
Tectonic uplift and sea level changes change accomodation space
What tells you what kind of sediment deposits you will get?
accomodation space (terrestrial, shallow marine, deep marine)
metamorphism
changes in rocks; always forming and destroying igneous and sedimentary rocks; plate tectonics will bury rocks, heat them up and squash them (recycling)
What is a preexisting rock called?
protolith
What happens when something metamorphoses?
Rock stays solid, but gets a change in minerality due to temperatures and pressures; only matters beneath the Earth’s surface
What rock has compositional bands?
gneiss
What are textural changes in rock linked to?
recrystallization and new mineral growth
What is mechanical realignment and deformation?
When forces change rocks (Get squashed or elongated clasts)
Can you see the results of chemical changes and deformation on rocks?
Yes
What are some causes of deformation?
- high pressures due to deep burial (sedimentary basins, subduction zones)
- stresses due to tectonic deformation
- high temperatures foe to deep burial or contact with magma
- **Plate tectonics are almost always the ultimate driver
What is foliation?
the planar fabric due to metamorphic processes; can be compositional (gneiss) or mechanical (cleavage)
What is gneiss?
- light and dark bands
- usually made up of quartz, mica
- cuts through rock and something where a rock will break
- from the basement of stable continental shields, or craters; the interior of deforming organic belts
Metamorphic rocks depend on what?
the protolith and the conditions and time
Which is older oceanic or continental crust?
continental crust
recrystallization
changing the mineral fabric, not changing the mineral compostions
necrystallization
new minerals form from the old; protoliths become unstable and undergo reactions and reform in new ways (recycling)
pressure solution (physical processes)
mineral grains dissolve where surfaces press together (spherical to elliptical grains); reprecipitates, which requires a small amount of water
What is plastic deformation?
squashing or stretching the individual grains; change shape without breaking; depends on temperature, pressure, and mineralogy
What is shearing in fault zones caused by?
strike-slip motion
Do chemical formulas change with phase changes? If not, what does change?
No. They have the same chemical formula. The crystal structure changes, so new minerals form
diogenesis
changes that happen at low temperatures, not usually considered metamorphism
How is blue schist formed?
through subduction metamorphism
What do you call the intensity of metamorphism?
grade
What is the first grade of foliation?
slate: mineral growth along bedding planes, making it easier to break
What is the second grade of foliation?
phyllite: start to see new mineral growths, rocks look less like original
What is the third grade of foliation?
schist: strong foliation, not necessarily associated with bedding plane, dominates how it breaks
What is the fourth grade of foliation?
gneiss: distinct compositional layering, not just structural layering
facies
distinctive mineralogy formed in distinctive conditions
What is thermal/contact metamorphism?
- heat from magma invades host rock
- zoned bands of alteration zoned from high grade near pluton to low grade away from the pluton
Subduction metamorphism
- unique low temp, high pressure minerals
- forms rare blue schist, only found at subduction zones
Organic metamorphism
- compression smashes rocks and buries them deeply where they are heated
- creates huge volumes of metamorphic rocks
- probably the most important process
What causes an earthquake?
Stress is stored in the earth due to plate motions. When plates stretch and deform, earthquakes occur
What is an earthquake?
Shaking of the earth due to sudden motion of crust
What are planes of weakness that generate earthquakes?
faults
Can volcanic eruptions and magma movement cause earthquakes?
Yes
How do earthquakes happen?
Strain is built up over years and if you keep applying stress, it will fail
What waves cause the most shaking?
Surface waves
compressional waves
back and forth motion in the direction of propogation
What are compressional body waves called?
primary waves
What are compressional surface waves called?
Rayleigh waves
shear/transverse waves
back and forth motion at right angles to propogation
What are transverse body waves called?
secondary waves
What are transverse surface waves called?
love waves
How do seismometers work?
A heavy weight has great inertia. When the earth shakes, it does not, but the frame holding it does. A pencil attached to the weight draws on a paper to register the activity
How are modern seismometers different?
use a coil to generate a current rather than drawing on paper
Which travels faster, compressional p-waves or transverse s-waves?
compressional p-waves
What does the delay between the p-waves and s-waves indicate?
The distance from the earthquake
How can you pin point a source of an earthquake?
By getting several readings from several stations and triangulating it
hypocenter
The 3D location of an earthquake
epicenter
The location of an earthquake projected to the earth’s surface
Do shallow earthquakes shake more than deeper earthquakes?
Yes
magnitude of an earthquake
Based on the amplitude of shaking recorded on a seismometer corrected for distance
earthquake intensity
a measure of the local shaking (high close to rupture, smaller further away from it)
main shock
the largest quake in a sequence
fore/after shocks
before/after the main shock
Are definitions of fore shocks and after shocks post hoc?
Yes. We can’t identify a foreshock until the main shock occurs
How are earthquakes related to plate tectonics?
Earthquakes are how relative motions between plates are detected
trace
where a fault meets the surface
scarp
a developed ridge line
blind fault
cannot see the blind fault on the surface
footwall
the higher wall in a fault situation
hanging wall
the lower wall in a fault situation
Where are earthquakes concentrated?
on faults and plate boundaries
What causes smooth plate motions to turn into jerks and earthquakes?
friction at faults
Thrust/Reverse/Compressional faults
compression, uplift; hanging wall up, footwall down; thrust faults are shallow, reverse faults are steep
deformational boundary
find old rocks on top of young rocks due to thrusting
Normal/Extensional faults
due to stretching/subsidence; hanging wall down; footwall up; block in the middle drops down
marine terraces
waves cut notches, then earth uplifted, more notches cut, uplifted again (forms a stair structure)
Strike Slip
due to lateral, translational motions; plates moving past eachother
What are some effects of seismic waves?
- shaking of buildings
- landslide
- liquefaction
What is an intraplate earthquake?
A quake that happens away from a plate boundary; continental crust is old, and there may have been a plate boundary thre in the past
How do we assess seismic hazards?
- plate tectonics context (how much deformation is going on)
- seismic history of the region
- instrumental records
paleoseismology
looking for the record of ancient of earthquakes to extend the records and better understand geological behavior of faults
How can we protect people?
through building codes and the resiliency of buildings; should consider the worst case scenarios
Does the smallest earthquake mean the smallest risk?
No
Strategies in case of an earthquake
- understand earthquake behavior
- understand region specific risks
- warning and mitigation strategies
Are short term, precise prediction of earthquakes possible?
No. Only long term forecasts
What are some “precursors”?
- animal behaviors
- foreshocks
- low frequency radio signals
What is seismology?
Uses the seismic waves earthquakes generate to determine the earth’s structure
Can s-waves travel through liquids? Can p-waves travel through solids?
- No. S-waves can only travel through solids
- Yes. P-waves can travel through solids, liquids and gases
Can waves be reflected and refracted?
Yes
What does the angle of reflection equal?
The angle of incidence
Angle of refraction depends on the direction/magnitude of the velocity contrast. What does this mean?
increases in velocity=bent towards the horizontal
decreases in velocity=bent towards the vertical
Can you get wave conversions with seismic waves? How?
Yes. When an up and down wave strikes at an angle, it causes shaking side to side
What do reflection and refraction of waves affect?
travel times of waves
moho
boundary between the crust and the mantle
Seismic velocity usually increases with….
…depth. Gets refracted more as you go deeper
How can we find the earth’s core?
No direct p-waves arrive at the surface on the other side of the earth. They are refracted, creating shadow zones.
Do s-waves make it to the other side of the Earth?
No. They can’t travel through liquids, and the core is liquid.
Isolated mountain ranges are _____ in origin.
igneous
orogen
a linear chain/range of mountains produced by deformation or “orogenesis”
thicker crust means
higher topography
cordillera
several different ranges produced by different events
convergent
ocean/continent collision; subduction
True or False: Continental crusts subduct easily
False. It is almost impossible to subduct continental crusts
Episodic collision of exotic terranes means…
…the growth of an orogen is not constant. Find rocks of various make-ups; exotic implies that they don’t belong there
Are subuction zones isolated?
No. They continue further back after exotic terrane is fused with the coast
Continent/continent collision
Plates collide and everything in the middle gets crumpled up
Because continental crust can’t subduct, motion cases what?
Deformation and the thickening of crust
Can mountains form in extensional settings?
Yes. Crust is stretched apart, then the middle chunk rotates
Why are mountains so high?
Archimedes principle (buoyance). The density of the crust is less than the density of the anthenosphere, so the crust “floats” on top. The thickest block of crust floats the highest and sinks the deepest
compressional stress
squashed up; volume remains the same
tensile/extensional stress
stretched out and extends in the direction of the applied force
shear/stress
distorted, rotated
Brittle deformations form what?
faults
Ductile deformations form what?
folds
tilting
distortion of bedding
folding
crumpled rock
flexural slip
brittle; different layers move past each other when under compression
passive flow
ductile
Deformations are structured on what?
planes and lines
Is there displacement on joints?
No. Joints are just breaks in rocks
two limbs
planar beds dipping in opposite directions from each other; dips shallow towards hinge
hinge
where the axial plane intersects with surface
axial plane
plane is the middle of the folding; can be vertical or tilted, depending on fold shape
anticline
arch, oldest rocks at the hinge
syncline
bowl, youngest rocks at hinge
monocline
a kink; both limbs have similar orientation (almost creates a step)
